3. Proceedings of a Round-Table seminar organised by the Commission of the European Communities,
Directorate-General Science, Research and Development, Environment Research Programme, held in
Liebefeld, Switzerland, 8–10 May 1985
4. FACTORS INFLUENCING SLUDGE
UTILISATION PRACTICES IN
EUROPE
Edited by
R.D.DAVIS
Water Research Centre, Marlow, UK
H.HAENI
Forschungsanstalt für Agrikulturchemie und Umwelthygiene,
Liebefeld, Switzerland
and
P.L’HERMITE
Commission of the European Communities, Brussels, Belgium
ELSEVIER APPLIED SCIENCE PUBLISHERS
LONDON and NEW YORK
6. FOREWORD
This publication constitutes the proceedings of a seminar held at the Federal Research Station for
Agricultural Chemistry and Hygiene of the Environment, Liebefeld (Switzerland), 8–10 May 1985, under
the auspices of the Commission of the European Communities, as part of the Concerted Action COST 681
‘Treatment and Use of Sewage Sludge and Organic Waste’. The seminar was convened by Working Party 5
(Environmental Effects) of the Concerted Action to consider factors influencing sludge utilisation practices
in Europe.
Increased treatment of sewage in Europe to improve the quality of effluents for discharge to rivers
inevitably generates, as a by-product, sewage sludge which has to be disposed of safely and economically.
Utilisation on agricultural land is an important disposal route for sewage sludge with the advantages of
recycling organic matter and supplying nutrients for crop growth. But there are attendant problems
associated in particular with possible effects of contaminants in the sludge on crop growth and composition,
soil fertility and contamination of groundwater and eutrophication. Management of sludge utilisation on
land therefore requires a sound understanding of the associated risks and benefits leading to a scientific
basis for disposal policy. The seminar provided a forum for the exchange of recent findings on most aspects
of sludge utilisation on agricultural land, including contributions from researchers in Europe, Scandinavia
and Canada. Ten papers are included with discussions and conclusions.
7. CONTENTS
Foreword v
Session I
Geological and pedological factors affecting the heavy-metal load capacity of soils
H.KUNTZE (Lower Saxony Geological Survey, Institute of Soil Technology, Bremen,
Federal Republic of Germany)
2
Heavy metal availability in long term experiments
C.JUSTE and P.SOLDÂ (Station d’Agronomie, I.N.R.A., Centre de Recherches de
Bordeaux, Pont-de-la-Maye, France)
12
Basis for metal limits relevant to sludge utilization
E.VIGERUST (Department of Soil Fertility and Management) and A.R.SELMER-
OLSEN (Chemical Analytical Laboratory, Agricultural University of Norway)
25
Soil ingestion by grazing animals: a factor in sludge-treated grassland
G.A.FLEMING (An Foras Taluntais, Johnstown Castle Research Centre, Wexford,
Republic of Ireland)
40
Groundwater quality in relation to land application of sewage sludge
M.AHTIAINEN (National Board of Waters, Water District Office of North Karelia,
Finland)
46
Session II
Predictability of estimated mobilizable N pool in sludge and soils
A.RUDAZ and S.K.GUPTA (Swiss Federal Research Station for Agricultural
Chemistry and Hygiene of Environment, Liebefeld-Berne, Switzerland)
56
Summary of investigations in Italy into effects of sewage sludge on soil microorganisms
S.COPPOLA (Istituto di Microbiologia agraria e Stazione di Microbiologia
industriale, Università di Napoli, Italy)
62
Effects of long-term sludge additions on microbial biomass and microbial processes in
soil
S.P.McGRATH and P.C.BROOKES (Soils and Plant Nutrition Department,
Rothamsted Experimental Station, Harpenden, UK)
69
8. Political and administrative considerations in the formulation of guidance for sludge
utilization
H.M.J.SCHELTINGA (Ministerie van Volkshuisve sting, Ruimtelijke Ordening en
Milieubeheer, Arnhem, The Netherlands) and T.CANDINAS (Forschungsanstalt für
Agrikulturchemie und Umwelthygiene, Liebefeld-Bern, Switzerland)
78
Future developments in sludge disposal strategies
M.D.WEBBER S.BERGLUND (Swedish Environment Protection Board, Solna,
Sweden)
91
Conclusions 102
List of Participants 104
Index of Authors 110
vii
9. SESSION I
Chairman : H.HAENI
Rapporteurs : S.GUPTA
G.PORTEOUS
S.MCGRATH
Geological and pedological factors affecting the heavy-metal load capacity of soils
Discussion
Heavy metal availability in long term experiments
Discussion
Basis for metal limits relevant to sludge utilization
Discussion
Soil ingestion by grazing animals; a factor in sludge-treated grassland
Discussion
Groundwater quality in relation to land application of sewage sludge
Discussion
10. GEOLOGICAL AND PEDOLOGICAL FACTORS
AFFECTING THE HEAVY-METAL LOAD CAPACITY OF
SOILS
Herbert KUNTZE
Lower Saxony Geological Survey
Institute of Soil Technology Bremen
Summary
The present German Sewage Sludge Regulations are inadequate to sufficiently differentiate the
sources and availabilities of heavy metals in different soils for different plants. Because they are
primary constituents of rocks, heavy metals are often present in natural soils in higher
concentrations than allowed by the Sewage Sludge Regulations without being plant available.
These heavy metals are mobilized, i.e. converted to soluble forms, by the processing of mineral
resources or the weathering of rocks and associated soil formation. Important parameters
influencing the mobility of heavy metals in soils are:clay content, type of clay minerals,
presence of organic material and degree of humification, pH, metal oxides, and salt content.
Heavy metals are adsorbed more readily by soils than desorbed. A project has been begun in the
Fed. Rep. of Germany to quantify the sources of heavy metals in the soil. Several hundred standard
profiles in different subsoil types are being surveyed in terms of soil chemistry and physics
using the vegetation typical for each site. The results will be used as the basis for a later survey
to map the heavy metal load and capacity with a better geoscientific differentiation in order to
revise the German Sludge Regulations. This is also a contribution to the Soil Protection
Programme.
1.
CRITIQUE OF THE GERMAN SEWAGE SLUDGE REGULATIONS
The German Sewage Sludge Regulation of 1983 issued following the Federal Waste Disposal Law of 1972
gives values for the maximum concentration of heavy metals, that may be tolerated in soils. Before sewage
sludge is added to soils, the total concentration of Cd, Ni, Hg, Cu, Pb, and Zn are to be determined in both
soil and sludge after digestion in hot aqua regia. It is assumed, that this procedure will show the potential
maximum, long-term hazard with respect to heavy metals. But the different sources and thus the solubility of
heavy metals are not considered, nor are the properties of the soils (pH, clay, iron, and organic matter
content) and plant species that influence these. This is inadequate from a pedological and ecological/
chemical viewpoint.
11. 2.
SOURCES AND MOBILITIES OF HEAVY METALS
Heavy metals are not artificial substances in our environment, in contrast to many of the organic pollutants.
They belong to the natural system of elements (fig. 1).
Elements with a density higher than 4, 5 g/cm3 are called heavy metals. Therefore, even iron (Fe) is a
heavy metal but a non toxic one. Some heavy metals are essential elements or micro-nutrients (e.g. copper)
as long as their concentration remains rather small. Others (e.g. Cd, Pb, Hg) are not essential. They are
originally toxic for plants, animals, and especially for men.
Using modern analytical methods (e.g. atomic adsorption spectroscopy and X-ray spectrophotometry),
heavy metals can be detected in extremely small concentrations (ppm, ppb). In these low concentrations
they are called trace elements or micro-elements. Many rocks and minerals contain very small amounts of
heavy metals. From there they will come into the soils and the food chain by two ways (see figure 2):
a) Weathering and soil forming processes.
b) Industrial processing and emissions.
Soils become the central part of heavy metal accumulation, mobilization or immobilization within the
ecosystems. Heavy metals are subject to changes in their type of binding, solubility and plant availability
within ecosystemar cycles.
2.1
GEOLOGICAL FACTORS
Heavy metals are present in rocks in the crystal lattice of minerals, e.g. silicates or sulfides. In this state they
are nearly insoluble. Several rock types from Northwest Germany are listed in Table I, which can contain
certain heavy metals at concentrations in the order of magnitude of the values given in the German Sewage
Sludge Regulations. But, the significance of these background values of naturally occurring heavy metals is
not yet known.
The industrial processing of raw materials that contain heavy metals always involves the danger, that
these heavy metals will be released into the environment. Industrial dusts from high temperature
processings mostly contain oxides of heavy metals. These are ± soluble. Heavy metal emissions lead to a
diffuse distribution; deposition of wastes containing heavy metals or the long term use of sewage sludge in
agriculture create a high concentration in one place. The heavy metals in these new accumulations are no
FIGURE 1—Heavy metals—Definitions
3
12. longer bound in their natural insoluble form, but are present as unfixed ion, exchangeable adsorbed by clay
minerals and humic substances, as free oxide or sulfate, and thus more easily enter the food chain (s. fig. 2).
The various weathering processes also free the heavy metals from their insoluble form in the original
rocks. Even rocks, that have a very low heavy metal content, can lead to soils with a high concentration of
heavy metals. This enrichment can be explained by the fact, that several meters of limestone must be
weathered to produce several decimeters of soil. The primary clay minerals in the soil or the secondary ones
formed by weathering, are then available as sorbent for heavy metal ions.
Table I
Rock Units in Lower Saxony with Elevated Heavy Metal Contents According to Archive Documents of the NLfB
sampled till May 1982
Series Rock Type Zn Pb Cu Cd Ni Cr Co
L. Cretaceous Alb phosphorite + +
Lias clay + +
Keuper – + + + +
FIGURE 2
The Cycle of Heavy Metals
4
13. Series Rock Type Zn Pb Cu Cd Ni Cr Co
U. Muschelkalk trochite limestone + + +
M. Muschelkalk dolomite + +
Buntsandstein Hardegsener clay + + + +
Zechstein copper schist + + + + + + +
Rotliegendes basalt + +
U. Carboniferous gabbro and shale + + +
L. Carboniferous shale + + + +
U. Devonian banded shale + +
M. Devonian calciola shale + + + +
L. Devonian shale +
(+means concentration greater than the maximum tolerable value according to the German Sewage Sludge
Regulations)
2.2
PEDOLOGICAL FACTORS
A natural acidification of the soil takes place in humid climates. This leads to migration (leaching) and at
least to decomposition (podsolization) of clay minerals, which in turn results in a mobilization and
accumulation of heavy metals in specific soil horizons. Therefore, it is not sufficient to analyze only the top
soil for heavy metals as set forth in the German Sewage Sludge Regulation. Also it must be taken into
consideration, that heavy metals in an acid soil are more mobile than those in rocks.
FIGURE 3
Heavy metals on ion exchangers are replaced especially by hydrogen ions. Therefore, the pH of the soil
solution is important; and this is affected by the input of acids through precipitation, fertilization, plant roots
and other biological activities. For example, we have determined a 14 % decrease in heavy metal uptake in
test plants by decreasing the acid content of the soil by one pH unit (12).
5
14. Anthropogenic heavy metals introduced in the soil via sewage sludge, for example, are highly mobile at
first, but are immobilized within a relatively short period of time (Fig. 3). At first the heavy metals remain
organically bound in the soil solution. Depending on their binding force and concentration and the cation
exchange capacity of the soil, they are adsorbed soon by clay minerals, organic substances, and metal
oxides in the soil. Their adsorption and desorption depends on the specific ion exchanger. Mumbrum &
Jackson (11) concluded on the basis of infrared studies of copper and zinc smectite, vermiculite, and
kaolinite, that heavy metal cations are bound on the OH-groups of layer silicates. Thus, the kind of clay
mineral present has more influence than the clay content on how much heavy metal ions will be adsorbed.
Figure 4 shows an example. The solubility of Cd increases with decreasing pH more in the presence of
Kaolinite than Illite or organic matter. The greatest solubility will be reached in equilibrium with hematite
below its ZPC at pH<5, 5. Brümmer et al. (3) determined the following adsorption capacity for Zn (μmol/
1): CaCO3 (0.44)<bentonite (44)<humic acids (842)<amorphous metal oxides (1190–1540). Thus metal
oxides and humic acids are able to bind 20–40 times the amount of heavy metals than clay minerals can.
Organic substances and metal oxides have a relatively high proportion of charges that vary with pH and
adsorb increasing amounts to heavy metals with increasing pH. Fe- and Mn-oxides can occlude heavy
metals by further deposition of oxides (5), thus immobilizing them until the oxide is decomposed. This
explains, why heavy metals are adsorbed in the soils more easily than they are desorbed (Fig. 5) and also
why the difference increases with increasing pH (10). Lead is more strongly adsorbed than zinc, nickel or
cadmium; the plant availability of these metals increases in the same order (11).
The heavy metals introduced into a soil via sewage sludge are first present mainly as soluble, negatively
charged organic complexes. When the chloride concentration is relatively high, soluble chlorocomplexes
may be formed (2, 6). The heavy metals are removed from the soil solution by adsorption and occlusion, to
a lesser extent by precipitation (as carbonate, phosphate or hydroxide, for example). The strength of
adsorption varies depending on the heavy metal, the type and quantity of ion exchangers in the soil and on
FIGURE 4—Solubility of Cadmium depending on pH and soil constituents acc. Federal Environmental Office Berlin
1980
6
15. the pH. The strength of adsorption of heavy metals is greater than that of the alkaline earth metals and thus
they can be only partially remobilized by desorption.
FIGURE 5—Adsorption and Desorption of Zn depending on ZN- or Mg- addition on a black soil
7
16. Own tests have shown, that in humus- and ironrich soil, that have been fertilized with sewage sludge, the
availability of cadmium decreases considerably within three years (9) (s. fig. 6).
The German Sewage Sludge Regulation assumes average soil conditions. It is clear from the phenomena
discussed above, that in the future soil properties, that influence heavy metals, must be taken into
consideration to a greater extent. This means, that acid soils with a low clay, humus, or metal oxide content
are less suitable for amelioration with sewage sludge than alkaline soils with a high clay, iron or humus
content.
3.
QUANTIFICATION OF THE EFFECTS OF HEAVY METALS
Lithogenic, pedogenic, and anthropogenic heavy metals probably have different availabilities. Therefore,
they must be treated differently. With this in mind, the State Geological Surveys of the Federal Republic of
Germany have begun a joint project with the support of the Federal Environmental Office. In this project,
about 600 representative profiles with different types of substratum with and without lithogenic, pedogenic,
and anthropogenic load throughout the Federal Republic are being investigated in terms of soil chemistry
and physics. Collected at the same time in an annual cycle at sites with an especially high concentration of
heavy metals and others with essentially no heavy metal accumulation, cultivated and noncultivated plants,
soil and water samples from different depth are being analyzed for their heavy metal content.
Pot tests are made to determine the uptake of heavy metals (Cu, Pb, Cd) by heavy-metal-sensitive plants
(e.g. lettuce and spinach) or plants, that accumulate heavy metals (e.g.grass) grown on a heavy-metal-rich
substratum (lithoge nic), subsoil (pedogenic), and top soil (anthropogenic) with and without the addition of
heavy metals. The rate of uptake by the plants is an indication of the mobility of the heavy metals. For the
FIGURE 6—Cd-Content of Raygras (2nd cut) growing on 3 soils enriched with Cd by sewage sludge
8
17. determination of the mobility, methods for extracing the plant available, i.e. toxic proportion of the total
heavy metal content are necessary. In another joint research project (University of Bonn, Federal
Agricultural-Research Center in Braunschweig-Völkenrode, and the Soil Technological Institute of the Soil
Survey Office of Lower Saxony) it was recently found, that extraction of a soil with a 0.1 M CaCl2 solution
simulated rather well the amount of cadmium, that is taken up by the test plants (9). The extensive data from
this project is to be evaluated with respect to the heavy metal balance in the soil and correlated with
pedological and geological parameters. The project is preliminary to a later survey for mapping heavy metal
load or load capacity of soils, which should better show the interaction between geogenic background,
pedogenic alterations, and anthropogenic load. The soil protection concept in the Federal Republic of
Germany among its different aims is looking for a better precau-tion against the immissions of noxious
substrates like persistent heavy metals. An ecological land-register is planned with special maps, which
shall show e.g. the soil qualities for heavy metal loading. Up today the long term effects of contaminants are
unknown. Permanent observation plots in the different soil regions are necessary to control the conditions,
which may increase or decrease the solubility and plant availability of heavy metals. Our project will
contribute to this soil protection programme and results will be published later.
5.
REFERENCES
1 () Bittell, J.E. a. R.J.Miller: Lead, Cadmium, and Calcium Selectivity Coefficients on a Montmorillonite, Illite,
and Kaolinite. Madison, J.Environ. Quality, 3, 250–252, 1974
2 () Bloomfield, C., W.I.Kelso a. G.Pruden: Reactions between metals and humified organic matter. London, J.
Soil Sci. 27, 16–31, 1976
3 () Brümmer, G., K.G.Tiller, U.Herms, a. P.Clayton: Adsorption-desorption and/or precipitation—dissolution
processes of zinc in soils. Amsterdam, Geoderma 31, 337–354, 1983
4 () Fauth, H., U.Sievers: Bäche—von der Natur selbst belastet. Stuttgart, Bild der Wissenschaft 5, 77–100, 1983
5 () Grimme, H.: Die Adsorption von Mn, Cu, Cd und Zn durch Goethit aus verdünnten Lösungen. Weinheim, Z.
Pflanzenernaehr. Bodenkd. 121, 58–65, 1968
6 () Hahne, H.G.A. a. W.Kroontje: Significance of pH and chloride concentration on behaviour of heavy metal
pollutants: Mercury (II), cadmium (II), Zinc (II) and lead (II). Madison, J. Environ. Qual. 2, 444–450, 1973
7 () Kloke, A.: Auswirkungen von Schwermetallen auf Boden-fruchtbarkeit, Flora und Fauna sowie deren
Bewertung für die Nahrungs- und Futterkette. Zürich, in G. Duttweiler Institut, Die Verwendung von Müll- und
Müllklärschlammkomposten in der Landwirtschaft, 58–87, 1980
8 () Kuntze, H., U.Herms a. E.Pluquet: Schwermetalle in Böden-Bewertung und Gegenmaßnahmen. Hannover,
Geol. Jb. A 75, 301–322, 1984
9 () Kuntze, H. a. Chr.Förster: Cd-Dynamik leichter Böden. UBA-Forschungsprojekt Nr. 441, unveröffentlicht
10 () Fleige, H. a. W.Müller: Untersuchungen der Filtereigen-schaften natürlich gelagerter Böden gegenüber
emittierten Metall- und Arsenverbindungen. Hannover, Forschungsbericht NLfB 85978, 1980
11 () Mubrum, L.E.de a. M.L.Jackson: Infrared adsorption evidence on exchange reaction mechanism of copper and
zinc with layer silicate clays and peat. Madison, Proc. Soil Sci. Soc. Amer. 20, 334–337, 1956
12 () Pluquet, E.: Die Bedeutung des Tongehaltes und des pH-Wertes für die Schwermetallaufnahme einiger
Kulturpflanzen aus kontaminierten Böden. Berlin, UBA Texte 40, 1984
DISCUSSION
TJELL (Denmark): It is agreed that as proposed in the paper there should be different metal limits
for different soils. Professor Kloke suggests a limit for the increase in cadmium
9
18. in the soil of 3 mg/kg which for Denmark seems too high. What limit do you
suggest for cadmium?
KUNTZE (FRG): The geology and pedology of Danish soils, consisting largely of glacial till, are
fairly uniform and therefore a soil limit of 1 to 2 mg Cd/kg may be about right.
In Germany there are about 70 different substrates at various stages of
weathering, giving 30 different soil types and the 3 mg Cd/kg limit suggested
by Kloke in the late 1970s was an average value to be applied to an average
soil. It has been observed that under certain geological and pedological
conditions, soil background cadmium is greater that 3 mg/kg, for example in
the Black Forest it can be as high as 10 mg/kg, but in most of these cases the
proportion of the total cadmium available to plants is small. Other soils can be
acid, low in clay or organic matter or contaminated from anthropogenic
sources and the cadmium may be more available to plants so a limit of 1 to 2
mg/kg would be more appropriate for these.
The heavy metal limits are to be revised by the FRG in 1988.
McGRATH (UK): You showed that the decrease in availability of cadmium was greatest in the
first year after application, and the decrease levelled off in successive years.
This seems to be a common experience. Can you comment further?
KUNTZE: Metals of anthropogenic origin can take up to 3 years to achieve equilibrium in
soils, but if soil factors such as pH or organic content change, it may take
several more years before a new equilibrium is reached.
WEBBER (Canada): You have suggested that subsoils with less organic matter and lower metal
contents than the topsoil may show high metal availabilities. Will you amplify
your views on soil profile investigation.
KUNTZE: Most metal is usually taken up by plants from the surface soil where the metal
is more concentrated, but the soil moisture profile and organic content affect
root growth and metal uptake. Experiments have shown that the type of organic
matter added to soils influence metal availability. Readily decomposable
materials such as farmyard manure or roots lead to an increase in metal
solubility, whereas stabilised peat decreases solubility and can cause metal
deficiencies in animals and plants.
FLEMING (Eire): You have said that organics and oxides can absorb as much as 20 times more
metal than clay. Does the effect of oxides depend on their large surface area?
KUNTZE: Yes, and many forms of industrial pollution deposit oxides with very high
surface areas.
DAVIS (UK): I agree that it may be preferable not to use only total metal content for soil
guidelines and that the extractable fractions by neutral salts such as calcium
chloride provide a better measure of availability. However, environmentalists
point out that soil management can change availabilities. How can regulations
take care of this?
KUNTZE: Present regulations cover the worst case. For better regulations we need to know
more about metals of geological and pedological origin which are generally of
low availability and may be ignored and we need more information on
properties of soils such as pH and oxide, clay and organic contents. Total metal
10
19. contents indicate potential mobility and are needed as well as neutral salt
extractabilities.
DESAULES (Switzerland): To obtain an indication of soil pollution both available metals from
anthropological sources and geochemical background metals have to be
considered. The question is which part of the soil profile should be taken to
establish background levels.
KUNTZE: One needs information from all three soil horizons to know the influences of
metal accumulations. Horizon A gives the anthropological load, Horizon B the
pedological load and Horizon C the geological background load.
DESAULES: If in a soil profile Horizon B is well defined but Horizon C less well defined,
how should the background be assessed?
KUNTZE: The metal concentrations in Horizon B usually vary, decreasing with depth, so
if analyses are made at small increments of depth, say 5 cm, this will give an
indication of the pedological processes and the geological background.
LESCHBER (FRG): The draft CEC Sludge Directive proposes two limits for some metal
concentrations in soils, one a Recommendation and the other Mandatory. In
FRG we use both limits but mostly the Recommended value. Have you any
comment?
KUNTZE: No comment.
CHAIRMAN: In Switzerland we use two limits, one based on total metal and the other based
on sodium nitrate soluble metal. This is one way of coping with the problem.
11
20. HEAVY METAL AVAILABILITY IN LONG TERM
EXPERIMENTS
C.JUSTE and P.SOLDÂ
STATION D’AGRONOMIE, I.N.R.A.
Centre de Recherches de Bordeaux
B.P. 131–33140 PONT-DE-LA-MAYE—FRANCE
Summary
Several rates of two sewage sludges were applied, from 1974 to 1984, in an acidic, coarse sandy
soil cultivated with a continuous maize crop.
Depressive effect on yields was observed only in the case of heavy application (100 t/ha/2
years dry matter) of a sewage sludge very polluted by cadmium and nickel.
P content of plants was always decreased by sewage sludge application. Concentrations of
most heavy metals decreased with ageing of plants. Cd, Zn and, at minor extent, Cu appear as
the most available metal originating from sewage sludge. Sewage sludge application reduced Fe
and Mn availability. The findings of the study indicated also that Cd and Ni uptakes were likely
dependent of each other.
INTRODUCTION
The purpose of the experiments was to measure the effects of high loading rates of sewage sludge on:
– the yield of a continuous maize crop grown in soil amended with a sewage sludge containing a low level
of heavy metals (“Ambares” sewage sludge applied from 1974 to 1984) or with a sewage sludge
containing a high level of heavy metals (“Louis Fargue” sewage sludge applied from 1976 to 1984);
– the major (N, P) and minor (Cd, Cu, Cr, Pb, Ni, Zn, Fe, Mn) elements content of maize;
– the organic and mineral status of soil.
A/
METHODS AND MATERIALS
Location of field experiments and initial soil characteristics
The field study was conducted on gravel sandy soil (70 % coarse sand) with a pH of 5, 5 and an organic
matter content of 2%. The field experiments were located in an experimental farm of I.N.R.A., near
Bordeaux (France).
21. Test plant
The same maize cultivar (I.N.R.A. 260) was used throughout the experiment period.
Treatments
Treatments consisted of mineral fertilized check plots (A) and sludge amended plots (B and C treatments).
Sewage sludge was applied at a rate of 10 tons/ha/year (dry matter basis) in treatment B, and 100 tons/ha/2
years in treatment C. Mineral fertilizers were added to adjust the total N-P-K-Ca and Mg content of soil at
the same level il all plots.
Experimental design
Each plot was replicated five times in a randomized complete block design. The areas treated with sludge
and fertilizer were 3, 0 m by 6, 0 m.
Sewage sludges
The “Ambares” sewage sludge was an anaerobically digested filter band deshydrated sewage sludge.
The “Louis Fargue” sewage sludge was an anaerobically digested sludge deshydrated by the Porteous
thermic process. The Cd and Ni content of this sludge was excessively high because a battery factory
rejected his wastes in the treatment plant.
Analysis and measures
Field weight of maize grain was determined (kg/ha dry matter).
The sixth leaf was analyzed for Cd, Cu, Cr, Pb, Ni, Zn, Fe, Mn, N and P at the twelth fully emerged leaf
stage. The same element were measured in the grain.
Multifactorial analysis including measure of the annual, treatment and interaction annual/treatment
effects were used as statistical methods. Levels of significance were determined using the Bonferroni test.
B/
RESULTS
Sewage sludge analysis
Amounts of heavy metal added to soil as sewage sludge are shown in table 1. In the case of the high rate of
“Louis Fargue” sewage sludge application, cumulation amounts of 641 kg/ha Cd and 1 337 kg/ha Ni were
added to soil.
Table 1
13
22. Heavy metal added to soil—Aqua regia extractable content
Metal Ambares (500 t/ha)
1974–1982
L.Fargue (300 t/ha)
1976–1980
kg/ha ppm kg/ha ppm
Fe 20 774 4 418 11 354 3 470
Mn 4 151 419 234 81
Cu 122 35 170 46
Zn 1 973 352 976 158
Cd 18 5 641 110
Ni 124 7, 5 1 337 269
Pb 443 92 231 49
Cr 32 12 64 18
Maize grain yields
Yields from the high rate of “Ambares” sewage sludge application (600 t/ha dry matter) were significantly
higher than mineral fertilized controls (+7% during the complete experiment period)—Table 2.
Table 2
Mean average of maize grain yield (1974–1984) in plots receiving sewage sludge with low heavy metal content
(Ambares)
Grain yield (kg/ha) Control Sewage sludge
110 t/ha 600 t/ha
9 230 9 410 9 830
Control . . . . . . . – NS TS
110 t/ha sewage sludge NS – TS
600 t/ha sewage sludge TS TS –
NS: no signif. differerence TS: signif. at 1 % level
“Louis Fargue” sludge treatments significantly decreased grain yields (−10% and −18% respectively for the
low and high rate of application). However in 1980, as shown in Fig. 1, yield was very adversely affected:
(−50%) in highly sewage sludge treated plots; purpling of seedling leaves, similar as a severe phosphorus
deficiency sign, was observed in the plots (Table 3)
Table 3
Mean average (1976–1984) of maize grain yield (L.Fargue)
Control Sewage sludge
50 t/ha 300 t/ha
Grain yield (kg/ha) 8 544 7 733 7 122
Control . . . . . . . – TS TS
50 t/ha sewage sludge TS – TS
300 t/ha sewage sludge TS TS –
14
23. Control Sewage sludge
50 t/ha 300 t/ha
TS: significative at 1 % level
Major element content
N content of plants was significantly increased by Ambares sewage sludge application, whereas it was
decreased for Louis Fargue sewage sludge treated plants.
Sewage sludge application induced a strong decrease in P uptake even in the case of the smaller rate
(Table 4).
Table 4
Mean average (1974–1984) of P content in the sixth fully emerged leaf of maize
(Field experiment sewage sludge with low metal content: Ambares)
Control Sewage sludge
110 t/ha 600 t/ha
P content (%) 0, 63 0, 39 0, 46
Control . . . . . . . – TS TS
110 t/ha sewage sludge TS – TS
600 t/ha sewage sludge TS TS –
TS: significative at 1% level
Minor element content
–General features–
No effect of sewage sludge spraying was observed on Cr and Pb content of plants.
Concentration of most heavy metals decreased with ageing plants (Table 5). This decrease in heavy metal
concentration is likely due to a dilution effect, as well as the poorly metal enriched subsoil colonization by
roots.
Table 5
Mean average (1974–1984) of heavy metal content in maize growing in enriched sewage sludge plots
Stage
12 fully emerged leaves sixth leaf Silking Ear leaf Maturity Grain
Mn * 173 143 75
Fe * 129 159 24
Zn * 163 121 40
Cu * 12 13 1
Cd * 55 28 0, 5
Ni * 9 13 2, 4
N ** 4, 40 4, 10 1, 70
15
25. Stage
12 fully emerged leaves sixth leaf Silking Ear leaf Maturity Grain
P ** 0, 36 0, 41 0, 35
* ppm dry matter basis—** % dry matter basis
Cd, Zn and, at minor extent, Cu are the most sewage sludge available metals (Table 6).
Table 6
Heavy metal availability in aerial parts of maize plants
(1) Metal concentr. increase in plant (2) (3)
Metal added Availability index
(4) (5)
Sewage sludge N°l N°2 N°1 N°2 N°1 N°2
Zn 195 25 3 937 976 4,95 2,56
Cd 1,1 36 21 631 5, 19 5, 71
Cu 2, 7 1, 5 127 170 2, 10 0, 94
Ni 5, 3 1 387 0, 38
Mn 64 4 927 1, 30
(1) ppm dry matter basis.
(2) high rate sewage sludge application during 9 or 10 years.
(3)
(4) sewage sludge with low level of heavy metals (Ambares)
(5) sewage sludge ” high ” ” ”(L.Fargue)
Except for the high rate of Ambares sewage sludge, the waste application strongly decreased Fe and Mn
uptake by maize. This would suggest either an antagonistic effect excersed by other metal or an
immobilization of Mn and Fe resulting from organic matter enrichment or a pH increase. (Tables 7 and 8).
Table 7
Iron (ppm dry matter)—sixth leaf
(Ambares sewage sludge)
Control Sewage sludge
110 t/ha 600 t/ha
142 133 123
Control . . . . . . . – TS TS
110 t/ha sewage sludge TS – TS
600 t/ha sewage sludge TS TS –
Significative a 1 % level.
Table 8
Manganese (ppm dry matter)—Sixth leaf
17
26. (Ambares sewage sludge)
Control Sewage sludge
110 t/ha 600 t/ha
85 50 173
Control . . . . . . . – TS TS
110 t/ha sewage sludge TS – TS
600 t/ha sewage sludge TS TS –
Significative a 1% level.
–Particular features
Plots fertilized with Ambares sewage sludge
–Zinc–
According to the data in Fig. 2, a very strong accumulation of Zn (up to 480 ppm) occured in Ambares
sewage sludge treated plants without toxic effect. In the year following the high rate sewage sludge
application, a rapid decrease of Zn content was observed but Zn tended to increase in the course of time.
–Manganese–
Due to the very high content in sludge, metal concentration in maize was strongly increased the year of
plots treatment, but in the following year Mn availability was sharply reduced due either to a pH effect or rather
at the immobilization of remaining metal by organic matter. Thus, at opposite of Zn, Mn availability tended
to decrease or was not changed in the course of time (Fig. 3).
Plots fertilized with Louis Fargue sewage sludge
The most striking feature concerns Cd and Ni availability.
As evidenced in Fig. 4 and 5, Cd and Ni accumulations were likely dependent of each other. This feature
was specially displayed in 1980 : indeed a strong increase in Ni uptake was observed this year, whereas in
the same time Cd uptake was reduced despite of the very high rate of metal addition through sludge
application.
The low soil temperature prevailing in the first stage of maize growth in 1980 likely explains Cd and Ni
behaviour. Possibly Cd uptake was depressed by low temperature level in rooting zone whereas Ni uptake
was less affected bringing a strong decrease in maize yield.
CONCLUSION
Even applied at caricatural rates, sewage sludges containing high level of heavy metals appear as poorly
toxic for maize crops cultivated in the mild climatic characteristics of the South-West of France. Only cold
environment of roots prevailing during spring 1980 induced a strong depressive effect on maize yield,
resulting probably from an increase in Ni toxicity.
This findings of this study strongly indicates that more research is needed for estimating physiological
process involved in:
– heavy metal uptake and translocation in plants grown in nutrient medium containing several metals;
18
27. – temperature effect on the first stage of heavy metals uptake by plants.
Until adequate knowledge become available, use of chemical extractants to predict metal uptake would be
made with caution.
REFERENCES
(1) JUSTE C., SOLDA P., 1977. Effets d’applications massives de boues de stations d’épuration urbaines en monoculture
de maïs: actions sur le rendement et la composition des plantes et sur quelques caractéristiques du sol. Sci. Sol, 3,
147–155.
(2) JUSTE C., SOLDA P., 1979. Effect of heavy application of sewage sludge with high content of Cd and Ni on a
continuous maize crop. First Europ Symp. “Treatment and use of sewage sludge”, Cadarache, France, 372–382
(3) JUSTE C., SOLDA P., 1980. Effect of heavy application of sewage sludge with very high content of Cd and Ni on
lettuce and maize crops. Second Europ. Symp. “Characterization , treatment and use of sewage sludge”, Vienna,
Austria, 718–720
(4) JUSTE C., SOLDA P., 1984. Factors influencing heavy metal availability in field experiments with sewage sludges.
C.E.E. “Chemical methods for assessing bio-available metals in sludges and soils”. Elsevier appl. Sem. Publ.,
82–88.
DISCUSSION
KUNTZE (FRG): Your experiment was on a very acid sandy soil. In the treatment where 600 t of sludge
was applied per ha, approximatley 30 t of lime would have been added to the soil. How
did this affect the soil pH and organic content?
JUSTE (France): Every two years Dolomite limestone was added and by 1984 the pH on all plots was 6.
3. There was a small increase in organic matter in the plots which received the 100 t/ha
sludge treatment, but those receiving the 10 t/ha treatment showed little change over
the control plots.
DAVIS (UK): The Ni and Cd concentrations in the sludge were 4000 and 2000 mg/kg dm
respectively. How do these compare with the sludge normally utilised on land in
France?
JUSTE: The sludge was from the vicinity of a battery manufacturing factory, and this would
not normally be applied to land.
McGRATH (UK): The soil pH increased during the experiment; was this the reason for the decrease in
plant uptake of manganese and iron?
JUSTE: The uptake of manganese by plants is low, and the .2 pH increase in the soil in the
year following sludge addition would have had no noticeable effect on uptake.
FLEMING (Eire): Soil moisture increases manganese uptake by plants. Should this be taken into account
with soil pH change?
JUSTE: In this experiment soil moisture content was maintained constant on all plots by
irrigation, so the sludge had no effect on the overall moisture content of the soil.
WEBBER (Canada): You observed a depression in plant yield due to nickel in one year only—1980. Can
you explain this?
JUSTE: The Spring in that year was very cold, and this led to slow growth in the early stages.
Soil temperature affects nutrient availability and plant growth. The uptake of cadmium
19
29. may have been depressed by an antagonistic effect of nickel, as nickel uptake continues
at low temperature and could have led to nickel toxicity.
FIGURE 3—Manganese 6th leaf—Ambares
21
30. KUNTZE: The toxicity effect may have been due to a deficiency of phosphorus which is less
available at cold temperature. Most heavy metals form insoluble phosphates which
may worsen phosphorus deficiency. In the cold north area of FRG, liquid phosphate is
applied to maize crops to counteract the deficiency.
JUSTE: I do not think there was a phosphorus deficiency.
FIGURE 4—Cadmium 6th leaf—Louis Fargue
22
31. GOMEZ (France): There was no phosphorus deficiency as large amounts were supplied in the sludge.
The problem was not formation of insoluble phosphates, but physiological effects due
to metal toxicity reducing phosphorus uptake.
FIGURE 5—Nickel 6th leaf—Louis Fargue
23
32. WILLIAMS (UK): An observation on the interaction of manganese and zinc. We have a trial with plants
growing on soils with 750 mg Zn/kg, and have alleviated zinc toxicity in some
cultivars by spraying the foliage with manganese. There are differences in cultivar
response.
JUSTE: We used different cultivars each year.
24
33. BASIS FOR METAL LIMITS RELEVANT TO SLUDGE
UTILIZATION
E.VIGERUST* and A.R.SELMER-OLSEN**
Summary
Several field experiments showed in average only weak effect of applied sewage sludge on the content of
Pb, Cd, Fe, Ni and Cu in the yield.
Increasing amount of sludge increased the Zn content in plants markedly and regular. In a field
experiment, 28 different crops were grown in 0, 10 (incorporated) and 40 cm decomposed sludge. The
heavy metal content varied greatly from crop to crop. Different parts of the plant contained different
amounts of the various elements. Increasing amount of sludge affected the average content in plants in this
order: Zn > Mn > Ni>Cu>Pb, Cr. In a pot experiment increasing temperatures resulted in higher content of
Mn, Fe, Zn and Cd, while the content of Ni, Cu and Mo were little influenced.
1.
INTRODUCTION
The guidlines for sludge utilization with regard to metal limits are very different in different countries. Extra
applications of metals to soil through sludge is more doubtful if the strain from other sources e.g. air
pollution is high. There can be large variations between districts as regards this strain.
Although there are differences in the farming managements, the types of crops grown and the heavy metal
strain in different countries, there is probably little basis for such great differences in the guidelines for
sludge utilization.
Recent, relative extensive research on the heavy uptake from sludge—amended soil has just been carried
out in Norway (VIGERUST and SELMER-OLSEN, 1985). Investigations on the effect of temperature on
heavy metal uptake have also been reported (SIRIRATPIRIYA, VIGERUST and SELMER-OLSEN, 1985).
Even if the problem in Norway may be different from the problems in other countries, the above mentioned
investigations may serve as a basis for a more general discussion of the problem. The magnitude of the
experimental data may, however, restrict reference in short and simple term.
*Department of Soil Fertility and Management
**Chemical Analytical Laboratory Agricultural University of Norway
34. 2.
EXPERIMENTAL RESULTS
a. Sludge for agricultural purpose
For agricultural purpose 16 field experiments with increasing applications of sludge were carried out.
Most of the trials lasted for 2 growing seasons and results from 28 harvests are refered here. Lime treated
sludge is excluded.
The main crop was cereal but grass and fodder rape have also been used in some of the experiments.
Analyses for heavy metals were carried out on yield from plots without sludge but with N-fertilizer and
plots with sludge but without N. These were compared.
Mean heavy metal content in sludge used in the trials was, mg/kg DM;
Cd Pb Zn Ni Cu Mn Cr Hg
3 108 693 36 356 271 71 3
The mean values obtained here are in close agreement with the mean and median values from the analyses
of sludge from different sewage purification plants in Norway (HALLBERG and VIGERUST, 1981). The
content of heavy metal in sludge used in the trials can be characterized as low but representative.
For reasons of simplification mean values for each metal, based on all the harvests and all crops, were
calculated and expressed as relative figures (concentration for treatment without sludge=100). The relative
figures for each sludge amount was calculated based on just the same experiments with control treatments.
Table 1. Heavy metal content in plants from field experiment, expressed as relative numbers, without sludge=100.
Numbers of experiment harvests in brackets.
Sludge, tons DM per hectare
0 15 20 45 60 120
Cd 100 65(3) 91(6) 93(14) 108(7) 112(10)
Pb 100 97(2) 93(3) 99(2) 104(1)
Zn 100 109(4) 131(11) 141(18) 166(8) 208(12)
Ni 100 89(4) 111(11) 99(16) 145(8) 154(11)
Cu 100 92(4) 119(11) 130(18) 128(8) 134(12)
Mn 100 100(3) 102(5) 112(12) 120(4) 124(7)
Fe 100 101(2) 130(3) 105(8) 110(1) 96(2)
Sludge application has, only to a little degree changed the Cd-content of the plants while the content of Pb
was practically unchanged. The Zn amounts in the plants have been greatly increased by increased sludge
applications but the levels were scarcely phytotoxic. Sludge application rates of 60 and 120 t/ha DM lead to
a marked increase of the Ni content in plants. This was observed in 2 experiments in the first year. This can
partly be attributed to the decline in pH upon sludge application, but this pH effect lasted for only one year.
Mn and Cu levels in the plants were continuously raised by increasing sludge doses.
Crop response to sludge application was somewhat greater for meadow grasses and rape than for cereal
grains.
26
35. b. Trials with different crops grown on 0, 10 and 40 cm decomposed sludge Green areas commonly
require higher applications of sludge compost than agricultural land. Our trials indicate that a 4–10 cm layer
is adequate.
As our experiments on the use of sludge on agricultural land indicated that the metal content in yields,
except for Zn, is changed within a certain margin of error, it was considered necessary to lay out our present
trials using high rates viz: 0, 10 and 40 cm layers of decomposed sludge. The 10 cm layer was incorporated
into the top 20 cm of the soil. The soil was a sandy loam with 8% organic matter. Altogether 28 crops were
grown for each treatment. Some of the crops were grown for 3 years, some for 2 and some for only 1 year.
The heavy metal content in the sludge used was, mg/kg DM:
Cd Pb Zn Cu Cr Mn Ni
5.5 271 516 492 148 268 42
pH in the top soil was ordinarily 6.2. During the first summer a drop in the pH in pure sludge to 5.0 was
observed in the upper 15 cm. Even though a rise in the pH was later recorded in sludge and sludge-treated
soils, this never reached the pH level of the top soil without sludge.
Cd, Fig. 1.
The Cd-content in different plants and different parts of the plants differed greatly. The content in the
plants as little influenced by the Cd-amounts applied with the sludge. Crops such as lettuce, maize and red
beets had, however, high Cd contents as a results of sludge treatment. Cereal grains and potato tubes,
important food crops in Norway, had low Cd-contents and, compared to the other food stuffs, were little
affected by the treatment.
Pb
Sludge application increased the Pb content in lettuce while the other crops were little or not affected.
Zn, Fig. 2.
The Zn-content in plants increased with increased amounts of applied sludge. Crops such as fodder beet,
lettuce, red beet and red clover had especially high Zn-content in the leaves. Some of these crops did not
grow well,probably because of toxic Zn-effect. High rates of sludge or waste compost may result in prolonged
crop failure and the Zn-content may be a decisive factor in this connection.
Ni, Fig. 3.
Increasing sludge applications have enhanced the nickel content in the plants. The increase in the plants
was, however, considered moderate in relation to the high amounts of applied Ni,. although the element is
regarded as relatively easily plant available.
Cu, Fig. 4.
Variations in sludge applications did not lead to great differences in Cu-content in plants. Plant response
to Cu was not as regular as was found for Cd and Zn.
Mn, Fig. 5.
Incorporating a 10 cm sludge layer into the soil resulted in only a slight change in the Mn-contents in the
plants. Grown in pure sludge on the other hand resulted in high concentrations of the metal in the plants or
parts of the plants. This may be attributed to sludge decomposition, pH-changes and red/ox conditions
leading to a greater availability of Mn.
Fe
There was a clear tendency that high sludge applications resulted in decreased Fe-content in the plants.
This is probably connected to the sludge decomposition and the effect can be altered with time. DOWDY
and LARSON (1975) pointed out that sludge applied to acid soil decreased the Fe-content in the plants.
27
36. They supposed that the reason might be that Fe forms complexes with other compounds in the soil and is
tendered less available.
Other elements
The treatment had little or no effect on the content of Cr, Hg or Co in plants. Grown in pure sludge
enhanced the B-content in the vegetative parts of the plants. For barley, wheat and partly oat, this lead to
symptoms of B-toxicity which became less after one or two years.
Recapitulatior
The mean content of each metal in all the crops including parts of the plant has been calculated and
presented as a guide (table 2). FIGURE 1—mg Cd pr. kg dry matter
Table 2. Concentration of heavy metals, mean values for different crops and part of plants. Treatment with sludge
calculated as relative numbers, concentration without sludge=100.
Applied sludge
0
mg/kg
10cm
relative
40cm
numbers
Cd 0.5 127 168
Pb 3.4 115 127
Zn 46 269 420
Ni 2,4 130 218
Cu 10.6 114 157
Cr 1.0 110 110
Mn 53 109 485
Increasing amounts of sludge affected the content of the different heavy metals in this order:
Zn>Mn*>Ni>Cd>Cu>Pb, Cr
Some crops as beans, red beet, maize and partly lettuce did not grow quite well in pure sludge. This
might be caused by a toxic effect of one or more of the heavy metals.
Several crops showed higher concentrations of Zn and partly Cu than what DAVIS and CARLTON-
SMITH (1980) and SAUERBECK (1982) give as indication of critical limits. The content of Ni, Cd or Pb,
however, did not exceed their indicated limits.
c. Effect of liming
Application of 8000 kg CaO/ha to pure sludge increased pH only 1 unit, As an average for different crops
this lime application only reduced the metal content in plants by 5–20% as compared to unlimed sludge.
This effect of liming on metal uptake must be characterized as very little compared to the common lime
effect on soils. It could probably be related to the increased decomposition as a result of liming and the
metal-fixing power of intermediate decay products. According to CHRISTENSEN and TJELL (1983)
increased CO2 production might also lead to metal precipitation.
d. Effect of organic matter
In a frame experiment the following yields of ryegrass, g/m2, was obtained:
a) Control (including N-fertilizer) 384
b) 60 tons sludge/ha (No N-fertilizer) 389
c) Heavy metals as b), given as chlorides (N-fertilizer) 322
d) Sludge 20cm layer on top (No N) 491
28
37. e) Heavy metals as d), given as chloride (N-fertilizer) 0
FIGURE 2—mg Zn pr. kg dry matter
29
40. These results show that the plants can tolerate much higher amounts of metals when they are part of the
sludge compared to application as inorganic salts.
e. Effect of temperature
FIGURE 5—mg Mn pr. kg dry matter
32
41. Pot trials conducted in phytotrone showed that different temperatures (9, 12, 15, 18, 21 and 24°C) have
an effect on the content of some heavy metals in lettuce (fig. 6)
Decreasing temperatures very clearly lowered the content of Zn, Mn, and Fe in the plants. This was also
true for Cd but not so regular for both harvests. Ni, Cu and Mo were not significantly affected by
temperature.
3.
RESULTS OF SOME PUBLISHED INVESTIGATIONS
Published results from trials with sludge are collected and the mean values are calculated for different crops
and presented in Tab. 3. Although reservations must be made for such a presentation, it is desirable to give a
picture of the effects.
It is obvious that high variations in sludge application and composition of sludge exist in the material. In
some of these trials sludge with high or even very high content of heavy metals was used, and only in a few
trials the sludge was at the same low level as sludge used in our investigations.
For each crop an average metal content in plants is calculated for treatments without sludge (mg/kg DM).
For treatment with sludge these mean values are given as relative numbers, concentration without sludge=
100. Tab. 3 represent data from 26 publications, references number: 1, 2, 4, 6, 7, 8, 12, 13, 16, 17, 18, 20, 2
1, 22, 23, 25, 26, 27, 28, 29, 31, 32, 34, 35, 36, 38. The calculations include more than 117 experiment
harvests, The calculated average of sludge application rates was high, and is given in a separate column.
Tab. 3 indicates that application of sludge has affected the content in plants in this order:
Zn>Cd>Ni>Cu>Pb, Hg, Cr
Compared to this data our results showed less content of most of the metals from sludge treated soils,
especially Cd and Cu.
* The Mn-content was little changed at 10 cm, while pure sludge gave high contents in plants.
Fig. 6. The effect of declining temperatures (24–9°C) upon heavy metal content in lettuce expressed relatively;
concentration at 24°C=100. (From: SIRIRATPIRIYA, VIGERUST and SELMER-OLSEN, 1985).
Temperatures: 24, 21, 18, 15, 12 and 9°C
33
43. Cd Pb Hg Ni Zn Cu Cr
O S O S O S O S O S O S O S tons
DM,
ha
veg.
part
0.50
(2)
160 5.10
(2)
92 5.0
(2)
52 34
(8)
259 6.4
(6)
173 56
TOM
ATO
fruit 0.46
(8)
235 5.60
(6)
132 24
(8)
146 8.3
(7)
133 180
veg.
part
0.80
(3)
75 5.60
(3)
98 30
(3)
140 6.7
(3)
128 90
SAL
AD
0.81
(19)
285 4.6
(11)
117 4.42
(2)
100 4.2
(6)
119 43
(11)
300 10.0
(13)
120 79
Mean rel.
numbers
184 98 104 164 217 156 102 78
4.
DISCUSSION
Different factors are important when considering the actual limits and regulations in sludge utilization:
– Utilization of sewage sludge is especially precarious where the heavy metal strain as a whole is high.
– Results obtained in sludge experiments in Norway clearly show that only a very little part of applied
metals through sludge is taken up by the plants per year. This indicates that a possible problem might be
long lasting. According to ELINDER et al (1978) the Cd-concentration in kidney cortex of Swedes in
1974 were not at a level where injury could be expected. This can, however, be changed in the future if
the Cd-strain is increased. In addition it is shown that Cd in kidney accumulates with age (l.c.). This also
underlines that the strain over several years are important.
– The most effective way to prevent problem caused by sludge is to ensure that only sludge with low
concentration of critical metals are allowed to be spread.
– Limitation of the yearly amount of sludge which can be spread will ensure good distribution of metals
applied. This will, however, not reduce the total amounts of metals applied to agriculture land and will
scarsely change the total metal-content in the agricultural products as a whole. By spreading sludge to
area where e.g. cereals are the main crop, an eventual enhanced content may very effectively be
“diluted”, because the grain from different areas are mixed. Also products which are marketed (sold) are
over years “mixed” with others and thus an effective dilution takes place.
– In general the heavy metal uptake is higher in vegetables than in e.g. grain of cereals. The total amount
of metals brought into circulation by the products are relatively high for vegetables. In Norway we
recommend that sludge should not be used on area where vegetables normally are grown.
– Utilization of sludge on typical green areas should not involve any risk for contamination of food. In the
free marketing of sludge—or waste—compost there is a certain risk for use of high doses in private
gardens including soil where vegetables are grown for their own use.
– Composting is expensive and the product ought to be sold if this treatment shall be an actual alternative.
The marketing is, however, difficult if certain regulations are required.
35
44. – High doses of sludge, which seem to be of special interest on green areas, involve a certain risk for
phytotoxic effects. Our investigations indicate that, at a normal ratio in concentration between different
metals in sludge, this risk follows this order:
Zn>Cu>Ni
Mn-toxicity may occur if the compost is unripe or if anaerobic conditions exist especially in the first
one or two years.
– Liming is an effective way to reduce the plant availability of most of the heavy metals, according to our
results in this order:
Mn>Zn>Ni, Cd>Cu>Cr, Pb, Fe
Liming reduces the metal uptake by plants in the short term. The metals, however, are preserved in the
top soil and could be potentially available. The problem can therefore be more long lasting. In areas or
countries where the heavy metal problem is considered only as a long term risk, little is gained by
requiring a certain limestatus in soil when sludge is to be spread. Where metals, for different reasons,
might have toxic effects, liming can be an effective counteractor regardless of the fact that the toxicity is
to plant, animal or man.
– Cd is considered to be the most precarious as far as health risks are concerned. The plant uptake of the
metal, however, is reduced by increasing the amount of available Zn in soil, (CHANEY 1974). It is
desirable that the Cd-content in the sludge does not exceed 0.5% of the Zn-content (l.c) According
ELINDER and KESSLER (1983) the Cd absorption from the gastrointestinal tract is relatively low if
there is a simultaneous low intake of, among other metals, Zn. Our results do show that sludge
application gives especially high Zn uptake in plants. Zn applied through sewage sludge, therefore, may
reduce possible harmful effects of Cd both by reduced uptake by plants and lower absorption from food.
Everything which reduces the metal uptake tends to make the problem more long lasting. Liming, high
Zn-content, high organic matter content in soil and sludge postpone the uptake in plants. These factors
reduce the uptake of Cd and increase the possibilities of dilution in our food.
– In our pot experiment increasing temperatures increased the content of Zn, Mn, Fe and Cd in lettuce. If
this is true, also under field conditions, one could expect the heavy metal problem being less in colder
than in warmer climate.
– Considerations of the heavy metal problem from sewage sludge are based on a series of experiments.
Many of these experiments are, however, carried out with higher doses of sludge or with higher heavy
metal content in the sludge than what is recommended or allowed to be used in practice. Some data may
also be based on pot experiments, which are not directly comparable to field experiments (De VRIES et
al, 1978; KUNTZE et al, 1983). On one hand it is possible that the experimental data partly overestimate
the uptake from sludge. On the other hand short term experiments do not give realistic answers on the
future situation when sludge is spread for decades.
– We have calculated the amount of sludge produced in different geographical parts of our country in
relation to the total area of agricultural land. The amount of sewage sludge produced in Oslo and
Akershus per unit cultivated area is about 10 times higher than the equivalent amount in any other county
(fylke) in Norway. The total amount of metals applied to land by sludge on agricultural land close to
towns are much higher than in typical rural districts. In general the pollution from other sources are also
higher in these areas. We also must take into account that it is precisely these areas that are especially
important for production of food for the population center of the district. In the nordic countries almost
only dewatered sludge is utilized, facilitating transportation over fairly long distances. Liquid sludge
which has a high N-value, is often applied in lower doses than dewatered sludge. In the long run,
however, liquid sludge can give higher strain than dewatered sludge on the agricultural land close to the
36
45. bigger towns because of limited transport possibilities. We believe that this type of distribution in the
long run is much more precarious than if certain areas receive high doses for 10 or 20 years.
– Compared to most of the EEC-countries the heavy metal problems as a whole seem to be moderate in
Norway. The metal content in sludge is normally low or very low. The farming management is
dominated by one-sided cereal production in areas where use of sludge has particular interest. We also
have a relatively cold climate. The farmers are interested in high sludge applications per unit of area. It
is, however, strongly recommended to utilize the sludge primarily on soil in poor physical conditions.
The sludge should not be used on soils where vegetables normally are grown.
REFERENCES
1 () ANDERSSON, A. and K.O.NILSSON, 1976. Influence on the levels of heavy metals in soil and plant from
sewage sludge used as fertilizer. Swedish J. agric. res., 6:151–159.
2 () BÆRUG, R. and J.H.Martinsen, 1977. The influence of sewage sludge on the content of heavy metals in
potatoes and on tuber yield. Plant and Soil, Vol 47, No. 2:407–417.
3 () CHANEY, R.L. 1974. Recommendations for management of potentially toxic elements in agricultural and
municipal wastes. USDA National Program Staff Soil, Water and Air Sciences Beltsville, U.D.
4 () CHANEY, R.L., S.B.HORNICK and P.W.SIMON, 1977. Heavy metal relationships during land utilization of
sewage sludge in the northeast. Land as a Waste Management Alternative . U.S. Dep. of Agric. Beltsville,
Maryland: 283–310.
5 () CHRISTENSEN, T.H. and J.C.TJELL, 1983. Interpretation of experimental results on cadmium crop uptake
from sewage sludge amended soil. CEC-Proceedings of the Third International Symposium, Brighton. Sept. 83:
358–369.
6 () CUNNINGHAM, R.D., D.R.KEENEY and J.H.RYAN, 1975. Yield and metal composition of corn and rye
forage grown on sewage sludge amended soil. J. Environ. Qual.Vol.4, No. 4:448–454.
7 () DAMGAARD-LARSEN, S., K.E.LARSEN og P.SØNDERGAARD KLAUSEN, 1979. Årlig tilførsel af slam
fra rensningsanlæg til landbrugsjord. Tidsskr. f. Planteavl. 83:349–386.
8 () DAMGAARD-LARSEN, S., P.SØNDERGAARD KLAUSEN og K.E.LARSEN, 1979. Engangstilførsel af
slam fra rensningsanlaeg til landbrugsjord. Tidsskr. f. Planteavl. 83:387–403.
9 () DAVIS, R.D. and C.CARLTON-SMITH, 1980. Crops as indicators of the significance of contamination of
soil by heavy metals. Water Research Centre T.R. 140, 44p. Medmenham Laboratory.
10 () DE VRIES, M.P.C, and K.G.TILLER, 1978. Sewage sludge as a soil amendment, with special reference to Cd,
Cu, Mn, Ni, Pb and Zn-Comparison of results from experiments conducted inside and outside a glasshouse.
Environ. Pollut, 16:231–240.
11 () DOWDY, R.H. and W.E. LARSON, 1975. Metal uptake by barley seedlings grown on soils amended with sewage
sludge. J. Environ. Qual. Vol.4, No.2:229–233.
12 () DOWDY, R.H. and W.E.LARSON, 1975. The availability of sludge borne metals to various vegetable crops. J.
Environ. Qual., Vol.4, No. 2:278–282.
13 () DUDAS, M.J. and S.PAWLUK, 1975. Trace elements in sewage sludges and metal uptake by plants grown on
sludge-amended soils. Can. J. Soil Sci. 55, 239–243.
14 () ELINDER, C.-G., L.FRIBERG og M.PISCATOR, 1978. Hälsoeffekter av kadmium. Läkartidningen. Vol.75,
Nr.47:4365–4367.
15 () ELINDER, C.G. and E.KESSLER, 1983. Toxicity of metals. CEC-Proceedings of a Seminar Uppsala 1983.
16 () FURR, A.K., W.C.KELBY, C.A.BACHE, H. GUTENMANN and D.J.LISK, 1976. Multielement absorption
by crops grown in pots on municipal sludge-amended soil. J. AGRIC. Food Chem. 24,889–892.
17 () GAYNOR, J.D. and R.L.HALSTEAD, 1976. Chemical and plant extractability of metals and plant growth on
soils amended with sludge. Can. J. Soil Sci. 56:1–8.
37
46. 18 () GIORDANO, P.M., J.J.MORTVEDT and D.A.MAYS, 1975. Effect of municipal wastes on crop yields and
uptake of heavy metals. J. Environ. Qual. Vol. 4:394–399.
19 () HALLBERG, P.A. og E.Vigerust, 1981. Slamdisponering 3. Tungmetaller i kloakkslam. Prosjekt 2.2.15.
Utvalg for fast avfall, NTNF, 82s.
20 () HAMAR, T.O., 1974. Kloakkslam til plantedyrking. Hovedoppgave Inst. f. jordkultur, NLH. 127s.
21 () JOHN, M.K. and C.J.VAN LAERHOVEN, 1976. Effects of Sewage Sludge Composition. Application Rate,
and Lime Regime on Plant Availability og Heavy Metals. J. Environ. Qual. Vol.5, No. 2:246–251.
22 () KELLING, K.A., D.R.KEENEY, L.M.WALSH and J.A.RYAN, 1977. A field study of the agricultural use of
sewage sludge: III Effect on uptake and extractability of sludge-borne metals. J. Environ. Qual. Vol.6, No. 4:
352–358.
23 () KOSKELA, J., 1978. Disposal of municipal sludges containing heavy metals in agriculture. Seminar on Heavy
Metals, Technological Methods for the Limitation of Discharges. Copenhagen 4.–7. June. 3.5:1–12.
24 () KUNTZE, H., E.PLUQUET, J.STARK and S.COPPOLA, 1983. Current techniques for the evaluation of metal
problems due to sludge . Prosessing and use of sewage sludge. Proc. of the Third International Symp. Birghton.
Sept. 1983 D.Reidel.
25 () LATTERELL, J.J., R.H.DOWDY and W.E.LARSON, 1978. Correlations of extractable metals and metal
uptake of snop bean grown on soil amended with sewage sludge. J. Environ. Qual. Vol. 7, No.3:435–440
26 () LINNMAN, L., A.ANDERSSON, K.O.NILSSON, B.LIND, T.KJELLSTRØM and L.FRIBERG, 1973.
Cadmium uptake by wheat from sewage sludge used as a plant nutrient source. Archiveo. Environ. Health, Vol.
27:45–47.
27 () MARTINSEN, J.H., 1976. Kloakkslam som gjødsel og jordforbedringsmiddel. Inst. f. jordkultur, NLH.
Stensiltrykk. 221s.
28 () MCINTYRE, D.R., W.J.SILVER and K.S.GRIGGS, 1977. Trace elements uptake by field-grown plants
fertilized with waste water sewage sludge. Compost Sci. 18, 5:22–29.
29 () SABEY, B.R. and W.E.HART, 1975. Land application of sewage sludge: I. Effect on growth and chemical
composition of plants. J. Environ. Qual . Vol. 4, No. 2:252–256.
30 () SAUERBECK, D., 1982. Welche Schwermetallgehalte in Pflanzen dürfen nicht überschritten werden, um
Wachstumsbeeinträchtigungen zu vermeiden. Kongressband 1982. Vorträge 94. VDLUFA-Kongress, Münster.
Sept. 1982, s.108–129.
31 () SCHAUER, P.S., W.R.WRIGHT and J.PELCHAT, 1980. Sludge-borne heavy metal availability and uptake by
vegetable crops under field conditions. J. Environ. Qual. Vol. 9, No. 1:69–73.
32 () SHEAFFER, C.C., A.M.DECKER, R.L.CHANEY and L.W.DOUGLASS, 1979. Soil temperature and sewage
sludge effects on metals in crop tissue and soils. J. Environ. Qual. Vol. 8, No. 4:455–459.
33 () SIRIRATPIRIYA, O., E.VIGERUST and A.R.SELMER-OLSEN (in press) Effect of temperature and heavy
metal application on metal content in lettuce. Sci. reports of the agric. university of Norway.
34 () SORTEBERG, A., 1972. Kloakkslam og tungmetaller. Norsk Landbruk nr. 22. 7s.
35 () TORP, M., 1980. Kloakkslam til jordbruksformål. Hovedoppgave Inst. f. jordkultur, NLH. 125s .
36 () VALDMAA, K., 1972. Jordbrukets krav på slamkvalität. Åttonde nordiska symposiet om vattenforskning.
Nordforsk. Publikation 1972–3: 223–236.
37 () VIGERUST, E. og A.R.SELMER-OLSEN, 1985. Tungmetallopptak ved bruk av kloakkslam. Rapport fra Inst.
f. jordkultur, NLH. Serie B 2/85, 58s
38 () ZWARICH, M.A. and J.G.MILLS, 1979. Effects of sewage sludge application on the heavy metal content of
wheat and forage crops. Can. J. Soil Sci. 59:231–239.
DISCUSSION
KUNTZE (FRG): You have suggested that the organic matter in sludge causes a more rapid
decrease in availability of metals than occurs in soil alone, but here you are
comparing two different systems. Soil is better aerated and therefore has a
38
47. higher redox potential than sludge. You also observed that with increasing
temperature the crop uptake of cadmium, zinc, manganese and iron
increased. Microbial activity and lime in sewage sludge both have a warming
effect and contribute towards the higher metal uptake from sludge than from
soil.
VIGERUST (Norway): We did not grow plants in sludge alone. The temperatures in the soil with
and without sludge were similar throughout the seasons during our
experiment.
SCHELTINGA (Netherlands): You seemed to suggest that heavy additions of metals to the soil was
acceptable because of mixing of agricultureal products such as grain and
wide distribution in marketing. Is this policy in Norway?
VIGERUST: I did not suggest we should allow high levels of metals in food; low levels
are essential. We grow only 20% of food and this is mixed with imported
food. In general metal levels are low in Norwegian sludges.
GOMEZ (France): In your studies on the effect of temperature on metal availability, was there a
difference between soil and atmospheric temperatures?
VIGERUST: The temperature was uniform for roots and tops in each plant growing room,
but different growing rooms were maintained at different temperatures.
GOMEZ: You compared the effects of metal salts and metal-containing sludge. The
sludge contained large amounts of iron, did you add iron in the metal salt
treatments?
VIGERUST: No we did not add iron.
GOMEZ: Can you explain the initial drop in pH after sludge addition?
VIGERUST: The change in pH was not understood. In some cases it increased, and in
others it decreased.
FROSSARD (Switzerland): Was the humidity in the laboratories controlled?
VIGEREST: We tried to control humidity. Water consumption was greater at higher
temperatures.
FROSSARD: The transport of elements such as copper and nickel by mass transfer in the
transpiration stream is affected by temperature.
39
48. SOIL INGESTION BY GRAZING ANIMALS; A FACTOR IN
SLUDGE-TREATED GRASSLAND
G.A.Fleming,
An Foras Taluntais,
Johnstown Castle Research Centre,
Wexford,
Republic of Ireland
INTRODUCTION
While the application of metal-rich sewage sludge to land has received considerable attention in recent
years most studies have been concerned with its incorporation into tillage soils. On grassland different
conditions obtain necessating different approaches and strategies for application. While its effect on grass
production may be considerable (O’Riordan 1983) the surface accumulation of metals in grass swards can
be undesirable under grazing systems. Some indication of the extent of this surface accumulation is shown
in Fig. 1.
Fig. 1. Surface accumulation of zinc in a grassland soil after application of a high Zn sludge. (O’Riordan 1983).
SOIL INGESTION BY ANIMALS
It is well known that involuntary ingestion of soil together with herbage takes place during grazing. The
beneficial effects of such ingestion were recognised in the eighteenth century (Fraser 1794) when cobalt
deficiency in sheep in England was successfully treated by dosing with a suspension of soil in water.
49. Likewise the classical cure for piglet anaemia involved the provision of upturned sods from which the
young pigs received sufficient amounts of iron to offset the condition. On the other hand increased tooth
wear of sheep resulting from ingested soil has been reported (Healy and Ludwig 1965, Nolan and Black
1970).
The amount of soil ingested by grazing animals varies to a considerable extent and close grazing animals
such as sheep may under extreme conditions ingest over 400 gm of soil per day (Field and Purves, 1964).
Normally amounts are much smaller and typical data are shown in Table 2.
Table 1. Intake of herbage and soil by animals.
Animal Herbage Soil Soil intake
(gm/day D.M.) % of D.M.
Sheep 600 100 14
Cow 13,000 1,000 8
D.M.=Dry matter.
FACTORS AFFECTING SOIL INGESTION
Soil type.
Soils with good structure are associated with low soil contamination of pasture and vice versa. When
structure is poor and drainage bad, treading by animals results in much poaching. Consumption of grass is
then attended by relatively large soil intakes by animals. In modern farming practice, however, soils with
good drainage and structure are more likely to suffer from over stocking and thus soil ingestion becomes of
greater consequence.
Stocking rate and Season
It is to be expected that soil intake by animals will increase when stocking rate is increased. Likewise
seasonal effects can be anticipated; when for instance rainfall becomes more abundant, soil contamination
of pasture is enhanced and thus soil intake rises. Some quantification of these factors is shown in Fig. 2.
In this experiment (McGrath et al. 1982), sheep at two stocking rates were used and soil intake measured. In
both the high (HSR) and the low (LSR) stocking rates, animal numbers were reduced as the season
advanced and grass on offer became more scarce but the mean stocking rates were—HSR 30 and LSR 20
sheep per hectare. The data clearly indicate greater soil ingestion by the animals on the high stocking rate
while for both rates ingestion increased as the season advanced and the quantity of grass declined. This is
especially evident in the case of the highly stocked animals.
Stock management.
In modern management systems animals may be either set stocked or rotationally grazed. In the former
instance a group of animals are confined to a grazing area until all grass has been consumed while in the
latter case animals are moved at frequent intervals—often daily—and they are returned to the original
paddock or grazing area in three to four weeks. The less frequent the changes the closer is the
approximation to set stocking. The increase in soil intake by sheep on a seven day grazing cycle as opposed
to a twenty-eight day one is shown by the data of Table 2.
41
50. Table 2. Soil ingestion and grazing pattern1
Stocking rate ewes/ha Grazing cycle (days) Soil in faeces (% D.M.)
37 7 37
37 28 10
1 Healy (1973).
Other factors influencing the degree to which soil is ingested include the soil content of conserved material
(silage) and the duration of supplementary winter feeding (meals and concentrates).
Earthworn activity
Increased dry matter production is associated with greater earthworm activity and in wet periods
especially, more worm casts appear on the soil surface. Movement of animals spreads these casts with
resultant contamination of pasture and cast height and shape facilitates their consumption. Worm casts also
tend to proliferate in open type swards rather than on those having a surface mat. Newly reseeded pastures
of high producing ryegrasses are characterically of the open sward type.
MEASUREMENT OF SOIL INGESTION
The amounts of soil ingested by grazing animals can be measured by estimation of the soil content of faeces.
This may be done by collection of fresh faecal material in the field or more precisely by collection of faeces
from animals fitted with a suitable harness. In this case, daily faecal output can be readily measured and
determination of the ash content of the faeces provides an estimate of soil content. A refinement of this
method involves treatment of the ash with dilute mineral acid thus correcting for ash contribution from
undigested herbage. The acid insoluble residue (AIR) is then taken as a measure of soil ingested and is
related to it by the formula.
Fig. 2. Effects of stocking rate and season on amounts of soil ingested by sheep. (McGrath et al. 1982).
42
51. AIR in faeces is normally calculated by the method of Healy and Ludwig (1965). About 4 gm of faeces are
ashed overnight and a portion of the ash (usually 0.5 gm) digested with 6 N HCl (20 ml) on the water bath
for 1 hour. The residue is then washed free of acid on filter paper and reignited in the furnace. AIR is
calculated as a percentage of digested ash in oven-dry faeces.
Soil in faeces may also be measured by relating the titanium (Ti) content of faeces to that of the soil. The
method is based on the principal that the Ti content of faeces can be taken as being essentially derived from
soil only. This assumption is based on the known wide disparity between the Ti level in soils (0.2–1%)
compared with that in uncomtaminated herbage (0.5–2 ppm).
Soil ingestion is then calculated from the following formula. (Thornton and Abrahams 1983).
Titanium may be determined by atomic absorption or by X-ray fluorescence (XRF) as described by Healy
(1968).
SOME NUTRITIONAL IMPLICATIONS FOR ANIMALS
It is now recognised that ingested soil is an important pathway for metal absorption by animals especially in
areas which are naturally contaminated (geochemical pollution) or where enhanced metal levels have
resulted from industrial activities. Ingested soil as it passes through the animal’s alimentary tract it is
subjected to a range of conditions inherent in the digestive process. In particular the differences in pH
between the abonasum (c. pH 3.0) and the rumen (c. pH 7.0) are important and must exercise significant
effects on metal absorption. Other processes such as complexation may also be involved. Alimentary tract
conditions therefore may increase or decrease heavy metal availability to the animal.
Lead poisoning in cattle in Ireland has resulted from consumption of soil-contaminated beet tops from an
old mining area and from dust blown on to soil and herbage adjacent to mine tailings ponds.
Studies in England in areas where metalliferous mining and smelting were carried out in the past, have
revealed that under the prevailing conditions up to 80% of lead and up to 90% of arsenic assimilated by
cattle could be attributed to ingested soil (Thornton 1983).
Similarly selenium poisoning of animals which was reported in Ireland many years ago (Fleming 1962)
was subsequently observed to be more prevalent in dry summers (Twomey et al. 1977). Under such
conditions when forage becomes scarce animals ingest greater quantities of soil than normal, and this increased
soil intake would seem to offer at least a partial explanation for the observed increase in selenosis in dry
summers.
43
52. Even where soils do not contain anomalous levels of elements it is thought that soil ingestion exercises
some effects. Thus Statham and Bray (1975) considered that iodine intake by sheep from ingestion of a clay
soil was greater than that from a sandy one, as sheep grazing on the latter had more goitrous lambs than
those on the former.
One of the most common trace element disorders associated with livestock production is that of copper
deficiency. This is frequently associated with high levels of molybdenum in herbage and is exacerbated by
high intakes of sulphur. Iron has now been implicated in the complex mechanisms that bring about
hypocupraemia in animals (Suttle et al. 1982) and this being so, soil intake is brought into sharp focus, as it
can be the major source of ingested iron. Recently it has been suggested that a possible mechanism for
copper depletion may first involve precipitation of FeS in the rumen followed by release of sulphide in the
more acid abomosum milieu with resultant trapping of potentially absorbable copper as insoluble CuS
(Suttle et al. 1984). Other elements such as zinc and cadmium may also be involved and can also act as
antagonists towards copper absorption.
The occurrence of the swayback condition in lambs results from a copper shortage in the parent ewe. The
condition has been related to the length of time of snow cover on winter pastures insofar as less swayback is
experienced when snow lies on the ground for relatively long periods. Under these conditions ewes
obviously ingest less soil and also receive more supplementary feed thereby increasing their chances of
receiving more copper (Thornton 1983).
The above examples serve to illustrate some of the effects of soil ingestion on animals. Disposal of
sewage sludge on grassland must take these factors into account and—apart from the more obvious dangers
associated with organic pathogens—the possible repercussions from enhanced heavy metal intake from soil
ingestion must be considered.
REFERENCES
FIELD, A.C. and PURVES, D. (1964). The intake of soil by grazing sheep. Proc. Nut. Soc. 23:24.
FLEMING, G.A. (1962). Seleniun in Irish soils and plants. Soil Sci. 94: 28–35 28–35.
FRASER, R. (1794). General view of the county of Devon. Quoted by Hopkirk, C.S.M. and Patterson, J.B.E. “The story
of cobalt deficiency in Animal Health”. Mond-Nickel, Co. London.
HEALY, W.B. (1968). Ingestion of soil by dairy cows. N.Z. Jl. agric. Res. 11:487–499.
HEALY, W.B. (1973). Nutritional Aspects of Soil Ingestion by Grazing Animals. In “Chemistry and Biochemistry of
Herbage” Vol. 1. ed. G.W. Butler and R.W.Bailey. Acad. Press London, 567–588.
HEALY, W.B. and LUDWIG, T.G. (1965). Wear of sheep’s teeth 1. The role of ingested soil. N. Z. Jl. agric. Res. 8:
737–752.
MC GRATH, D., POOLE, D.B.R., FLEMING, G.A. and SINNOTT, J. (1982). Soil ingestion by grazing sheep. Ir. J.
agric. Res. 21:135–145.
NOLAN, T. AND BLACK, W.J.M. (1970). Effect of stocking rate on tooth wear in ewes. Ir. J. agric. Res. 9:187–196.
O’RIORDAN, E.G. (1983). The chemical composition of Irish sewage sludges and their effects on soil properties and
grass growth. Unpub. Ph. D. thesis, University College, Dublin pp 591.
STRATHAM, M. and BRAY, A.C. (1975). Congenital goitre in sheep in Southern Tasmania. Aust. J. agric. Res. 26:
751–768.
SUTTLE, N.F. ABRAHAMS, P. and THORNTON, I. (1982). The importance of soil type and dietary sulphur in the
impairment of copper absorption in sheep which ingest soil. Proc. Nut. Soc. 41:83A.
SUTTLE, N.F. ABRAHAMS, P. and THORNTON, I. (1984). The role of a soil x dietary sulphur interaction in the
impairment of copper absorption by ingested soil in sheep. J. agric. Sci. Camb. 103:81–86.
44
53. THORNTON, I. (1983). Soil-plant-animal interactions in relation to the incidence of trace element disorders in grazing
livestock. In “Trace Elements in Animal Production and Veterinary Practice”. Occ. Publ. No. 7 Br. Soc. Anim.
Prod. Ed. N.F.Suttle, R.G.Gunn, W.M.Allen, K.A.Linklater and G.Weiner. BSAP Edinburgh 39–49.
THORNTON, I. and ABRAHAMS, P. (1983). Soil ingestion—a major pathway of heavy metals into livestock grazing
contaminated land. Sci. Total Envir. 28:287–294.
TWOMEY, T., CRINION, R.A.P. and GLAZIER, D.B. (1977). Seleniun toxicity in cattle in Co. Meath. Ir. vet. J. 31:
41–46.
DISCUSSION
McGRATH (UK): You related the percentage of acid insoluble residue to percent soil ingestion. Is
there a formula for the relationship?
FLEMING (Eire): Yes, this is published. If an X-ray fluorescence spectrometer is available the
titanium marker method is better.
WILLIAMS (UK): In reference to copper deficiency you mentioned FeS formation. Does this take
place in the animal?
FLEMING: Yes, a black deposit is formed in the gut.
JUSTE (France): Do the stomach contents of the animal extract metals from the ingested soil and
does the liquor give a good indication of the heavy metal intake?
FLEMING: Yes, metals particularly selenium and cobalt but not copper are extracted from
ingested soil. However, the liquors of the duodenum and ilium have different
pH values and therefore solubilise different amounts of metals.
COPPOLA (Italy): It has been shown that germ-free animals have different metal uptake. Should
the effects of micro-organisms in the gut be included in the factors influencing
metal status?
FLEMING: Yes, this is an important factor and one which is not familiar to most of us.
WILLIAMS: Have you established whether there should be limits for any elements such as
fluorine or lead to safeguard against contamination of herbage?
FLEMING: No, we have not investigated limits, but this could be a subject for research.
FROSSARD (Switzerland): Is the splashing of soil onto plants by rain important?
FLEMING: Yes, herbage splashed by soil has been found to have a much higher cobalt
analysis than uncontaminated herbage. In dry conditions, blown soil dust can
also cause herbage contamination.
45
54. GROUNDWATER QUALITY IN RELATION TO LAND
APPLICATION OF SEWAGE SLUDGE
M.Ahtiainen
National Board of Waters, Water District Office of North Karelia, Finland
Summary
At present the most hazardous pollution phenomenon in groundwaters is the nitrateproblem. The extent of
N-removal will determine the feasibility of most sludge application projects. From a practical standpoint,
the annual loading rate can be estimated using a N-mass balance. The annual loading rate can be adjusted in
accordance with proper monitoring technique. The upper limit for nitrogen fertilizers has been emphasized
to be 100 kg/N/ha, when the groundwater pollution is hindered.
Several research studies confirmed that little, if any, migration of heavy metals occur through the soil, if
moderate amounts of sewage sludge have been applied. The heavy metal load into groundwaters will become
more serious, if the acidification process of the soils is allowed to continue with acid rains. Consequently a
more effective pretreatment of industrial effluents must be reconsidered in the near future.
The fecal bacteria are known to accumulate better in the top soil layer than viruses. More information is
required about the behaviour of virus percolation and survival in groundwaters.
Our knowledge of toxic organic chemicals is scarce concerning the filtration processes into
groundwaters. At present the runoff phenomena of these compounds appear in surface waters in a more
prominent and harmful way than in groundwaters. When focusing on the groundwater contamination we
should keep in mind the numerous other sources, which in the long run can seriously affect the groundwater
quality. In a wider context, land application of sewage sludge plays a minor role, but locally land
application should be carried out with extreme care.
1.
Introduction
In recent years concern has been expressed for the pollution question of European groundwaters. When
discussing the application of sewage sludge it should also be borne in mind that more effective agriculture,
industrialization as well as urbanization are also to be blamed for.
Most of nothern Europe has been glaciated. The area is therefore covered with quarternary stratifications.
A high proportion of the groundwater consumed thus derives from these stratifications, which are of great
importance.
A simple geohydrological model of a landscape in central Sweden can serve as a basis for estimates of
where the risk of the impact of land application is great and where it is absent or small (Figure 1).
55. Naturally only the groundwater in the permeable layers is of interest in terms of water supply. The
magnitude of the impact of land application on groundwater quality is dependent on the local conditions
such as climate, type of soil, type and amount of sludge, and chemical conditions (7).
In central Europe the aquifers are in sedimented rock layers, which are significantly larger and deeper
than the Scandinavian ones. The border of ekers and rivers are of special concern. Naturally different kinds
of crackers and ruggedness in soil can assist the sludge infiltration into the deeper soil layers as well.
2.
Nitrate-nitrogen
The nitrate-nitrogen concentrations have elevated in every European country. At the same time plant and
animal production and the use of fertilizers in agriculture have increased. The nitrate content of
groundwater is usually observed to be higher in areas where water can easily percolate through the soil than
in clay soil areas (20).
In Denmark the nitrate content of groundwater has increased threefold in the past 20–30 years and is
continuously growing (14). In Holland in cultivated areas the nitrate concentrations of shallow aquifers is
hudredfold compared with the natural state of groundwaters in sandy soils (15).
Because of slow infiltration rate the effects of fertilizers cannot be observed immediately. In Sweden the
present NO3-concentrations are said to reflect the fertilization levels of the 1960s. Therefore, it is predicted
that NO3-N concentrations of groundwaters will be elevated in the near future. (1).
If the amount of fertilizers exceeds the need for plants, the amount of percolating nitrogen increases. If
the fertilization limit is over 170 kg N/ha it is the main NO3-source of groundwaters (17). According to
Andersson (1) the critical level is 100 kg/ha N.
For sound fertilization and water management sludge application rates that would not elevate groundwater
or soilwater NO3-N levels above the 10 mg/1 potable water standards were recommended as 9.5 dry Mg of
undigested sludge/ha of red pine plantation, 16 dry Mg of digested sludge/ha of red pine and white pine
plantation and 19 dry Mg digested sludge/ha of aspen sprout stand (Figure 2). These rates differ because of
the faster N-mineralization rate in undigested sludge and the greater nutrient uptake rate in the young aspen
stand (2).
According to Higgins aerobically digested liquid sewage sludge was applied to Sassafras sandy loam
soils for 3 consecutive years. Sludge was applied at rates of 22.4 and 44.8 Mg of dry solids/ha. Annual
application rates of 22.4 Mg of dry solids/ha resulted in the contamination of the groundwater beneath the
test plots and immediately offsite. Annual application rates of 44.8 Mg of dry solids/ha grossly
contaminated the groundwater. Nitrate-N concentrations in groundwater sampled from within the plots
receiving sludge increased to≤50 mg/1 in proportion to the amount of sludge applied.
Once sludge application ceased, normal levels quickly resumed; therefore it appears that the effects of
sludge application≤44.8 Mg of dry solids/ha on groundwater NO3-N are temporary and easily recoverable in
this area. The results of this study show that leaching, particularly NO3-N, will occur in late fall and winter.
Cover crops will mitigate the leaching effects on groundwater.
Application of the 22.4 Mg of dry solids of sludge is clearly at the upper limit to ensure protection of the
groundwater quality on this site according to the federal drinking water standards. Application rates, at or
slightly below the 22.4 Mg of dry solids/ha application rate are sufficient for providing plant nutrient for
corn and rye. (10)
47
56. In conclusion I would like to emphasize the fact that the nitrogen deposition of the air has increased
everywhere. What is more, other activities such as the use of artificial fertilizers, liquid manures, furfarming,
and clear cutting of forests have elevated NO3-N concentrations.
3.
Heavy metals
Contrary to the nitrogen and contagion problems, which can be managed adequately with existing
knowledge and technology, the metals involve rather complicated considerations before a satisfactory
assessment of the problem can be reached (5).
The mobility of heavy metals in the soil, their retention and release is governed by precipitation,
complexation, adsorption and oxido-reduction. The total maximum acceptable amounts of sludges are
calculated in function of the heavy metal contents of the sludge and the receiving soil. From this it appears
that the most limiting elements are Cu, Zn, Cd and Cr.
The yearly dose will, however, in the first order be restricted by the nitrogen content, while heavy metals
accumulate from year to year restricting their further input in the distant future (4).
To estimate the effect of pollution of the soil with heavy metals and other elements from sewage sludge
on surface and groundwater quality, data on the physical and chemical parameters involved in the
Fig. 1 A geohydrological model of a landscape in central Sweden (7)
48
57. adsorption processes in soils are essential. (5). Adsorption is affected by speciation of the elements in the
soil solution and by pH, Eh, ionic strength and composition of the soil solution as well as by the clay and
organic matter content of the soil.
Cadmium is considered the most harmful among heavy metals, mercury and lead are other clearly toxic
elements.
According to Huylebroeck raised concentrations of heavy metals in groundwater have been raported to a
minor extent. According to several Danish and Dutch researchers (6, 8, 9) even high doses of sludge (up to
30 tn/ha DM) did not increase leaching of heavy metals (Cd, Pb, Ni) into subdrains and groundwater.
Mostly Cd has been found to accumulate in the top soil layers. Only lead and zinc had been noticed to leach
below 0, 5m and only the content of zinc had increased in groundwater. In the field experiment of Liperi
and Maaninka elevated concentrations of heavy metals could not be detected either (13).
In an early mentioned study (10) sewage sludge application—44.8 Mg of dry solids/ha did not contribute
heavy metals to groundwater samples taken within the test-plots nor 30.5 m off-site. According to this
Fig. 2. Recommended sludge application rates as related to soil water and groundwater NO3-N concentrations. (10)
49
58. writer application of 22.4 Mg of dry solids of ha sludge is clearly at the upper limit to ensure protection of
groundwater quality on this site according to the federal drinking standards. Hence the results indicate that
no detectable contaminant of the groundwater occur as a result of sludge application even at the highest
rate. These results confirm previous research findings that little, if any, migration of heavy metals occurs
through the soil.
There is little risk from a single sludge application on arable land, but it is necessary to examine the
situation created by an increasing sludge production and its future disposal. Therefore, the only acceptable
attitude is to keep the total amounts of heavy metals in the soil below sufficiently safeguard limits
concerning the increasing sludge production, and the limited absorption capacity of soils for heavy metals.
The treatment of effluents will have to be conducted in the future in such a way that heavy metals should be
eliminated where necessary (4).
Moreover, there may be a natural heavy metal explosion to be expected, if the acid rains do lower the soil
pH below a certain level.
4.
Patogens
It would be fair to assume that the microbial load of the sewage will vary from community to community
and that within each community it will vary according to the enteric infections prevalent at the time of
testing. It is important that the patogen load in the sludge be known before operations commence. It is
equally important that the characteristics of the soil with regard to pH, clay content, proximity to the water
table, infiltration capacity and drainage pattern be known (19). In addition, it is essential that accurate
records be kept of sludge application to land so that retrospective investigation can establish the operating
conditions in case of problems.
Salmonella are probably the most important bacteria present in sludge. Patogens might cause human
illness by contaminating surface waters by runoff and percolation. It appears that patogen movement in soil
is related directly to hydraulic infiltration rate and inversely to media particle diameter, in general patogens
do not travel to any great extent in soils and remain principally in the upper layers. It has been presented
that most of the total and fecal coli-forms removed to the top soil, but fecal streptococcs were found as deep
as 14 m and at the distance of 183 m horizontally from the infiltration area of waste waters. (Table 1 after
Lahti).
The possibility of viral contamination of surface and groundwaters as a result of the land application of
domestic wastes poses one of the major concerns. (Table 2 after 12).
Vaughn studied lateral movement of groundwaters entailed viruses from a subsurface waste-water
disposal system in Long Island New York. Virus movement could be traced at least up to 67.05 m the septic
source. There was also no correlation between the presence of viruses in groundwater and the counts of fecal
coliform bacteria.
It has been stated however that the land disposal of sewage sludge is much safer than landfilling,
incineration and discharge to water bodies.
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