Contamination of coastal versus open ocean surface waters

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Marine Pollution Bulletin, Volume 26, No.3, pp. 128-134, 1993.

Contamination of Coastal versus Open
Ocean Surface Waters
A brief meta-analysis

W.JACKSON DAVIS
Department of Biology, University of California and The Environmental Studies Institute,




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Contamination of coastal versus open ocean surface waters

  1. 1. Marine Pollution Bulletin Marine Pollution Bulletin, Volume 26, No.3, pp. 128-134, 1993. Printed 0025-326X/93 $6.00+0.00 © 1993 Pergamon Press Ltd in Great Britain. Contamination of Coastal versus Open Ocean Surface Waters A brief meta-analysis W. JACKSON DAVIS Department of Biology, University of California, Santa Cruz, 2309 Empire Grade, Santa Cruz, CA 95060, USA The relative contamination of coastal and open ocean surface waters by several classes of marine pollutants is compared by re-analysis of data published by GESAMP (1990) on the state of the oceans. This re-evaluation, together with analysis of recent IAEA data, suggests that marine pollutants can be divided into three broad categories: 1. those that are more concentrated in the open ocean environment than in coastal waters, including PCBs and (arguably) radioactive wastes; 2. those that are equally concentrated in open ocean and coastal waters, including DDT and its metabolites; and 3. those that are somewhat more concentrated in coastal waters than the open ocean, including chlorinated hydrocarbons and the heavy metals. The data do not support the conclusion drawn by GESAMP that although coastal waters are contaminated, "the open sea is still relatively clean". Instead the data support the general conclusion that, with respect to the contaminants examined here, open ocean waters are approximately as contaminated as coastal waters. C4. 95064; and The Environmental Studies Institute, * agencies and issued by the United Nations Environmental Program (UNEP). This report notes that coastal regions are deteriorating seriously world-wide: "destruction of beaches, coral reefs and wetlands, including mangrove forests, as well as increasing erosion of the shore, are evident all over the world:' In contrast, the GESAMP report concluded, in summary, that "the open sea is still relatively clean". The purpose of this brief communication is to present a partial re-evaluation of the database on which the GESAMP summary conclusions are founded. This reanalysis does not support the 'dirty coast clean seas' hypothesis. Instead it suggests, for the several contaminants examined, that the surface waters of the open seas are approximately as contaminated as coastal waters. This conclusion has implications for both scientific and policy decisions in the area of marine pollution. Methods There is widespread perception that coastal waters may suffer point sources of significant pollution, but "the open sea is still relatively clean" (GESAMP, 1990). Such a perception reduces the motivation for global action to preserve the marine environment. Moreover, this "dirty coasts clean seas" hypothesis is self-perpetuating, because it inhibits the research and monitoring of the open ocean that could test the accuracy of the perception. The perception that the open ocean is still relatively clean therefore has both policy and scientific ramifications. The 'dirty coast clean seas' hypothesis originates in part from a recent analysis of the health of the marine environment by GESAMP-the authoritative Group of Experts on the Scientific Aspects of Marine Pollution (GESAMP), sponsored by several United Nations *A California Non-Profit Corporation founded in 1981 for purposes of research and public education on scientific issues related to environmental policy. 128 The data on which the GESAMP conclusions are based are contained in technical annexes to the GESAMP report (UNEP, 1990). The present analysis is confined to data on the concentration of marine contaminants in coastal and open ocean surface waters, contained in the excellent review by Fowler (1990). Data published in the literature, and therefore in Fowler's review, are generally based on random or pseudorandom sampling, rather than systematic sampling techniques, especially in regard to the open oceans. Moreover, means of several measurements from a single locale are typically presented, without reference to the population variance. It was impossible, therefore, to test hypotheses about means using t-tests or their nonparametric equivalents. Instead, means of means are reported here, and compared across the two categories of coastal surface waters and open ocean surface waters. Such procedures do not enable statistically valid conclusions, but rather provide a broad qualitative impression of the state of the oceans.
  2. 2. Volume 26/Number 3/March1993 It is to be emphasized, however, that the database employed here is identical to that employed by GESAMP. Therefore, although the procedures used here cannot satisfy normal standards of scientific confidence, they nonetheless permit a critical evaluation of GESAMP's conclusions. Data are summarized in the form of histograms comparing the mean concentration of specific contaminants in coastal and open ocean surface waters, in various regions of the world (Figs 19). Results Polychlorinated biphenyls (PCBs) are more generally concentrated in open ocean waters than in coastal waters (Fig. 1). Average concentrations range from less than one-tenth of a nanogram per litre of sea water water (Kanechlor in the Antarctic) to more than 75 nanograms per litre (Aroclor 1254 in the Atlantic and Pacific). The higher concentrations in the open ocean presumably reflect the atmospheric input of PCBs to ocean water (GESAMP, 1989). Radioactive wastes may likewise be more concentrated in the open ocean environment, although these are not covered in the GESAMP report. This conclusion is based on the historical fact that the deliberate dumping of radioactive wastes at sea (IAEA, 1990), combined with the loss of several naval nuclear reactors at sea, have deposited far more radioactivity in the open ocean than has entered coastal waters (Davis, 1990; Davis and Van Dyke, 1990). Radioactive wastes, however, to the extent that they have escaped containment, have relatively high sediment binding (distribution) coefficients, which restricts their concentration in ocean surface water. The global distribution of DDT and its metabolites follows a slightly different pattern from that of PCBs. Where comparisons are possible between concentrations in coastal and open ocean waters, the values are approximately equal (Fig. 2). In approximately half the comparisons, concentrations are greater in the open oceans than in coastal waters. By far the greatest levels are found in the northeast Atlantic, where concentrations of about 500 nanograms per litre are substantially greater than concentrations in comparable coastal Phenoclcr D-P5 10 Aroclor zones. As a generality, concentrations are larger in the open ocean in regions of the world where terrestrial use of DDT's has been curtailed (e.g. the northern hemisphere), while coastal concentrations are greater in regions where terrestrial use continues (e.g. the southern hemisphere). This distribution pattern presumably reflects the input of this contaminant to the ocean from riverine sources. Remote regions, where terrestrial DDT use has never occurred (e.g. the Antarctic), also show higher concentration in open oceans, though generally not as high as in industrialized regions, suggesting incomplete ocean mixing. Assuming a relatively long residence time for DDT in comparison with mixing rates, existing concentrations in these remote regions may be expected to increase over time as mixing becomes more complete. A similar analysis for chlorinated hydrocarbons illustrates that concentrations in sea water are generally slightly (less than a factor of two; north Pacific, northwest Atlantic) to substantially (approximately an order of magnitude; Mediterranean Sea) higher in coastal waters (Fig. 3). Only in remote regions, such as the Antarctic, are concentrations of chlorinated hydrocarbons higher in open ocean waters. The final class of pollutants examined here, namely the heavy metals, includes cadmium, lead and mercury. Cadmium is generally moderately to substantially more concentrated in coastal zones than the open ocean (Fig. 4). Quantitative analysis shows, however, that over the entire globe the concentration is only about 2.3 times higher in coastal waters than in the open ocean. Inspection of the sources of cadmium contamination (Fig. 5) suggests that much of it originates from local coastal "hot spots" such as the New York Bight in the Atlantic, and various North Sea point sources. When these local hot-spots (defined, for this analysis, as regions in which the concentration exceeds twice the mean value) are eliminated from the means, the concentration ratio (coast/ocean) drops to 1.6. In other words, the concentration of cadmium in coastal waters is less than twice as great as in the open ocean waters. These data are consistent with a dynamic source model in which cadmium originates largely from land based sources and is introduced into coastal regions, largely by run-off but also (potentially) atmospheric input. Considering that the open ocean surface waters represent a Aroelor 1260 1254 18 8 15 75 6 12 60 9 45 6 30 3 15 Kanechlor 0.10 4 2 0 0 O/G Med./France 0.08 0.06 0.04 O/G A/A.P 0 0.02 0.00 O/G Fig. 1 Mean concentrations of PCBs in ocean (0) and coastal (C) surface waters litre). Abbreviations: Med., Mediterranean Sea; A, Atlantic; P, Pacific; Data are means of means presented in tables in Fowler (1990). Numbers represent the 'sample' size (where individual samples are, in some cases, several measurements). O/G AntlAnt AP/AP (nanograms per Ant, Antarctic. above each bar mean values of 129
  3. 3. Marine Pollution Bulletin vastly greater volume than coastal surface waters, these data demonstrate that the bulk of cadmium has found its way to the open seas. Lead exhibits a similar pattern to cadmium. Lead concentrations are generally higher in coastal waters, although occasional comparisons reveal greater concentration in the open ocean (Fig. 6). The global ratio of coastal to open ocean concentration is approximately 2.4, but when localized hot-spots are eliminated (Fig. 7), the ratio drops to 1.6. Finally, mercury concentrations present a similar pattern to cadmium and lead. Concentrations are generally, but not always, higher in coastal waters, but the difference is generally moderate (Fig. 8). Elimination of local hot-spots again yields roughly equivalent concentrations in coastal and open ocean waters (Fig. 9). North A,N (1~2 5[fP'N L ~ ~ ,...-'''T-- P,NE : 20 2 10 ~ (J~ 01 G 1 A,NE ~ 600 500 () ~ aIG 0 O/G I 1 W ,./'? A Mid iJ:: 1l0 ::. AS O/G 04 02 a 00 0:30.06 0.04 lndian ~:~; 0-001 0.02 000 O/G Fig. 2 Mean concentrations of DDT and its metabolites (nanograms per litre) in open ocean (0) and coastal (C) surface waters. Abbreviations: 0, concentration in ocean surface waters; C, concentrations in coastal surface waters. Histograms are positioned in the approximate regions where measurements were made. Further abbreviations: N, north; Chin, China Sea; NW, northwest; S. south; otherwise as in Fig. 1. Data are means of means presented in tables of Fowler (1990). Baltic ~'~JjP'N ~ 0 O/G 0.04 0.4 0.02 0.2 0.0 A' O'~: 0.6 0.00 ~ "-a O/G I G '"--"'- ~'~rIA'S 0.6 0.4 Antarctic O.8r---- 0.2 0.0 a a (JIG Fig. 3 Mean concentrations of chlorinated hydrocarbons (nanograms and coastal (C) surface waters. Otherwise as in Fig. 2. 130 I 001 0.00 0.0 1.Jr;r0.02 ~ 0.02 ~O ~ .u~ : ~ 200 per litre) in open ocean (0) o a o
  4. 4. Volume 26/Number 3/March 1993 Discussion Re-analysis here of the admittedly incomplete data based employed by GESAMP in its recent report on the state of the oceans suggests that ocean contaminants can be divided into three broad categories. The first category, including PCBs and arguably radioactive wastes (IAEA, 1990), is more concentrated in the open ~[i o Ti o 0 ole ole a a Fig.4 Mean concentration of cadmium (nanograms surface waters. Otherwise as in Fig. 2. per litre) in open ocean (0) and coastal (C) Coastal Surface Waters Open Ocean Surface Waters 300 300 E .2' 0> <Ii 200 M ec 0> M co (]> ::. ::. 150 100 .2 C 21 :;: .2 c 21 :;: M co 0> o :.c o ro Q. M '" 0 0 z 0 (]> W .... z; '" 2 ·0 ~ :a ~ ro u 0 '" Q. ~ ;;; ro ~ '~ s: s: ~ ~ ' ;t " t: t:" s: '" s: t: t: z W 1'0 (]> ;;; 50 ~ 250 18 250 Q. '" Q. eo ~ t: s: ;,; 00 ~ z, 0> N· co en ::. GO 0> ..• 00 en ::::. t: s: CD CD ~ 00 ::::. ~ .;, ~ 6 CD 0> '" •• ~ •• 8 (j) 0 ~ al 150 c co 100 (j) s: t: 0 Z -~~ N"'" 200 "_0 ~-> ::,..g ~ ,,~ ~~z g< ~~ ~'i3 --,~ uSJ "0 c '" '6 .£ 50 0 z z 0 0 50 50 40 40 30 30 20 20 10 10 a 0 of cadmium (nanograms per litre) in open ocean (left Fig. 5 Histograms showing concentrations panels) and coastal (right panels) surface water, by region, illustrating locally high concentrations (point sources or 'hot spots). Lower graphs are of the same data in the upper graphs but on an expanded scale. Data are means of means presented in tables of Fowler (1990). 131
  5. 5. Marine Pollution ocean than in coastal regions, reflecting their input from atmospheric sources (PCBs) or past dumping at sea (radioative wastes). The second category of contaminants, including DDT and its metabolites, is approxi- Bulletin mately equally concentrated in the open ocean and coastal waters, suggesting inputs from land sources that have reduced over time. And the third class of contaminants, including chlorinated hydrocarbons and Baltic ~f1 o O/C :~~ o 01 C a Fig.6 Mean concentration of lead (nanograms surface waters. Otherwise as in Fig. 2. per litre) in open ocean (0) and coastal (C) '" ~ -g 500 450 400 co ~ '" ,:, ~ co ~ 350 co M co a. 300 CD '" o 250 200 150 100 50 M co i Q. " t: ~ ~ ~ ~ ~ ~ .!l :e :( c ~ •• co s: ..; .. .. "in M co '" e c: o c " Q. •• .. ~ ;;: .s :e c M co a. '" "in ;r co z, '" e a; .. ii ::E ~ 400 ~ 350 300 ..; co z, '" •• e If) s: 0 If) t: z ~ < '" J; co '" co ~ .t: -c: ~ ~ '" c " 8 250 200 ., M '" u C !! 150 100 « ~ z :E .!1 ~ '§ Iii C .'! I;' c .. '" ~ ~ ,! 0. .!l' M ! "8 o "' ~ ;n., CD « o; CD ~ . g- . . : <i ;n'" z, '" e .s c i ~ "' ~ •... (ij" " ~ " e J:; CD 450 ..: ~ co 100,-------------------------------, " :;; 0 ~ ~ iD 1! e :E a; ~ a:. s: .!l' '" C < '" .3 .~ ~ '" ~ ~ c ~~ <i o ~ 't; ~ o '" ::; 0 "' u .g M 0 0. ~ '" 60 40 20 20 o o Fig.7 132 'I I•• I. s: "' CD 80 40 '" :::. . '" "iii 100 60 ., ~ '" '" .• '"~ •• .. ~ . '" e ~ : '" c ~ ·E 50 80 c .; eX 0 0 " u: 1;'--0:)_'0 500 e co ~ i '" Coastal Surface Waters Open Ocean Surface Waters II Histograms showing concentrations of lead (nanograms per litre) in open ocean (left panels) and coastal (right panels) surface waters, by region, illustrating locally high concentrations (point sources or 'hot spots'). Otherwise as in Fig. 5. ~ .; .!1 0. .!1 '.ij ell E l t: ~ ~ (!I M '" u "E ell u:- ~ 0 .• " ~ ~ ~ 8- ~ ~ .• 1; ~ '" i' ~ e .• c '" ::i .,; eX ..s •• 's: " '".; " 15 's: t: Z 0 z s: t: ~ ~ ~ l t- .. C ~ c .'l! ~
  6. 6. Volume 26/Number 3/March 1993 the heavy metals, is generally somewhat more concentrated in coastal waters, although elimination of especially large point sources of contamination Chot spots') in coastal waters nearly eliminates the difference with the open oceans. The distribution pattern of the third class of contaminants presumably originates from continuing coastal inputs. Although the data reviewed here do not enable statisArc Baltic North 3 4 Ber j~~~r. 0.0 0.4 0.2 ole ~r.i li o Fig.8 o 0.4 0.3 D ole 90 0.2 Coastal Surface Waters ;;:- 100 z; Gl eo ., :E .2 .c: 80 iii ~ ;( Z co 70 ~ 70 r::- >Ol 60 '" J z; to ea 50 40 40 30 30 20 20 aL~~ ~U.u.~~ ~ ~ en ~ .2 ~ ~ "@ w Z '" Z Ol ;:;ec Ol ~ Gl co Ol t: '" Ol >- e- ~ '~ iii '" " '" iii >- '" a. e ::> ;;; ii'> ",-a> '" Ol Ol 90 80 a per litre) in open ocean (0) and coastal (C) (/) 60 I 0.5fjP'SW 0.0 Mean concentrations of mercury (nanograms surface waters. Otherwise as in Fig. 2. 50 ole .0.1 100~----------------------------. o~ a ole Open Ocean Surface Waters 10 0.0 W z .,; 18 en CD r-, to cc Z en ii'> eo en .2 <: ::> cZ Cd <l> (/) >. .c: 0 '" " ~ z 0 z; z; ~ S a. <II '" z; to ec Ol 'E .2. u. e II? '" > ~ '" ~ 10 0 10~----------------------------, 10 8 8 6 6 4 4 2 2 0 o Fig.9 Histograms showing concentrations of mercury (nanograms per litre) in open ocean (left panels) and coastal (right panels) surface waters, by region, illustrating locally high concentrations (point sources or 'hot spots'). Otherwise as in Fig. 5. 133
  7. 7. Marine Pollution ticallyvalid conclusions, the data are identical to those on which GESAMP based its summary conclusions. The data do not support the unqualified 'dirty coast clean seas' hypothesis. Instead, they indicate that the open oceans are approximately as contaminated as coastal waters. Therefore, if coastal waters are considered to be seriously impacted, as stated by GESAMP, then so also are open ocean waters. Coastal zones suffer greater pollution from erosion, turbidity, direct sewage discharge and riverine inputs; but by the same token, the open oceans may suffer more from deliberate dumping, which, with the exception of dredged materials, is generally not undertaken in coastal waters; and from atmospheric inputs, if ony because the receptive surface area of the open ocean is far greater. The levels of contamination in open ocean surface waters revealed by the available data merit more detailed attention for several interacting reasons: 1. 90% of biological productivity occurs there, and this productivity is concentrated in surface waters; 2. The concentrations and biological impacts of literally hundreds of ocean contaminants are unknown; 3. Concentrations recorded in the open ocean (as high as hundreds of nanograms per litre) appear greater than those known, for some pollutants (e.g., tributyl tin), to produce significant biological defects (1-2 nanograms per litre; Smith, 198]; Goldberg, 1990); 4. The additive, or interactive, effects of ocean stressors, such as the combination of increased ultraviolet radiation from ozone depletion with existing levels of contamination, are largely unknown; 5. The surface micro layer is lipophilic owing to the concentrations of biological membrane, and hence concentrates organic contaminants such as PCBs; 6. Concentration factors in living unicellular organisms can be as high as I00 000 times above the ambient water concentration; 7. Developmental events crucial to most ocean life forms occur within the surface micro layer; 8. Approximately one-third of ocean pollution is transmitted to ocean waters through this surface microlayer from the atmosphere (GESAMP, 1989, 1990); 9. 134 Bulletin Concentrations of contaminants in the surface microlayer have generally not been measured; and 10. Potential damage from these contaminants may occur in a binary or discontinuous (threshold) mode and be irreversible owing to long time lags. The GESAMP report on the state of the oceans acknowledges the general inadequacy of the available database, and especially the paucity of data available for the open ocean. The GESAMP report also warns of the need for concerted international action within the next decade if serious and potentially irreversible degradation of the oceans is to be averted. The present re-examination of available data supports that recommendation, but suggests further that the oceanic ecosystem may presently be more vulnerable than suggested by GESAMP's summary conclusions. Davis, W. J. (1990). Global aspects of marine pollution policy: The need for a new international convention. Mar. Po!. 14, 191-197. Davis, W. J. & Van Dyke, J. M. (1990). Dumping of decommissioned nuclear submarines at sea. A technical and legal analysis. Mar. Pol. 14, 467-476. Fowler, S. W. (1990). Concentration of selected contaminants in water, sediments and living organisms. In UNEP: Technical annexes to the report on the state of the marine environment. UNEP Regional Sea Reports and Studies No. 11412. UNEP, 1990, pp. 209-230. Goldberg, E. D. (1990). Selected contaminants: Tributyltin and chlorinated hydrocarbon biocides.ln UNEP. Technical annexes to the report on the state of the marine environment. UNEP Regional Seas Reports and Studies No. 11412. UNEP, 1990, pp. 209-230. GESAMP (1989). The Atmospheric Input of Trace Species to the World Ocean, 1989, Rep. Stud. GESAMP (38). GESAMP (1990). The state of the marine environment. Rep. Stud. GESAMP (39). International Atomic Energy Agency. Inventory of Radioactive Material Entering the Marine Environment. Part I: Sea Disposal of Packaged Low Radioactive Waste. Issued in draft form in Sept. 1990 as document LDC/3/INF.23 by the London Dumping Convention. Vienna: IAEA, and London: International Maritime Organization (1M 0). Smith, B. S. (1981). Male characteristics in female snails caused by antifouling bottom paints. 1. Appl. Toxicol. 1,22-25. UNEP (1990). Technical annexes to the report on the state of the marine environment. UNEP Regional Seas Reports and Studies No. 11412. UNEP, 1990 (Volumes 1 and 2).

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