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Effect of land use change from paddy to vegetable field
on the residues of organochlorine pesticides in soils
Hongtao Hao a,c
, Bo Sun a,*, Zhenhua Zhao b
a
Institute of Soil Science, Chinese Academy of Sciences, No. 71 East Beijing Road, P. O. Box 821, Nanjing 210008, China
b
College of Environmental Science and Engineering, Hehai University, Nanjing 210098, China
c
Graduate School of the Chinese Academy of Sciences, Beijing 100039, China
The OCPs residues especially DDTs changed significantly with tillage time after the conversion from paddy to vegetable field.
a r t i c l e i n f o
Article history:
Received 30 August 2007
Received in revised form 26 January 2008
Accepted 27 April 2008
Keywords:
Organochlorine pesticides
DDT
HCH
Land use change
Vegetable field
Paddy field
a b s t r a c t
The effect of land use change from paddy to vegetable field on the residues of organochlorine pesticides
(OCPs) was investigated. Soil residues of OCPs were analyzed in vegetable fields which had been con-
verted from paddy fields for 0, 5, 10, 15, 20, 30, 50 year in Yixing, China in 2003. The mean concentrations
of OCPs followed a sequence of:
P
DDTs (13.7 mg kgÀ1
) >
P
HCHs (8.6 mg kgÀ1
) > > HCB (2.09 mg kgÀ1
) >
a-endosulfan (1.30 mg kgÀ1
) > endrin (1.08 mg kgÀ1
) > PCNB (0.76 mg kgÀ1
) > dieldrin (0.58 mg kgÀ1
). The
mean residues of OCPs especially DDTs increased significantly with vegetable planting time after land
use change in the first 15 years, then decreased from 20 to 30 years and increased a little afterward. The
time under anaerobic and aerobic conditions was suggested to control mainly the change of the residues
of OCPs.
Ó 2008 Elsevier Ltd. All rights reserved.
1. Introduction
Organochlorine pesticides (OCPs) are of great concern due to
their high bioaccumulation potential, ubiquity, persistence in the
environment, deleterious effect and high toxicity to non-target
organisms (Loganathan and Kannan,1994; Willett et al.,1998; Jones
and de Voogt, 1999). The OCPs were widely used and produced in
China from 1960 to 1983 when they were forbidden from being
used. It has been estimated that about 4.46 million tons of technical
HCHs (1,2,3,4,5,6-hexachloro-cyclohexane) (Li et al., 1998) and
0.435 million tons DDTs (1,1,1-Trichloro-2,2-bis-(p-chlorophenyl)
ethane) (Hua and Shan, 1996) entered the environment during
1960–1980. Recent investigations showed that the persistence of
DDTs and HCHs has left residual amounts in soils for many areas (Li
et al., 2006; Wang et al., 2007; Zhu et al., 2005;Cai et al., 2008).
The OCPs residues in soils showed a temporal and spatial
changes in the world (Skrbic and Durisic-Mladenovic, 2007),
because the residue level of OCPs depends on the balance of inputs
and dissipation (such as decomposition, leaching and volatiliza-
tion) and is affected by many factors including application history,
agricultural practices (Boul et al., 1994; Spencer et al., 1996; Wang
et al., 2006), physico-chemical properties of soil such as soil organic
matter, pH and water content (Boul, 1996; Wenzel et al., 2002;
Gong et al., 2003, 2004; Zhang et al., 2006), as well as meteoro-
logical factors such as temperature, rainfall and solar radiation
(Samuel and Pillai, 1989; Haynes et al., 2000). In China, there was
a large spatial variability in the residues of OCPs at the regional
scale (Gong et al., 2003, 2004; Zhao et al., 2005; Li et al., 2006). The
spatial distribution of soil residual concentrations of DDTs and
HCHs in China shows a regional pattern of south > central > north,
which is consistent with the use pattern of the pesticides (Wang
et al., 2005). The largest amount of pesticide application was in
Southeast China with the average annual usage of the active in-
gredients of OCPs varying from 2.4 to 4.5 kg haÀ1
(Cao et al., 2007).
Land use patterns affect the application history and the dissipation
of OCPs through changing the soil conditions, consequently affected
the OCPs residues in soils. Wang et al. (2005) found that the soil res-
idues of HCHs and DDTs invegetable fields were larger thanthat in the
farmland in South and Central China. Li et al. (2006) investigated the
residues of HCHs and DDTs in soils in the Pearl River Delta in SE China,
and found that their mean concentrations decreased in the order of
upland crop soil > paddy soil > natural soil. Wang et al. (2007) found
that the total OCPs residues were higher in agricultural soils than in
uncultivated fallow land soils in the Tai Lake region in East China, and
the ratios of p,p0-(DDD þ DDE)/DDT in soils were in an order of paddy
* Corresponding author. Tel.: þ86 25 8688 1282; fax: þ86 25 8688 1000.
E-mail address: bsun@issas.ac.cn (B. Sun).
Contents lists available at ScienceDirect
Environmental Pollution
journal homepage: www.elsevier.com/locate/envpol
0269-7491/$ – see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.envpol.2008.04.021
Environmental Pollution 156 (2008) 1046–1052

3. Author's personal copy
field > forest land > fallow land, which indicates that land use has an
influence on the degradation of DDT in soils.
In the last two decades, many paddy soils with a long history of
rice planting have been converted to vegetable cultivation to meet
the demand for vegetables with increasing urbanization in China.
According to the China Agricultural Yearbook (ECCAY, 1982, 2004),
the cultivated land for rice planting decreased from 33.3 M ha in
1981 to 26.5 M ha in 2003, whereas the area for vegetable planting
increased from 3.5 to 17.9 million ha. Some researchers have
studied the residues of OCPs in vegetable soils (Chen et al., 2005;
Gonzalez et al., 2005) and in paddy soils (Babu et al., 2003)
separately. A comparison of OCPs residues between paddy soil and
other land use has been reported recently (Li et al., 2006; Wang
et al., 2007). However, the impact of the pattern and history of land
use change on the residues of OCPs has not been investigated so far.
In this paper, Yixing city was selected as a case study area, which is
located in the middle of the Yangtse River Delta region and is
undergoing the large loss of paddy soil due to urbanization (Pan
and Zhao, 2007). We compared the OCPs residues in a series of soils
with different ages of vegetable planting since the conversion from
paddy field, with the aim to assess the impact of land use change on
the OCPs residues in soil.
2. Material and methods
2.1. Investigation area and soil sampling
The investigation area is located in Yixing city, Jiangsu province, China
(312201800N, 1194904500E). The area is near the Tai Lake and in the middle of the
Yangtze River Delta. It has a subtropical monsoon climate with the average annual
temperature of 15.7 C and the average annual rainfall of 1158 mm.
Soil samples were collected from paddy and vegetable fields in Yicheng town,
Yixing city in 2003. All the fields sampled were in a vegetable production base.
Different tillage ages after conversion from paddy fields to vegetable fields were
selected as follows: 0, 5, 10, 15, 20, 30, 50 years, with three replicates for each tillage
age. The continuous paddy fields were used as the control treatment with 0 con-
version age. All the fields had been used as paddy fields for more than 100 years
before the conversion. The paddy soil belong to Fe-leachi Stagnic Anthrosols (CSTRG/
ISSCAS and CRGCST, 2001) which are derived from the fluvio-limnic deposition.
Soil samples were collected from the surface layer (0–15 cm) and the sub-
surface layer (15–30 cm). Each sample was a composite of 8–10 sub-samples that
were mixed, sieved (2 mm) and freeze-dried prior to analysis. De Boer and Smedes
(1997) found that the storage conditions had little impact on the contents of
chlorobiphenyls and DDT components in the wet biological samples which were
stored in screw-cap jars at À5, À25 and À70 C and in the freeze-dried sample which
was stored in the dark at ambient temperature up to 2 year. Each sample was divided
into two portions, one for OCPs analysis and the other for soil-geochemical analysis.
The hydrometer method was used to determine texture and soil particle size. Soil pH
was obtained from a 1:2.5 water–soil slurry and determined by a pH meter (Jackson,
1964). Total P was determined according to the colorimetric method with molyb-
denum vanadate as the color reagent (Jackson, 1964).
Table 1 shows the basic properties of the soil samples. The texture of all soils was
silt according to the USDA texture classification, with a mean content of silt (0.002–
0.05 mm) of 79.1%. The soil nutrient content was higher in surface layer than the
sub-surface layer. Mean soil organic C contents in the surface and sub-surface layer
were 20.2 and 13.4 g kgÀ1
, respectively. Soil cation exchange capacity (CEC) was
similar in the two layers. All soils were acidic especially in the surface layer which
had a mean value of pH of 5.3.
2.2. Reagents and instruments
Standard samples of organochlorine pesticides including a-, b-, g- and d-HCH
[hexachlorocyclohexane], o,p0-DDT [1,1,1,-trichloro-2(p-chlorophenyl)-2-(o-chloro-
phenyl)ethane], o,p0-DDE [1,1-dichloro-2-(p-chlorophenyl)-2-(o-chlorophenyl)
ethylene], p,p0-DDT [1,1,1,-trichloro-2,2-bis(p-chlorophenyl)ethane], p,p0-DDD [1,1-
dichloro-2,2-bis (p-chlorophenyl)-ethane], p,p0-DDE [1,1-dichloro-2,2-bis (p-
chlorophenyl)ethylene], a-endosulfan, dieldrin, endrin, HCB [hexachlorobenzene]
and pentachloronitrobenzene (PCNB) were purchased from Dr. Ehrenstorfer
(Germany) and National Research Center for Certified Reference Materials of China
at concentrations of 100.0 mg lÀ1
, respectively. 2,4,5,6-tetrachloro-m-xylene
(TCMX) was purchased from Supelco (Bellefonte, PA, USA) and was used as a sur-
rogate for organochlorine pesticides. The standards were further diluted with
hexane to prepare working standards. Hexane (HPLC-graded) was from Tedia
Company, USA. All other solvents were of the analytical grade and were redistilled
before use. Anhydrous sodium sulphate (Na2SO4, AR, Nanjing Chemical Reagent
Plant, P.R. China) was used as a desiccant. Silica gel (60 w 100 mesh, Dalian
Chemical and Physical Institute, P.R. China) and Florisil (E. Merck Company,
60 w 100 mesh) were activated in an oven at 225 C for 12 h, then deactivated by
adding 5% deionized water, and other chemical reagents were of the analytical
grade as required.
2.3. Organochlorine pesticides analysis
Analytical procedures were adapted from the standard operating procedures
specified in the State Environmental Protection Administration of China methodol-
ogy guidelines (SEPA, 1993). Ten grams of freeze-dried soil samples in glass
Table 1
The mean values of main properties of soil samples
Soil layer Yeara
pH (H2O) SOC (g kgÀ1
) TN (g kgÀ1
) TP (g kgÀ1
) TK (g kgÀ1
) CEC (cmol kgÀ1
) Clay (2 mm) (%) Silt (2–50 mm) (%)
0–15 cm 0 5.7 14.1 1.50 0.57 10.67 17.0 0.07 82.45
5 4.4 12.0 1.89 1.45 9.77 16.0 0.46 71.77
10 5.1 17.5 1.90 0.98 11.10 18.9 0.14 81.14
15 5.7 27.4 2.78 2.50 10.92 18.8 0.29 71.00
20 5.3 22.2 2.28 2.39 10.96 19.8 0.35 79.24
30 5.3 18.3 1.87 1.93 9.70 15.9 0.24 81.46
50 5.5 16.9 1.96 1.49 10.37 18.6 0.12 83.67
15–30 cm 0 6.8 6.58 0.78 0.50 12.32 16.2 0.32 74.45
5 5.8 9.93 1.07 0.73 9.61 14.6 0.36 69.64
10 6.5 7.71 1.02 0.62 13.00 17.9 0.67 88.99
15 5.7 17.6 1.68 1.31 11.07 18.1 0.51 82.54
20 5.4 13.0 1.60 1.50 11.26 18.5 0.49 79.03
30 5.9 9.10 1.04 1.06 9.46 17.5 0.34 87.75
50 5.3 14.1 0.93 0.85 10.13 16.9 0.32 74.45
SOC: soil organic carbon, TN: total nitrogen, TP: total phosphorus, TK: total potassium, CEC: cation exchange capacity.
a
Year refers the year under vegetable planting after conversion from paddy field.
Table 2
The detection limit, recovery and repeatability of the method
OCPs Detection limit (ng/g) Recovery (%)a
Repeatability (% RSD)
a-HCH 0.10 85.8 3.01
b-HCH 0.10 87.4 3.67
d-HCH 0.10 85.9 4.04
o,p0
-DDT 1.0 98.9 3.36
p,p0
-DDT 1.0 96.5 4.83
p,p0
-DDD 1.0 92.8 3.25
o,p0
-DDE 0.10 100.5 4.22
p,p0
-DDE 0.10 101.8 4.07
a-endosulfan 0.10 83.4 2.75
HCB 0.05 102.2 3.99
Diel 0.10 87.2 3.14
Endrin 0.50 97.5 3.22
PCNB 0.08 98.4 4.05
a
Values as mean of three determinations.
H. Hao et al. / Environmental Pollution 156 (2008) 1046–1052 1047

4. Author's personal copy
centrifuge tube were extracted twice with a 50 ml hexane–dichloromethane mixture
(1:1 v/v) for 1 h in an ultrasonic bath and then the extract was separated by centri-
fugation at 7500 Â g for 10 min. The extracts were combined and evaporated to about
1 ml in glass pearshaped bottle by rotary evaporator under reduced pressure in
a water bath at 45 C (degree of vacuum is 500 kpa), The concentrated extract was
transferred to a glass solid phase purifying column (SPPC, 12 cm length,12 mm I.D.)
containing 1 g activated Silica gel and 2 g Florisil, and 1 g of anhydrous sodium sulfate
on top of the column. Before the concentrated extract was loaded, the SPPC was
leached by 15 ml of 10% dichloroethanes/hexane eluent (v:v) in order to wash the
stuffing of SPPC and push out the air into column. Then, the fraction containing OCPs
in column with the concentrated extract was rinsed by 20 ml n-hexane followed by
20 ml of 10% dichloroethanes/hexane eluent (v:v) after the concentrated extract was
loaded. The elution was evaporated by rotary evaporator and blew down to 1 ml for
GC analysis using a gentle stream of clean dry nitrogen.
Quantification of organochlorine pesticides was carried out with an Agilent
6890 GC/mECD gas chromatograph and HP7683 automatic sampling injector with HP
chemical workstation (Hewlett–Packard, USA). The separation was performed on
a fused silica capillary column (HP-5, 30 m, 0.25 mm I.D., and 0.25 mm film
thickness). The carrier gas was high purity N2 (99.999%) with a flow of 1.0 ml minÀ1
and the make-up gas at 20 ml minÀ1
. The injector and detector temperatures were
220 C and 280 C, respectively. The GC oven temperature was programmed as
follows: initial temperature 60 C held for 1 min, increased to 140 C at a rate of
20 C minÀ1
, then increased to 280 C at a rate of 12 C minÀ1
and kept at 280 C for
4 min. Samples (1 ml) were injected in splitless mode. GC-peaks were identified by
accurate assignment of retention times for each standard (Æ1%), quantitative
calculation was conducted with external standard method. The OCPs residues were
quantitatively determined by comparing the area under each peak with the area
under the standard peak. The resulting correlation coefficients for the calibration
curves of the OCPs were all greater than 0.995.
2.4. Quality control
To reduce or eliminate contamination problems, certain techniques were
employed for sampling, solvents, glassware, etc. Soil was sampled using an acid-
cleaned stainless steel hand auger and the soil layer in contact with the auger was
discarded, then the rest was packed in a clean aluminum foil and deeply frozen for
storage. All soil samples were dried on a Christ Delta 1 freezy-drying apparatus from
Kue`hner AG, Birsfelden for 40 h at a final temperature of 25 C. All solvents were
redistilled in an all-glass system before use and anhydrous sodium sulfate was first
washed with hexane, then heated at 600 C for 12 h before use. Glassware was
prepared by successive treatments in the following order: washing with acetone and
water, soaking in 5% K2Cr2O4 sulfuric acid solution overnight, washing with water
and distilled water in turn, drying at 350–400 C, then rinsing with acetone and
hexane just before use.
For accuracy and precision of analysis, method blanks were run first using the
same solvents as for real samples. No contaminants of organochlorine pesticides
were found in the method blanks (n ¼ 3). The average recovery experiments were
done in triplicate by spiking known concentrations of standards in a matrix blank,
and no significant difference in recovery of organochlorine pesticides studied was
observed between two drying methods by freezy-drying or air-drying treatment on
the spiked matrix with known concentrations of standards. The limits of detection
(LODs) were taken as three times the response of the signal-to-noise (S/N), the
determination of the signal-to-noise ratio is performed by comparing measured
signals from samples with known low concentrations of analyte with those of blank
samples and establishing the minimum concentration at which the analyte can be
reliably detected. These parameters are given in Table 2. At the same time, before
extraction, each of the soil samples was spiked with a known amount of TCMX as
a surrogate to compensate for the loss of components. Recoveries of the TCMX
surrogate were 75.41–107.6% (mean 86.02%). The recoveries of surrogate were
satisfactory and no correlation of analytical data was applied to the samples. The
method blank and matrix blank were measured in duplicate with each batch of 10
samples.
2.5. Statistical analysis
All data were analyzed statistically by the Statistical Package for Social Sci-
ence (SSPS 13, SPSS Inc., Chicago, IL). The Post Hoc Multiple Comparisons of
ANOVA (analysis of variance) was used to compare means of OCPs
Table 3
Average concentrations (ng/g dry weight) of organochlorine pestisides in the Taihu Lake area
Soil depth OCPs Time under vegetable planting after conversion from paddy field
Year
0 5 10 15 20 30 50
0–15 cm
P
HCHs 10.66aa
8.77abc 8.69bc 10.54a 9.60ab 10.46a 7.47c
(0.85)b
(1.28) (0.94) (0.41) (0.15) (0.71) (0.06)
P
DDTs 9.77d 14.04bc 19.32b 20.50a 14.75bc 8.77d 12.12cd
(2.25) (0.45) (1.46) (0.71) (0.66) (0.40) (0.85)
a–endosulfan 0.78c 1.62bc 0.73c 3.51a 1.42c 1.16c 2.65ab
(0.05) (0.59) (0.22) (0.22) (0.06) (0.45) (0.37)
Dieldrin 0.52ab 0.56ab 0.47a 0.63ab 0.53ab 0.39b 0.66a
(0.09) (0.05) (0.06) (0.13) (0.00) (0.03) (0.09)
Endrin 0.85c 1.13abc 0.77bc 1.68a 1.36abc 0.82c 1.62ab
(0.12) (0.08) (0.08) (0.20) (0.09) (0.12) (0.42)
HCB 1.92c 1.88c 1.83c 2.44b 2.06bc 3.91a 1.84c
(0.04) (0.10) (0.11) (0.34) (0.00) (0.05) (0.04)
PCNB 0.79ab 0.81ab 0.66ab 0.99a 0.89ab 0.70b 0.78ab
(0.03) (0.04) (0.07) (0.18) (0.02) (0.03) (0.04)
P
OCPs 25.28b 28.82b 32.46b 40.29a 30.61b 26.20b 27.13b
(3.38) (2.23) (1.15) (2.03) (0.86) (1.38) (0.92)
15–30 cm
P
HCHsa
7.71a 8.19a 8.21a 8.35a 9.50a 9.10a 7.42a
(0.35) (0.35) (1.13) (0.49) (0.68) (1.02) (0.54)
P
DDTsb
8.37c 16.48b 19.90a 20.28a 19.19a 9.27c 10.20c
(1.42) (1.35) (0.33) (0.59) (0.58) (0.19) (0.27)
a–endosulfan 0.48a 0.73bc 0.72bc 1.86a 0.85bc 0.52c 1.15b
(0.02) (0.12) (0.08) (0.18) (0.06) (0.04) (0.33)
Dieldrin 0.33a 0.69a 0.53a 0.80a 0.71a 0.63a 0.63a
(0.03) (0.04) (0.08) (0.16) (0.03) (0.03) (0.06)
Endrin 0.64c 1.02bc 0.79bc 1.86a 0.85ab 0.52c 1.15c
(0.11) (0.05) (0.06) (0.05) (0.10) (0.08) (0.01)
HCB 1.73a 1.83a 1.81a 2.19a 1.98a 2.12a 1.75a
(0.10) (0.11) (0.03) (0.32) (0.01) (0.09) (0.05)
PCNB 0.43c 0.82ab 0.63b 1.09a 0.89ab 0.60b 0.62b
(0.02) (0.03) (0.00) (0.11) (0.02) (0.01) (0.01)
P
OCPs 19.69c 30.22b 32.58a 35.14a 33.56a 22.62c 22.20c
(1.08) (0.74) (1.38) (1.46) (0.11) (0.93) (0.79)
P
HCHs was the total sum of three isomers of HCH, i.e. a-, b-, and g-HCH.
P
DDTs was the total sum of five fractions of DDT, i.e. o,p0
-DDT, p,p0
-DDT, o,p0
-DDD, o,p0
-DDE and p,p0
-
DDE.
a
The values shown in parentheses are standard error of mean.
b
Means in a line followed by the different letters are significantly different at P ¼ 0.05.
H. Hao et al. / Environmental Pollution 156 (2008) 1046–10521048

5. Author's personal copy
concentrations among the different land uses. LSD (least significant difference)
calculation at P ¼ 0.05 was used to identify the significant difference. Analyses
were also separately carried out for exploring the relationships between OCPs
and soil properties (soil organic matter, pH and silt content). Principal compo-
nent analysis (PCA) was used to analyze the distribution of five DDT compounds
and the correlation between OCPs and soil characteristics. Rotation method is
Varimax with Kaiser Normalization. In order to interpret the significance of
retained PCs (principal components) in terms of the original variables, only those
loadings (coefficients) whose absolute value was greater than 60% of the maxi-
mum coefficient in each PC was considered.
3. Results and discusssion
3.1. The organochlorine pesticides
The concentration of total OCPs in all soil samples ranged from
15.5 to 56.8 mg kgÀ1
with an average value of 27.8 mg kgÀ1
, which is
lower than the China National Soil Quality Standard (GB15618-95).
The concentrations in the sub-surface layers were similar to those
in the surface layers. The major groups of OCPs in the soil belong to
the DDT and HCH families, and the residue of DDTs was more
abundant than HCHs. The concentration of total DDTs (including
o,p0-DDT, p,p0-DDT, o,p0-DDD, p,p0-DDE and p,p0-DDD) in all soil
samples ranged from 6.2 to 36.9 mg kgÀ1
with a mean value of
13.7 mg kgÀ1
, while the total HCHs (including a-, b-, and g-isomers)
ranged from 5.7 to 12.3 mg kgÀ1
with a mean value of 8.6 mg kgÀ1
.
Although the use of some OCPs has been banned in China since
1983, the results disclosed in this paper show that residues still
persist in the vegetable soils at considerable concentrations after
more than 20 years.
The concentrations of other OCPs were very low, with a mean
value of 2.09,1.30,1.08, 0.76 and 0.58 mg kgÀ1
for hexachlorobenzene
(HCB), a-endosulfan, endrin, and pentachloronitrobenzene (PCNB),
and dieldrin, respectively (Table 3). These results are consistent with
those of related studies on the vegetable soils in other regions in
China (Chen et al., 2005).
Compared with the paddy soil, the concentrations of total OCPs
increased from 5 to 15 years of vegetable planting, then decreased
from 20 to 30 years, after which their concentrations increased
a little (Table 3). The concentrations of total OCPs, especially of
DDTs in the vegetable fields after 30 years of conversion, were
similar to that in continuous paddy fields, whereas in the vegetable
fields within 20 years of conversion was significantly higher. Li et al.
(2006) also found that the HCHs and DDTs residues in upland crop
soil were higher than those in paddy soil.
The incubation experiment (Bhuiya and Rothwell, 1973) showed
that DDTs was recalcitrant in the soil kept at 15% moisture, while
the anaerobic conditions obtained by flooding the soil caused
reductive dechlorination of p,p0-DDT and enhanced its conversion
to p,p0-DDD. Boul (1996) conducted a 42-day laboratory microcosm
experiment and also observed that the flooding soil have a higher
capacity to transform p,p0-DDT to p,p0-DDD. At the conclusion of
the experiment, the mean binding of p,p0-DDT and p,p0-DDE ranged
between 6.7 and 9.7% under unflooded conditions, while the
binding was increased to 24.5% for p,p0-DDT and 11.5% for p,p0-DDE
under flooded conditions. In the paddy fields, the decomposition of
DDTs is favored by anaerobic conditions such as those encountered
in soils that are either periodically or permanently flooded (Xu
et al., 1994). For this reason, the residue of DDT, which has been
banned for use for 20 years, is the lowest in paddy fields. The
decomposition of DDTs is expected to be slower under aerobic
conditions for vegetable planting. This explains why the residues of
DDTs increased significantly with the age of conversion from paddy
to vegetable fields after the banning in 1983.
Before DDTs were forbidden from being used in 1983, the
application amount of DDTs was higher in paddy fields than in
vegetable fields. Therefore, the soil residues of DDTs were higher in
the vegetable fields with an age of conversion from paddy field
more than 20 years than those less than 20 years. The slower
decomposition process of DDTs under the 50-years of vegetable
Fig. 1. The residues of isomers of DDT and HCH in vegetable fields converted from paddy field.
H. Hao et al. / Environmental Pollution 156 (2008) 1046–1052 1049

6. Author's personal copy
planting than the 30-years made the mean residues of DDTs in the
older vegetable fields a bit higher, however, their differences were
not significant (Table 3).
3.2. DDTs
Among the various compounds of DDTs in soil, p,p0-DDT was the
most dominant (38%), followed by p,p0-DDD (22%) and p,p0-DDE
(21%) (Fig. 1). This is different from other studies on vegetable soils
in North Jiangsu province (Yang et al., 2008) and in Guangzhou city
in South China (Chen et al., 2005), which found that p,p0-DDE was
the predominant component followed by p,p0-DDT. This was
possibly caused by the slow decomposition process in vegetable
soils after conversion from paddy fields.
The commercial grade DDTs generally contain 75% p,p0-DDT,15%
o,p0-DDT, 5% p,p0-DDE, 0.5% p,p0-DDD, 0.5% o,p0-DDD, 0.5%
o,p0-DDE and 0.5% unidentified compounds (WHO, 1979). DDT-
isomers have a long persistence in the environment, gradually
degrading to DDE and DDD under both aerobic and anaerobic
conditions. Dimond and Owen (1996) estimated that the ‘‘half
time’’ for disappearance of DDT residues is 20–30 years. It has been
well established that DDTs are biodegraded, although very slowly,
by two distinct microbial processes, which are aerobic oxidative
degradation and anaerobic reductive dechlorination (Wiegel and
Wu, 2000). Effective transformation of DDTs in the environment
mainly occurs through anaerobic processes by which DDT is
reductively dechlorinated to DDD and then dehydrochlorinated to
DDE (Quensen et al., 1998). High DDT contents relative to DDD and
DDE suggest that DDTs may be hardly decomposed or there is
a new input (Aigner et al., 1998; Zhang et al., 2005).
The mean ratio of p,p0-(DDT/(DDE þ DDD)) is 0.93 in the topsoils
and 1.04 in subsoils in the present study (Fig. 3). These ratios are
similar to those of the vegetable soils investigated in Guangzhou,
which ranged from 0.05 to 3.54 with a mean value of 0.86
(excluding two soil samples with a value more than 14) (Chen et al.,
2005). However, our results are lower than those reported by Yang
et al. (2008) for the vegetable soils in North Jiangsu province, which
have a mean ratio of 1.83 for topsoil and 1.86 for subsoil. Gong et al.
(2004) found that low pH promoted the decomposition of DDTs.
The vegetable soils in our study were acidic with soil pH being
lower than those of the soils in North Jiangsu province investigated
by Yang et al. (2008). Another possible reason is the application of
dicofol in the North Jiansu province, which caused the high DDTs
residues in the surface layer (Yang et al., 2008). In contrast, there
has been no recent DDTs input in the vegetable soils in our in-
vestigated area.
Although the residue of DDTs in vegetable fields increased
during the 15 years of conversion from paddy to vegetable field,
there was no significant difference in the ratio of p,p0-DDT/
(DDE þ DDD) among the vegetable soils with different conversion
ages in both the surface and sub-surface layers. This can be
explained by the similar history of DDTs applications to these soils.
The transformation of DDTs to DDE and DDD was the same in the
vegetable soils without the new application of DDTs from 20 years
ago.
3.3. HCHs
The HCH isomers have different physico-chemical properties. b-
HCH has the lowest water solubility and vapor pressure and is the
most stable isomer and relatively resistant to microbial degradation
(Ramesh et al., 1991). a-HCH can be converted to b-HCH in the
environment (Wu et al., 1997). Commercial HCHs contains 55–80%
a-HCH, 5–14% b-HCH, 12–15% g-HCH, and other chloroorganic
compounds, respectively (Kim et al., 2002). In soils, the average
half-life of g-HCH is 20–50 days while that for a-HCH is 20 weeks
(FAO, 2000). Because the ratio of a-HCH/g-HCH is relatively
constant in the commercial grade HCHs, which ranges from 4 to 7, it
can be used as an indicator for the level of degradation of HCHs
(Kim et al., 2002). The predominance of the a-isomer in some soil
samples reflects the recent use of the technical HCHs.
The total HCHs concentrations remained constant among
different ages of vegetable soils (Fig. 1), suggesting that land use
change had little effect on the HCHs residues which have a shorter
half-life than the DDTs.
The contents of HCHs in the vegetable soils in this study varied
in a similar range to that in Guangzhou (Chen et al., 2005). The
predominant isomer is g-HCH in this study, which accounted for
39.2% of the total HCHs residues. For comparison, b-HCH was the
predominant isomer in the study of Guangzhou soils, accounting
Fig. 2. The ratio of p,p0-(DDT/(DDD þ DDE)) and a-HCH/g-HCH in vegetable fields converted from paddy field.
Table 4
The correlation coefficients among the residue of organochlorine pesticides and soil properties
Soil property
P
OCPs
P
HCHs
P
DDTs a-endosulfan Dieldrin Endrin HCB PCNB
SOC 0.452** 0.298* 0.302* 0.426** 0.440** 0.724** 0.315* 0.696**
pH À0.201 À0.166 À0.112 À0.285 À0.057 À0.217 À0.215 À0.318*
Silt À0.116 À0.089 À0.094 À0.143 À0.014 À0.079 0.065 À0.08
Significant correlation at *P ¼ 0.05 (two-tailed), and at **P ¼ 0.01.
H. Hao et al. / Environmental Pollution 156 (2008) 1046–10521050

7. Author's personal copy
for 52.5% of the total (Chen et al., 2005). The ratio of a- to g-HCH
was 0.89 in the topsoil and 0.74 in the subsoil (Fig. 2), which was
much lower than that in the commercial HCHs, also lower than the
mean value in Guangzhou (2.43). The results indicate that there has
been no recent use of technical HCHs, and the b-HCH in the HCH
residues in vegetable soils can be decomposed or transformed into
other HCH isomers after a long time. This is different to the change
of HCH isomers in soils with new pesticide application such as
lindane (Li et al., 2006; Chen et al., 2005).
3.4. The relationship of OCPs residues with soil characteristics
Soil organic C (SOC) is an important factor affecting the OCPs
behavior in soils. Analysis showed there were positive correlations
between SOC and the different OCPs (Table 4). Also SOC was sig-
nificantly correlated with p,p0-DDD, o,p0-DDT, o,p0-DDE, and a-HCH,
with the correlation coefficient (r) of 0.593, 0.712, 0.762 and 0.695,
respectively. Soil pH was significantly correlated only with a-HCH
at the P 0.0 level (r ¼ 0.593). In contrast, soil clay and silt contents
had no significant correlations with OCPs. This is probably because
there was a little variation in the clay and silt contents in the soils
used in the present study.
Gong et al. (2004) found a significant correlation between total
soil organic C (TOC) and DDTs, although soil pH appeared to have an
effect on the residues of DDTs in Tianjin. Zhang et al. (2007) also
observed that soil pH and TOC had a significant correlation with a-
HCH in Hong Kong soils. In contrast, Zhang et al. (2005) found that
soil pH had no significant correlation with the contents of DDTs and
HCHs in soils from Beijing. These results show that the degradation
of OCPs is complex and is affected by many factors. It is therefore
impossible to use a single soil-geochemical factors to predict the
distribution of OCPs residues in soils at the regional scale.
3.5. Source apportionment of OCPs
The principle component analysis (PCA) was applied here to
examine the source of OCPs in vegetable soils. The first four
principle components (PC) explain 77% of the total variance
(Fig. 3). PC1, accounting for 36.3% of the total variance, correlated
significantly with a-endosulfan, dieldrin, endrin, PCNB, o,p0-DDT
and o,p0-DDE, indicating that these minor components of OCPs
might have come from the same inputs. PC2 explained 17.3% of
the variance with the pesticides from the DDX group (p,p0-DDT,
p,p0-DDD, p,p0-DDE) having a significant loading. This principle
component represented the largest part of the OCPs and related
to the historical technical DDTs applications. Accounting for 15.7%
of the total variance, PC3 substantially described the character-
istics of a-HCH, b-HCH and HCB, showing that they were of the
same origin. HCB has been found as an impurity in some chlo-
rinated pesticides including lindane.1
PC4 explained 7.8% of the
variance and correlated well with g-HCH, suggesting that the
isomation of g-HCH was different from the other two isomers of
HCH.
4. Conclusions
The OCPs residues in the vegetable fields that had been
converted from paddy fields were investigated in Yixing city,
Jiangsu province, China. Significant residues of DDTs and HCHs
were found in these vegetable fields after their applications being
banned since 1983. The mean concentration of the component in
OCPs followed the sequence of
P
DDTs
P
HCHs HCB, a-
endosulfan, endrin, PCNB, dieldrin.
Land use change from paddy to vegetable fields had an impor-
tant effect on the residues of OCPs. The residues of total OCPs
especially DDTs increased with tillage time after conversion from
paddy to vegetable fields during the first 15 years, then decreased
from 20 to 30 years after conversion and increased a little
afterward.
There was no significant difference for the OCPs residues
between the topsoil and the subsoil. The close relationship between
soil organic carbon and most components of OCPs indicated that
SOC was a very important soil property affecting the residues of
OCPs, whereas soil pH only showed a correlation with the residue of
a-HCH.
The ratio of a-HCH/g-HCH and of DDE/DDT indicated there was
no recent usage or discharge of HCH and DDT into the soils in the
area studied. The PCA results confirmed that most of OCPs had the
same origin from the past applications.
Fig. 3. Loadings plot of principal components (PCs) for the residues of organochlorine pesticides in soils.
1
Barber, J., Sweetman, A., Jones, K., 2005. Hexachlorobenzene-sources,environmental
fate and risk characterization. Science Dossier, Euro Chlor, Belgium. http://www.euro
chlor.org.
H. Hao et al. / Environmental Pollution 156 (2008) 1046–1052 1051

8. Author's personal copy
Acknowledgements
This research was funded by Knowledge Innovation Program of
Chinese Academy of Sciences (KSCX2-YW-N-038) and National
Basic Research Program of China (Project No. 2005CB121108). We
also gratefully acknowledged Dr. Fangjie Zhao and the two anon-
ymous referees for their valuable comments.
References
Aigner, E.J., Leone, A.D., Falconer, R.L., 1998. Concentrations and enantiomeric ratios
of organochlorine pesticides in soils from the U.S. Corn Belt. Environ. Sci.
Technol. 32, 1162–1168.
Babu, G.S., Farooq, M., Ray, R.S., Joshi, P.C., Viswanathan, P.N., Hans, R.K., 2003. DDT
and HCH residues in basmati rice (Oryza sativa) cultivated in Dehradun (India).
Water Air Soil Pollut. 144, 149–157.
Bhuiya, Z.H., Rothwell, D.F., 1973. Conversion of DDT to DDD in flooded soil. Plant
Soil 396, 193–196.
Boul, L.M., 1996. Effect of soil moisture on the fate of radiolabelled DDT and DDE in
vitro. Chemosphere 31, 855–866.
Boul, H.L., Garnham, M.L., Hucker, D., Baird, D., Aislabie, J., 1994. Influence of
agricultural practices on the levels of DDT and its residues in soil. Environ. Sci.
Technol. 28, 1397–1402.
Cai, Q.Y., Mo, C.H., Wu, Q.R., Katsoyiannis, A., Zeng, Q.Y., 2008. The status of soil
contamination by semivolatile organic chemicals (SVOCs) in China: a review.
Sci. Total Environ. 389, 209–224.
Cao, H.Y., Liang, T., Tao, S., Zhang, C.S., 2007. Simulating the temporal changes of OCP
pollution in Hangzhou, China. Chemosphere 67, 1335–1345.
Chen, L.G., Ran, Y., Xing, B.S., Mai, B.X., He, J.H., Wei, X.G., Fu, J.M., Shen, G.Y., 2005.
Contents and sources of polycyclic aromatic hydrocarbons and organochlorine
pesticides in vegetable soils of Guangzhou, China. Chemosphere 60, 879–890.
Chinese Soil Taxonomy Research Group/Institute of Soil Science, 2001. Chinese
academy of sciences, cooperative research group on Chinese soil taxonomy
(CSTRG/ISSCAS, CRGCST). Key to Chinese Soil Taxonomy, third ed. University of
Sciences and Technology of China Press, Hefei, China, p. 275 (in Chinese).
De Boer, J., Smedes, F.,1997. Effects of storage conditions of biological materials on the
contents of organochlorine compounds and mercury. Mar. Pollut. Bull. 35, 93–108.
Dimond, J.B., Owen, R.B., 1996. Long-term residue of DDT compounds in forest soils
in Maine. Environ. Pollut. 92, 227–230.
Editor Committee of China Agricultural Yearbook (ECCAY), 1982, 2004. China
Agricultural Yearbook. China Agriculture Press, Beijing, China (in Chinese).
FAO Information Division, 2000. Assessing Soil Contamination (a reference manual).
In: FAO Pesticide Disposal Series, No. 8 Rome.
Gong, Z.M., Cao, J., Li, B.G., Xu, L.F., Tao, S., Shen, W.R., Zhang, W.J., Han, B.P., Sun, R.,
2003. Residues and distribution characters of HCH in soils of Tianjin area. China
Environ. Sci. 23, 311–314.
Gong, Z.M., Tao, S., Xu, F.L., Dawson, R., Liu, W.X., Cui, Y.H., Cao, J., Wang, X.J.,
Shen, W.R., Zhang, W.J., Qing, B.P., Sun, R., 2004. Level and distribution of DDT in
surface soils from Tianjin, China. Chemosphere 54, 1247–1253.
Gonzalez, M., Miglioranza, K.S.B., Aizpun de Moreno, J.E., Moreno, V.J., 2005. Eval-
uation of conventionally and organically produced vegetables for high lipophilic
organochlorine pesticide (OCP) residues. Food Chem. Toxicol. 43, 261–269.
Hua, X.M., Shan, Z.J., 1996. The production and application of pesticides and factor
analysis of their pollution in environment in China. Adv. Environ. Sci. (China) 2,
33–45 (in Chinese).
Haynes, D., Mu¨ller, J., Carter, S., 2000. Pesticide and herbicide residues in sediments
and seagrasses from the Great Barrier Reef world heritage area and Queensland
coast. Mar. Pollut. Bull. 41, 279–287.
Jackson, M.L., 1964. Soil Chemical Analysis (Jiang Baifan, et al., Trans.). Science
Publishing House, Beijing.
Jones, K.C., de Voogt, P., 1999. Persistent organic pollutants (POPs): state of the
science. Environ. Pollut. 100, 209–221.
Kim, S.K., Oh, J.R., Shim, W.J., Lee, D.H., Yim, U.H., Hong, S.H., Shin, Y.B., Lee, D.S.,
2002. Geographical distribution and accumulation features of organochlorine
residues in bivalves from coastal areas of South Korea. Mar. Pollut. Bull. 45,
268–279.
Li, J., Zhang, G., Qi, S.H., Li, X.D., Peng, X.Z., 2006. Concentrations, enantiomeric
compositions, and sources of HCH, DDT and chlordane in soils from the Pearl
River Delta, South China. Sci. Total Environ. 372, 215–224.
Li, Y.F., Cai, D.J., Singh, A., 1998. Technical hexachlorocyclohexane use trends in
China and their impact on the environment. Arch. Environ. Contam. Toxicol. 35,
688–697.
Loganathan, G.B., Kannan, K., 1994. Global organochlorine contamination trends: an
overview. AMBIO 23, 187–190.
Pan, X.Z., Zhao, Q.G., 2007. Measurement of urbanization process and the paddy soil
loss in Yixing city, China between 1949 and 2000. Catena 69, 65–73.
Quensen III, J.F., Mueller, S.A., Jain, M.K., Tiedje, J.M., 1998. Reductive dechlorination
of DDE to DDMU in marine sediment microcosms. Science 280, 722–724.
Ramesh, A., Tanabe, S., Murase, H., Subramanian, A.N., Tatsukawa, R., 1991. Distri-
bution and behaviour of persistent organochlorine insecticides in paddy soil
and sediments in the tropical environment: A case study in South India. En-
viron. Pollut. 74, 293–307.
Samuel, T., Pillai, M.K.K., 1989. The effect of temperature and solar radiations on
volatilisation, mineralisation and degradation of [14C]–DDT in soil. Environ.
Pollut. 57, 63–77.
Skrbic, B., Durisic–Mladenovic, N., 2007. Principal component analysis for soil
contamination with organochlorine compounds. Chemosphere 68, 2144–2152.
Spencer, W.F., Singh, G., Taylor, C.D., LeMart, R.A., Cliath, M.M., Farmer, W.J., 1996.
DDT persistence and volatility as affected by management practices after 23
years. J. Environ. Qual. 35, 815–821.
Wang, F., Bian, Y.R., Jiang, X., Gao, H.J., Yu, G.F., Deng, J.C., 2006. Residual
characteristics of organochlorine pesticides in Lou soils with different
fertilization modes. Pedosphere 16, 161–168.
Wang, T.Y., Lu, Y.L., Zhang, H., Shi, Y.J., 2005. Contamination of persistent organic
pollutants (POPs) and relevant management in China. Environ. Int. 31, 813–821.
Wang, F., Jiang, X., Bian, Y.R., Yao, F.X., Gao, H.J., Yu, G.F., Munch, J.C., Schroll, R., 2007.
Organochlorine pesticides in soils under different land usage in the Taihu Lake
region, China. J. Environ. Sci. (China) 19, 584–590.
Wenzel, K.D., Manz, M., Hubert, A., Schu¨u¨ rmann, G., 2002. Fate of POPs (DDX, HCHs,
PCBs) in upper soil layers of pine forests. Sci. Total Environ. 286, 143–154.
WHO, 1979. DDT and its derivatives. Environmental Health Criteria 9. World Health
Organization, Geneva, Switzerland. 1-194.
Wiegel, J., Wu, Q.Z., 2000. Microbial reductive dehalogenation of polychlorinated
biphenyls. FEMS Microbiol. Ecol. 32, 1–15.
Willett, K.L., Ulrich, E.M., Hites, S.A., 1998. Differential toxicity and environ-
mental fates of hexachlorocyclohexane isomers. Environ. Sci. Technol. 32,
2197–2207.
Wu, W.Z., Schramm, K.W., Henkelmann, B., Xu, Y., Yediler, A., Kettrup, A., 1997.
PCDD/Fs, PCBs, HCHs and HCB in sediments and soils of Ya–Er Lake area in
China: results on residual levels and correlation to the organic carbon and the
particle size. Chemosphere 34, 191–202.
Xu, B., Jianying, G., Zhang, Y., Haibo, L., 1994. Behaviour of DDT in Chinese tropical
soils. J. Environ. Sci. Health B29, 37–46.
Yang, X.H., Wang, S.S., Bian, Y.R., Chen, F., Yu, G.F., Jiang, X., 2008. Dicofol application
resulted in high DDTs residue in cotton fields from northern Jiangsu province,
China. J. Hazard. Mater. 150, 92–98.
Zhang, H., Lu, Y., Dawson, R.W., Shi, Y., Wang, T., 2005. Classfication and ordination
of DDT and HCH in soil samples from the Guanting reservoir, China.
Chemosphere 60, 762–769.
Zhang, H.B., Luo, Y.M., Zhao, Q.G., 2006. Residues of organochlorine pesticides in
Hong Kong soils. Chemosphere 63, 633–641.
Zhang, H.Y., Gao, R.T., Huang, Y.F., Jia, X.H., Jiang, S.R., 2007. Spatial variability of
organochlorine pesticides (DDTs and HCHs) in surface soils from the alluvial
region of Beijing, China. J. Environ. Sci. (China) 19, 194–199.
Zhao, B.Z., Zhang, J.B., Zhou, L.Y., Zhu, A.N., Xia, Mi., Lu, X., 2005. Residues of HCH
and DDT in typical agricultural soils of Huang–Huai–Hai plain, China I. Residues
in surface soils and their isomeric composition. Acta Pedol. Sin. 42, 761–768 (in
Chinese).
Zhu, Y.F., Liu, H., Xi, Z.Q., Cheng, H.X., Xu, X.B., 2005. Organochlorine pesticides
(DDTs and HCHs) in soils from the outskirts of Beijing, China. Chemosphere 60,
770–778.
H. Hao et al. / Environmental Pollution 156 (2008) 1046–10521052