DDT In Soil Research Articles

First evidence for covalent linkage of acidic metabolites of metalaxyl and DDT as non-extractable pesticide residues in soil and sediment

Soils and sediments are a major sink for lipophilic organic pollutants. The remobilization potential of non-extractable residues is an important aspect of the environmental risk assessment and is directly linked to the binding modes of xenobiotics to macromolecular geopolymers. For instance, weak binding will favour rapid release of toxic metabolites, whereas strong binding will favour release in the long run. So far there is few strong evidence on the precise nature and strength of pollutant binding to organic matter. We used 1,1,1-trichloro-2,2-bis(chlorophenyl)ethane (DDT) contaminated sediment and metalaxyl spiked microbial active soil for alkaline hydrolysis reaction with 18O-sodium hydroxide (Na18OH). Gas chromatography–mass spectrometry analyses showed 2 Da shifts in molecule ions of 2,2-bis(chlorophenyl)acetic acid methylester (DDA-methylester) and additionally in fragment ions of 18O-metalaxyl indicating monolabeled derivatives of both pesticide metabolites.18O-labeling of the carboxyl moiety during hydrolysis proved the cleavage of the metabolites from organic macromolecules. This is the first concrete evidence for stable ester linkage of acidic metabolites of DDT and metalaxyl in soil and sediment matrices.

Influence of Hydroxypropyl-β-cyclodextrin on the Extraction and Biodegradation of p,p′-DDT, o,p′-DDT, p,p′-DDD, and p,p′-DDE in Soils

Dichlorodiphenyltrichloroethane (DDT) is one of the persistent organic pollutants (POPs) that are highly toxic to the environment. Effective evalu- ation on the bioavailability of DDTs in soils is essen- tial for risk assessment and soil remediation. The aims of this study were to verify the feasibility of the hydroxypropyl-β-cyclodextrin (HPCD) extraction method for predicting the bioavailability of DDT, dichlorodiphenyldichloroethane (DDD), and dichlorodiphenyldichloroethylene (DDE) in soils, and to examine the effect of HPCD on their biodeg- radation in different soils. Four soils were aged with a mixture of p,p'-DDT, o,p'-DDT, p,p'-DDD and p,p'- DDE (0.25 μ gg −1 for each compound) for 20 and 100 days, respectively. For each of the DDTs, a sig- nificant positive correlation between HPCD- extractable fraction and biodegradable fraction in each soil was observed. It was demonstrated that the amounts of HPCD-extractable p,p'-DDT and o,p'- DDT were not significantly different from the amounts that were degradable as assessed from their degradation by Enterobacter sp. LY402 (p>0.05). Such 1:1 relationship between extraction and degra- dation was not obtained in the cases of p,p'-DDD and p,p'-DDE, as the amounts of degradable p,p'-DDD and p,p'-DDE were lower than the amounts that were extractable with HPCD. Additionally, the biodegra- dation of p,p'-DDT, o,p'-DDT, p,p'-DDD, and p,p'- DDE was inhibited in the presence of HPCD, which could be due to the binding of the compounds to HPCD, making them less available to access the bac- teria for degradation. This study provides the possi- bility of using the HPCD extraction method to predict the bioavailability of p,p'-DDTand o,p'-DDTin soils. But when HPCD was used as an additive in the bioremediation of DDT-contaminated soils, it might have a negative effect on biodegradation.

Occurrence and assessment of organochlorine pesticides in the agricultural topsoil of Three Gorges Dam region, China

Sixteen organochlorine pesticides (OCPs) were investigated in the 80 agricultural topsoil samples of Three Gorges Dam region, China. The concentration of OCPs ranged from 1.26 to 22.15 ng g−1, with a mean concentration 6.49 ng g−1. Dichlorodiphenyltrichloroethanes (DDTs) and hexachlorocyclohexanes (HCHs) were predominant compared to other OCPs, with mean concentrations 1.80 and 1.27 ng g−1, respectively, accounting for 28 and 20 % of the total OCPs. Ratio analysis indicated that there is new input of DDTs in this study area. However, HCHs residual was mainly from historical use and atmospheric deposition. Other OCPs were due to the historical use in the studied area. Based on the soil quality guideline, both DDTs and HCHs pollution were in the low pollution level. Cancer risk assessment indicated that OCPs concentrations in this area presented a low cancer risk level. The study can offer some reference to the land management in the Three Gorges Dam region.

Residual characteristics of HCHs and DDTs in soil and dust of some parks in Ulaanbaatar, Mongolia

The residual characteristics of HCHs and DDTs in park soils and dusts in Ulaanbaatar, Mongolia were determined by GC-ECD to evaluate their potential pollution risk. The residual concentrations of total HCHs and DDTs in the park soil samples were ranged in 11.36-53.14 ng·g-1 and 11.96-24.70 ng·g-1 while it was ranged in 32.28-92.68 ng·g-1 and 13.45-24.41 ng·g-1 in the park dust samples, respectively. We have studied the ratio of α-HCH/γ-HCH in order to determine pollution sources which may come from either technical HCHs or lindane. The study revealed that concentration of DDTs in soil has direct correlation on usage rate of the dicofol and technical DDT in the sampling area. The soil pollution assessments based on the single pollution index of HCHs and DDTs indicated that Ulaanbaatar city’s park soil and dust were not polluted with these compounds.The single pollution index of HCHs reached to 1.85 in A park dust samples，indicating the park dust environment was potentially polluted. DOI: http://doi.dx.org/10.5564/mjc.v15i0.315 Mongolian Journal of Chemistry 15 (41), 2014, p15-20

Chiral signature of α-HCH and o,p′-DDT in the soil and grass of the Central Tibetan Plateau, China

Enantiomeric fraction (EF) of organochlorine pesticides (OCPs) has been used as a signature for tracing the source and following pathways. The chiral analysis was performed for α-HCH and o,p′-DDT in paired soil and grass samples from the Central Tibetan Plateau (CTP), a unique background region. In the case of α-HCH, excess of (−) α-HCH was predominant in 83.3% of soil samples, and 80% of grass samples showed excess of (+) enantiomer. For o,p′-DDT, 90.9% of grass samples showed excess of (−) o,p′-DDT while 50% of soil samples showed excess of the (−) enantiomer. A correlation between EFs of soil and grass was not observed for either compound. The EFs of both compounds were correlated with soil concentration and with change of sampling altitude, within EFs being lower than racemic. However, these trends were not found in grass. Our study provides a database of EFs and signatures for OCPs in the CTP, one background region of the world.

Assessment of tolerance and efficiency of crop species in the phytoremediation of DDT polluted soils

Soil contamination by organic compounds is of great concern worldwide since it could act as a major environmental repository. The success of phytoremediation is conditioned by two main factors: the availability and toxicity of the compound to be remediated, and the plant species ability to incorporate or degrade the contaminants. This study aimed to assess the potential of different plants species for remediation of aged DDTs residues in soil. Tomato, sunflower, soybean and alfalfa plants were grown in contaminated soils (p,p′-DDE 455.3, p,p′-DDT 63.5ngg−1 dry weight) for 15 and 60 days. Phytoremediation was evaluated by studying the pollutant dynamics in the soil–plant system and lipid peroxidation (LPO) as an effect biomarker. Results showed that soil DDTs levels were diminished after 60 days of plant growth, due to the combined effect of DDTs uptake by roots and rhizospheric degradation. The relative accumulation of each compound was dependent on soil levels (p,p′-DDE>p,p′-DDT>p,p′-DDD) and all species presented root >aerial accumulation pattern, evidencing DDTs translocation. Tomato plants were the most effective in the enhancement of pollutants bioavailability in the rizospheric soil. Plants growth induced physicochemical changes in soil and those are evidenced by increasing dehydrogenase activity and DDTs metabolism, mainly in soybean and tomato soil fractions. Root bioconcentration factors >1 were observed in 15 days tomato and alfalfa plants. Growth dilution effect was observed in roots of all species at 60 days, except soybean. DDTs uptake nor affected tomato and alfalfa plants growth neither caused oxidative stress. Considering the accumulation potential, tolerance (expressed as no evident phytotoxicity effects) and interaction with soil matrix in terms of metabolism and availability, tomato plants seems to be the best phytoremediator candidates for aged soil DDTs residues.

Investigation of organochlorine pesticides from the Indus Basin, Pakistan: Sources, air–soil exchange fluxes and risk assessment

Present study aimed to evaluate the contamination status of organochlorine pesticides (OCPs) and their associated potential for air–soil exchange and health risks from ecologically important sites of the Indus Basin, Pakistan. Among different OCPs investigated, ΣDDTs and ΣHCHs were more prevalent compounds in the agricultural soils and ambient air samples of the study area. The average concentrations for DDTs were found higher at downstream agricultural sites, particularly at Head Panjnad (Soil: 320ng/g; Air: 743pg/m3) and acting as an ultimate sink of ΣOCP burden in soils. Spatial distribution patterns inferred ubiquitous distribution of ΣDDTs in soils and air of the study area. Source diagnostic ratios demonstrated that studied OCPs either are illegally being used in agricultural practices or/and they are residues of past use in the environment. Fugacity fraction model revealed wide variations (ff=0.12–0.94) with 20% of OCPs above equilibrium range and net volatilization of α-endosulfan, β-HCH and o,p′-DDD. Assessment of cancer risks for OCPs indicated a higher cancer risk (CR>1×10−6) for the residents of the Indus Basin. According to the available soil quality guidelines, DDTs and HCHs were above the permissible limits and pose a threat to natural habitat and biodiversity of the Indus Basin.

Influence of 3 Kinds of Organic Fertilizers on the Degradation of p, p′-DDT in Clay under Flooding Conditions

Using pot experiment to study the influence of three organic fertilizers of chicken manure compost (CM), activated sludge (AS) and cassava residue compost (CR) on the degradation of p, p'-DDT in clay soil under flooding conditions. The results showed that the two kinds of organic fertilizers of AS and CM could effectively accelerate the degradation of p, p'-DDT in clay soils, and the degradation effect was the best when adding 2% CM or 3% AS in clay soil. However, the influence of CR on the degradation of p, p'-DDT was not obvious. The degradation rates of P, P′-DDT in the treatment on adding 1% AS were from zero to 7.4% higher than that of 1% CM. The degradation rates of P, P′-DDT in the treatment on adding 2% AS were from zero to 11.3% higher than that of 2% CM. The degradation rates of P, P′-DDT in the treatment on adding 3% AS were from 8.3% to 27.4% higher than that of 3% CM. which indicated that AS is more conducive to the degradation of p, p'-DDT in the clay.

DDT and HCH (Organochlorine Pesticides) in Residential Soils and Health Assessment for Human Populations in Korba, India

ABSTRACTDichlorodiphenyltrichloroethane (DDT), hexachlorocyclohexane (HCH), and their isomers’ levels in residential soils were determined for the assessment of health risk in Korba, India. Observed concentrations of total HCH and total DDT in soils were more or less comparable with other parts of India and the world. ΣHCH and ΣDDT concentrations ranged between 0.9–20 μg kg−1 and 2–315 μg kg−1, respectively, which were lower than recommended soil quality guidelines indicating low ecotoxicological risk. Carcinogenic and non-carcinogenic impacts of HCH and DDT on human populations through soil ingestion were evaluated and presented. The incremental lifetime cancer risk (ILCR) for adults and children ranged between 7.8 × 10−10–1.6 × 10−7 and 4.1 × 10−9–8.2 × 10−7, respectively. Non-cancer health hazard quotient (HQ) ranged between 5.9 × 10−7–1.8 × 10−3 and 3.1 × 10−6–9.4 × 10−3, respectively, for adults and children. The estimated ILCR and HQ were within the safe acceptable limits of 10−6–10−4 and ≤1.0, respectively, indicating low risk to human populations from exposure to organochlorine pesticides (HCH and DDT) in the study area.

Adsorption of DDT from Contaminated Soil using Carbon Nanotubes

This paper presents results of an investigation into the use of carbon nanotubes (CNTs) for the adsorption of DDT in soil and solution. DDT is a known endocrine-disrupting chemical with observed persistence, harm to the environment, and a human health concern. Thus, it is important to clean it up from the environment. In this study, CNT is selected because it has high surface area for adsorption. Adsorption experiments were conducted using the batch equilibrium technique with a fixed soil:solution ratio. Adsorption of DDT onto the CNTs was characterized by an initial rapid adsorption, which eventually became constant within 22 hours, perhaps due to limited surface area of the CNTs available for DDT adsorption. Results of the study demonstrated the relative adsorption increase with increasing solution concentration. The results obtained indicate the importance of CNTs in the adsorption of DDT and show that they have a great potential application for remediation of DDT from contaminated soil.

A Novel Method for Degradation of DDT in Contaminated Soil

A novel method for remediation of DDT contaminated soil based on advanced oxidation processes including reactions with hydroxyl radicals and ozone has been developed. On the basis of the conducted experiments the authors concluded that ozone did not degrade DDT in soil. Analysis of degradation products that were formed during exposure to a stream of gaseous ozone indicated that hydroxyl radicals might play a key role in degradation of this compound. In the modified fluidized bed reactor where hydroxyl radicals could be generated from ozone and water vapor, reduction of over 90% of DDT residue level has been achieved. Authors proposed a pathway of DDT degradation, under the influence of hydroxyl radicals and ozone. As a result of this research, an effective method for remediation of DDT-contaminated soil has been proposed.

Effect of Seaweeds on Degradation of DDT in Soils

Seaweed was investigated as an amendment to enhance remediation of 1,1,1-trichloro-2,2-bis (p-chlorophenyl) ethane (DDT)-contaminated soil. Under anaerobic conditions, the addition of seaweeds increased DDT degradation between 61 % and 88 % of the original concentration after 14 days of incubation whereas only 33 % of DDT was degraded in unamended soil. DDT was degraded to metabolites such as 1,1-dichloro-2,2-bis (p-chlorophenyl) ethane (DDD), 1,1-dichloro-2,2-bis (p-chlorophenyl) ethylene (DDE), and 1-chloro-2,2-bis (p-chlorophenyl) ethylene (DDMU). Seaweed-amended soils converted 35–56 % of DDT to DDD while the unamended soil formed only 15 % DDD. Seaweed amendments modified soil conditions which include soils’ dissolved organic carbon (DOC), ionic strength, redox potential, and pH. These significant physicochemical changes influenced the increase in DDT bioavailability and transformation in seaweed-amended soils compared to the unamended soils. Multiple linear regression analysis also suggested that factors such as DOC, calcium, redox potential, and pH are involved against DDT degradation (p = 0.02).

Organochlorine pesticides in surface soils and sediments from obsolete pesticides dumping site near Lahore city, Pakistan: contamination status and their distribution

Surface soil and sediment samples were collected from the surroundings of Lila stream, which passes through the obsolete pesticides dumping area Kalashah Kaku near Lahore city, to evaluate the residual levels of 19 organochlorine pesticides (OCPs), their distribution and potential sources. OCPs followed the order: ∑ DDT>∑ HCH>dicofol>endrin>heptachlor>dieldrin. Ratios of β to γ-HCH highlighted an old source of technical HCH in the study area, whereas the predominance of p, p′-DDT and p, p′-DDE indicated presence of technical DDT in surface soils. Factor analysis based on principal component analysis identified the origin of OCPs from industrial activities in Kalashah Kaku and waste dumping from Ittehad Chemical Industries via open drains into Lila stream. Greater levels of DDTs and HCHs above quality guideline pose potential exposure risk to biological organisms, safety of agricultural products and human health in the surrounding of Lila stream.

Fate and plant uptake of persistent organic pollutants in soil

Many persistent organic pollutants (POPs), notably hexachlorocyclohexanes (HCHs), chlorinated cyclodienes, and dichlorodiphenyltrichloroethanes (DDTs), remain in Japanese farming soils, more than 40 years after their use as insecticides was prohibited. In recent years, residues of chlorinated cyclodienes in cucurbit fruits have become a problem. But, though HCHs and DDTs have been staying in the soil, residues of these chemicals in crops have not been a problem. So we compared the fates of HCHs (α-, β-, γ-HCHs), chlorinated cyclodienes (dieldrin, endrin, heptachlor exo-epoxide), and DDTs (DDE, dichlorodiphenyldichloroethylene; DDD, dichlorodiphenyldichloroethane) in soil and investigated their uptake by several non-cucurbits and cucurbits. As for the fate of POPs in soil, not only the total concentrations but also the concentrations in soil solution as bioavailable POPs were determined. The half-lives of total β-HCH and DDTs in soil were the longest, and α- and γ-HCHs the shortest. On the other hand, the half-lives of bioavailable POPs ranged from 1/3 to 1/20 of those of total POPs. The ratio of the half-lives of bioavailable POPs to those of total POPs decreased in the order of HCHs > chlorinated cyclodienes > DDTs. Because hydrophobic chemicals were adsorbed strongly to the soil, the bioavailable POPs in soil are controlled by their hydrophobicity, indicated by the values of log K OW (K OW: n-octanol-water partition coefficient). The shoot concentrations of chlorinated cyclodienes and DDTs were higher in cucurbits than in non-cucurbits. However, among POP insecticides, HCHs did not show clear differences. As for the root concentrations, all tested POPs were higher in cucurbits than in non-cucurbits. Through the determination of POPs in soil solution, we could compare the abilities of plants to take up the chemicals using soil solution bioconcentration factors (BCFSS). The values of BCFSS increased with the magnitude of log K OW, in the order of HCHs < chlorinated cyclodienes < DDTs. In addition, BCFSS did not show marked differences among isomers or chemicals with similar structure. Therefore, plant uptake ability was influenced mainly by log K OW. After being applied to agricultural land, α- and γ-HCHs seemed to disappear quickly, β-HCH persisted longer but the uptake in roots was low because of the low log K OW, and DDTs also persisted longer but the bioavailability decreased rapidly in the soil because of their high log K OW. Chlorinated cyclodienes have remained in the soil and have remained available, because they are less likely than HCHs (except β-HCH) to disappear and less likely than DDTs to become adsorbed to the soil. In addition, their higher log K OW than that of HCHs makes them more easily taken up by roots. However, shoot concentrations were high only in cucurbits, for which they remain a problem in Japan.

Distribution, sources and potential risk of HCH and DDT in soils from a typical alluvial plain of the Yangtze River Delta region, China

Spatial distribution, sources and potential health risks of organochlorine pesticides (OCPs), including hexachlorocyclohexane (HCH) and dichlorodiphenyltrichloroethane (DDT), in surface soils (n = 544) collected from a typical alluvial plain of the Yangtze River Delta region, China, were elucidated. Concentrations of ΣHCH and ΣDDT in soils ranged from less than the limit of detection (<LOD) to 99.0 ng g(-1), dry weight (dw) (mean 3.23 ng g(-1) dw) and <LOD to 600 ng g(-1) dw (mean 88.8 ng g(-1) dw), respectively. Historical applications of HCH and DDT were the major sources of the residue in soils. HCH was mainly distributed in Anthrosols in the southern part of the watershed, while DDT was mainly distributed in Cambosols in the northern part. The 95 % cumulative probability incremental lifetime cancer risks (ILCRs) of different age groups such as children, youths, and adults all exceeded the acceptable risk level of 10(-6) recommended by USEPA for carcinogenic chemicals. The spatial distributions of ∑ILCRs were consistent with concentrations of OCPs in soils, while they were slight different for the different age groups. Adult females had the greatest risk of OCPs in soils, followed by children, while youths had the least risk. The ingestion of OCPs in soils was the more important route of exposure compared with dermal and inhalation exposures. The concentration of OCPs in soils, the particulate emission factor, the fraction of dermal exposure ratio, and the soil ingestion rate were the major contributing variables to total ILCRs according to sensitivity analyses.

Enhancement of Ligninolytic Activity of Trametes versicolor U97 Pre-grown in Agricultural Residues to Degrade DDT in Soil

The presence of 1,1,1-trichloro-2,2-bis(4-chlorophenyl) ethane (DDT) in the environment is becoming a serious problem because of its strong toxicity and mutagenicity. Utilization of agricultural residue, oil palm empty fruit bunch (EFB), in the environmental technology area is still limited. On the other hand, wood meal showed the ability to be used for pre-grown source of fungi. For that reason, the ability of Trametes versicolor U97 pre-grown in wood meal and EFB to degrade DDT in soil was investigated. DDT in soil was degraded 45 and 54 % by T. versicolor U97 pre-grown in wood meal and EFB during 30 days incubation, respectively. Focusing in T. versicolor U97 pre-grown in EFB, response surface methodology based on a Doehlert experimental design showed that the presence of veratryl alcohol and MnSO4 are needed to maximize degradation of DDT by using ligninolytic enzymes of this strain. Addition of ethylenediaminetetraacetic acid revealed that peroxidase enzymes play a role in degradation of DDT in soil in which several metabolic products were produced.

Degradation and mineralization of DDT by the ectomycorrhizal fungi, Xerocomus chrysenteron

One strain of ectomycorrhizal fungi, Xerocomus chrysenteron, had been investigated for its ability to degrade 1,1,1-trichloro-2,2-bis(4-chlorophe-nyl) ethane (DDT) by measuring unlabeled DDT and identifying its metabolites, and determining the mineralization of [13C]DDT in pure cultures. After 45d incubation, about 55% of the added DDT disappeared from the culture system, less than 5% remained in the nutrient solution, and about 44% was retained in the mycelium. Inoculation with mycelium enhanced the degradation of DDT in soil, and alleviated enrichment of DDT in plants. The metabolites identified by gas chromatography–mass spectrometry were 1,1-dichloro-2,2-bis(4-chlorophenyl) ethane (DDD), 1,1-dichloro-2,2-bis(4-chlorophenyl)ethylene (DDE), and 4,4′-dichlorobenzophenone (DBP). There were significant differences in the δ13C of released CO2 between [13C]DDT and DDT cultures, which indicated X. chrysenteron was able to mineralize DDT to CO2.

Adsorption of DDT in soil using a single and combined effect of cadmium and Tween80

Batch equilibrium experiments were carried out to investigate the single and combined effect of cadmium and Tween80 on the sorption of DDT. The results indicate that in the binary system of Tween80-DDT, when initial Tween80 concentration is below its CMC (critical micelle concentration, 15.7 mg/L), the sorption of DDT is promoted; as the initial Tween80 concentration increasing to slightly higher than its CMC, DDT adsorption amount is rather the same as that of CK (control check); and when initial Tween80 concentration is much more than its CMC, the sorption of DDT is inhibited. As to binary system of cadmium-DDT, coexistent heavy metal salt inhibits the sorption of DDT. The inhibition is mainly caused by the competitive adsorption of Cd2+, and anion Cl− and have little effect. Moreover, the coexistence of Tween80 and Cd2+ makes the competitive adsorption more obvious, which inhibits the sorption of DDT. The combined effect of coexistent Tween80 and cadmium on the sorption of DDT is proved to be an antagonism effect, which has a more significant influence on the adsorption amount than that in binary system, and the antagonism effect becomes gradually insignificant with the increasing concentration of coexistent pollutant.

Co-remediation of DDT-contaminated soil using white rot fungi and laccase extract from white rot fungi

2,2-Bis(p-chlorophenyl)-1,1,1-trichloroethane (DDT), one of the most widely used organochlorine pesticides in soil, was banned in the 1970s for agricultural use because of its detrimental impacts on wildlife and harmful effects on human health via the food chain. However, high levels of DDT are frequently detected in agricultural soils in China. Considering this situation, this study investigated the use of white rot fungi and laccase derived from white rot fungi to co-remediate DDT-contaminated soil. A culture of white rot fungi was used to inoculate soil samples and also to extract laccase from. Soil was contaminated with four components of DDT (p,p′-DDE, o,p′-DDT, p,p′-DDD, and p,p′-DDT). Individual DDT components and the sum of the DDT components (p,p′-DDE, o,p′-DDT, p,p′-DDD, and p,p′-DDT—collectively referred to as DDTs) were both analyzed by GC at various stages during the incubation period. The efficacy of co-remediating DDT-contaminated soil using white rot fungi and laccase was tested by investigating how degradation varied with varying amounts of white rot fungi, sterilizing soil, temperature, soil pH, concentrations of DDT, and concentration of the heavy metal ion Cd2+. “”It was concluded that the reduction of DDTs in soil using white rot fungi and laccase was higher than reduction using only white rot fungi or laccase by nearly 14 and 16 %, respectively. Five milliliters fungi per 15 g soil and 6 U laccase per gram soil were the optimal application rates for remediation, as shown by a reduction in DDTs of 66.82 %. The difference in the reduction of individual DDT components and DDTs between natural and sterilized soils was insignificant. The optimal temperature and pH in the study were 28 °C and 4.5, respectively. In addition, reduction of individual DDT components and DDTs increased with increasing concentrations of DDT and decreased with increasing concentrations of Cd2+. Compared with the remediation of DDT using only white rot fungi or laccase, the co-remediation of DDT using white rot fungi and laccase degraded DDT in soil more rapidly and efficiently; the highest reduction of DDTs was 66.82 %.

Occurrence of organic chlorinated pesticides and their ecological effects on soil protozoa in the agricultural soils of North Western Beijing, China

The occurrence of ∑HCHs, ∑DDTs, protozoa abundance and their community structure in surface soils of orchards, vegetable lands, and barren lands in northern west outskirts of Beijing were detected in order to investigate the protozoa responses to low dose organic chlorinated Pesticides (OCPs) after long-term field-based exposure. Significant differences in total concentrations of HCHs and DDTs were found among the three general groups ranking in decreasing order of concentration from orchard>vegetable lands >barren lands. Ciliate was the rare group in surface soils of all the sampling groups. The abundance of flagellate, ciliate, and amoebae in vegetable soils were significantly higher than those in orchard soils. The abundance of all the taxa of protozoa was strongly negative correlated with the residue level of ∑HCHs and ∑DDTs (P<0.05) in agricultural soils. However, no negative correlation between the residue levels of OCPs and protozoa abundance was shown in both the orchard and the barren soils. This field study demonstrated a considerable long-term impact of the OCPs residue on the abundance of protozoa in soils, and that the abundance of soil protozoa was much more influenced by land use type in association with different soil properties.