Organochlorine Pollutants Residue And Their Ecological Risk In Agricultural Soils From Yangtze Delta

DDT and HCH pollution concentration in agriculture soil in north of Zhejiang province, and PCBs pollution concentration in south of Jiangsu province were investigated, including several soil types such as vegetable field, paddy field, dry field and so on. Statistical methods were used to study the distribution and contamination of these pollutants in the soils, and the relationship between pollutant residues and environmental factors were also analyzed. Besides, the concentrations of those pollutants were compared with toxic data to evaluat their environmental risk. This is one of the comprehensive and meaningful studies to investigate the residue level of DDT, HCH and PCBs in the agricultural soils, which offers the basic statistics for the soil risk assessment of POPs in Yangtze Delta. Although the residue levels of DDT, HCH and PCBs in the agricultural soils were proved to be low, the ecological effects of the combined pollution system of these pollutants on soil microorganisms were still unknown. Then the ecological effects of DDT and PCBs in laboratory controlled conditions were studied, which was based upon our previous investigation in Yangtze Delta. The results are showed as follows:(1) Residues of HCH and DDT in agriculture soils of Northern Zhejiang and its risk EvaluationDDT and HCH were determined in agriculture soils from north of Zhejiang province. All methods were rigorously tested and adequate quality control was ensured. The results showed the concentration of EHCHs and SDDTs in the soils ranged from 0.20-20.1ng/ g and 1.50-326.8 ng/g respectively, and the mean of them were 1.73 ng/ g and 44.68 ng/ g. Especially SDDTs concentrations in some samples (19 out of 81) exceeded the quality standard for soils in China. Soil type was a significant factor for the difference of concentrations of HCH and DDT, while the organic carbon content showed a weak relativity with the residues. With a simple risk assessment, concentration of DDT was above the maximum permissible concentration for soils which is based on the bioaccumulation in terrestrial food webs.(2) Occurrence and congeners-specific of polychlorinated biphenyls in agriculture soils from Southern JiangsuA total of 198 agricultural soil samples was collected from Zhangjiagang and Changshu in southern Jiangsu for 13 polychlorinated biphenyls (PCBs) analysis. All methods were rigorously tested and adequate quality control was ensured. Only onesite had no PCBs residues, and the maximum concentration of PCBs in these surficial soils was 32.83 ng/g. The mean concentrations in Changshu and Zhangjiagang were 4.96 ng/g and 3.31ng/g respectively, which showed that the pollution there was in low level. Tetrachlorobiphenyls, pentachlorobiphenyls and hexachlorobiphenyls were dominant in soil samples, accounting for > 75 % of PCBs in the soil samples. PCB118 was the most abundant congener in all samples. The PCB118/ï¿¡PCBs was around 20% of all congeners. The organic matter content showed a weak relativity with the residues of all PCB congeners, and strength of this relationship was greater for the more volatile PCB congeners than for the heavier homologues, probably predicting the greater impact of air transportation and air-soil partition on the soil pollution. Correlation between ï¿¡PCBs in soils from farmland near factories and soil organic matter (OM%) was higher than the one for the common farmlands, which might suggest the proximity to source region as the main factor of the PCBs distribution. Besides, soil types also had influence on the pollution;paddy fields had the higher XPCBs than dry fields.(3) Ecological effects of DDT and PCBs combined pollution system on soil microorganismsInfluences of trace DDT and PCBs combined pollution system on soil microbial biomass, catalase and dehydrogenase activities were investigated in laboratory controlled conditions. The results showed that catalase, dehydrogenase, microbial biomass were all inhibited or stimulated at the first time of 30 days, but the effects disappeared quickly before 75 days and the toxic effects of the pollutants were not simply dose-related. Dehydrogenase activity was the most sensitive parameter and it was inhibited by the pollution system on the whole. In sum, those parameters might not serve as good bioindicators for the doze-effect relationship of pollution since these parameters were potentially influenced by the increase in fungal (probably resistant of organochlorine pollutants) counts.A significant interaction effect on soil microbe of DDT and PCBs combined pollution system has been shown by the experiment results for the there parameters in different reaction time. But it was difficult to describe the type of interaction of the combined action.