Abstract
Due to the adverse impact of DDTs on ecosystems and humans, a full fate assessment deems a comprehensive study on their occurrence in soils over a large region. Through a sampling campaign across China, we measured the concentrations, enantiomeric fractions (EFs), compound-specific carbon isotope composition of DDT and its metabolites, and the microbial community in related arable soils. The geographically total DDT concentrations are higher in eastern than western China. The EFs and δ13C of o,p’-DDT in soils from western China show smaller deviations from those of racemic/standard compound, indicating the DDT residues there mainly result from atmospheric transport. However, the sources of DDT in eastern China are mainly from historic application of technical DDTs and dicofol. The inverse dependence of o,p’-DDT and p,p’-DDE on temperature evidences the transformation of parent DDT to its metabolites. Initial usage, abiotic parameters and microbial communities are found to be the main factors influencing the migration and transformation of DDT isomers and their metabolites in soils. In addition, a prediction equation of DDT concentrations in soils based on stepwise multiple regression analysis is developed. Results from this study offer insights into the migration and transformation pathways of DDTs in Chinese arable soils, which will allow data-based risk assessment on their use.
Highlights
Totally different between eastern and western part of China
Among the six DDT components, p,p’-DDE, which is the main metabolite of DDT, had the highest mean concentration (3.29 ng/g)
Regional variation of DDT concentrations and compositions in arable soils across China was mapped in Fig. 1 and Supplementary Fig. 1
Summary
Totally different between eastern and western part of China. A combination of EF analysis and CSIA might offer additional insights into the migration and transformation of organic contaminants[11,14,15], especially on a large scale. After 30 years of ban, the main degradation production of DDTs was found to be DDE in Chinese arable soils[7]. Because of their different sources, DDT and DDE may exhibit distinct isotope characteristics. In this study, we conducted a nationwide farmland sampling campaign across China and measured the concentrations, EFs and carbon isotope compositions (δ13C) of DDT and its main metabolites in arable soils. The obtained data were used to estimate the migration and transformation of DDTs on a large scale and to explore the underlying influencing physicochemical and microbiological factors in arable soils after 30 years of DDT ban in China. Results from this study would provide basic scientific data for the contamination management and risk avoidance of DDTs in Chinese soils
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