Enantiomer signature and carbon isotope evidence for the migration and transformation of DDTs in arable soils across China

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.

The role of soils in the disposition, sequestration and decontamination of environmental contaminants

“…[12][13][14]. However, microbial degradation of persistent organic pollutants (POPs) such as dichlorodiphenyltrichloroethane (DDT) and per-and polyfluorinated alkyl substances (PFAS) is either impossible or extremely slow, raising the issue of widespread biomagnification [15,16].…”

Applications of Compound-Specific Isotope Analysis for Determining Persistent Organic Pollutant Origin, Transport and Transformation in the Aquatic Environment

“…In fact, one of the only two studies to take advantage of the explanatory power of CSIA in a distinctly environmental situation was published only a year ago (Niu et al, 2016) and was focused on fractionation effects between the soil and atmosphere, thus removed from the aquatic systems this review has sought to encapsulate. The other, , makes a compelling case for CSIA as a tool to track biotransformation in the environment, though findings were limited to establish the probable existence of-rather than fully quantifying or pinpointing-a biotransformation process in a marine ecosystem in Sweden.…”

“…In addition to these examples of the indispensability of CSIA for source apportionment research without a necessary role of biotransformation, several examples can also be cited of the indispensability of CSIA for controlling source apportionment studies for biotransformation. These include the study by Niu et al (2016) of soils in China, in which the degradation pathway of DDT, modeled by CSIA, was used to elucidate original signatures and thus establish source influences. Finally, in , Tang et al (2016) and Tang et al (2017), CSIA is applied exclusively to understand biotransformation, where other methods fall short.…”

“…Nonetheless, valuable clues are offered as to the likely prevalence of biotransformation processes on DDT isotope abundances in a variety of media. (Niu et al, 2016) Prominent transformation-related fractionation effects had previously been documented not only for δ 13 C, but also for δ 37 Cl and δ 2 H, two other interesting parameters for chlorinated organic pesticides. , 65 performed CSIA using deuterium fractionations associated with the DDT to DDD conversion.…”

“…(Fang et al, 2015) 4. Niu et al, (2016) were able to infer the sourcing of DDT contaminations in eastern versus western China, and they also established several important fractionations relevant to the joining of these methods. CSIA was used to model the degradation pathway of DDT in these areas, while isomeric signatures were applied primarily to differentiate between difocol and technical sources of DDT.…”