The occurrence of dichlorodiphenyltrichloroethanes (DDT) and its metabolites in Chinese forest soils: Implications for sources and environmental processes

Dichlorodiphenyltrichloroethane (DDT) and its metabolites are highly toxic and pose chronic effects to the biosphere. As a natural storage pool, forests have great potential to capture them from the atmosphere and migrate them to the forest soil, which, in turn, influences the safety of the forest ecological environment. In this study, a systematical survey of DDT and its metabolites has been carried out to measure their spatial variations in Chinese forest soils. The main objectives of this study were to (1) investigate the levels, distribution and sources of DDT and its metabolites, and further estimate their mass inventories in Chinese forest soils, (2) explore the impact of soil properties on their distribution, and (III) assess the ecological and health risks of DDT and its metabolites. The research results were as follows. The average concentration of ΣDDTs reached up to 9.75 ng/g, and p,p’-DDT is the main component. Significant difference in the concentration of ΣDDTs was observed between the southeast and northwest regions (p<0.01), which may be related to multiple factors such as pesticide use, rainfall and altitude. The forest soil quality inventory is about 0.58×103 tons, which is lighter than that of domestic farmland soil. 56.1% of soil samples were less than the low value of risk assessment (ERL). The concentration of ΣDDTs in the East and middle is higher than that in the West, and the high value is mainly distributed in the coastal areas. DDTs were mainly from the input of the mixed source composed of industrial DDT and dicofol, of which at least 97% came from industrial DDT and up to 4% from dicofol. ΣDDTs was only positively correlated with precipitation and population density (p<0.05). The degradation of DDT in soil occured from primary stage to high stage. The possible degradation pathways involved in DDTs entering forest soil were preliminarily deduced. Firstly, the surrounding pollution sources volatilize DDTs from soils to the atmosphere through secondary emission. In this process, DDT was continuously transformed into DDE through photodecomposition. The atmosphere rich in DDTs were transported to the forest area and then into the forest surface soil through atmospheric dry and wet deposition. Then, DDT transported continuously accumulated and degraded in forest soil. In the alternation of anaerobic and aerobic process, the main degradation pathways are DDT→DDD→DDMU, DDT→dicofol+DBP, DDT→DDE→DDMU, DDMU→DDNU.