The occurrence of organochlorine pesticides (OCPs) in riverine sediments of hilly region of southern China: Implications for sources and transport processes

Abstract

Rivers serve as important water resources for socio-economic development as well as the sink of anthropogenic pollutants—especially pesticides, thus being responsible for the riverine transport and distribution of such chemicals. Therefore, the spatial-temporal distribution of organochlorine pesticides (OCPs) was investigated based on their content in major rivers located in the hilly region of southern China. The research objective was to identify this region's riverine transport of OCPs and their potential affecting factors. Higher concentrations of OCPs were detected in the wet season (52.0 ± 46.5 ng/g dw) than in the dry season (24.9 ± 26.5 ng/g dw). Wet-season OCP input from tributaries was associated with increased water runoff and sediment discharge. Dichlorodiphenyltrichloroethanes (DDTs) and hexachlorocyclohexanes (HCHs) were the major OCP contributors, accounting for 30.4% ± 20.4% and 24.3% ± 10.9% of the total OCPs, respectively. These results corresponded well with the historical production and application of OCPs in China. The spatial differences among rivers and basins were ascribed to the regional usages in history, while the transport of OCPs in rivers was along the water flow direction and related to suspended substances. Moreover, black carbon (BC) played a crucial role on retention and accumulation of OCPs in sediments. Ecological risk assessments based on sediment quality guidelines (SQGs) suggested that γ-HCH, p,p′-DDE, and p,p′-DDD posed high ecological risks, especially in the lower reaches of rivers. Additionally, the human health risk assessment revealed negligible carcinogenic risk associated with OCP contamination.