Seasonal bioaccumulation and biomagnification of typical organochlorine pesticides in the Pearl River Estuary, South China.

As a typical organochlorine pesticide, dichlorodiphenyltrichloroethane (DDT) and its metabolites (dichlorodiphenyldichloroethane (DDD), dichlorodiphenylmethane (DDM), dichlorodiphenyldichloroethylene (DDE), and bis(p-chlorophenyl)-chloroethylene (DDMU)) (collectively referred to as DDXs), have been widely detected in the Pearl River Estuary (PRE). However, seasonal variations in land runoff and the transformation of DDXs complicate their bioaccumulation characteristics in the PRE. The present study analyzed the sediment and aquatic organisms from both dry and wet seasons to investigate the seasonal characteristics of bioaccumulation of DDXs in the PRE. The median concentration of DDXs in sediments was significantly higher during the wet season (0.60 ng/g dw) than that in the dry season (0.25 ng/g dw), and the median concentration of DDXs in aquatic organisms was significantly higher during the dry season (518 ng/g lw) than that in the wet season (189 ng/g lw). Based on δC and δN values, the aquatic food web is composed of terrestrial and marine food chains. Using an improved trophic position (TP) quantification model (TP), significantly different correlation trends of DDXs in the food chain during the dry season were observed: along with the increasing of TPs, the abundance of DDT and DDM + DDMU decreased, while the abundance of DDD + DDE increased, which likely due to the DDX biotransformation. Additionally, this study found that elevated terrestrial nutrient input and the maternal-offspring transfer of DDXs could conceal the DDX bioaccumulation process during the wet season. Compared to the traditional TP quantification model (TP), the TP model, which differentiates terrestrial from marine sources, can effectively reveal the significant correlation between the DDX composition and TPs. This emphasizes the need to integrate environmental conditions and biological processes for a comprehensive analysis of the biological behavior of pollutants.