Spatial-temporal accumulation, microbial response, and integrated risk assessment of organochlorine pesticides in urban bioretention facilities.

Bioretention facilities face increasing sustainability challenges due to the long-term sequestration of non-point source pollutants. Organochlorine pesticides (OCPs) represent a particularly concerning class given their persistence, bioaccumulation potential, and historical prevalence in urban and agricultural catchments. This study investigated the spatiotemporal distribution and multi-dimensional potential risks of OCPs across eight field-scale facilities with varying operational ages, filler types, and runoff ratios. Results revealed a pronounced spatial stratification after the rainy season, with the uppermost layer functioning as the primary accumulation zone. The predominance of DDT metabolites indicated that the detected OCPs were mainly associated with historical contamination, while stormwater runoff served as an important pathway for their transport and accumulation within the facilities. OCP accumulation was accompanied by shifts in microbial community structure, with genera such as Sphingomonas, Dongia, and Skermanella becoming more abundant, whereas dehydrogenase activity generally declined. Risk assessment results showed that facilities with longer operational histories and higher hydraulic loading tended to exhibit greater OCP accumulation, stronger ecological responses, and higher human health risks. These findings suggest that prolonged operation and intensive runoff loading can enhance the accumulation of OCPs in surface media. Periodic maintenance of the upper 5-10 cm media layer may help reduce contaminant accumulation and associated risks, providing new insights into the long-term management of bioretention-based LID infrastructures.