Spatial distribution and sources of organochlorine pesticides in surface waters of Shanghai, China

The concentrations, distribution, influencing factors, and sources of 26 organochlorine pesticides (OCPs) were investigated in surface waters of Shanghai. Surface waters in this study refer to the freshwater that contains particles smaller than 0.45 μm in size. Total concentrations of OCPs ranged from 5.90 to 158.16 ng/L with a mean value of 78.11 ng/L. The OCP concentrations were generally low, but with a few relatively high concentrations at sites in the northern and southern regions of Shanghai. Dissolved oxygen, electrical conductivity, pH and oxidation–reduction potential had an important impact on the distribution of OCPs, which showed a significant negative correlation (p < 0.01). Source apportionment was carried out using isomer ratios of OCPs and Absolute Principal Component Scores-Multiple Linear Regression. Six principal components of OCPs were identified, and the contribution rates and contribution amounts were ranked: Heptachlor epoxide > HCHs > Endosufan and Methoxychlor > Propachlor > Heptachlor and DDTs > Dacthal and Chlordane. The contribution of historic residual HCHs in Shanghai’s surface waters was not significantly different from that of atmospheric deposition, and a part of HCB was likely from the degradation of HCHs. DDTs were mainly from historical residues, although some were derived from recent inputs, and the main sources of heptachlors were also the historical residues. However, the recent input and historical residues of aldrins were both noticeable. The fluctuation of OCPs pollution levels and source differences among different intensive land-use types were relatively insignificant (p > 0.05).