Seasonal variations of PCDD/Fs in fishes: inferring a hidden exposure route from Na-PCP application for schistosomiasis control.

Japanese schistosomiasis was endemic in Dongting Lake, the second largest freshwater lake in China. The technical sodium pentachlorophenate (Na-PCP) was widely used during the period between the early 1960s and early 1990s to kill oncomelania, the intermediate host of Schistosomes. However, polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) also contaminated the environment of Dongting Lake due to trace impurities of Na-PCP. In this study, 13 species of freshwater fish were collected from Dongting Lake and analyzed in wet and dry seasons. Temporal (wet and dry season) variations in PCDD/Fs in fishes from Dongting Lake were observed. The concentration of PCDD/Fs was considerably higher in the wet season than in the dry season and in areas in China where Na-PCP was not applied. The higher level of PCDD/Fs in the wet season may be attributed to the use of Na-PCP in the past and to the increase in the migration of PCDD/Fs from sediments to water in the wet season. The results indicate that the risk of PCDD/Fs contamination is connected with prior consumption of fishes that live in the Na-PCP application area. However, there was no difference in the concentrations of polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs) between the wet and dry seasons.