| Organophosphorus pesticides (OPs) and synthetic pyrethroid pesticides (SPs) are significant stressors in the aquatic ecosystem of lakes due to their extensive use in agriculture. Chaohu Lake, one of the most eutrophic lakes in Eastern China. Domestic research maily focus on the nutrient elements of N/P and heavy metals about Chaohu, while pay little attention to trace organic compounds, such as pesticides. To understand the potential ecotoxicological risk of OPs and SPs, the concentrations of twelve OPs and twelve SPs in water, surface sediment and core sediment from three inflowing rivers and one outflowing river of Chaohu Lake were determined by soxhlet extraction-solid phase extraction-gas chromatography-mass spectrometer (SE-SPE-GC-MS). The OPs and SPs residues as well as the distribution and sources were also evaluated.The results show that OPs were frequently detected around the lake, with detection frequencies of more than 60%. Dichlorvos was the predominant OP, comprising 89.6% of the total concentration of the 12 OPs in all samples. High concentrations of OPs were found in estuaries of rivers flowing from agricultural lands, indicating that the OPs were mostly due to cultivation, and the vertical distribution of OPs in core sediments clearly showed the application history of OPs over the past few decades. The intercorrelation between OPs was likely affected by their sources, degradation rates and deposition pathways. The poor correlation between OPs and total organic carbon (TOC) in the core sediments of Chaohu Lake might be ascribed to multiple sources of the TOC in Chaohu Lake. Despite previous studies demonstrated that most OPs were not detectable in bottom sediments due to their high water solubilities and reduced persistence, in the present study, we found that most of the selected OPs were frequently detected in bottom sediment samples collected around Chaohu Lake, which have been identified with long-term eutrophication, suggesting that the OPs likely migrated from the water to the bottom sediment due to the occurrence of massive amounts of phytoplankton. Therefore, the environmental behavior and fate of OPs in a eutrophic lake require more attention given their ecotoxicity. As for SPs, all SPs selected were detectable with the first generation SPs of domestic sources (permethrin, bioallethrin and tetramethrin) dominant in water samples, but with the second generation ones of agricultural sources including cypermethrin, esfenvalerate, fenvalerate and cyhalothrin predominant in sediment samples. Vertical distribution in compositional patterns of SPs shows that the domestic SPs generally increased, but the agricultural ones tended to decrease, from bottom to top samples. Fugacity based assessment of the water-sediment exchange also suggests that the domestic SPs were primarily transferred into sediment from water column, but the agricultural ones were released back to the water column. These results could potentially imply the shifting from the use of the agricultural SPs to the domestic ones. The possible reason on this pattern shifting is due to the fact of the widespread urbanization and the rural-to-urban migration around Chaohu lake, because the domestic SPs are widely used in hygiene, while the agricultural SPs are mostly applied for the fruit and vegetable insect control in rural areas. Therefore this study provides the important information on the residues of SPs in the aquatic environments which depended on the socioeconomic development related pesticides usage patterns.In summary, the OPs and SPs are widespread and worth concerned in water and sediment around Chaohu Lake, and there are many extend work to do. |
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