Risk Assessment and Identification of Factors Influencing the Historical Concentrations of Microcystin in Lake Taihu, China.

Understanding the history of microcystins(MCs)pollution in large lakes can help inform future lake management.We collected sediment cores from Lake Taihu to:investigate the long-term record of MCs(MC-LR,MC-YR,and MC-RR),explore the main environmental drivers of MCs,and assess their public health and ecological risks.Results showed that MCs content in all cores increased over time.The core from north Taihu had the highest MC con-centrations,with an average total MCs(sum of MC-LR,MC-YR,and MC-RR=TMCs)content of(74.31±328.55)ng/g.The core from eastern Taihu showed the lowest average TMCs con-tent of(2.91±3.95)ng/g.PCA showed that sediment MCs at the three sites were positively correlated with sediment chlorophyll-a.MC-LR and MC-YR in northern and western Taihu negatively correlated with both the sediment total organic carbon/sediment total nitrogen ratio(STOC/STN)and water nitrate(NO3--N)concentration,but three MC congeners at east-ern Taihu showed positive correlations with water orthophosphate(PO43--P),NO3--N,and STOC/STN.Generalized additive model analysis at each site revealed that NO3--N was the main TMCs driver in northern and western Taihu where phytoplankton dominated,whereas PO43--P was the main TMCs driver in eastern Taihu where macrophytes dominated.At the whole lake scale,total phosphorus(TP)and PO43--P were the most important environmen-tal drivers influencing MCs;TP explained 47.4％,44.2％,and 47.6％while orthophosphate ex-plained 34.8％,31.2％,and 34.7％of the deviance on TMCs,MC-LR,and MC-YR,respectively.NO3--N also showed a strong effect on MCs variation,especially on MC-YR.Risk assess-ment showed that both ecological and public health risk has increased in recent years.We conclude that while control of phosphorus and nitrogen input should be a major focus for future lake management,lake zone-specific management strategies may also be important.