Ecological risks of microcystins and the implications on their adverse effects to freshwater ecosystems under multiple temperature scenarios

Highly toxic microcystins (MCs) released by harmful cyanobacterial blooms (HCBs) can damage aquatic ecosystems and jeopardize human health through bioaccumulation and transfer in the food chain. Global warming not only exacerbates the occurrence of HCBs but also affects the release and toxicity of MCs to aquatic organisms. However, little is known about temperature-dependent hazard and ecological risks of MCs to freshwater ecosystems under climate change and extreme weather. Through a meta-analysis and the construction of species sensitivity distributions, this study systematically evaluated the hazard and ecological risks of three MC congeners (i.e., MC-LR, MC-RR, and mixture MCs) to freshwater organisms, with temperature-specific analysis for MC-LR across three ranges (18–20 °C, 20–25 °C, and 25–29 °C). The results showed that there were no significant differences in hazards among the three MC congeners, or across temperatures for MC-LR. However, MC-RR and mixture MCs exhibited higher ecological risks than MC-LR, challenging the previous view that MC-LR is the most toxic congener. For MC-LR, ecological risks were higher at low (18–20 °C) and high temperature scenarios (25–29 °C) compared to the optimal range (20–25 °C), highlighting the potential for extreme weather events and HCB outbreaks to significantly impact aquatic organisms. Overall, our findings improve the understanding of the MCs hazard and risks associated with HCBs outbreaks in freshwater environments, particularly in the context of climate change and extreme weather events, providing critical implications for congener-inclusive monitoring and management of HCBs.