Cyanobacterial blooms are of global concern due to the multiple harmful risks they pose towards aquatic
ecosystem and human health. However, information on the fate of organic pollutants mediated by
cyanobacterial blooms in eutrophic water remains elusive. In the present study, endocrine disruptive
potentials of phytoplankton samples were evaluated throughout a year-long surveillance in a large and
eutrophic freshwater lake. Severe cyanobacterial blooms persisted during our sampling campaigns. Estrogenic
agonistic, anti-estrogenic, anti-androgenic, and anti-glucocorticogenic effects were observed in
the phytoplankton samples using in vitro reporter gene bioassays. 27 endocrine disrupting chemicals
(EDCs) of different modes of action were detected in the samples via UPLC-MS/MS system. Results from
mass balance analysis indicated that the measured estrogenic activities were greater than the predicted
estrogenic potencies from chemical analysis, demonstrating that chemical analysis of targeted EDCs is
unable to fully explain the compounds responsible for the observed estrogenicities. Results from
Spearman's correlation analysis concluded that the concentrations of ten EDCs in phytoplankton samples
were negatively correlated with cyanobacterial biomass, suggesting the potential occurrence of biomass
bio-dilution effects of EDCs due to the huge biomass of cyanobacteria during bloom seasons. The present
study provided complementary information about the potential endocrine disruptive risks of cyanobacterial
blooms, which is important for understanding and regulating EDCs in eutrophic lakes.