Ecological risks assessment of organophosphorus pesticides on bloom of Microcystis wesenbergii

Hormesis induced by organophosphorus pesticides (OPPs) on Microcystis wesenbergii was studied to demonstrate the mechanism of water bloom. The dosage response of OPPs on M. wesenbergii was detected in the presence and absence of inorganic phosphorus. The results showed median inhibitory effect concentrations of phoxim, trichlorphon, dimethoate and glyphosate-isopropylammonium on fluorescence of chlorophyll a at 96 h were 13.48, 148.52, 382.34, 6.84 μmol l−1, respectively. Fluorescence of chlorophyll a was stimulated significantly in low OPPs treatments, ranged among 1/10,000–1/20 EC50 concentrations. However, remarkable increase in the maximum photochemical efficiency was only detected under certain treatments and time points. Physiological traits showed no remarkable difference between OPPs as sole phosphorus treatments and non-phosphorus treatments. However, both decreased significantly when compared with inorganic phosphorus (PO43−) treatments. The results indicated that M. wesenbergii was not capable of utilizing OPPs as phosphorus and the stimulatory effect caused by inert ingredients was negligible. Hormetic response induced by OPPs increased competitive advantage to overcome other species. Therefore, this study confirmed that abusive utilization of OPPs had stimulatory impact on population dynamic of M. wesenbergii.