Microcystin persistence in Lake Erie foreshore sands

Research into the persistence of microcystin (MC) in foreshore sands is limited. Lake water and foreshore sand samples were collected weekly from three swim coves at Maumee Bay Park Beach (OH) during the recreational swim season to assess the accumulation and persistence of MC in foreshore sands. Enzyme-linked-immunosorbent-assay (ELISA) analysis showed that 14 % of lake water samples exceeded the EPA no-contact threshold for MC in recreational waters (8 µg/L), with a maximum concentration of 17 µg/L occurring during a bloom event. Average MC concentrations in surface foreshore sands (4 µg/L porewater) were significantly higher, on average, than in deeper sands (2 µg/L porewater), while peak sand MC concentrations exceeded 29 µg/L during two bloom events. Overall, MC concentrations in both shallow and deep sand exceeded water MC concentrations in 56 % of samples, indicating accumulation of MC in foreshore sands. MC persistence was determined in laboratory microcosms containing either autoclaved or non-autoclaved sands augmented with MC. ELISA analysis showed a 46 % reduction in MC concentration in autoclaved sands over 7 weeks. In non-autoclaved sands, the MC concentration decreased by 100 % during the study, with approximately 99 % of the added MC degrading during days 21–28, suggesting that a biological mechanism drove degradation. Our findings reveal that beach sands can act as MC reservoirs, accumulating and concentrating MC during and following bloom events.