Effects of two copper compounds on Microcystis aeruginosa cell density, membrane integrity, and microcystin release

Microcystin release following Microcystis aeruginosa cell lysis after copper-based algaecide treatment is often cited as a concern leading to restricted use of algaecide in restoration of natural water resources. To examine this concern, bench-scale experiments were conducted to study responses of M. aeruginosa to 8-day copper exposures as copper sulfate and copper ethanolamine (Cu-EA). M aeruginosa UTEX 2385 was cultured in BG11 medium to cell density of 10(6) cells/mL with total and extracellular microcystin of 93 and 53 mu g/L, respectively. Exposures of copper concentration ranged from 40 to 1000 mu g Cu/L. Cell membrane integrity was indicated by etythrosine B. In the end of experiment, total microcystin and cell density in untreated control (313 mu g/L and 10(7) cells/mL) was 33 and 10 times greater than pretreatment value, respectively. Minimum amount of copper required to reduce M. aeruginosa population within 8 days was 160 mu g Cu/L as copper sulfate and 80 mu g Cu/L as Cu-EA, where total and extracellular microcystin concentrations (47 and 44 mu g/L for copper sulfate; 56 and 44 mu g/L for Cu EA) were degraded with degradation rate coefficient 0.1 day(-1) and were less than pretreatment values. Given a copper concentration at 80 mu g Cu/L as Cu-EA, M. aeruginosa cells were intact and less microcystin were released compared to treatments at 160-1000 mu g Cu/L, where lysed cells and relatively greater microcystin release were observed. Based on the laboratory results, a minimum amount of copper required for reducing M. aeruginosa population could decrease total microcystin concentration and not compromise cells and minimize microcystin release. (C) 2015 Elsevier Inc All rights reserved.