Combined effects of the cyanobacterial toxin microcystin-LR and environmental factors on life-history traits of indigenous cladoceran Moina macrocopa.

Environmental factors are important in that they might interact with toxicants and could affect the concentration-response relationship of the toxicants in the water environment. Microcystins (MCs) produced by algal blooming are natural toxins that exert severe impacts on aquatic organisms. Despite the possibility of interaction effects between environmental factors and MCs, very few studies have been carried out to date. In the present study, the authors evaluated the effect of 3 environmental factors on chronic toxicity of MC-leucine-arginine (MC-LR; 0 µg/L, 0.8 µg/L, 4 µg/L, 20 µg/L, 100 µg/L, 500 µg/L) to the freshwater invertebrate Moina macrocopa. Three environmental factors were determined to reflect the reasonable worst conditions of the water body in South Korea: high water temperature (25 °C), the highest concentration of nutrients (ammonia-nitrogen [NH3 -N] = 3.8 mg/L; nitrate-nitrogen [NO3 -N] = 8.5 mg/L) during the occurrence of algal bloom, and 2 pH conditions of 7.0 and 9.0, which satisfy the test acceptance criteria for the Daphnia test. Among the various environmental factors being tested, high water temperature and NO3 -N elevated chronic toxicity of MC-LR, whereas NH3 -N reduced toxicity. Water pH did not influence chronic toxicity of MC-LR to M. macrocopa. This observation suggests that those environmental factors are responsible for changing the trend of MC-LR toxicity.