Survey of microcystins in environmental water by a highly sensitive immunoassay based on monoclonal antibody

By using a highly sensitive enzyme-linked immunosorbent assay (ELISA) based on a monoclonal antibody, microcystin (MC) concentration was analyzed in environmental water samples (total, 134), collected in 1993-1995 from ponds, lakes, reservoirs, and rivers in Japan, Thailand, Germany, and Portugal. MCs detected in the water samples filtered over a glass filter were designated as free MCs, and those samples that were freeze-thawed twice before the filtration were designated as total MCs. MCs (> 50 pg/ml) were detected in 14 of 24 samples collected from the lakes that were used as recreation and water supply in Japan in different regions. In the MC-positive samples, the concentration of free MCs was only a few percentages of the total MCs, indicating that the most part of MCs found in the water samples was present in algal cells. An additional trial on 33 samples collected continuously from Lake Inbanuma, Japan, during June-September 1994-1995 revealed that the total MCs were in a range of 52-52,000 pg/ml. In Chiang Mai, Thailand, 6 of 10 samples were positive, with the mean and highest of 161 and 354 pg/ml, respectively. In the Frankfurt area. Germany, 4 of 10 and 7 of 8 samples collected in the same lakes for recreation in July 1993 and November-December 1994 showed the presence of MCs, with their mean and highest values of 257 and 407 pg/ml, respectively. Another survey of MCs in dense bloomed samples collected with plankton net revealed a contamination of MCs up to 36,000 pg/ml. In Portugal, 28 of 29 samples from 4 lakes, 20 rivers, and 5 reservoirs were positive for MCs, with the respective means of 13,664, 11,048, and 2,278 pg/ml. These data indicated that MCs contaminate environmental water in ponds, rivers, lakes, and reservoirs worldwide. The present ELISA is considered to be a reliable tool for the mass monitoring and risk assessment of MCs in water supplies.