ENZYME-IMMUNOASSAY FOR DIRECT DETERMINATION OF MICROCYSTINS IN ENVIRONMENTAL WATER

An enzyme-linked immunosorbent assay (ELISA) was developed for direct quantitation of microcystins (MCs), a group of freshwater cyanobacteri al toxins. An anti-MG monoclonal antibody exhibiting broad cross-react ivity to major MC derivatives was used, The detection limit and linear range of the ELISA standard curve with microcystin-(leucine-arginine) (MCLR), a variant of MCs, were 20 and 20-500 pg/mL, respectively, For analysis of MC released from cyanobacterial cells, water sample filte red through a glass fiber filter was applied directly to ELISA. Far an alysis of total MC (released MC plus intracellular WIG), intracellular toxin was extracted by freeze-thawing twice before filtration, Mean r ecovery of MCLR added to tap water and toxin-free environmental water was 101%, with a coefficient of variation (CV) of 7.3% at toxin levels of 20-500 pg/mL. Mean recovery of MCLR added to toxin-free cyanobacte rial extracts was 93%, with a CV of 12.5% at toxin levels of 50-500 pg /mL. At 20 pg/mL, an increasing matrix effect on assay variance was ob served; therefore, both released MC and total MC were measured in the range 50-500 pq/mL. Comparative studies with a liquid chromatographic (LC) method showed that the ELISA gives a reliable correlation with LC for analysis of MC in water extracts of natural blooms and cultured c yanobacterial cells (r = 0.98), The ELISA was applied to water samples collected from lakes and ponds in Japan. In 4 of 13 and 12 of 17 samp les, 81-800 pg released MC/mL and 64-94000 pg total MC/mL were detecte d, respectively, By LC separation followed by the ELISA analysis, the presence of MCLR, microcystin-arginine-arginine, and microcystin-tyros ine-arginine were confirmed in 4 ELISA-positive samples selected rando mly, The newly developed ELISA is a reliable and powerful method for m ass monitoring of MC levels in environmental water.