Development of a bioanalytical phosphatase inhibition test for the monitoring of microcystins in environmental water samples

A phosphatase inhibition assay using commercially available components has been developed for the detection of cyanobacterial toxins in drinking and s urface water samples. The assay is simple, economic and rapid. Results are obtained in 1 h on a 96-well microtitre plate. The test uses a type 2A prot ein phosphatase whose activity is inhibited proportionally to the toxin con centration and is measured by means of a colourimetric reaction. Two proced ures of the tests have been optimised using the same phosphatase, but diffe rent working conditions. The first one allows a direct estimation of the co ncentration of microcystin-la in the range 0.4-10 mu g/l and is used to cal culate the sample dilution required for the second procedure, which has bee n optimised in order to be much more accurate with a working range between 0.2 and 0.8 mu g/l (concentration in the sample, which corresponds to 0.1-0 .4 mu g/l in the well). An enrichment using solid phase extraction on octad ecyl silica has been described for samples containing less than 0.2 mu g/l of microcystin. A repeatability of 8% at the IC50 level has been obtained a nd the IC50 value is 0.21 +/- 0.02 mu g/l (concentration in the well). Inhi bition of enzyme activity by other toxins such as microcystin-YR and microc ystin-RR has also been evaluated. Particular attention has been paid to the effect of the sample matrix on the assay. Several drinking and surface wat ers have thus been investigated. Validation of the assay has been performed by comparing the phosphatase inhibition assay results to the liquid chroma tography results for the same samples. A good correlation (R-2 = 0.96) has been observed for samples containing microcystin-LR. (C) 1999 Elsevier Scie nce B.V. All rights reserved.