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CURRENT ISSUES IN HTE DETECTION OF HUMAN EXPOSURE TO THE CYANOBACTERIA TOXINS, MICROCYSTINS
Citation:
Hilborn, E D., W. Carmichael, J. Servaites, AND S. H. Azevedo. CURRENT ISSUES IN HTE DETECTION OF HUMAN EXPOSURE TO THE CYANOBACTERIA TOXINS, MICROCYSTINS. Presented at 16th Conference of the International Society for Environmental Epidemiology, New York, New York, August 1-4, 2004.
Description:
Introduction: Toxic cyanobacteria are contaminants of surface waters worldwide. Microcystins are some of the most commonly detected toxins. Biological evidence of human exposure has been difficult to obtain due to technical, temporal, and biological limitations. However, evidence of exposure improves the specificity of epidemiologic studies. We will provide results of a recent application of an enzyme-linked immunosorbant assay (ELISA) to detect microcystins in human serum, and an overview of current methods to detect biological evidence of exposure in humans.
Methods: We analyzed ten serum samples collected from dialysis patients who were involved in an outbreak of microcystin intoxications that occurred during 1996 in Caruaru, Brazil. We applied a commercially available ELISA method to detect free total microcystins in serum collected from exposed persons. We compared the ELISA to a reference method, liquid chromatography/mass spectrometry (LC/MS) that detects free microcystin-LR-equivalents in serum. The Spearman correlation coefficient was calculated using concentrations derived by the two methods.
Results: Serum concentrations were similar when detected by the two methods. The ELISA detected total microcystins, median=19.9 ng/ml. The LC/MS detected microcystin-LR-equivalents, median=21.2 ng/ml. We found good correlation of microcystin concentrations between the two tests (Spearman r=0.99, p<0.0001).
Discussion: Although detection of microcystins in human serum may be achieved, interpretations of results are not clear. Animal studies involving intraperitoneal injections report a rapid decline in serum microcystin concentrations as microcystins are bound in the liver. Human clinical evidence suggests that microcystins may be released from the liver back into circulation. Microcystins' tissue distribution may complicate attempts at back-calculations of total absorbed dose, but may also allow detection of toxin from serum samples for an extended period of time. Because tissue evidence suggests that the Caruaru outbreak involved mixed microcystins, we expected ELISA-derived concentrations to be higher than LC/MS concentrations. Because this was not seen, the ELISA can only be considered a semi-quantitative screening method for use in human serum until method comparisons using serum from individuals with well-defined exposures can be performed.
The views expressed in this abstract are those of the individual authors and do not necessarily reflect the views and policies of the U.S. Environmental Protection Agency.