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In November 2001, a cyanobacterial bloom dominated by Microcystis and Anabaena occurred in the Funil Reservoir and the Guandu River, both of which supply drinking water to Rio de Janeiro, Brazil. Using ELISA, microcystins were detected at a concentration of 0.4 microg/L in the drinking water, whereas a concentration of 0.32 microg/L was detected in activated carbon column-treated water for use at the renal dialysis center of Clementino Fraga Filho Hospital (HUCFF) at the Federal University of Rio de Janeiro. A total of 44 hemodialysis patients who received care at this center were believed to be exposed. Initial ELISA analyses confirmed the presence of serum microcystin concentrations > or = 0.16 ng/mL in 90% of serum samples collected from these patients. Twelve patients were selected for continued monitoring over the following 2-month period. Serum microcystin concentrations ranged from < 0.16 to 0.96 ng/mL during the 57 days after documented exposure. ELISA-positive samples were found throughout the monitoring period, with the highest values detected 1 month after initial exposure. ESI LC/MS analyses indicated microcystins in the serum; however, MS/MS fragmentation patterns typical of microcystins were not identified. LC/MS analyses of MMPB for control serum spiked with MCYST-LR. and patient sera revealed a peak at retention time of 8.4 min and a mass of 207 m/z. These peaks are equivalent to the peak observed in the MMPB standard analysis. Taken together ELISA, LC/MS, and MMPB results indicate that these renal dialysis patients were exposed to microcystins. This documents another incident of human microcystin exposure during hemodialysis treatment.

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