The presence of toxic microcystin, produced by algal blooms, in drinking source water is a threat to human health. Source water toxin indicates that harmful algal blooms have occurred in proximity to drinking water treatment plants. Algal blooms that produce toxins are caused by excessive nutrients, such as nitrogen and phosphorus. The threshold for human exposure to microcystin in drinking water is lower that the threshold of exposure by skin contact.
How is it scored?
Source water toxin was used as an indicator in both the watershed and lake analysis. Year-round data for 2018 were analyzed. For each sample, the measurement was compared to the threshold on a pass/fail basis. Site scores were averaged into an overall region source water toxin score.
The source water toxin threshold used for both the western Lake Erie basin analysis and watershed analysis was the Ohio EPA public drinking water supply beneficial use cyanotoxin indicators threshold 1 μg/L.