Selenium is a trace element that is naturally present in many foods. In the environment, selenium is dispersed naturally by weathering of selenium-containing rocks. However, human activities can increase local concentrations of selenium through fossil fuel processing and combustion, as well as from the irrigation and runoff from soils high in selenium. High concentrations of selenium can bio-accumulate in wildlife and can cause metabolic problems at extremely high concentrations.

Hardness adjusted dissolved metal concentrations which were compared against the acute and chronic standards for the California Toxics Rule (CTR). Only copper and selenium were measured in concentrations that exceeded either of the CTR criteria and are presented here.

On the map on your left explore the proportion of water samples that exceeded regulatory standards for each region of the San Gabriel watershed for Selenium:

-  No Acute CTR
-  Exceeded Chronic CTR
-  No CTR Exceedances