Selenium Threatens Irrigators, Wildlife

Irrigation drainage water has seldom been treated to remove pollutants, but it soon will be treated in California. Drainage from a large portion of the San Joaquin Valley must be treated to remove selenium. That metal killed over 1,000 water birds in the Kesterson reservoir in 1983, and has slashed the annual hatch of birds. The selenium originates in the soils beneath part of the valley. Several approaches to removing it are described; one involves anaerobic bacteria which convert it from a soluble form to an insoluble. Another involves sharp reductions in amount of irrigation water used. Ironically, selenium in low concentrations appears to be necessary for the health of humans and other animals.