Selenium, selected inorganic elements, and organochlorine pesticides in bottom material and biota from the Colorado River delta

Concentrations of selenium (Se) in bottom material ranged from 0.6 to 5.0 μg g−1, and from 0.5 to 18.3 μg g−1in biota; 23% of samples exceeded the toxic threshold. Concentrations of DDE in biota exceeded the toxic threshold in 30% of the samples. Greater concentrations of selenium in biota were found at sites with strongly reducing conditions, no output, alternating periods of drying and flooding or dredging activities, and at sites that received water directly from the Colorado River. The smallest Se concentrations in biota were found at sites where an outflow and exposure or physical disturbance of the bottom material were uncommon.