Selenium in reducing waters.

The analysis of selenium species in reducing waters provides important insight into the element's biogeochemical cycle. The absence of selenate and selenite in reducing waters suggests that some removal mechanism could be operative, but the presence in these waters of about 1 nanomole per liter of dissolved organic selenide indicates that the regeneration of selenium in the form of organic species may be the dominant process. The data demonstrate that the regenerative and biogeochemical cycles of selenium are quite complex.