What do losses in selenium and arsenic bioavailability signify for health?

Levels of As and Se in human foods and animal feeds respectively have decreased in recent years as a result of official limits and other factors. The reduction of SeO2 by SO2 to Se0 results in less bioavailability in the food cycle. Acid rain further reduces the pH of Se-depleted soils and soluble forms of Se are bound by metal ions in fallout from burning of fossil fuels. However, there is evidence that Se and As act as essential nutrients with anticancer value. The need for As in nutrition was shown by three laboratories in four mammalian species. Selenium inadequacies among people, as well as animals, are being recognized worldwide in the form of Se-responsive diseases. Reported data indicate that we have yet to learn the optimal intake levels for Se or As and how their decreased bioavailabilities affect human health.