Nitrogen fertilizer as an oxidizing agent to mobilize trace constituents from soil

Dissolved nitrate in ground water can oxidize and mobilize trace constituents from soils derived from organic-rich shales in arid and semiarid environments. Organic-rich shales of Cretaceous age in the Western US contain trace constituents such as arsenic, selenium, uranium, and vanadium. Nitrate can function as an electron acceptor for the chemical oxidation of trace constituents, or poise the redox potential high enough to inhibit the reduction of the trace constituents. Denitrification also could affect trace-constituent oxidation. Water-quality data collected by the US Department of the Interior National irrigation Water-Quality Program indicated that positive correlations exist between dissolved nitrate and dissolved trace constituents that could be accounted for by nitrate oxidation of reduced trace constituents. Laboratory experiments on the oxidation of selenium by nitrate indicated that reduced selenium species are oxidized to mobile selenium oxyanions over a period of days. Wherever irrigation occurs on soils derived from organic-rich shales in arid or semiarid environments, the oxidation and mobilization of trace constituents by nitrogen fertilizers could result in a substantial contribution to contaminant loads in irrigation drainage. Further research is needed on the speciation of trace constituents in the solid phase, on the source of nitrogen (fertilizer or animal-produced nitrogen) that affects oxidation of trace constituents, and on whether the oxidation of trace constituents is a biotic or abiotic process