Redox active trace elements chromium and arsenic pose a threat to human and ecosystem health. The present case in Asia, where more than 57 million people are being exposed to hazardous levels of arsenic in drinking water within Bangladesh alone, exemplifies the devastating impact such toxins can have on human health. While chromium and arsenic have many commonalities, they have opposing responses to oxidizing-reducing soil conditions. The hazards imposed by arsenic are most severe under reducing conditions, while chromium is of greatest concern within well oxidized regimes. Furthermore, the response of arsenic results from both (biogeo)chemical changes to the contaminant and environmental matrix, while that of chromium can be attributed largely to the toxin itself. Arsenic persists dominantly in the trivalent (arsenite) or pentavalent (arsenate) states. Arsenate binds tenaciously to soil/sediment minerals except under highly alkaline conditions, and thus arsenic tends to be of limited concern in aerated environments. Arsenite binding is more complex and yet to be fully resolved. In order to discern the fate of arsenite, or arsenic in general, one must consider its reaction chemistry with soil minerals and the coupling with biogeochemical cycles of iron and sulfur. Here the importance of considering binding strength as a separate entity from binding magnitude are expressed along with the intricate link between iron biochemical cycles and arsenic partitioning. Chromium, in contrast to arsenic, is most problematic under well aerated conditions. Reduction of chromate to Cr(III) results in a relatively non-toxic species that adsorbs strongly on mineral surface or precipitates as a sparingly soluble hydroxide. Various constituents of anaerobic soils and sediments are facile reductants of chromate, but microbial metabolites such as ferrous-iron and sulfide dominate reduction. A comprehensive model of chromium biogeochemistry essentially comprises Cr(III) oxidation by Mn-oxides completing against biologically induced reduction.