A critical assessment of chromium in the environment

This article reviews the emissions, environmental fate and transport, analytical chemistry, uptake and metabolism, toxicology, and human epidemiology of chromium. Chromium is unique among regulated toxic elements in the environment in that different species of chromium, specifically chromium (III) and chromium (VI), are regulated in different ways. in contrast to other toxic elements where the oxidation state is not distinguished. In both industrial and environmental situations chromium (III) and chromium (VI) can inter-convert, with reduction of chromium (VI) to chromium (III) generally being favored in most environmental situations. Chromium released into the air, water, and soil can be transported among the various environmental media through various intermedia transport processes. Once in the environment, chromium can be taken up by human and other ecological receptors. Chromium (III) is generally absorbed through cell membranes albeit to a significantly lesser degree than chromium (VI). Because most of the biosphere is reducing for chromium (VI) and chromium (III) is relatively immobile, there is little bioconcentration or biomagnification of chromium (VI). Chromium appears to be a nutrient for at least some plants and animals, including humans, although chromium (VI) species have been reported to be toxic to bacteria, plants, and animals. Human toxicity includes lung cancer, liver, kidney and gastric damage, and epidermal irritation and sensitization. However, it is noted that medical, toxicological, and epidemiological evidence suggests that not all compounds containing chromium (VI) species (e.g., chromate salts) are carcinogenic.