Chromium is a naturally occurring element found in rocks, animals, soil, and in volcanic dust and gases. It is present in the environment in several different forms, the most common being trivalent chromium (Cr III) and hexavalent chromium (Cr VI).
Chromium is steel-grey, lustrous and hard and is used on a large scale in the metallurgical and chemical industries. The metallurgical industry commonly uses chromium for the production of stainless steels, alloy cast iron and nonferrous alloys as well as for plating steel. In the chemical industry, chromium is used primarily in pigments (Cr VI and Cr III), metal finishing and electroplating as well as in wood preservatives (Cr VI only) and leather tanning (Cr III only). In the past, chromium was also used in cooling towers as a rust and corrosion inhibitor and as a fungicide.
Chromium in the human body
Trivalent compounds (Cr III) do not cause any serious damage to body tissue, in fact, it is an important component of a balanced human and animal diet and its deficiency is detrimental to the glucose and lipid metabolism in mammals. The toxic action of chromium is confined to the hexavalent compound (Cr VI), which is a highly toxic carcinogen and may cause death to humans and animals if ingested in large doses.
One of the most well known cases of how Cr (VI) impacts the human body is depicted in the movie blockbuster Erin Brockovich. This true story involved a controversial lawsuit against the world’s largest utility, Pacific Gas and Electric Company (PG&E) as a direct result of a massive communications effort mounted by Ms Erin Brockovich.
PG&E was using Cr (VI) as an anti-corrosive in the cooling tower of a gas compressor station in the Mojave Desert town of Hinkley. During this time, officials from PG&E advised California regulatory authorities that they had detected hexavalent chromium (Cr VI) at levels of 580 μg/L (over 11 times the state’s 50 μg/L limit for total chromium) in a groundwater monitoring bore.
For some time, residents of Hinkley had been experiencing a disturbing array of health problems: liver, heart, respiratory and reproductive failure, Hodgkin disease, and frequent miscarriages as well as cancer of the brain, kidney, breast, uterus and gastrointestinal system. PG&E denied that these health defects were a result of the compressor station’s unlined wastewater ponds. In 1993, as a result of Erin Brockovich’s actions, residents of Hinkley were successful in seeking damages from PG&E.
Because of the great differences in environmental effects, the ANZECC health-based threshold for further investigation for sensitive sites for Cr VI is 100 mg/kg whilst the criteria for Cr III is 12 per cent (120 000 mg/kg)!
Chromium in the environment
Chromium exists in food, air, water and soil, mostly in the Cr III form. It is only as a result of human activities that substantial amounts of Cr VI become present. Cr III is comparatively insoluble while Cr VI is quite soluble and is readily leached from soil to groundwater or surface water.