Chromium

Chromium's industrial career began in the 19th century with leather tanning and chrome plating, processes that generated enormous quantities of chromium-6 waste [1]. The story that captured public attention was the Pacific Gas & Electric contamination of Hinkley, California — a decades-long leakage of chromium-6 from a compressor station that poisoned the groundwater of an entire community. The legal battle was immortalized in the 2000 film Erin Brockovich, resulting in a $333 million settlement. But Hinkley was not unique: chromium-6 contaminated groundwater from industrial facilities, chrome plating shops, cooling towers, and steel manufacturing operations across America [2]. Chromium-6 also forms naturally in some aquifers where chromium-bearing minerals contact oxygen. A 2016 Environmental Working Group analysis found chromium-6 in water supplies of more than 250 million Americans in all 50 states, most at low but not zero concentrations [3].

Drinking water is the primary concern for chromium-6: it is soluble, persistent, and not removed by standard water treatment [1]. Private wells near industrial sites and areas with chromium-bearing geology are at highest risk. Inhalation is the major route for occupational exposure — chrome plating workers, stainless steel welders, and chromate pigment manufacturers breathe chromium-6 fumes and mist [2]. Trivalent chromium-3, by contrast, is in the food you eat (broccoli, whole grains, meat) and is actually required for normal insulin function in trace amounts. The distinction matters: chromium-3 supplements marketed for blood sugar control are essentially harmless; chromium-6 in water is a carcinogen. Tobacco smoke contains chromium-6, providing another reason to avoid smoke exposure [3].

Chromium-6 is classified as a known human carcinogen [1]. When inhaled, it causes lung cancer — this has been established since the 1940s in chromate production workers. When ingested in drinking water, it causes stomach and gastrointestinal tumors in animal studies, and epidemiological evidence is accumulating for stomach cancer in exposed human populations. The mechanism involves chromium-6 penetrating cell membranes and generating reactive oxygen species that damage DNA [2]. Skin contact with chromium-6 compounds causes a distinctive sensitization dermatitis called "chrome holes" in industrial workers. Unlike chromium-3, which your body excretes efficiently, chromium-6 binds to proteins and accumulates in tissues. The California safe drinking water goal is 0.02 ppb — far below the current federal action level of 100 ppb, which many researchers consider outdated [3].

People who rely on private wells in areas with historical chrome plating, leather tanning, or steel manufacturing operations face elevated groundwater risk [1]. Communities in arid regions of California, the Southwest, and the Midwest where chromium-bearing geology is common have elevated background levels. Workers in chrome plating, stainless steel welding, pigment manufacturing, and ferrochrome production face high inhalation exposures — lung cancer rates in these occupations are significantly elevated [2]. Individuals with skin contact with chromate compounds — construction workers handling cement (which contains chromate) — frequently develop allergic contact dermatitis.

Request your water utility's water quality report and look specifically for chromium-6 (not just total chromium) [1]. A reverse-osmosis filter certified for chromium removes both forms effectively. If you have private well water near industrial sites, test for chromium-6 specifically — standard water tests may only measure total chromium. Wear nitrile gloves when handling cement, mortar, or masonry products, which can contain chromate [2]. Workers in chrome plating and welding should insist on local exhaust ventilation (not just dilution ventilation), use NIOSH-approved supplied-air respirators during fume-generating operations, and have lung function monitored annually. Avoid purchasing imported goods from poorly regulated chrome plating operations — chromium-6 is not present in the final plated product but workplace contamination in supply chains is real [3].