A chemical which, in high concentrations, is likely to cause cancer and irritates the respiratory system and skin has been found in tap water in 31 of 35 American cities, according to a new study.

Hexavalent chromium is regarded as a probable cancer-causing toxin and irritant to human organs.   

The so-called “Erin Brockovich chemical,” was found in its highest concentrations in Norman, OK, Honolulu, HI, and Riverside, CA, according to the non-profit Environmental Working Group. The chemical was named after the environmental activist who pursued a case involving the toxin against a public utility company in California in the 1990s.

Hexavalent chromium is a toxic form of the element chromium. Compounds including the chemical are widely used in many different industries.

Among the major industrial sources of the chemical are pigments in various kinds of paints, some types of chrome plating, chemicals used in some smelting processes and in one of the most popular types of cement.

The Occupational Safety and Health Administration, a division of the U.S. Department of Labor, says workplace exposure  may cause lung cancer and irritation to the respiratory system if inhaled at high concentration levels, and irritation or damage to eyes if the chemical comes into direct contact at those levels.

Currently the U.S. Environmental Protection Agency classifies the chemical as “likely to be carcinogenic to humans” when consumed in drinking water. So far, the agency has not set a legal limit for Chromium-6 in tap water and does not require utility companies to test for it.

The concentration of the chemical exceeded California’s proposed Chromium-6 goal of 0.06 parts per billion.

The city of Norman, with a population of nearly 90,000, had tap water with a concentration of 12.9 ppb. Honolulu, with a population of 661,004, had a concentration of 2.00 ppb. Riverside, with more than 280,000 people had a concentration of 1.69 ppb.The next two highest cities, were Madison, Wisconsin, and San Jose, California with 1.58 ppb and 1.34 ppb respectively.