A carcinogenic chemical, chromium-6, has been discovered in dangerous levels in the tap water used by more than 200 million Americans across the country. This same chemical and its toxic effects were highlighted by environmentalist Erin Brockovich, whose story was turned into a Hollywood film.

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An environmentalist group called the Environmental Working Group released figures which revealed that more than 50 states in the US were exposed to unsafe levels of the chemical, the Daily Mail reported.

The toxic chemical was first brought into the spotlight when Brockovich, who worked at a law firm, took on a power company accused of leaking the chemical into waterways in California.

The environmental group systematically collected samples of water between 2013 and 2015.

Of the samples collected more than 70 percent contained the chemical. The existence of the chemical was at the level of 0.02 parts per billion. Researchers in California claim that the specific threshold of 0.02 - is the point at which the chemicals starts to pose the risk of cancer.

The state with the highest percentage of the chemical in its water was Phoenix. The level was more than 400 times the amount required for it to be at a healthy drinking level.

Brockovich speaking to Newsweek said she was shocked as she explained that she never imagined the issue was so widespread. While chromium- 6 is a naturally occurring chemical, it is produced in industries such as steel production, chrome plating and dyes and pigment production.

A National Toxicology study in 2008 reportedly found mice who ingested water with the chemical to have developed intestinal tumors.

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