Which Carcinogens Are Contaminating Your Tap Water?

Remember Erin Brokovitch? Julia Roberts plays a legal assistant investigating a rash of cancer cases plaguing a small town in California. She discovers that these cancer cases are directly linked to carcinogenic chemicals found in the drinking water throughout this town, and that toxic dumping by a California gas company led to this contamination. Sadly, this film is based on the true story of Pacific Gas and Electric Company’s dumping of hexavalent chromium near the town of Hinkley California. This tragedy raises an important concern about the safety of tap water and what type of carcinogens may be a cause for concern.

Hexavalent chromium

Hexavalent chromium, or chromium 6, is a chemical state of the element chromium. This chemical is used in a variety of industrial processes like textile dyes and as a rust-prevention strategy. Unfortunately, chromium 6 poses a significant health risk. This chemical can enter human cells, damaging the DNA, and possibly leading to cancer. Companies disposing of chromium 6 have three options to make its disposal safer: 1. Try to reduce the amount of chromium 6 in their wastewater through methods like filtration. 2. Try to contain the wastewater (for example, using a physical barrier to prevent it from spreading into public water sources.) 3. Reduce its toxicity by trying to convert it to another form of chromium.

In the United States, California has the strictest rules about hexavalent chromium in drinking water. California sets a limit of 0.02 ppb (parts per billion) meaning that for every billion particles in drinking water, the maximum number of chromium 6 particles is 0.02 (or, in a trillion drinking water particles, the maximum number of chromium 6 particles in 20.) Unfortunately, this standard has not yet been adopted nationally, and in September of this year, the Environmental Working Group (EWG) tested water from all 50 states and found that 75% of the samples contained more hexavalent chromium than California’s recommended level. Although some advocates, like EWG and Erin Brokovich herself, are pushing the Environmental Protection Agency (EPA) to change national chromium 6 regulations, the current laws set a chromium 6 limit of 100 parts per billion.


N-Nitrosodimethylamine, or NDMA, is a chemical byproduct that may also be a concern for tap water safety. NDMA is generated by some industrial processes, like making rocket fuel, but it may also be generated by water treatment processes themselves; chlorination intended to disinfect drinking water may break down other chemicals, producing NDMA. Methadone, which is increasingly present in wastewater due to its pharmaceutical and recreational use, is one such chemical that can break down into NDMA.

Unfortunately, NDMA is both very toxic and very difficult to eliminate. NDMA can damage the liver and also cause cancer. The EPA considers NDMA to be dangerous even in small amounts and advises that the maximum level is 0.7 nanograms for every liter of water (that works out to about 700 parts of NDMA for every trillion parts of water.) Even more unsettling, NDMA cannot be removed by certain purification techniques like activated carbon filtration. Reverse osmosis, another common purification strategy, only removes about 50% of NDMA. Fortunately, treatment with ultraviolet light can generally break down NDMA.

NDMA is still being investigated as a potential drinking water contaminant. The EPA does not currently regulate the amount of NDMA in drinking water, but tests for its presence because of its emerging threat as a potential contaminant. The EPA reported that as of 2011, NDMA had been found in 1,787 samples out of 17,900 water samples. Although there are no national limits set for NDMA, some states like Massachusetts and California have set their own guidelines and limits for NDMA.

Hexavalent chromium and NDMA represent two of the possible carcinogens that may contaminate public drinking water. The history of both of these toxins reveal that regulations on carcinogens in tap water are constantly evolving. Although the legislation is constantly changing, it is important to be aware of what the legal limits are for carcinogens, and when these limits may be out of date. Information on how to protect your tap water from carcinogens and other contaminants can be found throughout our website.

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