Users of Dawn and Suave soap and shampoo products may be inadvertently releasing carcinogen-forming chemicals into drinking water, according to a study published March 31 by chemical engineering professor William Mitch. The chemical, N-nitrosodimethylamine (NDMA), is used as an industrial solvent and has been identified by the Environmental Protection Agency as a potential drinking water contaminant.

“Most people haven’t considered that their shampoo is a contributor to carcinogen formation,” Mitch said.

Mitch and Jerry Kemper GRD ’09 investigated how personal care products such as shampoo come into contact with chlorine disinfectants to form NDMA. When waste water with traces of shampoo and soap goes through water treatment facilities, it is often disinfected with a chlorine product. Because this water is released into a stream or river, it is likely to be taken up by a drinking water processing facility.

NDMAs are often present in very high percentages in this water, he said, but until now, scientists were not sure of the source of the chemical. He and Kemper set out to identify where the NDMAs came from and concluded that dish soaps and shampoos were the main culprits.

For the experiment, Kemper went to a pharmacy and bought various brands of shampoo and soap. He dumped the products into a vat, added a chlorine disinfectant commonly used by water treatment facilities and let the mixture sit for 10 days. Using an organic solvent, Kemper analyzed the chemical make-up of the solution.

Dawn dish-washing hand soap was the main producer of NDMAs, while Cheer laundry detergent and Pantene shampoo produced no NDMAs, he said.

Mitch and Kemper said there is little the conscientious consumer can do to avoid introducing these toxins into the environment. Mitch explained that it is nearly impossible to identify a contaminating product on a pharmacy shelf.

“If someone were a chemist, maybe they could look up the structure of the chemicals listed on the back of the bottle,” Mitch said.

Even if specific polymers were eliminated from the soaps’ formulas, Kemper said that the companies will just replace one chemical with another, which could lead to other environmental or health concerns.

Kemper, who is currently employed by the EPA to work on regulation for these contaminants, said the presence of NDMA in drinking water is a symptom of an unhealthy industry attitude.

“As a society, we make 1,000 chemicals a year and bad things are bound to happen if you add something unnatural to the natural world,” he said. “Whatever we come up with there is going to be a problem. I hope somebody answers that for me.”