Dirty water from residential washing machines is a significant source of a toxin polluting Puget Sound, according to a study released Tuesday.

Dust that sloughs off hundreds of every day household products – including cosmetics, vinyl flooring, shower curtains and furniture – accumulates on people’s clothing and goes down the drain with the laundry-room suds, the study theorizes.

The study, conducted by the Seattle-based nonprofit, Washington Toxics Coalition, tested only for a single class of chemicals called phthalates, which accumulate in marine sediments and interfere with reproductive activity in marine creatures.

However, researchers say the washing machine pathway likely carries many other toxics as well.

“The phthalates are definitely an indicator chemical, a canary in the coal mine,” said Erika Schreder, the lead author of the study. “Besides being present in house dust, a lot of toxic household products, like cleansers, are going directly down the drain.”

In the study, conducted between November 2008 and May 2009, six homeowners from Tumwater to Whidbey Island volunteered their homes as test sites. Researchers took samples of water from washing machines following the first agitation cycle.

Extrapolating the data retrieved, the study concluded that residential washing machines send about 2,110 pounds of phthalates to wastewater treatment plants each year from household dust, about 17.5 percent of the total annual load.

Some phthalates settle into sludge in the sewage treatment process. The remainder – an amount that is unknown – is discharged into waterways, Schreder said.

Toxic effects of phthalates on wildlife have been documented in laboratory studies for decades, but no health-risk thresholds have been set for humans. In the marine environment, effects include changes in levels of enzymes in fish brains, muscles and livers.

In Tacoma’s Thea Foss Waterway, phthalates in the sediment have been shown to affect the reproduction and survival of mussel larvae and sand fleas.

To determine whether house dust was the source of the phthalates in the laundry water, the researchers collected dust samples from the homes and compared the concentrations of various phthalates to concentrations in wash water.

Dust concentrations of the most prevalent phthalate, DEHP, correlated strongly with concentrations of DEHP in the water, leading the researchers to conclude that dust generated in the house was in fact the source of the pollution.

The study helps answer a question that has perplexed scientists attempting to follow the trail of pollutants to Puget Sound sediment.

Aside from obvious sources – like industrial plants and runoff from concrete and asphalt surfaces – exactly how pollutants are deposited is poorly understood.

Heather Trim, a representative of the environmental group, People For Puget Sound, said while the study makes it clear that household products are polluting the Sound, the burden of stopping the process should fall on industry, not consumers.

“Instead of the consumers having to think when they go to the store, we want legislation that makes it so we know that everything is safe and not going to end up polluting Puget Sound,” Trim said.

Trim said People for Puget Sound intends to use the study results to argue for legislation that restricts harmful pollutants in consumer goods.

“It’s much more efficient to stop the pollution coming in than to clean it up afterward,” she said.

The ubiquity of phthalates will make regulation difficult.

The study found that many laundry detergents themselves contain phthalates, making it necessary for researchers to ask participants all to use the same phthalate-free brand of soap to keep from skewing results.

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