New fish toxicity study measures potential impact of untreated car washing

Why taking your vehicle to a car wash is a better idea
by Stefan Kovalenko

Car Wash Enterprises, Inc. commissioned a study to measure the potential impact of untreated car wash discharges into the stormwater system (and thereby to streams and lakes) using fish mortality as a measure.

Water from driveways, alleys, or fundraising car wash events typically runs down the street or parking lot and into the nearest storm drain. This wastewater, or effluent, may carry detergents, trace amounts of metals (copper from brake dust, zinc from tire wear, etc.), and small amounts of gasoline and diesel fuel, oil, grease and antifreeze. Detergents, including those that are biodegradable, can be harmful to fish by destroying their protective mucus membranes. In addition, detergents can damage fish gills and wash away natural oils that help fish absorb oxygen. Because it goes untreated into the nearest stream, this runoff has the potential to harm fish and other marine life in the streambed.

The fish toxicity tests were performed using a water runoff sample collected from a fundraising car wash event held in a parking lot and compared against a simulated runoff sample that was potable. The impact of chemicals in the car wash runoff was measured by assessing the mortality rate in juvenile Rainbow Trout. This was a practical way to show how harmful car wash runoff can be in our streams. These tests were termed “practical” fish toxicity tests because the runoff solutions were collected and prepared to represent the actual runoff water that would be expected to enter into the stormwater drains and eventually enter the streams and rivers of Puget Sound.

The car wash runoff sample caused 100 percent mortality of fish in all dilution steps tested, while all the fish survived in the potable water.

As a part of the study, calculations were performed for a hypothetical urban or suburban Puget Sound setting in which a small stream is subjected to car wash effluent via storm drains. Approximately 100,000 people were assumed to live in the watershed area. With only one percent of the cars washed in driveways on a typical summer weekend, the results showed that toxicity levels could easily meet or exceed the situations tested in the lab resulting in potential fish kills of 50 percent of a juvenile species.

The full fish toxicity study can be found at:

Car Wash Enterprises, Inc. dba Brown Bear Car Wash has also instituted a charity car wash program. The program provides non-profit groups an environmentally-safe alternative to driveway and parking lot car washing, as well as an effective method for fundraising.

Information about the Brown Bear Charity Car Wash Program can be found at:

Stefan Kovalenko is the Community Affairs Coordinator / Project Specialist for Car Wash Enterprises, Inc.