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Does Driveway Car Washing Impact Aquatic Ecosystems?
The Morro Bay National Estuary Program weighs in on a recent study's findings
What can individual residents do to reduce their contribution to water pollution? According to a new study, not washing your car in your driveway should be at the top of your list.
The problem starts when car wash runoff, including detergents and vehicle surface residue, is allowed to run into the nearest stormdrain, most of which carry such excess water into nearby waterways without providing any treatment. This wastewater carries not only detergents, but trace amounts of metals, fuel and automotive fluids.
To better understand the impacts that car wash runoff can have on aquatic ecosystems, Seattle-based Environmental Partners, Inc. conducted a series of scientific tests using fish mortality rates. They found that washing your car in the driveway and letting runoff enter stormdrains that empty into natural waterways can be deadly for local fish.
Juvenile rainbow trout (Oncorhynchus mykiss) were exposed to the runoff at varying concentrations in a 96-hour toxicity test. Trout were placed in solutions of 6.25%, 12.5%, 25%, 50%, or 100% car wash effluent diluted with potable water. The goal of the dilution was to find the concentration at which 50% of the fish survive. All tested concentrations of the car wash effluent water caused 100% mortality within 24 hours of test start.
A second test with lower concentrations was developed and run. This simulated effluent was mixed according to product container instructions and was further diluted to account for rinse water. Juvenile rainbow trout were exposed to a concentration series of the simulated effluent at solutions of 0.01%, 0.05%, 0.1%, 0.5%, 1%, and 10%. The simulated effluent solution caused 100% mortality in the 10% concentration solution and 2.5% mortality in the 1% concentration solution. The LC50 – the concentration of simulated car wash runoff at which half the fish are killed within 96 hours – was 3.046%, or approximately 1.6 parts per million.
The researchers then modeled the concentrations of detergent that could occur in a hypothetical Puget Sound setting in which a small stream is subjected to car wash effluent via storm drains. The estimated detergent concentration ranged from 0.2 ppm to 1.5 ppm for high and low stream flow conditions, respectively. Thus estimated detergent concentrations during low flow conditions were similar to the 1.6-ppm value that was found to be lethal to 50% of juvenile rainbow trout tested.
Thus, some fish in the stream could be killed and it would be likely that the detergent would wash protective mucus from the gills of other fish. The survivors would thus be more susceptible to other contaminants and disease. It is also possible that oxygen uptake necessary for survival may be impaired. Other freshwater organisms living in the stream would also likely be affected, depending on a species’ sensitivities.
If you live in an urban area with stormdrains, and taking your vehicle to a commercial car wash is not an option for you, consider this simple solution: washing vehicles on permeable surfaces such as gravel driveways or grass prevents runoff and allows for natural treatment of many pollutants. To read additional details on this study go to http://www.stormh2o.org/sw0710_practical.html.
This article can be found in the Morro Bay National Estuary Program's Winter Issue of "Turning the Tide."
The problem starts when car wash runoff, including detergents and vehicle surface residue, is allowed to run into the nearest stormdrain, most of which carry such excess water into nearby waterways without providing any treatment. This wastewater carries not only detergents, but trace amounts of metals, fuel and automotive fluids.
To better understand the impacts that car wash runoff can have on aquatic ecosystems, Seattle-based Environmental Partners, Inc. conducted a series of scientific tests using fish mortality rates. They found that washing your car in the driveway and letting runoff enter stormdrains that empty into natural waterways can be deadly for local fish.
The County of San Luis Obispo’s draft Stormwater Ordinance takes an ‘only rain down the drain’ approach that would prohibit the discharge of car wash runoff into stormdrains. As this goes to press, there has been considerable controversy over this proposed prohibition.The researchers ran two tests to measure acute impacts to juvenile rainbow trout at various concentrations of car wash runoff. For the first test, runoff was collected from the parking lot of an automotive service facility during a car wash fund-raising event. This water ran across approximately 30 feet of asphalt before collection and likely included contact with petroleum hydrocarbons and the grit and grime typically associated with a heavily traveled asphalt lot.
The study summarized in this article makes it clear that such runoff can be lethal to the fish in our creeks. We strongly encourage readers to use commercial car washes (that discharge wash water to a wastewater treatment system) or to wash your car where the runoff can soak into the ground rather than flow directly to our creeks and ocean.
Juvenile rainbow trout (Oncorhynchus mykiss) were exposed to the runoff at varying concentrations in a 96-hour toxicity test. Trout were placed in solutions of 6.25%, 12.5%, 25%, 50%, or 100% car wash effluent diluted with potable water. The goal of the dilution was to find the concentration at which 50% of the fish survive. All tested concentrations of the car wash effluent water caused 100% mortality within 24 hours of test start.
A second test with lower concentrations was developed and run. This simulated effluent was mixed according to product container instructions and was further diluted to account for rinse water. Juvenile rainbow trout were exposed to a concentration series of the simulated effluent at solutions of 0.01%, 0.05%, 0.1%, 0.5%, 1%, and 10%. The simulated effluent solution caused 100% mortality in the 10% concentration solution and 2.5% mortality in the 1% concentration solution. The LC50 – the concentration of simulated car wash runoff at which half the fish are killed within 96 hours – was 3.046%, or approximately 1.6 parts per million.
The researchers then modeled the concentrations of detergent that could occur in a hypothetical Puget Sound setting in which a small stream is subjected to car wash effluent via storm drains. The estimated detergent concentration ranged from 0.2 ppm to 1.5 ppm for high and low stream flow conditions, respectively. Thus estimated detergent concentrations during low flow conditions were similar to the 1.6-ppm value that was found to be lethal to 50% of juvenile rainbow trout tested.
Thus, some fish in the stream could be killed and it would be likely that the detergent would wash protective mucus from the gills of other fish. The survivors would thus be more susceptible to other contaminants and disease. It is also possible that oxygen uptake necessary for survival may be impaired. Other freshwater organisms living in the stream would also likely be affected, depending on a species’ sensitivities.
If you live in an urban area with stormdrains, and taking your vehicle to a commercial car wash is not an option for you, consider this simple solution: washing vehicles on permeable surfaces such as gravel driveways or grass prevents runoff and allows for natural treatment of many pollutants. To read additional details on this study go to http://www.stormh2o.org/sw0710_practical.html.
This article can be found in the Morro Bay National Estuary Program's Winter Issue of "Turning the Tide."
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