Pollution From Urban Sprawl Threatens Aquatic Life In Major U.S. Cities

The study blames increased traffic from urban sprawl for high levels of polycyclic aromatic hydrocarbons, or PAHs, in lakes and reservoirs around six metropolitan areas, including Washington, D.C., New York, Newark, N.J., Minneapolis, Dallas and Seattle. Effects due to vehicle traffic included PAH concentrations in reservoir sediments up to 100 times greater than pre-urban conditions, said Peter Van Metre, lead author of the study from the U.S. Geological Survey in Austin, Texas.

The compounds are unlikely to get into the drinking water supply and adversely affect human health because they stick to the sediments in water supplies, he said. In addition, it is safe to eat fish or crabs - because the substance does not accumulate in animals - but the substances can kill aquatic life due to their toxicity and mutagenic effects, the researchers noted. PAHs are comprised of a multitude of substances that are considered both known and suspected human carcinogens.

Though water pollution from PAHs is thought to have little effect on humans, it may pose a bigger threat to aquatic life in urban waterways than other more well-known contaminants, such as lead, the pesticide DDT or PCBs, Van Metre said.

"People realize that cars and traffic cause air pollution, but they are not aware that they also cause water pollution," Van Metre said. "Increased traffic is frequently linked to degraded air quality, but its effect on aquatic sediment is not as recognized."

The researchers examined sediment samples from 10 lakes in selected older and newly developed urban areas. Using sediment core samples that recorded contaminant concentrations over the past 30 years, they found high - and rising - PAH concentrations, Van Metre continued. Testing revealed that the PAH levels exceeded sediment guidelines at all the sites, in some cases by several orders of magnitude.

The results were somewhat surprising since previous studies showed decreasing levels of the materials after reaching highs in the 1950s, he said. The researchers, however, were unable to speculate on a direct correlation between air quality and water quality.

Sources of PAHs from traffic include, soot, asphalt, motor oil, tire and exhaust emissions. The contaminants can also come from industrial plants or other sources, but the researchers determined the increase was almost exclusively due to more cars on the roadways. The compounds are typically carried to the waterways by stormwater.

The research cited above was part of the U.S. Geological Survey's National Water Quality Assessment Reconstructed Trends program.