Toxic Metals Decreasing, PAHs Increasing in Puget Sound Sediment

16 August 2005

Long-term monitoring stations in Puget Sound.

While the concentration of toxic metals in the sediment of Puget Sound is decreasing, the concentration of polycyclic aromatic hydrocarbons (PAHs) in some locations is increasing, according to results of a long-term study recently published by the Washington state Department of Ecology.

Toxic metals enter the environment as wastes from industrial manufacturing, mining operations, combustion products and agricultural pesticides, while PAHs are formed by the incomplete burning of organic matter, including fossil fuels. They also are found in coal tar, crude oil, creosote and roofing tar.

PAHs can enter the environment from vehicles that discharge them into the atmosphere through exhaust emissions and onto roads and parking lots through oil and gasoline leaks. As the PAHs fall to the ground, stormwater runoff carries them into Puget Sound.

Recent research done by the USGS National Water-Quality Assessment (NAWQA) Program and the City of Austin has determined that parking lot sealcoat—a previously unidentified source of urban polycyclic aromatic hydrocarbons (PAHs)—may be the major source of PAH concentrations in urban water bodies in the United States. (Earlier post.)

In the study, “Temporal Monitoring of Puget Sound Sediments: Results of the Puget Sound Ambient Monitoring Program, 1989-2000,” scientists collected and tested sediments at 10 sites in Puget Sound over a period of 12 years.

The decline in metals may be due to federal clean-water and air regulations imposed in the early 1970s that have limited pollution discharges by industries and cities, according to Margaret Dutch, who led the study for Ecology. In turn, the rise in PAHs may be due to increasing urbanization and vehicle use near Puget Sound. Other marine-sediment experts agree with the theory, said Dutch.

Dutch said PAHs tend to bind to sediments and sink to the bottom. They can be toxic and cause cancer in marine life, including producing liver lesions and tumors in fish that live on or near the sediments. PAHs also can change the growth rates and behavior of sediment-dwelling invertebrates.

According to the EPA, PAHs are highly potent carcinogens that can produce tumors in some organisms at even single doses. Their effects are wide-ranging within an organism and have been found in many types of organisms, including non-human mammals, birds, invertebrates, plants, amphibians, fish, and humans.

In aquatic systems, PAHs tend towards increased toxicity with increased molecular weight. Although the rate of uptake from the environment is variable among species, bioaccumulation—the increase in concentration of a chemical in a biological organism over time, compared to the chemical’s concentration in the environment—tends to be rapid.

We’ve made progress controlling toxic discharges that accumulate in sediments, yet each time we fix one problem in Puget Sound, we discover another. PAHs and stormwater runoff are difficult new problems, directly tied to increasing population in the basin. Saving Puget Sound is ultimately about smarter land use and management of wastes in the basin. There are no easy solutions.

—Brad Ack, director of the Puget Sound Action Team

Resources:

• Temporal Monitoring of Puget Sound Sediments: Results of the Puget Sound Ambient Monitoring Program, 1989-2000, publication and full data supplement here

• Summary of the study here