Jump to main content.

Trends in Hydrophobic Organic Contaminants in Lake Sediments across the US, 1970-2001

Peter C. Van Metre and Barbara J. Mahler

United State Geological Survey, Austin Texas

A major shift in public policy in the United States toward environmental protection began about 1970, with the establishment of the Environmental Protection Agency and passage of key environmental legislation. However, over the same three decades, urban land use, population, and vehicle use have increased greatly. To assess the effects of these and other actions on the quality of streams and lakes across the United States, the U.S. Geological Survey collected and analyzed sediment cores from 41 lakes. Land use in the watersheds sampled ranged from undeveloped (nine sites), to light urban (17 sites), to dense urban (15 sites). Cores were analyzed for polycyclic aromatic hydrocarbons (PAHs) and chlorinated hydrocarbons (organochlorine pesticides and polychlorinated biphenyls) and contaminant trends were tested for statistical significance. Trends among the chlorinated hydrocarbons were mostly downward, and trends among the PAHs were mostly upward. One-half of the lakes, for example, had downward trends in DDE and no lake had an upward trend, and one-half of the lakes had upward trends in benzo(a)pyrene while only three were downward. Concentrations of all contaminants analyzed were much greater in dense urban settings than in reference settings. Chlordane was the compound that most frequently exceeded the probable effect concentration (PEC), a sediment-quality guideline, often by an order of magnitude at dense urban sites. PAHs were twice as likely to exceed the PEC in the 1990s as they were from 1965 to 1975, and DDT and PCBs were half as likely. The combination of increasing trends in PAH concentrations, the strong association of PAHs with urban settings, and the rapid urbanization occurring in the U.S. suggests that PAHs could surpass chlorinated hydrocarbons in the threat posed to aquatic biota in urban streams and lakes. And while improvements brought about by regulation of chlorinated hydrocarbons are occurring, the continuing high levels of chlordane, the slow rate of decreasing trends for DDT and PCBs (10- to 15-yr half-lives), and the continuing risks to human health from consumption of fish and shellfish indicate that chlorinated hydrocarbons will remain a concern for many years to come.

EMAP Home | About EMAP | Components | Data | Documents | Bibliography | News | Site Map

Local Navigation

Jump to main content.