MA1 Large-Scale Investigations of Contaminated Sediments
256 Portland Ballroom
8:00 AM - 12:00 PM, Monday
() National-Scale Trends in Metals in Urban and Reference Lake Sediment Cores, 1975 to Present.
Mahler, B1, Van Metre, P1, Callender, E2, 1 U.S. Geological Survey, Austin, Texas, USA2 U.S. Geological Survey, ret., Westerly, Rhode Island, USA
ABSTRACT- How have national legislation, regulation, and changing demographics and industrial practices over the past three decades affected concentrations of metals associated with sediments deposited in U.S. lakes and reservoirs? To answer this question, the U.S. Geological Survey analyzed trends in concentrations of seven metals (cadmium, chromium, copper, mercury, nickel, lead, and zinc) from 1975 to present in sediment cores from 42 reservoirs and lakes across the country, covering a land-use gradient from undeveloped (reference) to fully urbanized. Downward trends (decreasing concentrations over time) outnumbered upward trends for all metals except zinc. This tendency was most pronounced for chromium and lead (downward trends outnumbered upward trends by about 10 to 1), followed by nickel (5 to 1). Overall metals contamination, as evaluated on the basis of the mean probable effect concentration (PEC) quotient and the frequency of exceedence of the PEC, increases with urban density. Despite decreases since 1975 in the mean PEC quotient for both dense and light urban settings, the frequency of exceedences of individual PECs remains about the same, which indicates that metals contamination continues to be an environmental concern. In recently deposited sediments, lead accounts for more toxicity to aquatic benthic biota than any of the other six metals, on the basis of the PECs. However, upward trends in zinc in dense urban environments indicate that zinc might overtake lead as the most toxic metal related to urban land use. Decreases in atmospheric emissions could explain downward trends for many metals, whereas tire wear, combined with large increases in vehicle traffic, could explain upward trends in zinc in urban lakes.
Key words: trends, metals, sediment, contaminant