Anthropogenic Sources of Arsenic and Copper to Sediments in a Suburban Lake, Northern Virginia KAREN C. RICE,* ,† KATHRYN M. CONKO, ‡ AND GEORGE M. HORNBERGER § U.S. Geological Survey, P.O. Box B, Charlottesville, Virginia 22903, U.S. Geological Survey, MS 432 National Center, Reston, Virginia 20192, and Department of Environmental Sciences, University of Virginia, Charlottesville, Virginia 22903 M ass balances of total arsenic and copper for a suburban lake in densely populated northern Virginia were calculated using data collected during 1998. Mass-balance terms were precipitation; stream inflow, including road runoff; stream outflow; and contributions from leaching of pressure- treated lumber. More mass of arsenic and copper was input to the lake than was output; the 1998 lake-retention rates were 70% for arsenic and 20% for copper. The arsenic mass balance compared well with a calculated annual mass accumulation in the top 1 cm of the lake sediments; however, the calculated contribution of copper to the lake was insufficient to account for the amount of copper in this zone. Leaching experiments were conducted on lumber treated with chromated copper arsenate (CCA) to quantify approximate amounts of arsenic and copper contributed by this source. Sources to lake sediments included leaching of CCA-treated lumber (arsenic, 50%; copper, 4%), streamwater (arsenic, 50%; copper, 90%), and atmospheric deposition (arsenic, 1%; copper, 3%). Results of this study suggest that CCA-treated lumber and road runoff could be significant nonpoint sources of arsenic and copper, respectively, in suburban catchments. Introduction Arsenic (As) and copper (Cu) are priority pollutants (1). Arsenic is a human carcinogen (2), and Cu is an essential element to biota and humans but is toxic in excess (3-5). Because ofpotentialhealth effects to biota and humans, the presence of these elements in terrestrial and aquatic envi- ronments is of concern. For example, accumulation of As and Cu from industrial sources in lake and reservoir sediments has been observed (6-8).Anthropogenicimpacts to industrial environments have received more study than suburban environments because point sources of contami- nants are easier to quantify than are nonpoint sources. To explore the potential of similar impacts in a suburban environment (i.e., an enrichment of As and Cu in lake sediments over background concentrations), we developed a mass-balance model for a suburban catchment. A mass balancequantifiesthenaturalaswellasanthropogenicinputs and outputs of a given constituent for a catchment. If the catchment contains a lake, input of x to the lake - export of x from the lake ) contribution of x to the lake sediments, where storage of x in lake water remains constant. Potential sources of As and Cu to a suburban catchment include atmospheric deposition, geologic contribution, roadways, and pressure-treated lumber. Combustion of As- and Cu-containing coal and weathering of As- and Cu- containing bedrock provide a source of these elements in atmospheric deposition and streamwater, respectively. Cop- per can be deposited on roadways by motor-vehicle brake- component wear (9, 10);combustion ofgasoline,diesel,and lubricating oils (11);and tire wear (10). Rainfall can wash the Cu from impervious surfaces directlyinto streams and lakes. Chromated copper arsenate (CCA) is a wood preservative used in pressure-treated lumber,with insecticidalproperties provided by As and fungicidal properties provided by Cu (12). Typically, concentrations of As and Cu in the wood range from 1000 to 5000 mg/kg (13). Decks constructed of CCA-treated wood release As and Cu to the underlying soils: up to 350 mg/ kg As and 410 mg/ kg Cu accumulated in soils beneath decks, as compared to an average of 17 mg/kg As and 4 mg/kg Cu in control soils (13). Contact of lake water or rainwater with CCA-treated wood potentially can release As and Cu to the environment. Although leaching of As and Cu from bulkheads and dock pilings and accumulation in adjacent sediments have been observed in estuarine envi- ronments (e.g., refs 14-16), no previous studies are known to have documented trace-element leaching from CCA- treated lumber in a freshwater environment.Environmental managers are becoming aware of the potential of release of As from CCA-treated wood as indicated by the U.S. EPA’s announcement of the phase-out of As in treated wood for residentialusebyDecember31,2003(17).Thisstudyprovides an example for environmental managers of the effect that CCA-treated wood can have on the environment. Study Site. Our case study was of Lake Anne, a recre- ational, 10.9-ha lake created in 1964 in suburban northern Virginia (Figure 1). The 235-ha catchment is densely popu- lated (1116 people/km 2 ) and heavily developed, with dwell- ings surrounding the lake shoreline. Two tributaries con- tribute to the lake, but one drains another dammed lake within the catchment (Figure 1). Although excessive algal growth is common in Lake Anne, it does not serve as a drinking-water supplyand has not been treated with CuSO4‚ 5H2O.CCA-treated wood is used in the construction ofdecks and docks in and near Lake Anne and as a bank stabilization material along approximately 75% of the shoreline. Components of the mass balance of total As and Cu for Lake Anne for 1998 were atmospheric deposition; stream- water, which included runoff over impervious surfaces and constituents derived from weathering of the schist, gneiss, and phyllite bedrock (18); and inputs to the lake through leaching of CCA-treated lumber by both rainwater and lake water. Alaboratory leaching experiment was conducted on CCA-treated samples to quantify the approximate mass of As and Cu delivered to the lake from leaching CCA-treated lumber. For the water balance, the contribution of ground- water inflow to the lake and discharge from the lake was assumed to be equal, and the annual change in storage of lake water was assumed to be negligible. The calculated fluxes were compared to the annual mass accumulations at the top of three lake-sediment cores that were collected from Lake Anne in 1996 (boxand gravitycores) and 1997 (box core). Dry-weight concentrations at the top ofthe sediment cores ranged from 18 to 28 μg/ g As an d from 105 to 137 μg/g Cu, which are up to 23 and 5 times higher *Correspondingauthor phone: (434)297-0106;fax: (434)977-6751; e-mail: kcrice@usgs.gov. † U.S. Geological Survey, Charlottesville. ‡ U.S. Geological Survey, Reston. § University of Virginia. Environ. Sci. Technol. 2002, 36, 4962-4967 4962 9 ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 36, NO. 23, 2002 10.1021/es025727x CCC: $22.00  2002 American Chemical Society Published on Web 10/23/2002