Environ. Sci. Technol. 2003, 37, 2625
Comment on “Anthropogenic Sources of Arsenic and Copper to Sediments in a Suburban Lake, Northern Virginia” Rice et al. (1) presented mass balances for copper and arsenic in a suburban Virginia lake and attributed the estimated copper and arsenic loads primarily to road runoff and chromated copper arsenate (CCA)-treated wood, respectively. The purpose of this paper is to show, using the example of arsenic, why the measured data presented in Rice et al. (1) are not adequate to determine a reliable mass balance for the lake nor to attribute sources to the estimated element loads. First, the apparent number of samples collected is insufficient with respect to time and area to support a reliable mass balance. Specifically, measurements of arsenic were not made in all tributaries. The frequency of sampling events and the total number of samples collected were not presented. Apparently, just three grab samples of lake water and three sediment samples were collected from the 10.9-ha lake. No nearshore samples of water or sediment were taken. In addition, the link between arsenic from CCA-treated wood along the lake’s shore and arsenic in sediment in the center of the lake is unsubstantiated. Laboratory measurements were used to estimate arsenic loads from CCA-treated wood. From these measurements, the authors estimate 45 years for arsenic depletion from CCA-treated wood, which is a gross overestimate of leaching as shown by other laboratory and field data (e.g., refs 2 and 3). Upon proposing CCA-treated wood as the source of arsenic, the authors should have measured arsenic concentrations over time and alongside CCA-treated wood structures. Other published examples of chemical mass balances on water bodies include the use of targeted sampling locations or long-term sampling to help identify sources (e.g., refs 4 and 5). This is consistent with recommendations from the National Research Council (6). Alternative arsenic sources were not investigated. For example, arsenic runoff from soil where historical pesticide use occurred (e.g., lead arsenate) or current pesticide and fertilizer use is occurring can be highly localized (7) and timedependent (i.e., after pesticide and fertilizer applications), leading to arsenic point sources not captured in the limited sampling scheme used. Only some of the data and calculations used for the mass balance were provided, so the results are not reproducible.
10.1021/es034092e CCC: $25.00 Published on Web 05/06/2003
2003 American Chemical Society
For example, the measured and estimated inflows and corresponding arsenic concentrations were not given. Also, it is unclear how the authors identified CCA-treated wood. The authors state that the amount of CCA-treated wood in and around the lake was estimated based on “field reconnaissance and aerial photography analysis”; however, they do not provide further details. Weathered, stained, or painted CCA-treated wood is difficult to identify visually and is commonly misidentified (8). The use of chemical stains or portable X-ray fluorescence devices are effective at identifying CCA-treated wood. If visual inspection were the sole means of quantifying the surface area of CCA-treated wood at the lake, the estimate would be highly uncertain. We believe that additional information should be presented to allow the mass balance calculations described by Rice et al. (1) to be fully reproduced and that the substantial uncertainty in attributing sources to the arsenic and copper loads because of insufficient sampling should be addressed.
Literature Cited (1) Rice, K. C.; Conko, K. M.; Hornberger, G. M. Environ. Sci. Technol. 2002, 36, 4962-4967. (2) Shiau, R. J.; Smith, R. L.; Avellar, B. Wood Sci. Technol. 2000, 34, 377-388. (3) Cooper, P. A.; Jeremic, D.; Taylor, J. L. Forest Prod. J. 2001, 51 (10), 58-62. (4) Koh, C.-H.; Khim, J. S.; Villenueve, D. L.; Kannan, K.; Giesy, J. P. Environ. Toxicol. Chem. 2002, 21, 1796-1803. (5) Batterson, T. R.; McNabb, C. D. Environ. Toxicol. Chem. 1983, 2, 1-17. (6) National Research Council. Opportunities to Improve the U.S. Geological Survey National Water Quality Assessment Program; National Academy Press: Washington, DC, 2002; 238 pp. (7) U.S. Environmental Protection Agency. Baseline Human Health Risk Assessment Vasquez Boulevard and I-70 Superfund Site Denver, Colorado; U.S. EPA, Region VIII: Denver, CO, 2001. (8) Solo-Gabriele, H.; Hosein, N.; Jacobi, J.; Townsend, T.; Jambeck, J.; Hahn, D.; Moskal, D.; Iida, K. On-Line Sorting Technologies for CCA-Treated Wood Draft. Florida Department of Environmental Protection Innovative Recycling Grants Program, Tallahassee, FL. 2001; available online (1/20/03): http://www.floridacenter.org/publications/final_sara_draft_ m7_web.pdf.
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