Envlron. Scl. Technol. 1992, 26, 2147-2151
and codes for assessing the off-site consequences of nuclear accidents, Athens, 1990. (25) Cannell, R. J.; Goddard, A. J. H.; ApSimon, H. M. Radiat. Prot. Dosim. 1987,21, 111-116. (26) Simmonds, J. R.; Crick, M. J. Transferparameters for use in terrestrial food chain models.; NRPB-M63; NRPB:
Chilton, UK, 1988.
Received for review March 23,1992. Revised manuscript received June 22,1992. Accepted June 24,1992. Funded by the Natural Environment Research Council.
Anthropogenic Silver In the Southern California Bight: A New Tracer of Sewage in Coastal Waters Serglo A. Safiudo-Wllhelmy*~t-~ and A. Russell Flegalt
Earth Sciences Board, University of California, Santa Cruz, California 95064, and Instituto de Investigaciones Oceanoldgicas, Universidad Autdnoma de Baja California, Ensenada, Baja California, Mexico Silver concentrations were measured in coastal surface waters from Santa Barbara, CA (United States) to San Quintin, Baja California (Mexico) in the Southern California Bight. Silver distributions were characterized by decreasing longshore and increasing offshore concentration gradients (3-39 pM) with the highest levels near primary sources of anthropogenic inputs. The offshore concentration gradient demonstrated that silver is a particle reactive element with a short residence time (-34 days) in coastal waters, where it is rapidly scavenged in the same manner as lead. Mass balance calculations showed that anthropogenic inputs of silver from the Point Loma discharge off San Diego, CA can account for essentially all of the silver in coastal waters along the United StatesMexico border during summer conditions. This was substantiated by elevated concentrations of silver relative to lead in those waters (Pb/Ag = 3.0-3.6), which indicated that sewage outfall (Pb/Ag = 3.2-3.3) was the principal source of anthropogenic silver in coastal waters off Baja California, Mexico. In contrast, coastal surface waters removed from point source inputs of anthropogenic silver had Pb/Ag ratios similar to those in upwelled water (5.3). This indicates that silver concentrations and Pb/Ag ratios may be used to identify and trace wastewater discharges in coastal waters. Introduction While many trace element distributions in oceanic waters have been established, relatively little is known about silver concentrations and distributions in coastal waters. This is an environmental concern, because silver is one of the most toxic elements for marine invertebrates (I) and the highest silver levels in intertidal marine invertebrates in the northeast Pacific have been found near wastewater outfalls off Los Angeles and San Diego (2). Moreover, wastewater discharges of silver to the Southern California Bight have remained relatively constant over the past two decades (-25 tonnes year-l), while discharges of other trace elements (e.g., Zn, Cu, Cr, and Pb) have declined by at least 75% during that period (3). This concern has been heightened by the recent (February 1992) breakup of the Point Loma wastewater outfall off San Diego, which has caused widespread contamination of intertidal waters along the United States-Mexico coastline. That one outfall is the primary source of silver in coastal waters extending 250 km from San Diego (United States) to Baja California (Mexico), as we demonstrate in this paper with silver concentration gradients, Pb/Ag ratios, and mass balance calculations. 'University of California. Universidad AutBnoma de Baja California.
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0013-930X/92/0926-2147$03.00/0
This was surprising because we recently determined that several other trace element distributions within the Southern California Bight are dominated by natural inputs, rather than anthropogenic inputs (4). For example, cadmium concentrations in coastal waters along the United States-Mexico boundary are almost entirely (180%) due to natural inputs from upwelling and longshore transport by the California current system. This has been substantiated by analyses of cadmium concentrations in sediments within the Southern California Bight (5). Oceanic profiles of silver indicate that it is recycled with biogenic matter as a copper analogue (6-8). Our current data on silver distributions in the coastal waters of the Southern California Bight are generally consistent with those profiles, although we found that silver is recycled more like lead than like copper in neritic surface waters. These preliminary measurements also reveal longshore gradients with elevated concentrations of silver near major wastewater discharges, which demonstrate that silver may be utilized as a unique tracer of sewage inputs to coastal waters. Methods Surface seawater samples were collected on two surveys in the Southern California Bight. The first set of samples (unfiitered) was collected along a series of offshore (45 km) transects across the continental shelf from the United States-Mexico border (32" N) to San Quintin, Mexico (30" N) in June 1988 (Figure la). The second set of samples (0.40 km filtered) was collected from 15 nearshore (
