Selenium, arsenic, DDT and other contaminants in four fish species in the Salton Sea, California, their temporal trends, and their potential impact on human consumers and wildlife

Abstract

A summary of all existing information gathered since 1980 on contaminants in bairdiella (Bairdiella icistia), orangemouth corvina (Cynoscion xanthulus), and sargo (Anisotremus davidsonii) living in the Salton Sea is presented. Comparisons are made with an earlier analysis of contaminants in tilapia (Oreochromis mossambicus x O. urolepis hornorum hybrid). Risks are assessed for humans and piscivorous birds consuming these fish and for the health of the fish populations themselves. Of the 17 trace elements, 42 organic pesticides and 48 polychlorinated biphenyls (PCBs) sampled in whole-body and fillet samples of fish collected from the Salton Sea, only arsenic (As), selenium (Se), total DDT (tDDT), and total PCBs (tPCBs) were determined to be of potential concern for the health of human consumers. Recent average concentrations of total As in fillet tissue are 1.3 μg g−1 wet weight (ww) for bairdiella and 1.2 μg g−1 ww for corvina and tilapia, respectively, with the inorganic As fraction representing 0.3–0.4 percent of total As. Based on U.S. Environmental Protection Agency (U.S.EPA) guidelines, these levels do not pose a threat of non-cancer adverse health effects in anglers, but consumption of 360 g (13 oz) of bairdiella, 650 g (23 oz) of corvina, or 540 g (19 oz) of tilapia per week for 70 years would increase the upper bound cancer risk by 1 per 100,000 consumers exposed. Between 1997 and 2002, total As levels in these three species increased an average of ~22 percent per year. Recent geometric mean Se concentrations were 2.9, 2.8, 2.2 and 1.7 μg g−1 ww in fillet tissues of bairdiella, corvina, sargo, and tilapia, respectively. These levels were not found to present unacceptable risk for adverse health effects for adult anglers consuming up to 492 g (17 oz) of bairdiella, 571 g (20 oz) of corvina, 754 g (27 oz) of sargo, or 1000 g (35 oz) of tilapia per week, even when additional intakes of Se from other food items are taken into account. However, during 1997–2000, Se levels in at least corvina and tilapia may have been increasing by an average of ~16 percent per year though they still were lower than 20 years earlier. tDDT (mostly DDE) and PCBs were recently detected in all fish samples. Compared to screening values proposed by the U.S. EPA, these concentrations seem unlikely to cause adverse health effects in anglers consuming less than 70 g of Salton Sea fish per week, but the potential for endocrine disruptive effects warrants further study. tDDT levels have declined by ~50 percent between the early 1980s and the 1990s in bairdiella, corvina and tilapia, paralleling declines in tDDT levels in eggs of fish-eating birds at the Salton Sea. Salton Sea sportfish may be safer for human consumption than was previously thought, but these conclusions are strongly affected by the particular parameter values and assumptions used in risk analyses. Given the strong temporal trends documented for key contaminants in this changing and geochemically unusual lake, risk assessments can also become quickly out of date. Se concentrations may be elevated enough to negatively affect fish health or reproduction as well as the immune systems of piscivorous birds feeding on the fish. Levels of other contaminants in fish were not found to be of concern for birds, but given the paucity of recent analyses on whole fish, additional analyses would be deisrable. Rising salinity caused all these fish species except for tilapia to become extinct in the lake by 2003. If and when fish populations are reestablished, new asessements of contaminant levels and risks should be undertaken immediately.