Contaminant Concentrations in Fish from San Francisco Bay, 1997: Summary1 J.A. Davis, M.D. May, and S.E. Wainwright San Francisco Estuary Institute, Oakland, CA R. Fairey, C. Roberts, and G. Ichikawa Moss Landing Marine Laboratories, Moss Landing, CA R. Tjeerdema, M. Stoelting, and J. Becker Institute of Marine Sciences, University of California, Santa Cruz, CA M. Petreas, M. Mok, and M. McKinney Hazardous Materials Laboratory, Cal/EPA, Berkeley, CA K. Taberski San Francisco Bay Regional Water Board, Cal/EPA, Oakland, CA Introduction Methods   Summary and Conclusions   Acknowledgments   References

Introduction

In 1994 the Bay Protection and Toxic Cleanup Program (BPTCP) performed a pilot study to measure concentrations of contaminants in fish in San Francisco Bay (SFBRWQCB et al., 1995, Fairey et al., 1997). Screening values to identify chemicals of potential human health concern were calculated for the study based on U.S. EPA guidance (U.S. EPA, 1993). The study indicated that there were six chemicals or chemical groups that were of potential human health concern for people consuming Bay-caught fish: PCBs, mercury, DDT, dieldrin, chlordane, and dioxins.

As a result of this pilot study the Office of Environmental Health Hazard Assessment (OEHHA) issued an interim health advisory for people consuming fish from San Francisco Bay (OEHHA, 1994). The advisory states that:

1. Adults should limit consumption of Bay sport fish to, at most, two meals per month.

2. Adults should not eat any striped bass over 35 inches (89 cm).

3. Pregnant women or women that may become pregnant or are breast-feeding, and children under 6 should not eat more than one meal per month, and should not eat any meals of shark over 24 inches (61 cm) or striped bass over 27 inches (69 cm).

The advisory does not apply to salmon, anchovies, herring, and smelt caught in the Bay, other ocean-caught sport fish, or commercial fish. The advice was issued due to concern over human exposure to residues of methylmercury, PCBs, dioxins, and organochlorine pesticides in Bay-caught fish.

As a followup to the 1994 pilot study, an RMP Fish Contamination Committee, including representatives from government agencies, dischargers, and environmental groups, was set up to design a RMP component to measure fish contamination. The RMP Fish Contamination Committee developed two main objectives for the RMP fish contamination monitoring component:

1. To produce the information needed for updating human health advisories and conducting human health risk assessments.

2. To measure contaminant levels in fish species over time to track trends and to evaluate the effectiveness of management efforts.

 

A five-year workplan for the RMP fish contamination monitoring component was developed in 1997 and included: 1) a core monitoring program that is intended to be conducted every three years, 2) special studies, which are designed to answer questions that were brought up in the pilot study and will lead to a more scientifically sound and cost-effective monitoring program in the future, and 3) development of a study design and survey instruments to measure the rates at which people consume fish caught in San Francisco Bay. This article describes results for the fish tissue core monitoring program and special studies conducted in 1997. The fish consumption study is currently in progress and results will be presented in a technical report in mid-1999.

The core monitoring program targeted seven species that are frequently caught and eaten by Bay fishers and seven popular fishing areas in the Bay (see methods for more details). Special studies included in the 1997 sampling were: 1) collecting and analyzing samples to determine variance among individual fish to assist in the future development of a more cost-effective study design; and 2) a study to determine the difference in contaminant concentrations of fillets of white croaker with and without skin. The second study was designed to determine whether removing the skin from muscle fillets could significantly reduce exposure to organic contaminants. This information should be valuable to public information efforts. Due to space limitations, results of analyses of variance among individual fish (#1 above) are not discussed in this article, but will be included in deliberations concerning design of the sampling to be performed in 2000.

Although the main focus of this study is on human health, it is important to note that the chemicals discussed in this article accumulate in the Bay food web and may also have an effect on other species at higher trophic levels. Studies of piscivorous birds and marine mammals in the Bay have found concentrations of persistent contaminants that appear to be high enough to impair the health of these species (Davis et al., 1997; Davis, 1997; Young et al., 1998).

Methods

The species and fishing locations in the Bay were selected for sampling based on available information on frequencies of catch and consumption by Bay fishers, continuity with the 1994 pilot study, and to provide a broad geographic coverage of the Bay. The locations sampled are shown in Figure 6.12. Sampling details are provided in Table 6.3.

Fish were collected between May 27, 1997 and July 25, 1997. Special efforts to collect sturgeon only occurred on several days in both March 1997 and October 1997. A complete description of the sampling methods and a detailed cruise report are available from the San Francisco Estuary Institute.

U.S. EPA (1995) defines screening values as concentrations of target analytes in fish or shellfish tissue that are of potential public health concern. Exceedance of screening values should be taken as an indication that more intensive site-specific monitoring and/or evaluation of human health risk should be conducted. Screening values were calculated following U.S. EPA (1995a) guidance. Details about this approach are described in SFBRWQCB et al. (1995). A consumption rate of 30g fish/day that applies to recreational fishers was used in calculating screening values. The only changes in screening values from the pilot study were for mercury and PCBs. A screening value of 0.233 µg/g wet for mercury was applied to the 1997 data based on an updated reference dose (U.S. EPA, 1995b). The mercury screening value applied to the 1994 data was 0.140 µg/g wet (SFBRWQCB et al., 1995). A screening value of 23 ng/g wet for PCBs was applied to the 1997 data based on an updated cancer slope factor (U.S. EPA, 1998). The PCB screening value applied to the 1994 data was 3ng/g wet (SFBRWQCB et al., 1995).

Summary and Conclusions

Comparisons to Screening Values

As found in the 1994 pilot study (SFBRWQCB et al., 1995, Fairey et al., 1997), persistent toxic chemicals in Bay fish were found at concentrations of potential human health concern in 1997 RMP sampling (Tables 6.4 and 6.5).

Mercury exceeded the screening value in 44 of 84 samples. All collected samples of leopard shark and striped bass exceeded the mercury screening value. For some species, including leopard shark and striped bass, the older and larger fish accumulated higher mercury concentrations. Adjustment of the data for variation in length was useful in evaluation of trends in mercury concentrations in space and time. Data obtained for individual striped bass suggest the existence of two groups of striped bass in the Bay, one with higher mercury concentrations than the other. The reason that striped bass of similar size might display this sort of variability is unknown at this time.

Concentrations of trace organics were highest in white croaker and shiner surfperch. Overall, PCBs exceeded the screening value in 51 of 72 samples. All of the white croaker and shiner surfperch samples exceeded the screening value for PCBs. Other trace organics had lower numbers of samples above screening values: 27 of 72 for dieldrin (including all 14 white croaker samples), 16 of 72 for DDTs, and 11 of 72 for chlordanes. Species with low lipid content in their muscle tissue, such as halibut and leopard shark, had the lowest concentrations of trace organics.

Dibenzodioxins and dibenzofurans were measured in six samples of white croaker and one sample of striped bass. ITEQs (dioxin toxic equivalents due to dibenzodioxins and dibenzofurans) in these samples were all above the screening value of 0.15 pg/g wet weight. Total TEQs (including the contributions of dioxin-like dibenzodioxins, dibenzofurans, and PCBs) in these seven samples averaged 9.7 pg/g wet weight, with a minimum of 3.7 pg/g and a maximum of 19.7 pg/g. Dioxin-like PCBs accounted for 83% of total TEQs. Dibenzofurans and dibenzodioxins accounted for 10% and 7%, respectively, of total TEQs.

Spatial Patterns

Significant variation in contaminant concentrations among locations was observed in the three species (white croaker, shiner surfperch, and jacksmelt) employed to evaluate spatial patterns. Spatial variation in wet-weight concentrations was observed, indicating variation in potential human exposure to contaminants of concern. Oakland Harbor had significantly elevated wet-weight concentrations of mercury (in shiner surfperch and jacksmelt), PCBs (shiner surfperch, white croaker, and jacksmelt), DDTs (shiner surfperch), and chlordanes (shiner surfperch, white croaker, and jacksmelt).

Spatial variation was also evaluated by adjusting the data for the important factors length and lipid content. These adjusted data may provide a better indication of spatial and temporal variation in contamination of the Bay. Length-adjusted mercury concentrations were relatively high at Oakland Harbor and San Francisco Waterfront (in jacksmelt). Lipid normalized concentrations of PCBs (in jacksmelt and shiner surfperch), DDTs (shiner surfperch), chlordanes (jacksmelt and shiner surfperch), and dieldrin (shiner surfperch) were elevated at Oakland Harbor. Lipid normalized PCB concentrations at Oakland Harbor were 11 times higher than at the sampling location with the lowest PCB concentration. The observation of similar spatial patterns in multiple species support the conclusion that the Oakland Harbor location exhibits elevated concentrations of multiple contaminants. These findings are consistent with observations of high concentrations of PCBs and organochlorine pesticides in sediment at this location (Hunt et al., 1999). Overall, the results of the sampling for spatial patterns suggest that shiner surfperch and jacksmelt are useful indicators of spatial variation in contamination in the Bay.

Temporal Trends

Mercury concentrations in 1997 were not significantly different from concentrations in 1994. In 1997 lipid-normalized concentrations of PCBs were significantly lower than in 1994 in shiner surfperch, white croaker, and striped bass, suggesting a possible general decline in PCBs in the Bay. Significantly lower concentrations were also observed for lipid-normalized DDTs (striped bass), chlordanes (striped bass and white croaker), and dieldrin (striped bass and shiner surfperch). Decreasing concentrations of these synthetic chemicals would be consistent with restrictions on their use that have been in place for many years. Lipid-normalized dioxin ITEQs were also significantly lower in 1997 than in 1994.

Continued monitoring will be required to establish whether the apparent decreases observed for PCBs, organochlorine pesticides, and dioxin ITEQs are real indications of declining masses of contaminants in the Bay. Other possible causes of these apparent declines include variation in the physiology or behavior of the fish sampled, changes in the structure of the Bay's food web, variation in analytical methods, or simply short-term fluctuation that is not indicative of a persistent long-term trend. The reason for the large differences in lipid concentrations observed in 1994 and 1997 are not understood and further emphasize the need for continued monitoring to determine trends over time. Continued fish tissue monitoring will also allow detection of changes that have not yet been indicated by results from just two sampling events (1994 and 1997).

Other Conclusions

The use of multiple species for evaluating spatial and temporal trends proved to be valuable. Consistent trends were observed for multiple species, lending greater confidence to conclusions about spatial and temporal variation. The use of multiple species also offers the advantage of increasing the likelihood of obtaining target species, whose distribution in the Bay varies considerably.

Fish size (or age) and lipid content were identified as important factors influencing accumulation of persistent contaminants. Trophic level is probably also an important factor accounting for some of the variation in these results, but the trophic levels of the species sampled in the Bay are not well characterized. Understanding and accounting for these factors is essential to evaluation of spatial and temporal trends in contaminant concentrations.

Substantially lower concentrations of trace organics were measured in white croaker fillets with the skin removed. Concentrations of PCBs, DDTs, chlordanes, dieldrin, and dioxin ITEQs were reduced by 30­50%. These reductions were associated with lipid concentrations that were 33% lower in the fillets without skin. For some samples, skin removal resulted in reduction of chlordane and DDT concentrations to below screening values.

Acknowledgments

Many people in addition to the listed authors made substantial contributions to this report. Members of the RMP Fish Contamination Committee provided guidance in all phases of this monitoring. Members of the Committee included:

• Karen Taberski, Committee Chair, San Francisco Bay Regional Water Quality Control Board
• Jon Amdur, Port of Oakland
• Ray Arnold, Exxon Biomedical
• Audrey Chiang, Asian-Pacific Environmental Network
• Bob Fujimura, California Department of Fish and Game
• Margy Gassel, Office of Environmental Health Hazard Assessment
• Jordan Gold, Applied Marine Sciences
• Erika Hoffman, U.S. Environmental Protection Agency
• Azibuike Lawson, Communities for a Better Environment
• Diana Lee, California Department of Health Services
• Brian Sak, City and County of San Francisco
• Alyce Ujihara, California Department of Health Services
• Dan Watson, City of San Jose
• Kristine Wong, Save San Francisco Bay Association
• Steven Zeiger, Marin County Stormwater Pollution Prevention Program

Adrienne Yang and Nicole David worked on formatting the report and graphics. Jung Yoon and Samir Arora managed the data. Gabriele Marek assisted with contract management.

The illustration of the Leopard Shark and Jacksmelt are from A Field Guide to Pacific Coast Fishes of North America. Copyright (c) 1983 by William N. Eschmeyer, Olivia Walker Herald, Howard Hammann, and Jon Gnagy. Reprinted by permission of Houghton Mifflin Company. All rights reserved. The illustration of the Striped Bass and White Croaker are from Freshwater Fishes of California. Copyright (c) 1984 by Samuel M. McGinnis and Doris Alcorn. Reprinted by permission of the University of California Press. All rights reserved.

References

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