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Prevalence of Selected Target Chemical Contaminants in Sport Fish from Two California Lakes: Public Health Designed Screening Study
FINAL PROJECT REPORT
EPA Assistance Agreement No. CX 825856-01-0
The primary objective of this study was to measure the levels of selected target chemicals in fish from San Pablo Reservoir and Black Butte Reservoir in order to provide an initial data base to determine whether additional sampling or evaluation of health concerns was warranted for either lake. Preliminary comparison of the measured levels of chemicals to CLS-SVs suggests that there are potential health concerns from consuming fish from both lakes. The chemicals of concern and the species of concern differ somewhat between the lakes. Further health evaluation of the data is warranted for both lakes. However, the data are limited on some of the species for which additional sampling is necessary.
San Pablo Reservoir and Black Butte Reservoir were selected for study because of the potential for mercury to be elevated in high trophic level fish (e.g., largemouth bass). The largemouth bass population in both lakes was well sampled in this study and chemical analysis showed that mercury concentrations in this species in both lakes were elevated above the CLS-SVs. In addition, the results showed that the other species sampled in Black Butte Reservoir (i.e., channel catfish, crappie, and carp) have elevated mercury levels. This result is most pertinent for the largemouth bass in San Pablo Reservoir and the largemouth bass and channel catfish in Black Butte Reservoir because a sufficient number of samples for these species were collected to characterize the populations in the lakes. The populations of crappie and carp in Black Butte Reservoir were not well characterized for mercury level and further sampling and analysis are recommended.
In Black Butte Reservoir, one sample in eight catfish composites exceeded the CLS-SV for toxaphene, and one in nine bass composites exceeded the CLS-SV for PCBs. The mean concentration of these chemicals in these well characterized species did not exceed the CLS-SV and, as such, the findings do not indicate a health concern.
For San Pablo Reservoir, additional samples and analysis are recommended for the following: chlordane, dieldrin, PCBs and dioxin TEQ in resident carp; dieldrin and PCBs in the stocked rainbow trout; and chlordane, dieldrin, PCBs, toxaphene and dioxin TEQ in channel catfish. This is based on cases where CLS-CVs are exceeded but only two composites of each species were collected and analyzed.
As discussed above, the stocked trout and channel catfish should also be sampled directly from the fish farm(s) to clarify whether significant exposure to organic chemicals occurs before they are put in this lake. This sampling and analysis should be discussed and coordinated with representatives of the East Bay Municipal Utility District.
The results of this study are important for all fishers at these lakes. They are especially pertinent to certain fishing populations as described below.
At San Pablo Reservoir it is important to further investigate the channel catfish contamination because catfish were noted as the most frequently consumed species by Laotian fishers (by 47.4% of surveyed fishers) in Contra Costa County in the APEN (1998) survey. And many of these ethnic fishers fish at San Pablo Reservoir (APEN, 1998). According to the APEN survey trout were consumed almost as often (by 40% of survey fishers) as catfish and, based on the data in this study, there was not a health concern due to chemical contamination of this stocked species in this lake.
There is no comparable survey of ethnic fishers for Central Valley lakes and rivers. According to a local health staff (Women, Infants and Children Program/Department of Health Services, personal communication) largemouth bass was the species favored by Hmong fishers at Black Butte Reservoir. Consequently, the finding of elevated mercury concentrations in this species is especially pertinent to this fishing population.
The data collected from this project will be considered by OEHHA for an evaluation of the human health implications of consuming fish from San Pablo Reservoir and Black Butte Reservoir and for the development of fish consumption advisory options as appropriate.