Bioaccumulation of Contaminants by Transplanted Bivalves in the San Francisco Estuary: Status and Trends
Discussion and Conclusions
Appendix 1: Figures
Appendix 2: Data Tables
San Francisco Bay Area dischargers, through the Bay Area Dischargers Association (BADA) and the South Bay Dischargers, have analyzed bioaccumulation in transplanted bivalves for their Local Effects Monitoring Program (LEMP) since 1989. Five separate surveys have been conducted. The objective of this report is to:
1. provide information on the bioaccumulation of bivalves sampled in LEMP Rounds 3 and 4,
2. evaluate the similarities and differences in bioaccumulation among sampling locations (SFSE, EBMUD, CCCSD, and South Bay),
3. evaluate similarities and differences between reference sites and sites along outfall gradients wherever possible,
4. evaluate trends in bioaccumulation over time between sites located along transects along three outfall areas and their respective reference sites
5. compare the trends in bioaccumulation between outfall sites, Regional Monitoring Program reference sites, and State Mussel Watch sites in the Bay, and
6. compare wet season deployments with dry season deployments.
Beginning with the BADA surveys (Rounds 1-4), samples were located along gradients from three major estuary sewage outfalls belonging to the City and County of San Francisco (SFSE), the East Bay Municipal Utilities District, and the Contra Costa Central Sanitary District (CCCSD). Sites "near", "mid", "far" (from the outfall) and "out" (reference sites presumably outside outfall influences) were sampled. Bivalve deployments were made below the water surface and/or above the bottom in the case of SFSE and EBMUD, and just below the surface for CCCSD, and for 30 and/or 90 days. One to three replicate samples for analysis of trace metals and organics were collected at each station. Oysters, Crassostrea gigas, were used at CCCSD, and mussels, Mytilus californianus, were used at EBMUD and SFSE. These surveys collected samples during successive dry and wet seasons in the Estuary.
Differences between the 30- and 90-day deployments and between the shallow and deep deployments during Round 1 and 2 were described in previous reports. Those reports made several conclusions that are important in considering the results of Rounds 3 and 4 presented in this document. In general, the 90-day deployments had higher concentrations than the 30-day deployments except for PAHs which were more often higher in the 30-day deployments. There were no clear patterns of greater accumulation at the surface or bottom (deep) deployments. However, pesticides in Round 1 often had higher concentrations in the deep deployments.
Bioaccumulation of contaminants by transplanted bagged bivalves during LEMP Rounds 3 and 4 showed three general patterns:
1. For arsenic, cadmium, and chromium, there was no evidence of bioaccumulation in mussels. However, cadmium accumulated in some of the CCCSD oyster samples.
2. Only copper accumulated in all mussel and the great majority of oyster samples. Most other metals...