Trace Metals in San Francisco Bay Clams

Science Center Objects

The clams Potamocorbula amurensis and Corbicula fluminea were collected at a variety of sites in the San Francisco Bay/ Delta beginning July 1990 and ending February 2010. These invasive species were used as biosentinels of the fate, transport, and effects of trace metals in the San Francisco Bay ecosystem.

Introduction

The clams Potamocorbula amurensis and Corbicula fluminea were collected at a variety of sites in the San Francisco Bay/ Delta beginning July 1990 and ending February 2010. Both clams are invasive species in the San Francisco Bay/Delta and were used as biosentinels of the fate, transport, and effects of trace metals in the San Francisco Bay ecosystem. The trace metals analyzed were silver (Ag), cadmium (Cd), chromium (Cr), copper (Cu), nickel (Ni), lead (Pb), vanadium (V), and zinc (Zn). The two species were found together at three sites (2.1, 4.1, and MTZ006).  Cynthia L. Brown, Jessica L. Dyke and Samual N. Luoma contributed to this project.

 

Methods

Samples from the subtidal zone were collected with a Van Veen grab. Between 60 and 120 clams of all sizes were collected from a 2-mm screen sieve at each time and each site and placed into containers of water collected at the site. The clams were kept in this ambient water in a constant-temperature room at 10 °C to depurate for 48 hours. Clams from each site were separated into size classes of 1-mm difference, and composite samples were made of similar sized individuals. Samples of larger numbers of individuals were necessary for smaller size classes in order to obtain enough mass for analysis. Mean concentrations characteristic of a site and date were thus determined from analyses of 5 to 14 replicate samples, each containing 5 to 20 clams.

Tissue was removed from the shells and put into pre-weighed borosilicate glass scintillation vials. The samples were dried in an oven at 21 °C until completely dry (3 to 4 days) and then weighed. Concentrated nitric acid (HN03) was added to each vial to cover the tissue (3 to 5 ml of HN03). Each vial was digested by reflux in sub-boiling 16N HN03 until solution was light yellow to clear. The vials were then evaporated to dryness and reconstituted in 5-percent hydrochloric acid (HCl). The amount of HCl added to the sample depended upon the total dry weight in the vial. Five ml was added to samples of less than 300 mg, and 10 ml was added to samples greater than 300 mg. The samples were filtered with 0.45-µm disposable filters after sitting for 2 to 3 days. Concentrations of Ag, Cd, Cr, Cu, Ni, V, and Zn in the whole tissues of the clams were analyzed by inductively coupled argon plasma-atomic emission spectroscopy (ICAP-AES) (Brown and Luoma, 1995).

 

Data Calculation

Mean concentration data is reported as μg/g dry weight. When there was a significant relationship between length and concentration, the interpolated concentration for a 15 mm clam (P. amurensis) and a 24 mm clam (C. fluminea) was reported.

Content data is reported as μg/individual, interpolated from the regression of content and length for a 15 mm clam (P. amurensis) and a 24 mm clam (C. fluminea).

Condition index is reported as mg/standard clam length and is interpolated from the regression of weight and length of a 15 mm clam (P. amurensis) and a 24 mm clam (C. fluminea).

 

References

Brown, C.L., and Luoma, S.N., 1995a, Energy-related selenium and vanadium contamination in San Francisco Bay: Effects on biological resources? in Carter, L.M.H., ed., Energy and the Environment - Application of Geosciences to Decision - Making. Program and short papers, Tenth Annual McKelvey Forum on Mineral and Energy Resources, February 13 - 16, 1995, Washington D.C.: U.S. Geological Survey Circular 1108, p. 91-92.

Brown, C.L., and Luoma, S.N., 1995b, Use of the euryhaline bivalve Potamocorbula amurensis as a biosentinel species to assess trace metal contamination in San Francisco Bay: Marine Ecology Progress Series, v. 124, no. 1-3, p. 129-142.

Brown, C.L. and Luoma, S.N., 1998, Metal trends and effects in Potamocorbula amurensis in North San Francisco Bay: Interagency Ecological Program Newsletter, v. 11, no. 2, p. 33-35.

Brown, C.L., and Luoma, S.N., 1999, Metal trends and effects in Potamocorbula amurensis in North San Francisco Bay: U.S. Geological Survey Toxic Substances Hydrology Program – Proceedings of the Technical Meeting, Charleston, South Carolina, March 8-12, 1999: Water-Resources Investigations Report 99-4018B, p. 17-21.

Brown, C.L., Luoma, S.N., Parchaso, F., and Thompson, J.K., 2004, Lessons learned about metals in the estuary: The importance of long-term clam accumulation data: in San Francisco Estuary Institute (SFEI), 2004, The Pulse of the Estuary: Monitoring and Managing Water Quality in the San Francisco Estuary, SFEI Contribution 78, San Francisco Estuary Institute, Oakland, CA, pp. 38-45.

Brown, C.L., Parchaso, F., Thompson, J.K., and Luoma, S.N., 2003, Assessing toxicant effects in a complex estuary: A case study of effects of silver on reproduction in the bivalve, Potamocorbula amurensis, in San Francisco Bay: Human and Ecological Risk Assessment, v. 9, no. 1, pp. 95-119.

Flegal, A.R., Brown, C.L., Squire, S., Ross, J.R.M., Scelfo, G., and Hibdon, S., 2007, Spatial and temporal variations in silver contamination and toxicity in San Francisco Bay: Environmental Research, v. 105, pp. 34-52.

Luoma, S.N., Carter, J.L., and Brown, C.L., 1991, Assessing adverse effects of contaminants on benthic species at the San Francisco Bay Toxics Site: in Mallard, G.E., and Aronson, D.A., eds., U.S. Geological Survey Toxic Substances Hydrology Program-Proceedings of the technical meeting, Monterey, CA, March 11 - 15, 1991: U.S. Geological Survey Water Resources Investigative Report 91-4034, p. 667-671.

Parchaso, F., Brown, C.L., Thompson, J.K., and Luoma, S.N., 1997, In situ effects of trace contaminants on the ecosystem in the San Francisco Bay estuary, 1995: The necessary link to establishing water quality standards II: U.S. Geological Survey Open File Report 97-420.

Teh, S.J., Clark, S.L., Brown, C.L., Luoma, S.N., and Hinton, D.E., 1999, Enzymatic and histopathologic biomarkers as indicators of contaminant exposure and effect in Asian clam (Potamocorbula amurensis): Biomarkers, v. 4, no. 6, p. 497-509.

Thompson, B., Adelsbach, T., Brown, C., Hunt, J., Kuwabara, J., Neale, J., Ohlendorf, H., Schwarzbach, S., Spies, R., and Taberski, K., 2007, Biological effects of anthropogenic contaminants in the San Francisco Estuary: Environmental Research, v. 105, p. 156-174.

Thompson, J.K., Parchaso, F., Brown, C.L., and Luoma, S.N., 1996, In situ ecosystem effects of trace contaminants in the San Francisco Bay estuary: The necessary link to establishing water quality standards I: U.S. Geological Survey Open-File Report 96-437.