METHODS
Potamocorbula amurensis was collected from four subtidal sites within the northern reach of San Francisco Bay at near monthly intervals from 1990-1999. Clams were collected aboard aboard the R.V Polaris using a van veen grab. Grab contents were sieved through a course screen. Clam samples were collected within the ship channel from four sites, San Pablo Bay (SPB), Carquinez Strait (CS), Concord Naval Weapons Station (CNWS) and Mallard Island (MI) (site map). Upon collection, clams were depurated for 48 hours to remove gut contents, separated into size classes, shucked and dried. Trace metal concentrations were determined by first digesting tissues with nitric acid then analizing the extract using Inductively Coupled Plasma Absorption Spectrometry. Details of this method are described in Brown and Luoma (1995).

Reproductive activity was determined on clams collected concurrently with those for Ag analysis. Following clam preservation, gonadal tissues were examined under microscope. Individuals were characterized by sex and development stage. For data examination, animals were classed as either reproductive or non-reproductive. A detailed description of collection and determination of reproductive stage was described in detail in Parchaso and Thompson (2002).