Once a policy decision has been made regarding the most appropriate indicator organisms for the Bay, information can be developed to derive protective site specific objectives that account for the different biological availabilities of copper forms. Free ionic copper is the chemical form that causes toxic effects; however, free ionic copper is difficult to measure. An alternative is to modify dissolved copper measurements to account for binding (complexation) by organic ligands which reduces free ionic copper concentrations. USEPA has directly linked organic complexation of copper to reduced toxicity though a water effect ratio (WER) in its regulatory guidance.
Site specific measurements of organic complexation of copper are required to apply the USEPA guidance for developing site specific objectives for copper. Some measurements have been made in South San Francisco Bay. A more comprehensive survey is needed in the rest of the Bay segments, over an extended period of time, because copper complexation can change depending on where and when it is measured. For example, seasonal river inflow and plankton blooms can substantially alter the amount of complexing organic matter present. With accurate and comprehensive data on the organic complexation of copper, a water effect ratio can be derived, and free ionic copper concentrations can be calculated from dissolved ambient concentrations.