Estimates of environmental loading from copper alloy materials.

Metal release rates were measured from four different copper alloy-based materials used by the aquaculture industry: copper sheet machined into a diamond mesh, copper alloy mesh (CAM), silicon bronze welded wire mesh, and copper sheeting, and compared with conventional nylon aquaculture net treated with a cuprous oxide antifouling (AF) coating. Release rates were measured in situ in San Diego Bay using a Navy-developed Dome enclosure system at nine different time points over one year. As expected, copper was the predominant metal released, followed by zinc and nickel, which were fractional components of the materials tested. Release rates followed a temporal trend similar to those observed with copper AF coatings applied to vessel hulls: an initial spike in copper release was followed by a decline to an asymptotic low. Leachate toxicity was consistent with prior studies and was directly related to the metal concentrations, indicating the alloys tested had no additional toxicity above pure metals.

Use of laboratory toxicity tests with bivalve and echinoderm embryos to evaluate the bioavailability of copper in San Diego Bay, California, USA.

Copper concentrations in parts of San Diego Bay (CA, USA) exceed ambient water quality criteria (WQC; currently 3.1 microg/L dissolved, U.S. Environmental Protection Agency [U.S. EPA]). In order to better understand the bioavailability of copper to water-column organisms in the bay, toxicity tests were performed with copper added to surface water collected from various sites in the estuary over a three-year period. The species and endpoints used, bivalve and echinoderm embryo-larval development, are among the most sensitive in the U.S. EPA's national toxicity dataset, which is used to derive WQC. No toxicity was observed in ambient bay water samples, as indicated by high proportions of normally developed larvae in control treatments, averaging 93+/-5% across all sites and all sampling events. Median effects concentrations (EC50), obtained by copper spiking of ambient water samples, ranged from 1.7 to 3.4 times lower at sites located near the mouth compared to sites near the back of the bay. These data indicate a gradient in complexation capacity increasing from the mouth to the back of the bay, which is consistent with similar trends in dissolved organic carbon and total suspended solids. For the bay as a whole, estimates for total recoverable and dissolved water-effect ratios (WER) ranged from 2.07 to 2.27 and 1.54 to 1.67, respectively. Water-effect ratios of this magnitude suggest that adoption of a somewhat higher site-specific WQC for San Diego Bay still would achieve the level of protection that is intended by the WQC guidelines.

Copper toxicity to larval stages of three marine invertebrates and copper complexation capacity in San Diego Bay, California.

Temporal and spatial measurements of the toxicity (EC50), chemical speciation, and complexation capacity (Cu-CC) of copper in waters from San Diego Bay suggest control of the Cu-CC over copper bioavailability. While spatial distributions of total copper (CuT) indicate an increase in concentration from the mouth toward the head of San Diego Bay, the distribution of aqueous free copper ion (Cu(II)aq) shows the opposite trend. This suggests that the bioavailability of copper to organisms decreases toward the head of the bay, and is corroborated by the increase in the amount of copper needed to reach an EC50, observed for larval stages of three marine invertebrates (Mediterranean mussel, Mytilus galloprovincialis, sand dollar, Dendraster excentricus, and purple sea urchin, Strongylocentrotus purpuratus), and by the increase in Cu-CC heading into the head of the bay. The amount of Cu(II)aq required to produce a 50% reduction in normal larval development (referred to here as pCuTox,) of the mussel, the most sensitive of the three marine invertebrates, was generally at or above approximately 1 x 10(-11) mol L(-1) equivalents of Cu (i.e., pCuTox approximately 11 = -(log [Cu(II)aq])). These results suggest that the copper complexation capacity in San Diego Bay controls copper toxicity by keeping the concentration of Cu(II)aq at nontoxic levels.

Effects of dissolved and complexed copper on heterotrophic bacterial production in San Diego bay.

Bacterial abundance and production, free (uncomplexed) copper ion concentration, total dissolved copper concentration, dissolved organic carbon (DOC), total suspended solids (TSS), and chlorophyll a were measured over the course of 1 year in a series of 27 sample "Boxes" established within San Diego Bay. Water was collected through a trace metal-clean system so that each Box's sample was a composite of all the surface water in that Box. Bacterial production, chlorophyll a, TSS, DOC, and dissolved copper all generally increased from Box 1 at the mouth of the Bay to Box 27 in the South or back Bay. Free copper ion concentration generally decreased from Box 1 to Box 27 presumably due to increasing complexation capacity within natural waters. Based on correlations between TSS, chlorophyll a, bacterial production or DOC and the ratio of dissolved to free Cu ion, both DOC and particulate (bacteria and algae) fractions were potentially responsible for copper complexation, each at different times of the year. CuCl2 was added to bacterial production assays from 0 to 10 microg L(-1) to assess acute copper toxicity to the natural microbial assemblage. Interestingly, copper toxicity appeared to increase with decreases in free copper from the mouth of the Bay to the back Bay. This contrasts the free-ion activity model in which higher complexation capacity should afford greater copper protection. When cell-specific growth rates were calculated, faster growing bacteria (i.e. toward the back Bay) appeared to be more susceptible to free copper toxicity. The protecting effect of natural dissolved organic material (DOM) concentrated by tangential flow ultrafiltration (>1 kDa), illite and kaolinite minerals, and glutathione (a metal chelator excreted by algae under copper stress) was assessed in bacterial production assays. Only DOM concentrate offered any significant protection to bacterial production under increased copper concentrations. Although the potential copper protecting agents were allowed to interact with added copper before natural bacteria were added to production assays, there may be a temporal dose-response relationship that accounts for higher toxicity in short production assays. Regardless, it appears that effective natural complexation of copper in the back portions of San Diego Bay limits exposure of native bacterial assemblages to free copper ion, resulting in higher bacterial production.