Copper (II) is considered to be the most bio-available, as well as toxic, form of copper in aquatic environments. Mollusks are especially prone to copper toxicity and are commonly used in copper toxicity tests for estuarine and marine systems. This work reports the first copper speciation measurements in Humboldt Bay, where over 90% of California’s oysters are farmed for human consumption. The study used an established competitive ligand exchange-adsorptive cathodic stripping voltammetry (CLE-ACSV) method. Salicylaldoxime (SA) was used as the competitive ligand and samples were buffered to pH = 7.8 with EPPS. A hanging mercury drop electrode (HDME) was used in the subsequent experiments with a deposition potential of 0.15 V for 60 seconds, and then scanned in differential pulse mode from 0.15 V to 0.60 V at 20 mV/s. Copper speciation and total dissolved copper concentrations were determined in water samples using the described method, and the results show that essentially all of the copper in Humboldt Bay was bound to strong-binding ligands and was not bioavailable. Total dissolved concentrations of copper were below the EPA water quality criterion for saltwater ecosystems (samples ranged from or 0.12-1.39 ppb, or 2-22 nM, with an EPA mandated limit of 2.8 ppb). Electrochemical measurements of the speciation agreed with copper water effect ratio (WER) results from Humboldt Bay waters. The study concludes that there is low risk of copper toxicity to occur in Humboldt Bay.

Determination of total copper concentration and copper speciation in Humboldt Bay, California through use of competitive ligand exchange-adsorptive cathodic stripping voltammetry

253rd National Meeting (2017)

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