In this study, we determined the conditional stability constant (log K′) of copper for the gills of rainbow trout (Oncorhynchus mykiss; RBT) and brook trout (Salvelinus fontinalis; BT). Using toxicity‐based complexation bioassays, which measure the effect of competing organic ligands on copper toxicity, the RBT gill copper log K′ range was 6.4 to 7.2. Using a Scatchard analysis of gill Cu accumulation, the RBT log K′ was 7.50 and the BT log K′ was 7.25. The close agreement in RBT log K′ values between these two methods suggests that measurement of gill copper accumulation is an acceptable alternative for determining a toxicity‐based gill copper binding affinity. Our results also suggest that there is either a single gill copper binding component or, more realistically, multiple components with similar binding properties that function collectively to define a single toxicologically relevant copper conditional stability constant. These results suggest analytical approaches to measuring bioavailable metal concentrations, such as geochemical modeling where biological ligands are included in speciation calculations, may adequately simulate complex biological ligands. A method to convert gill copper accumulation to a bioavailable water criterion is also discussed.

Abstract-In this study, we determined the conditional stability constant (log KЈ) of copper for the gills of rainbow trout (Oncorhynchus mykiss; RBT) and brook trout (Salvelinus fontinalis; BT). Using toxicity-based complexation bioassays, which measure the effect of competing organic ligands on copper toxicity, the RBT gill copper log KЈ range was 6.4 to 7.2. Using a Scatchard analysis of gill Cu accumulation, the RBT log KЈ was 7.50 and the BT log KЈ was 7.25. The close agreement in RBT log KЈ values between these two methods suggests that measurement of gill copper accumulation is an acceptable alternative for determining a toxicity-based gill copper binding affinity. Our results also suggest that there is either a single gill copper binding component or, more realistically, multiple components with similar binding properties that function collectively to define a single toxicologically relevant copper conditional stability constant. These results suggest analytical approaches to measuring bioavailable metal concentrations, such as geochemical modeling where biological ligands are included in speciation calculations, may adequately simulate complex biological ligands. A method to convert gill copper accumulation to a bioavailable water criterion is also discussed.

From September to November 2000, United States Fish and Wildlife Service biologists investigated incidents involving 221 bird deaths at 3 mine sites located in New Mexico and Arizona. These bird deaths primarily involved passerine and waterfowl species and were assumed to be linked to consumption of acid metalliferous water (AMW). Because all of the carcasses were found in or near pregnant leach solution ponds, tailings ponds, and associated lakes or storm water retention basins, an acute-toxicity study was undertaken using a synthetic AMW (SAMW) formulation based on the contaminant profile of a representative pond believed to be responsible for avian mortalities. An acute oral-toxicity trial was performed with a mixed-sex group of mallards (Anas platyrhynchos). After a 24-h pretreatment food and water fast, gorge drinking was evident in both SAMW treatment and control groups, with water consumption rates greatest during the initial drinking periods. Seven of nine treated mallards were killed in extremis within 12 h after the initiation of dose. Total lethal doses of SAMW ranged from 69.8 to 270.1 mL/kg (mean ± SE 127.9 ± 27.1). Lethal doses of SAMW were consumed in as few as 20 to 40 min after first exposure. Clinical signs of SAMW toxicity included increased serum uric acid, aspartate aminotransferase, creatine kinase, potassium, and P levels. PCV values of SAMW-treated birds were also increased compared with control mallards. Histopathological lesions were observed in the esophagus, proventriculus, ventriculus, and duodenum of SAMW-treated mallards, with the most distinctive being erosion and ulceration of the kaolin of the ventriculus, ventricular hemorrhage and/or congestion, and duodenal hemorrhage. Clinical, pathological, and tissue-residue results from this study are consistent with literature documenting acute metal toxicosis, especially copper (Cu), in avian species and provide useful diagnostic profiles for AMW toxicity or mortality events. Blood and kidney Cu concentrations were 23- and 6-fold greater, respectively, in SAMW mortalities compared with controls, whereas Cu concentrations in liver were not nearly as increased, suggesting that blood and kidney concentrations may be more useful than liver concentrations for diagnosing Cu toxicosis in wild birds. Based on these findings and other reports of AMW toxicity events in wild birds, we conclude that AMW bodies pose a significant hazard to wildlife that come in contact with them.

Uncontaminated stream waters in the vicinity of a Co mine in Idaho were titrated with Cu to determine the Cu-binding characteristics of natural dissolved organic matter (DOM) and suspended particles. Nonlinear regressions of bound versus free Cu concentrations were consistent with a two-ligand model for DOM complexation of Cu, in which the conditional stability constants (log K) and complexation capacities (CC) were log K1 = 7.26, CC1 = 0.21 µmol Cu·mg dissolved organic carbon (DOC)-1 and log K2 = 5.13, CC2 = 2.89 µmol Cu·mg DOC-1. Copper-binding constants were similar in filtered (0.45 µm) and unfiltered water samples. Calcium, Mg, and Co did not compete appreciably with Cu for DOM complexation at concentrations present in site waters. Copper binding to amorphous iron oxide flocs also was not important at the Fe concentrations present in the stream waters. We selected a mixture of three organic acids, dipicolinic, oxalic, and malonic, to mimic the Cu-binding properties of this DOM. Geochemical models were developed to estimate Cu speciation and evaluate its bioavailability in companion fish toxicity tests using the DOM analogue (Marr et al. 1999. Can. J. Fish. Aquat. Sci. 56: 1471-1483).

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