Polychlorinated biphenyl (PCB) concentrations declined rapidly in environmental compartments and most biota following implementation of regulations in the 1970s. However, the metabolic recalcitrance of PCBs may delay responses to such declines in large, long-lived species, such as the endangered and highly PCB-contaminated resident killer whales (Orcinus orca) of the Northeastern Pacific Ocean. To investigate the influence of life history on PCB-related health risks, we developed models to estimate PCB concentrations in killer whales during the period from 1930 forward to 2030, both within a lifetime (∼50 years) and across generations, and then evaluated these in the context of health effects thresholds established for marine mammals. Modeled PCB concentrations in killer whales responded slowly to changes in loadings to the environment as evidenced by slower accumulation and lower magnitude increases in PCB concentrations relative to prey, and a delayed decline that was particularly evident in adult males. Since PCBs attained peak levels well above the effects threshold (17 mg/kg lipid) in ∼1969, estimated concentrations in both the northern and the more contaminated southern resident populations have declined gradually. Projections suggest that the northern resident population could largely fall below the threshold concentration by 2030 while the endangered southern residents may not do so until at least 2063. Long-lived aquatic mammals are therefore not protected from PCBs by current dietary residue guidelines.

An environmental chemist can quantify the presence of a hydrophobic organic contaminant at a 1 ng/L concentration in water. If a total mass of 10 ng of analyte is required, the obvious strategy is to obtain an adequate sample of the water, say 50 L, and increase the concentration by extracting it with an organic solvent, such as dichloromethane (DCM). If the extraction is completed with a total vol-BEVERLY DOYLE

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The impacts of pH and dissolved organic carbon (DOC) on the acute toxicity of Cu to larval fathead minnow (Pimephales promelas) were determined using natural soft water from two Precambrian Shield lakes in south-central Ontario. By artificially manipulating the pH and DOC levels of the water, we demonstrated that both acidification and the removal of DOC increased the toxicity of Cu. The 96-h Cu LC50s were determined over a pH range from 5.4 to 7.3 and a DOC concentration range from 0.2 to 16 mg∙L−1. The LC50s ranged from a low of 2 μg∙L−1 (pH 5.6, DOC 0.2 mg∙L−1) to a high of 182 μg∙L−1 (pH 6.9, DOC 15.6 mg∙L−1). A multiple regression model (log1096-h Cu LC50 = −0.308 + 0.192 pH + 0.136 (pH∙log10DOC)) was used to describe the relationship between Cu toxicity, pH, and DOC. The model was significant (p < 0.00001) and explained 93% of the variability in the toxicity data. These results suggest that current water quality objectives for Cu, and possibly for other metals, may not be sufficiently protective of aquatic life in soft, moderately acidic water containing low levels of DOC.