Including nanoparticle mixtures in human health risk assessment

Abstract

This article presents an integrated analysis using a Monte Carlo exposure model, dose–response effects model and habitat,and population dynamics models, all of which allow us to quantitatively estimate the effects of polychlorinated biphenyl (PCB)exposure on American mink (Mustela vison) abundance at the Portland Harbor Superfund Site (Site), and the associated uncertainties. The Site extends from river mile 1.9 of the Lower Willamette River, near its confluence with the Columbia River, to river mile 11.8, just downstream of downtown Portland, Oregon. The potential effects of PCBs on the American mink population were evaluated in the Baseline Ecological Risk Assessment (BERA) due to the historical presence of mink in the are a and because mink are known to be highly sensitive to the effects of PCBs. Hazard quotients (HQs) calculated in the BERA indicated that PCB concentrations measured in Portland Harbor fish were above levels known to cause reproductive effects in mink. Further analysis was needed to evaluate the potential magnitude of effects on the Site mink population. The integrated analysis presented herein demonstrates that if an effect of PCB exposure is a less than 30% reduction in kit production, then PCB remediation is not expected to have any effect on mink abundance. This is a Site‐specific conclusion that depends on the quality, abundance, and distribution of mink habitat in Portland Harbor. The PCB dose associated with a 30% reduction in kit production was calculated as 101 mg/kg bw/d (90% CI ¼ 69–146 mg/kg bw/d). The mink PCB dose estimates from the Portland Harbor BERA indicate that if mink are present, their baseline exposure levels probably exceed 101 mg/kg bw/d. Therefore, some level of reduction in PCB exposure could be beneficial to the species if the study area provides sufficient habitat to support a mink population. This analysis demonstrates that risk analysis for population‐level assessment endpoints benefits from analyses beyond those that calculate exposure and predict organism‐level effects. Evaluation of population‐level impacts provides risk managers with a richer perspective within which to evaluate the environmental protectiveness and cost effectiveness of feasibility study alternatives across a range of potential remediation goals.