Evaluation of Population-Level Ecological Risks of Dioxin-Like Polychlorinated Biphenyl Exposure to Fish-Eating Birds in Tokyo Bay and Its Vicinity

Abstract

Population-level assessments of the ecological risks of dioxin-like polychlorinated biphenyl (PCB) exposure to fish-eating birds in Tokyo Bay and its vicinity were performed to judge the need for risk management measures to protect aquatic wildlife from dioxin-like PCB contamination. Egg mortality risk and changes in the population growth rate (lambda) in relation to the contamination levels of dioxin-like PCBs in eggs of gray heron (Ardea cinerea), great cormorant (Phalacrocorax carbo), osprey (Pandion halieaetus), and kingfisher (Alcedo atthis) were determined by integrating the results of exposure analysis, effect analysis, and a life-history model for each species. The egg mortality risks for the gray heron, great cormorant, osprey, and kingfisher populations were calculated to be 5.8, 6.8, 12, and less than 1%, respectively. The estimated lambda for those populations were calculated to be 1.061, 1.405, 1.024, and 1.131, respectively. The percentage changes in lambda for those populations were estimated to be 1.2, 2.0, 1.6, and less than 1%, respectively. Our results implied that the levels of dioxin-like PCBs observed in the Tokyo Bay area alone would not have significant population-level effects on the fish-eating bird populations. It is concluded that along with the trend toward decreasing dioxin and dioxin-like PCB levels in Tokyo Bay, no urgent need exists for risk-reduction measures to protect fish-eating bird populations against dioxin-like PCBs.

Population‐level ecological effect assessment: estimating the effect of toxic chemicals on density‐dependent populations

“…Ecotoxicological experiments, which provide the practical basis for risk assessment, are typically conducted under density-independent conditions where intraspecific competition is removed. In addition, most previous population-level risk assessments also ignored density-dependent effects in population dynamics (e.g., Forbes et al 2001a;Lin et al 2005;Naito and Murata 2006;Raimondo et al 2006). However, density-dependence acts on most natural populations.…”

“…To promote population-level ecological risk management, the development of methods to estimate population-level effects of chemicals from individual-level laboratory toxicity test data are needed by risk assessors and managers. Previous studies of population-level ecological risk assessment have mainly employed intrinsic growth rate as an index of population-level effects (e.g., Forbes and Calow 2002;Forbes et al 2001a;Hendriks and Enserink 1996;Kuhn et al 2000;Lin et al 2005;Naito and Murata 2006;Raimondo et al 2006;Stark et al 2004). To estimate the effects of chemicals on intrinsic growth rates, mathematical models of population dynamics (e.g., logistic growth model, Leslie life-stage model) combined with knowledge of the relationship between a chemical's concentration and its effects on individual traits (e.g., individual survivability and fertility; hereafter, we consider toxic effects on these vital rates as individual-level effects) determined by laboratory tests have often been used (e.g., Lin et al 2005;Naito and Murata 2006;Raimondo et al 2006).…”

“…Most previous studies on population-level effects of toxic chemicals have the common problem that densitydependence is not considered (e.g., Forbes and Calow 2002;Forbes et al 2001a;Hendriks and Enserink 1996;Kuhn et al 2000;Lin et al 2005;Naito and Murata 2006;Raimondo et al 2006;Stark et al 2004), even though most natural populations are subject to a density effect. For example, Lin et al (2005) estimated population-level effects of chemical toxicity based on results obtained by density-independent laboratory experiments, and therefore did not consider density-dependent effects at all.…”