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M11 AM Using Stable Isotopes in Ecotoxicology
(PAT-1117-815938) An evaluation of stable nitrogen isotopes and PCBs as bioenergetic tracers in aquatic systems.
Paterson, G1, Drouillard, K1, Haffner, G1, 1 Great Lakes Institute for Environmental Research, Windsor, Ontario, Canada
ABSTRACT- The stable isotope of nitrogen (15N) has been used as a predictor of persistent organic pollutant accumulation in aquatic ecosystems. Such applications rely on two central assumptions; a constant trophic enrichment of 3.4‰ for 15N between predator and prey and that 15N and pollutants such as PCBs are tracking similar bioenergetic processes. In this study, we investigated 15N ratios and PCB concentrations in two fish species in relation to age, size and diet. Using a dietary mixing model and a growth and metabolism based accumulation model, 15N exhibited enrichment with increasing size and approached steady state with respect to dietary 15N values by the second year of growth. Young of the year fish, however, exhibited lower nitrogen isotope enrichment over the diet indicating that the commonly held trophic enrichment factor of 3.4‰ is more suitable for older, slow growing individuals. A PCB accumulation model predicted pollutant accumulation to transition from water based bioaccumulation (bioconcentration) in small rapidly growing individuals to accumulation dominated by dietary exposure (biomagnification) by a body size approaching 100g. Significant increases in PCB accumulation were also attributed to decreased specific growth rates such that ≤ 60% of body mass was gained on an annual basis. It was concluded that growth related changes in species bioenergetics regulate both contaminant accumulation and 15N dynamics. For contaminants such as PCBs, these mechanisms have been well defined. However, for stable isotopes, substantial research is required focusing on the kinetics of assimilation, fractionation, and elimination in aquatic species.
Key words: age, growth, diet, bioenergetics
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