Correlation between stable nitrogen isotope ratios and concentrations of organochlorines in biota from a freshwater food web

The relationship between total concentrations of hexachlorocyclohexane (∑HCH), ∑DDT, and chlorinated bornanes (toxaphene, ∑CHB) and the trophic position of biota from a subarctic lake was investigated using stable isotope ratios of nitrogen (15N/14N). Zooplankton, benthic invertebrates, and forage and piscivorous fishes were analysed for 15N/14N and organochlorines using mass spectrometry and high resolution capillary gas chromatography (GC-ECD), respectively. The trophic relationships of the biota were clearly defined, with 15N/14N increasing an average of 3.3%. from prey species to predator. Mean concentrations of ∑HCH were lowest in chironomids (subfamily Chironominae, 0.2 ng/g wet wt.) and highest in burbot liver (Lota lota; 30.2 ng/g wet wt.). Mean concentrations of ∑DDT and ∑CHB ranged from 0.5 and 2.0 (ng/g wet wt.), respectively, in snails (Family Limnaeidae), to 3430 and 2830 (ng/g wet wt.) in burbot liver. Regression analyses indicated that both the wet and lipid weight concentrations of ∑HCH, ∑DDT, and ∑CHB in the biota from this food web were significantly related to trophic position, as defined by δ15N. Results from this study indicated that δ15N can be used to predict concentrations of organochlorines in freshwater biota.