CORRELATION BETWEEN STABLE NITROGEN ISOTOPE RATIOS AND CONCENTRATIONS OF ORGANOCHLORINES IN BIOTA FROM A FRESH-WATER FOOD-WEB

The relationship between total concentrations of hexachlorocyclohexane (Sigma HCH), Sigma DDT, and chlorinated bornanes (toxaphene, Sigma CHB) and the trophic position of biota from a subarctic lake was investigated using stable isotope ratios of nitrogen (N-15/N-14). Zooplankton, benthic invertebrates, and forage and piscivorous fishes were analysed for N-15/N-14 and organochlorines using mass spectrometry and high resolution capillary gas chromatography (GC-ECD), respectively. The trophic relationships of the biota were clearly defined, with N-15/N-14 increasing an average of 3.3 parts per thousand from prey species to predator. Mean concentrations of Sigma 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 Sigma DDT and Sigma CHB ranged from 0.5 and 2.0 (ng/g wet wt.), respectively, in snails (Family Limnaeidae), to 3430 and 2820 (ng/g wet wt.) in burbot liver. Regression analyses indicated that both the wet and lipid weight concentrations of Sigma HCH, Sigma DDT, and Sigma CHB in the biota from this food web were significantly related to trophic position, as defined by delta(15)N. Results from this study indicated that delta(15)N can be used to predict concentrations of organochlorines in freshwater biota.