CORRELATION BETWEEN STABLE NITROGEN ISOTOPE RATIOS AND CONCENTRATIONSOF 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 CH B) and the trophic position of biota from a subarctic lake was investi gated using stable isotope ratios of nitrogen (N-15/N-14). Zooplankton , benthic invertebrates, and forage and piscivorous fishes were analys ed for N-15/N-14 and organochlorines using mass spectrometry and high resolution capillary gas chromatography (GC-ECD), respectively. The tr ophic 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 p redator. 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 S igma CHB ranged from 0.5 and 2.0 (ng/g wet wt.), respectively, in snai ls (Family Limnaeidae), to 3430 and 2820 (ng/g wet wt.) in burbot live r. Regression analyses indicated that both the wet and lipid weight co ncentrations of Sigma HCH, Sigma DDT, and Sigma CHB in the biota from this food web were significantly related to trophic position, as defin ed by delta(15)N. Results from this study indicated that delta(15)N ca n be used to predict concentrations of organochlorines in freshwater b iota.