PARENT SESSION

PW10 Bioaccumulation and Biomagnification
Exhibit Hall
8:00 AM - Wednesday

(PW170) Use of stable isotopes ratios of carbon and nitrogen to assess the food web effects of environmental contaminants.

Caquet, T.¹, ¹ INRA EQHC, Rennes

ABSTRACT- Measurements of stable isotope ratios of carbon (¹³C) and nitrogen (¹⁵N) are commonly used to trace pathways of organic matter among consumers. Values of ¹³C may be used to determine the origin of carbon (e.g. decaying organic matter vs. living preys) whereas the ¹⁵N value of an organism reflects its trophic level (i.e. the number of levels between itself and primary producers). Environmental contaminants may affect stable isotope ratios values through qualitative or quantitative shifts in the structure of food webs. In this study, ¹³C and ¹⁵N were measured in invertebrates collected in 18 m³ outdoor freshwater mesocosms used to assess the fate and ecotoxicological effects of a diphenyl ether herbicide, fomesafen, applied alone or in combination with Agral 90® (mixture of polyethoxylated derivatives of nonylphenol). Two taxa were chosen, the larvae of the common backswimmer (Notonecta glauca) which feed upon planktonic organisms, and the larvae of damselflies of the family Coenagrionidae which feed upon benthic organisms. Stable isotope ratios were measured using continuous-flow isotope ratio mass spectrometry (CF-IRMS). The results obtained in control ponds for ¹³C confirm that backswimmers and damselfies are located at the top of two different food chains. The herbicide and the mixture did not have any effect on the values of stable isotope ratios for damselfy larvae, therefore suggesting that the benthic food chain remained unchanged. The mixture caused a decrease in the value of ¹⁵N in backswimmers, which indicates a change in the structure of the pelagic/planktonic food chain. This result is in agreement with those obtained for zooplankton. Large-sized calanid copepods, which are vulnerable preys for backswimmers, were negatively affected by the mixture. These results confirm that stable isotope ratios of top-predators may be used as integrative descriptors of the changes induced in food webs by environmental contaminants.

Key words: food web, stable isotopes, indirect effect, mesocosms