Trophic level studies

Trophic level studies Indicated a decrease in Pu concentration with increase in trophic level (57). The CF values for benthic organisms and bottom feeding fishes were significantly higher than for piscivorous fish or for planktivorous fish ( v 1000 and 270 vs 4 and 20, respectively). Concentration factors derived from studies in a wide variety of freshwater and marine ecosystems are shown in Fig. 5. Invertebrates and algae exhibit higher CF values (10° - lO4) than fishes (0.0 - 50). The differences in CF values probably reflect differences in the source and chemical form of Pu at the various study sites. 

Nitrogen isotope ratios ( N/ " N) inerease from plants to herbivores to eami-vores and ean be used to estimate the degree of camivory in human diets. Some field studies observe a greater differenee in 5 N between trophie levels in dry, hot habitats than in wet, cool ones. Two hypotheses have been proposed to explain this variation in difference in 8 N between trophic levels. (1) Elevated excretion of -depleted urea in heat/water-stressed animals (2) recycling of nitrogen on protein-deficient diets. Both predict increased diet-tissue 8 N difference under stress. 

Additionally, the determination of THg levels in muscle of some fish species within the Flix reservoir has been studied (Diez, unpublished results). As expected, THg concentrations increased with trophic level. A comparison between mercury levels in muscle tissue of the individual fish species (p < 0.05) produced the following order European catfish > common carp > rudd > roach. Average THg concentrations (in ww) in muscle of European catfish (n = 9), common carp (n = 30), rudd (n = 20), and roach (n = 5) were 0.848 0.476 ig/g 0.333 0.155 pg/g 0.283 0.163 pg/g and 0.217 0.199 pg/g, respectively. The relative trophic level of the analyzed species is based on a generalized knowledge of the species and stomach contents of the studied adult fish populations [56, 60, 62, 71],... 

Canton, J.H. and W. Slooff. 1982. Toxicity and accumulation studies of cadmium (Cd2+) with freshwater organisms of different trophic levels. Ecotoxicol. Environ. Safety 6 113-128. 

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