Persistent organic pollutants in river food webs: influence of trophic position and degree of heterotrophy

Abstract

We investigated how the degree of autotrophy/heterotrophy and organism trophic position influenced the bioaccumulation of polychlorinated biphenyls (PCBs) in 10 benthic river food webs consisting of terrestrial detritus, periphyton, invertebrates, and age-0 brown trout (Salmo trutta) in southern Sweden. Concentrations of PCBs increased with trophic position, estimated from δ15N and δ13C, on a dry weight basis (ng·g–1 dry weight) but not on a lipid weight basis (ng·g–1 lipid). PCB biomagnification factors between the first and second trophic levels (invertebrates/ periphyton and invertebrates/detritus) ranged between 0.3 and 2.3 and between the second and third levels (trout/invertebrates) between 0.3 and 2.0 on a lipid weight basis. The mean proportion of carbon ultimately derived from terrestrial sources, α, was 0.82 ± 0.19 for invertebrates and 0.67 ± 0.28 for trout. Contrary to our hypothesis, PCB concentrations in trout were positively related to α (r2 = 0.58–0.77, p < 0.05). As α and the periphyton density (g C·m–2) in the rivers was positively related (r2 = 0.88, p < 0.01), we propose that this relationship was due to an increased retention and exposure of PCBs to trout in rivers with low grazing pressure and high periphyton density.