Comparison of trophic magnification factors of PCBs and PBDEs in Tokyo Bay based on nitrogen isotope ratios in bulk nitrogen and amino acids

Abstract

Trophic positions (TPs) are key parameters for determining trophic magnification factors (TMFs) of environmental pollutants. We used compound-specific nitrogen isotope analysis of amino acids (CSIA-AA), with which we expected to obtain precise TPs, to estimate the TMFs of polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs) in the pelagic and benthic food webs of Tokyo Bay. The objective of the present study was to evaluate the difference between TMFs derived from TPs estimated by CSIA-AA (TPGlu/Phe) and TMFs derived from TPs estimated by bulk stable isotope analysis (TPbulk). TPGlu/Phe tended to be lower than TPbulk for many pelagic and benthic fishes. In the pelagic food web, the slopes for the relationships between PCB concentrations and TPGlu/Phe exceeded those between PCB concentrations and TPbulk for many congeners in samples from December 2014, and TMFGlu/Phe values (0.89–6.9) were higher than TMFbulk values (0.92–3.8). However, there were no statistically significant differences between the slopes of the relationships between PCB and PBDE concentrations and TPbulk or TPGlu/Phe for any of the congeners (analysis of covariance, P ≥ 0.08). In the benthic food web, PCB concentrations correlated with TPGlu/Phe for 9 PCB congeners in the samples collected during December 2014, although the concentrations of none of the PCB congeners correlated with TPbulk. A decrease of TMFGlu/Phe and TMFbulk values from December 2014 to May 2015 suggested that variation of PCB and PBDE concentrations in the organisms had more effect than TPs on the TMFs.