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 (TP Glu/Phe ) and TMFs derived from TPs estimated by bulk stable isotope analysis (TP bulk ). TP Glu/Phe tended to be lower than TP bulk for many pelagic and benthic fishes. In the pelagic food web, the slopes for the relationships between PCB concentrations and TP Glu/Phe exceeded those between PCB concentrations and TP bulk for many congeners in samples from December 2014, and TMF Glu/Phe values (0.89–6.9) were higher than TMF bulk values (0.92–3.8). However, there were no statistically significant differences between the slopes of the relationships between PCB and PBDE concentrations and TP bulk or TP Glu/Phe for any of the congeners (analysis of covariance, P  ≥ 0.08). In the benthic food web, PCB concentrations correlated with TP Glu/Phe for 9 PCB congeners in the samples collected during December 2014, although the concentrations of none of the PCB congeners correlated with TP bulk . A decrease of TMF Glu/Phe and TMF bulk 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.