Trophic magnification factors of volatile methylsiloxanes measured and predicted in freshwater and marine environments

The trophic magnification factor (TMF) is an important metric for evaluating chemical biomagnification in food webs. However, reported TMF values of cyclic volatile methylsiloxanes (VMS) vary widely, presumably due to the spatial gradient of chemical concentrations and sampling biases. This study surveyed biota and sediment concentrations of cyclic VMS and two reference polychlorinated biphenyls (PCBs; PCB-153 and PCB-180) in the rocky and sandy areas of the Yugawara coast, Japan. Biota concentrations and TMFs were also predicted by the Multibox-AQUAWEB model for the food webs in the same areas. The predicted biota concentrations and TMFs of the cyclic VMS and PCBs were in good agreement with the measured values. In the rocky and sandy areas, the mean TMFs of cyclic VMS were <1 with strong or moderate statistical significance, suggesting trophic dilution, while the mean TMFs of the PCBs exceeded 1 with strong statistical significance, indicating trophic magnification. The Multibox-AQUAWEB model was applied to predict TMFs for three cyclic VMS and five linear VMS in six global aquatic food webs: Lake Erie, False Creek, Lake Pepin, Lake Ontario, Inner Oslofjord, and Tokyo Bay. Predicted TMFs ranged from 0.13 to 1.00 for all VMS-food web pairs, except for L5 in Lake Pepin (TMF = 1.10; 95th percentile confidence interval [0.75, 1.61]), lacking statistical significance (p > 0.05). It is noted that none showed TMFs of VMS >1 with statistical significance. Thus, it is unlikely that VMS would be trophically magnified in aquatic food webs. To improve model predictions, more precise measurements of dietary uptake efficiencies and somatic biotransformation rate constants of VMS are needed, as trends against molecular weight or logKOW were not clearly demonstrated.