Factors affecting bioaccumulation of cyclic volatile methyl siloxanes in a subarctic benthopelagic food web

Cyclic volatile methylsiloxanes (cVMS) are used in personal care products and are emitted to aquatic environments through wastewater effluents. Due to the high hydrophobicity of cVMS, sediments are expected to be an important source for exposure in benthic and benthopelagic food webs. However, details of exposure pathways have yet to be fully understood. The main objective of this study was to evaluate the role of sediments in the bioaccumulation of cVMS, using a north-Norwegian lake (Lake Storvannet, 70 °N, 23 °E) as a case-study. Concentrations of cVMS were measured in benthos (chironomid larvae and the pea clam Pisidium sp.) and fish (three-spined sticklebacks (Gasterosteus aculeatus), arctic char (Salvelinus alpinus), and brown trout (Salmo trutta)), while existing measurements of polychlorinated biphenyls (PCBs 101, 138, 153) were used to evaluate a new benthopelagic model. The aquatic module of the bioaccumulation model ACC-HUMAN was expanded to include a benthic filter feeder and a benthic predator/deposit feeder, and the model was parameterized for Storvannet. The pelagic version of the model over-predicted PCB concentrations in char and trout by factors of 3 to 16 compared to measurements (ratio between median values), and the benthopelagic model by factors of 2 to 7. Inclusion of the benthic link, therefore, improved predictions, particularly for char that feed mainly on benthos in this lake. D5 was the dominant cVMS congener in the lake, with measured concentrations of 2.0 ± 0.04, 17.8 ± 0.7, 3.2 ± 2.3, 3.8 ± 2.8, and 0.8 ± 0.6 μg/g lipid in chironomid larvae, Pisidium sp., three-spined sticklebacks, char, and trout, respectively. The benthopelagic model over-predicted cVMS concentrations in all species, but reproduced well the relationships between the different species. As Storvannet has temperatures around 0 °C for the majority of the year, the differing temperature-dependency of partitioning between organic phases and water for PCBs and cVMS was important for the model predictions. This was particularly pronounced in the benthic linkages within the model, where several differences in bioaccumulation behavior between PCBs and cVMS was observed. This highlights the need to increase the understanding of partitioning of cVMS at low temperatures. Also, it stresses the importance of understanding bioaccumulation behavior and biotransformation capacities in lower trophic levels, which are fundamental to understand also the higher trophic levels.