A review of bioaccumulation of volatile methylsiloxanes in aquatic ecosystems

Volatile methylsiloxanes (VMSs) are found in a broad range of industrial and consumer products. They are categorized as "high production volume chemicals" by the U.S. Environmental Protection Agency and listed as candidates of substances of very high concern in 2018, by the Registration, Evaluation, Authorization and Restriction of Chemicals (REACH). Industrial wastewater and treated effluents may contain VMSs in different amounts, which can be discharged in the receptor media and may lead to environmental contamination. This can result in direct exposure to aquatic receptors in the water column or to benthic invertebrates from contact and/or ingestion of sediments, and indirect exposures through the aquatic food chain. The possible toxicological effects of VMSs for the aquatic biota and human ecology are not very well known since published information regarding this topic is scarce. VMSs have been subjected to regulatory scrutiny for environmental concerns and have already been screened to determine their environmental risk and ecological harm. This paper aims to assess VMSs bioaccumulation and potential biomagnification on food webs, using several bioaccumulation metrics. The result is a high-level overview of all the collected data, comparing the findings and the experimental conditions applied during the assessments. Several studies present conflicting results regarding the bioaccumulation categorization. Some aquatic organisms demonstrated a high bioconcentration and bioaccumulation of these contaminants. Trophic magnification factors (TMFs) have been suggested as the most reliable tool to assess a chemical behaviour in food webs. However, bioaccumulation studies in food webs provided mixed information, with some studies indicating trophic dilution and others presenting a potential of trophic biomagnification of VMSs. Efforts should be directed to obtain field-based levels of VMSs at different trophic levels and a wider range of linear VMSs should be analysed, since most studies focused on D4, D5 and D6.