Cyclic volatile methylsiloxanes in archived German freshwater fish samples covering a period of two decades

Cyclic volatile methyl siloxanes (cVMS) are used in several industrial applications, as additives in fuel, in consumer products such as car polish, cleaners, and waxes, and in personal care and biomedical products. The cVMS octamethylcyclotetrasiloxane (D4), decamethyl-cyclopentasiloxane (D5), and dodecamethylcyclohexasiloxane (D6) have been identified as priority chemicals for environmental risk assessment due to their large volume of usage, their persistence in the environment, their toxicity and bioaccumulative properties. Their high octanol−water partition coefficient makes them prone to bioaccumulation in fish.  To reduce emission to the environment, the use of D4 and D5 in wash-off cosmetic products in concentrations ≥0.1% by weight is prohibited in the EU since January 31, 2020 (EU Regulation 2018/35).

Measuring bioaccumulation in aquatic organisms is thus one of the priorities in the risk assessment of these chemicals. Unfortunately, previous limitations and challenges in the analytical quantifications of cVMS in environmental matrices have limited the availability of empirical data on levels in the environment.

A group of German researchers now aimed at obtaining current data on the presence of cVMS in German waters by measuring the spatial and temporal occurrence of D4, D5 and D6 in fillets of bream from major rivers archived in the German Environmental Specimen Bank (ESB). For this purpose, samples of the ESB covering the time period from 1995 to 2017 were analyzed.

Formerly frozen fish tissue powder was extracted with acetonitrile/n-hexane using an orbital shaker. After centrifugation, the n-hexane phase was decanted and preconcentrated under a stream of nitrogen. After solid/liquid extraction, the speciation and quantification of cVMS was carried out with a gas chromatography-inductively coupled plasma-triple quadrupole mass spectrometry coupling method (GC-ICP-MS/MS). Detection by a triple quadrupole instrument together with the use of hydrogen as the reaction gas allowed for the elimination of interferences on the main silicon isotope (m/z=28), such as N₂⁺ or CO⁺ ions. Thus, improved limits of detection were below 17 and 31 ng/g for D4/D5 and D6, respectively. For validation, spike recovery experiments were performed, showing recoveries of better than 95%.  

As expected from the octanol-water partition coefficient, fish concentrations of D4 and D5 from all sites and all years revealed strong correlations with fat contents. D5 was found in the fish fillet samples from all analysed riverine sampling sites in 2017. Also, the results show that D5 concentrations were clearly higher than D4 and D6 concentrations. Highest cVMS burdens were found in fish samples from the Saar river. The comparison of the temporal behaviour revealed that the highest concentrations could be observed between the years 2007 and 2011.

The authors concluded that a further improvement of the methodology with respect to detection power would be necessary to determine cVMS in lake and marine fish. They also express their hope that the restrictions that came into action end of January will decrease the cVMS burdens of fish in the future.

Georg Radermacher, Heinz Rüdel, Charlotte Wesch, Anna Böhnhardt, Jan Koschorreck, Retrospective analysis of cyclic volatile methylsiloxanes in archived German fish samples covering a period of two decades, Sci. Total Environ., 706 (2020) 136011. DOI: 10.1016/j.scitotenv.2019.136011

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