Cyclic methylsiloxanes in fish

Fish are particularly heavily contaminated with cyclic methylsiloxanes where industrial companies produce and process the substances.

Cyclic volatile methylsiloxanes (cVMS) are industrially produced industrial chemicals that are used in large quantities, for example as intermediates in the production of silicone plastics or as ingredients in personal care products.

In 2018, the EU REACH authority classified octamethylcyclotetrasiloxane (D4), decamethylcyclopentasiloxane (D5) and dodecamethylcyclohexasiloxane (D6) as substances of very high concern. With fish samples from the German environmental specimen bank, researchers from the Fraunhofer Institute for Molecular Biology and Applied Ecology have elaborated an overview of the current and historical contamination of water bodies. To do this, they used a coupled GC-ICP-MS/MS method and started by spatially comparing the pollution of fish from the Rhine, Saar, Danube, Elbe and tributaries, Lake Belau (Belauer See) in northern Germany and the North Sea and Baltic Sea coasts.

In fish from all sampling sites and over the entire study period, the decamethylcyclopentasiloxane (D5) concentrations were significantly higher than the measured D4 and D6 concentrations. The Saar samples (near the German-French border) were the ones most contaminated with cVMS. Elsewhere, cVMS occurred in high concentrations especially at those sampling sites where industrial plants producing or processing cyclic methylsiloxanes are known in the river basin. This applies to the sampling sites in the Elbe near Dresden, Wettin in the Saale and Jochenstein in the Danube.

Fig. 1: Decamethylcyclopentasiloxane (D5) in bream musculature in 2017

The cVMS concentrations in fish from Lake Belau as well as North Sea and Baltic Sea fish were below the detection limits of the analytical method. This also provided evidence that there is no contamination of the samples in the course of routine sampling and processing.

At some selected sites, the temporal trends in fish contamination with cVMS were the subject of investigation. The highest D4 and D5 concentrations were detected in fish fillets from a Saar site in 2009 (approx. 320 and 7,400 ng/g fresh weight). It is striking that in most of the time series analysed, cVMS concentrations peaked between 2007 and 2011. Thereafter, cVMS concentrations in fish decreased considerably. The observed decrease in use is possibly related to the fact that the environmental safety of cyclic methylsiloxanes has also been discussed in European chemical safety bodies since 2009 (for example, in the EU PBT Expert Group) and manufacturers therefore increasingly reduced the use of cVMS.

Evaluation

To enable an assessment of the relevance of the detected cVMS fish tissue concentrations, they were compared with environmental quality standards (EQS) for D4 and D5 derived by Swedish authorities in 2019 for the European Water Framework Directive (WFD). The EQS for D5, which however does not apply in Germany, was exceeded at several sites in several years in the period 2003 - 2011 - for fish from one Saar site until 2017, the last year of the time series.
The time courses of the measured concentrations of D4, D5 and D6 are shown in Figures 2 to 4.

Fig. 2: Concentration of octamethylcyclotetrasiloxane (D4) in bream musculature in the years 1995 to 2017

Fig. 3: Concentration of decamethylcyclopentasiloxane (D5) in bream musculature in the years 1995 to 2017 Zoom in

Fig. 4: Concentration of dodecamethylcyclohexasiloxane (D6) in bream musculature in the years 1995 to 2017 Zoom in

Updated at: 2022-01-12

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