Silicone in the environment: A worst-case assessment of poly(dimethylsiloxane) (PDMS) in sediments

Silicone materials are used in a wide variety of consumer/industrial produc ts and process aids. Disposal to wastewater treatment is the primary source of entry for silicones (primarily poly(dimethylsiloxane) or PDMS) in aquat ic environments. However, limited information is available on the concentra tion ranges, distribution, and fate of silicone materials in surface sedime nts. In this study, PDMS was measured in the surface sediments of four mari ne and four freshwater areas heavily impacted by municipal wastewater disch arge to illustrate worst-case situations for the United States. Concentrati ons of PDMS were measured in 12-14 samples from each study area. Measured d ry weight concentrations of PDMS ranged from below detection (0.2 mu g.g(-1 )) to 309 mu g.g(-1). Low level concentrations (less than or equal to 0.6 m u g.g(-1)) that were measured in 25% of the sediments may have been natural silicon materials rather than PDMS. Generally, concentrations of PDMS were greatest in sediments from depositional areas near effluent outfalls. Mean concentrations of PDMS (+/-SE) ranged from 0.6 +/- 0.1 to 78 +/- 20 mu g.g (-1) and were lowest in areas having advanced levels of wastewater treatmen t. Concentrations of PDMS in these "worstcase" sediments were less than the "no observable effects concentration" (NOEC) established in laboratory stu dies using sediment-dwelling organisms.