Silicone in the Environment:  A Worst-Case Assessment of Poly(dimethylsiloxane) (PDMS) in Sediments

Abstract

Silicone materials are used in a wide variety of consumer/industrial products and process aids. Disposal to wastewater treatment is the primary source of entry for silicones (primarily poly(dimethylsiloxane) or PDMS) in aquatic environments. However, limited information is available on the concentration ranges, distribution, and fate of silicone materials in surface sediments. In this study, PDMS was measured in the surface sediments of four marine and four freshwater areas heavily impacted by municipal wastewater discharge to illustrate worst-case situations for the United States. Concentrations of PDMS were measured in 12−14 samples from each study area. Measured dry weight concentrations of PDMS ranged from below detection (0.2 μg·g-1) to 309 μg·g-1. Low level concentrations (≤0.6 μg·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 μg·g-1 and were lowest in areas having advanced levels of wastewater treatment. Concentrations of PDMS in these “worst-case” sediments were less than the “no observable effects concentration” (NOEC) established in laboratory studies using sediment-dwelling organisms.

Laboratory analyses of the potential toxicity of sediment‐associated polydimethylsiloxane to benthic macroinvertebrates

“…Application of PDMS to sediments was intended to be as realistic as possible, with target concentrations selected to range from those typically measured at wastewater treatment plant outfalls (about 26 mg/kg dry wt) to concentrations an order of magnitude greater than the greatest measured concentration (about 300 mg/kg dry wt) reported in the literature [9]. The PDMS‐amended treatments were prepared by spinning PDMS‐free sludge, 350‐cs PDMS fluid, and water in a round‐bottomed flask on a rotary evaporator in order to mix these components.…”

“…Concentrations of PDMS decrease with depth in sediments and are not detectable at depths that correspond to periods before the production and use of PDMS fluids [7, 8]. While PDMS tends to accumulate in sediments, concentrations can decrease in response to mass dilution and degradation [6] or if inputs are reduced or discontinued, for example, by enhanced wastewater treatment technology [9]. Mean measured PDMS concentrations in sediments from depositional areas downstream from wastewater treatment plant (WWTPs) range from less than the detection limit to 78 mg/kg (dry wt) at sites receiving point source inputs [9].…”

“…While PDMS tends to accumulate in sediments, concentrations can decrease in response to mass dilution and degradation [6] or if inputs are reduced or discontinued, for example, by enhanced wastewater treatment technology [9]. Mean measured PDMS concentrations in sediments from depositional areas downstream from wastewater treatment plant (WWTPs) range from less than the detection limit to 78 mg/kg (dry wt) at sites receiving point source inputs [9]. However, 90% of the sediments analyzed contained less than 26 mg PDMS/kg (dry wt) [9].…”

“…Mean measured PDMS concentrations in sediments from depositional areas downstream from wastewater treatment plant (WWTPs) range from less than the detection limit to 78 mg/kg (dry wt) at sites receiving point source inputs [9]. However, 90% of the sediments analyzed contained less than 26 mg PDMS/kg (dry wt) [9]. The biota exposed to PDMS in these areas would primarily be benthic invertebrates intimately associated with these sediments.…”

Laboratory Analyses of the Potential Toxicity of Sediment-Associated Polydimethylsiloxane to Benthic Macroinvertebrates

“…Concentrations of PDMS decrease with depth in sediments and are not detectable at depths that correspond to periods before the production and use of PDMS fluids [7,8]. While PDMS tends to accumulate in sediments, concentrations can decrease in response to mass dilution and degradation [6] or if inputs are reduced or discontinued, for example, by enhanced wastewater treatment technology [9]. Mean measured PDMS concentrations in sediments from depositional areas downstream from wastewater treatment plant (WWTPs) range from less than the detection limit to 78 mg/ kg (dry wt) at sites receiving point source inputs [9].…”