Volatilization and Sorption of Dimethylsilanediol in Soil

Abstract

Our previous studies showed that dimethylsilanediol (DMSD) was the main hydrolysis product of silicone (polydimethylsiloxane) polymer in soil. In the present study, volatilization of 14 C-DMSD from soil (1 mg kg Ϫ1 ) was investigated in open tubes, with weekly remoistening. Losses of 14 C from Londo sandy clay loam and Pipestone sand were about 3.6 and 7.7% wk Ϫ1 , respectively, and were attributed mostly to volatilization. For select samples, DMSD was trapped and identified as the volatilized compound. From 12 soils of variable properties, losses ranged from 1.4 to 6.4% wk Ϫ1 , with higher rates correlated with sandier textures. An estimated K d of 0.1 L kg Ϫ1 in wet soil suggests potential mobility of DMSD, but increased bonding with soil drying means that mobility will be retarded under field conditions. Results suggest that volatilization will be a major route of loss of DMSD from soil.

Life Cycle of Silicone Polymer, from Pilot-Scale Composting to Soil Amendment

“…After four weeks of incubation, PDMS degradation was similar in soils mixed with either food or yard compost (Table 1); and the polymer degraded equally well when no soil was added to the compost. Some degradation product, DMSD, was found, although the fact that PDMS + DMSD in these treatments only summed to 80-90% suggests that some DMSD had been evaporating or biodegrading, as noticed in previous studies (Lehmann and Miller 1996;Sabourin et al 1996;Lehmann et al 1998a). Degradation was somewhat faster in samples with less frequent watering, which agrees with laboratory studies showing faster PDMS degradation in drier soils (Lehmann et al 1998b).…”

“…Concentrations of the main hydrolysis product, DMSD, never reached above 5% of the original PDMS. This is expected from laboratory experiments showing both evaporation (Lehmann and Miller 1996) and biodegradation (Lehmann et al 1994b;Sabourin et al 1996;Lehmann et al 1998a) of the DMSD from soil. In addition, when soil under the pots (0-2.5, 2.5-5 ern) was extracted and analyzed, neither PDMS nor DMSD were detected, thus indicating that these compounds had not leaked out of the pots.…”

“…The hydrolysis occurs on the surface of soil clay minerals (Xu et al 1998). The relatively small DMSD molecule is biodegradable (Lehmann et al 1994b;Sabourin et al 1996;Lehmann et al 1998a) or it can volatilize from the soil (Lehmann and Miller 1996) and will degrade in the atmosphere in similar fashion to other small silicone materials (Atkinson 1991;Markgraf and Wells 1997;Sommerlade et al 1993). These processes may have been responsible for the observed loss of silicone from sludge-amended soils in greenhouse experiments , and in fields which had received municipal sludge (Fendinger et al 1997).…”

A Primer on the Analytical Aspects of Silicones at Trace Levels-Challenges and Artifacts – A Review

“…Reverse phase HPLC coupled to an ICP (inductively coupled plasma) detector has been applied to speciation and quantitation of low molecular weight silanols [57,59]. HPLC coupled to a refractive index detector was used to analyze DMSD generated from the degradation of PDMS in soil [61]. Good separation of metabolites (silanols) in urine collected from rats following administration of D 4 [62], D 5 and hexamethyldisiloxane [63], needed for fractionation and subsequent structure identification, has been reported.…”

Properties, performance and associated hazards of state-of-the-art durable water repellent (DWR) chemistry for textile finishing

“…The hydrolysis rate of PDMS is controlled by soil moisture, where the hydrolysis takes place more rapidly with lower moisture content, or when the weather is hot and dry (Lehmann et al, 1998). DMSD can further biodegrade to silicic acid [Si(OH) 4 ], due to the oxidation of the methyl groups of DMSD (Stevens, 1998), or can be released into the atmosphere since DMSD is relatively volatile (Lehmann and Miller, 1996).…”