To better understand the environmental fate of organopolysiloxanes (silicones), this study investigated the degradation of a 14 C-labeled poly(dimethylsiloxane) (PDMS) on 12 Ca-saturated clay minerals. The rates and products of PDMS degradation were determined at 22 °C and 32% relative humidity, via sequential extraction and highperformance size exclusion chromatography (HPSEC). The results showed that all of the clays tested were catalysts for PDMS degradation. However, clay minerals varied substantially in their catalytic activity: kaolinite, beidellite, and nontronite were the most active; goethite and allophane were least active. In addition, PDMS degradation products bound more strongly to goethite and smectites. These results demonstrated that soil factors such as clay content and clay type are very important in determining the degradation rates of PDMS in soil.
Amido-derivatives of Metals and Metalloids. Part X.l Reactions of Titanium(iv), Zirconium(iv), and Hafnium(iv) Amides with Unsaturated Substrates, and Some Related Experiments with Amides of Boron, Silicon, Germanium, and Tin(iv)
Cyclic volatile methylsiloxane (cVMS) compounds are
volatile, low-viscosity silicone fluids used as precursors in
the synthesis of high molecular weight PDMS and as
ingredients in certain personal care products. This study
investigates cVMS degradation and evaporation rates in soils
as influenced by molecular size, soil type, and moisture
level. A temperate Michigan soil and a highly weathered
Hawaiian soil were incubated with ∼40 μg of 14C-labeled
cVMS/g of soil at ∼22 °C; samples were kept at 32%,
50%, 92%, and 100% relative humidity (RH) both in open
and closed tubes. At each designated incubation time (from
0 to 21 days), the cVMS-containing soils were extracted,
and the extracts were analyzed by liquid scintillation counting
(LSC) and reverse-phase high-performance liquid chro
matography (RP-HPLC). The results showed that cVMS
degradation was more significant than loss by volatilization
in soil with low moisture levels. Degradation reactions
followed pseudo-first-order kinetics. The half-life of cVMS
fluids in air-dried soils ranged from 50 min to 5 days,
depending on soil type and cVMS molecular sizes. At high
humidity (particularly at 100% RH), the degradation
slowed, while volatilization was accelerated and became
a predominant process in regulating the cVMS removal from
soil. At any given moisture level, the degradation rates
of cVMS were much greater in highly weathered soils (e.g.,
Oxisols) than in temperate soils, and the differences
were more profound for small cVMS (e.g., D4). These findings
demonstrate that cVMS fluids are unlikely to persist in
any soils within the wide range of moisture conditions tested.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.