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 cVMSdegradation 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 ~40μg of 14{sup left}C-labeled cVMS/g of soil at～2℃; sampleswere kept at 32, 5n, 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 chromatography (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-orderkinetics. The half-life of cVMS fluids in air-dried soils ranged from 50 mm 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 apredominant 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 difterences were more profound for smallcVMS (e.g., D{sub}4). These findings demonstrate that cVMS fluids are unlikely to persist in any soils within the wide range of moisture conditions tested.
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