Silicone polymers (polydimethylsiloxanes, or PDMS) are used in numerous down-the-drain products which can eventually enter wastewater treatment plants, where they become incorporated into the sludge. Since sludge is sometimes composted before being applied to the land, this work investigates the fate of PDMS from its incorporation into sludge, through pilot-scale composting processes, to its degradation in compost-amended soil.Either yard or food waste streams were composted in 60 liter vessels with sludge which contained either no PDMS, or had been amended with 350 cs PDMS at 2000 mg/kg wet weight sludge. The four treatments (yard waste and food waste, no PDMS; yard waste and food waste with PDMS) were composted for six weeks and showed expected profiles of temperature, O2, and CO2 changes as the composts matured. Mature composts (pH of 8.4, ash content of 46%, degree of humification of 90%, and C:N ratio of 12) were extracted and showed no degradation of the PDMS during compost generation. Cress seeds (Lepidium sativum) were germinated and grown for two days in the presence of water extracts of the finished composts; results indicated no trends in phytotoxicity between the composts with and without PDMS.PDMS degraded when samples were submitted to weekly or twice-weekly wetting/drying cycles in the laboratory. Degradation in compost or compost/soil samples (15 to 20% in one month) compared to >80% for neat PDMS spiked into soil indicates that PDMS may need to move off the compost and onto the soil minerals for more rapid degradation to occur. PDMS degradation was confirmed in compost/soil mixes under field conditions: ~60% degraded during the 1998 growing season. In general, results show that PDMS will proceed inertly through the active composting process, and will then degrade both during outside storage of compost, and after compost is mixed with soil.