Fate and Effects of Silicone Polymer During the Composting Process

Silicone (polydimethylsiloxanes, or PDMS) fluids are widely used in industrial and consumer products, and may find their way into municipal biosolids that are eventually applied to the land. In soil PDMS breaks down into dimethylsilanediol which is then either volatilized or biodegraded. Since biosolids are often composted prior to land application, this paper investigates fate and effects of PDMS in compost. PDMS (0,3, or 30g) was added to 180g of matured compost and incubated at 58°C for six weeks. Some treatments also had 180g of wood ash and/or additions of 15g of alfalfa every two weeks. Releases of CO, from all treatments were identical to their respective controls (no PDMS), indicating no effects from these extremely high PDMS levels on the composting process. Wood ash caused an initial delay in CO, release after which results were similar to treatments without wood ash. After six weeks, PDMS was unchanged in molecular weight and concentration, indicating that it will be transferred intact, after composting, to the land where it can degrade in the presence of soil.