Silicone polymers poly(dimethylsiloxane)s, PDMS are used in down-the-drain consumer products and enter soil through disposal of municipal sludge. We examined PDMS hydrolysis over a range of soil moistures in soils from different geographicalregions. 14{sup left}CPDMS 350 cSt was added (50 mg kg{sup}-1) to a Michigan Alfisol (Londo sandy clay loam) at six water potentials. Hydrolysis (5-week incubation) was 16, 2.0, 0.14, and 0.09 wk{sup}-1 at -76, -18, -5.4, and -1.2 MPa,respectively. Hydrolysis at -0.26 and -0.05 MPa was too slow to distinguish from experimental variability. When dry Londo soil was amended with PDMS and then remoistened to -0.05 MPa, hydrolysis was 0.19 wk{sup}-1 meaning that remoistening of soil slowsthe reaction. Similarly, PDMS hydrolysis in remoistened soils (-0.04 to -0.1 MPa) from Ohio (Alfisol), Georgia (Ultisol), and Puerto Rico (Oxisol) was 0.41, 1.25, and 1.26 wk{sup}-1, respectively. Best-fit regression equations (R{sup}2 > 0.99) showed alinear dependence of rate constant on water potential from -0.04 to about -100 MPa. Results show that PDMS hydrolysis increased with decreased soil moisture and was faster inUltisols and Oxisols than in Alfisols at the same soil water potential.
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