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Dimethylsilanediol [(CH3)2Si(OH)2=DMSD] is a water soluble monomer formed in soil by the hydrolysis of organosiloxane polymers, such as polydimethylsiloxanes (PDMS), which enter soil through disposal of municipal sludge. Previous studies showed that DMSD evaporates and biodegrades from soil so readily that it is not detected in typical sludge-amended farm fields, but it has been found in experiments simulating spills and in sludge disposal areas. The current study examines fate of DMSD in soils planted with grass. First, methods were developed in the laboratory using perennial ryegrass (Lolium perenne) grown from seed in soils containing 5 mg kg−1 (dry weight) of 14 C -DMSD. After a week of grass growth, 14 C -DMSD was found in the grass clippings, and the fact that it was 100% water extractable indicates that it was not biochemically incorporated. When the grass clippings were incubated in soil, 14 C -DMSD slowly biodegraded to 14 CO 2 (0.3% per week). A subsequent experiment with this same soil showed that the 14 C -DMSD rapidly evaporated (60% in 2 days), indicating that DMSD is not immobilized in the plant tissue, but will dissipate from the soil. Finally, experiments with (non- 14 C ) PDMS (100 mg kg−1) in soil pots outside showed that, although 27% of the PDMS was lost from the soil, a maximum of 0.03% was found as DMSD in grass clippings. As a general conclusion, the small percentage of DMSD which enters grass, combined with the low toxicity of this material, means that uptake of DMSD into grass will be of negligible importance in the overall environmental fate and effects of organosiloxane polymers. |
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