Distribution and Elimination of Trifluoropropylmethylsiloxane Oligomers in Both Biosolid-Amended Soils and Earthworms

During a primary screening in 2015 and 2016, tris-(trifluoropropyl) trimethylcyclotrisiloxane (D3F) and cis-/trans-tetrakis(trifluoropropyl)tetramethylcyclotetrasiloxane isomers (cis-D4F, trans-D4Fa,b,c) were detected in 12 biosolid-amended soils from Laixi and Shijiazhuang Cities of China, with mean concentrations being 10.3 ng/g dry weight (dw) and 2.7 ng/g dw for D3F and D4F, respectively. Subsequently, one further systematical survey found that although repeatedly amended by biosolids containing trifluoropropylmethylsiloxanes (4.2-724 ng/g dw), these compounds had no increasing trend in biosolid-amended soils (n = 100) collected from Laixi City at five sampling events from February 2017 to June 2019. Simulated experiments indicated that hydrolysis half-lives (1.8-28.0 days) of trifluoropropylmethylsiloxanes in soils were 3.0-18.3 times shorter than volatilization half-lives (7.4-362 days). Compared with those of octamethylcyclotetrasiloxane (D4), the hydrolysis rates of D4F isomers were faster in soils with total organic carbon (TOC) <= 80 mg/g but lower in soils with TOC >= 150 mg/g. In earthworm bodies, trifluoropropylmethylsiloxanes had 1.03-1.5 times lower biota-soil accumulation factors (1.3-3.2) but 1.4-3.0 times longer half-lives (2.6-5.7 days) than D4. The stronger persistence of fluorinated-siloxane than the corresponding dimethylsiloxane in both soils (at high TOC levels) and earthworms indicated that environmental risks of these compounds deserve further investigation.

Automated summary

The study found that trifluoropropylmethylsiloxanes in soils have shorter hydrolysis half-lives and longer half-lives in earthworms, indicating the need for further investigation into the environmental risks of these compounds.