Occurrence, Bioaccumulation, and Elimination of Trifluoropropylmethylsiloxanes in Sediments and Mollusks of Bohai Bay
Trifluoropropylmethylsiloxanes (D3F and D4F) are emerging contaminants whose environmental behavior remains poorly understood. This study investigated their occurrence, bioaccumulation, and elimination in sediments and mollusks collected from 60 sites across 12 coastal cities along Bohai Bay, China. Concentrations in sediments ranged from <LOD to 17.1 ng/g dry weight (dw) with a detection frequency of 30% and a mean of 5.6 ng/g dw. In mollusks, concentrations ranged from <LOD to 20.2 ng/g wet weight (ww) with a detection frequency of 21.7% and a mean of 4.1 ng/g ww. Compared with cyclic dimethylsiloxanes (D4, D5, D6), trifluoropropylmethylsiloxanes exhibited 1–2 orders of magnitude lower concentrations and 1.4–2.2 times lower biota-sediment accumulation factors (BSAF: 0.67 for D3F, 0.61 for D4F). However, from 2017 to 2023, trifluoropropylmethylsiloxanes showed higher annual accumulation rates in sediments (21.5%) and mollusks (32.8%) than dimethylsiloxanes (10.2% and 6.7%, respectively). This discrepancy is attributed to their higher usage growth, stronger sorption (lg KOC: 6.77 for D3F, 8.81 for D4F vs. 4.22–5.99 for D4–D6), and slower elimination in mollusks (half-lives: 11.1 d for D3F, 20.1 d for trans-D4Fa vs. 5.4–8.6 d for D4–D6). The primary degradation product, methyl(3,3,3-trifluoropropyl)silanediol, was detected in sediments (mean 15.7 ng/g dw, detection frequency 33.3%) and mollusks (mean 31.2 ng/g ww, detection frequency 33.3%). Its accumulation rate in mollusks was 1.4 times faster than in sediments, suggesting its potential as an exposure indicator. These findings highlight distinct environmental behaviors of trifluoropropylmethylsiloxanes, necessitating further monitoring and risk assessment.