Phenylmethylsiloxanes in the typically human-impacted Xiaoqing River of China: Their distribution and degradation in both waterbodies and mussels.

Based on sampling from Xiaoqing River of China and elimination experiments, this study first investigated spatial/seasonal profiles and fates of phenylmethylsiloxanes (PMSs), as modified products of dimethylsiloxanes (DMSs), in natural waterbody. Overall, the average water (6.7 ng/L) and sediment (28.5 ng/g dw) concentrations of total six cis-/trans- isomers of 2,4,6-triphenyl-2,4,6-trimethylcyclotrisiloxanes (P3) and 2,4,6,8-tetraphenyl-2,4,6,8-tetramethylcyclotetrasiloxanes (P4) in river segments located in industrial areas were respectively 7.37 and 6.13 times higher than those near residential areas, indicating that industrial activities may have larger contribution to PMSs emission than living activities. Compared with paired DMSs with same Si number, PMSs had lower hydrolysis but faster photolysis, and these two pathways influenced isomeric differences in river water: (1) slower hydrolysis of trans-isomers (t = 45.6-334 h) than cis-isomers (t = 38.1-251 h) might cause actual cis/trans ratios (0.18 for P3 and 0.092 for P4) lower than theoretical values (0.33 for P3 and 0.14 for P4) in water, especially in acidic (pH=6.1-6.3) and alkaline (pH=8.0-8.4) segments; (2) faster indirect photolysis of trans-isomers (t = 54.7-177 h) than cis-isomers (t = 73.4-191 h) might lead to larger mean cis/trans ratios in summer (0.31 for P3) with stronger illumination than those in winter (0.08 for P3). The Σ(P3 + P4) concentrations in 140 mussels (Anodonta woodiana) from 14 sites of the Xiaoqing River were