Distribution and evaluation of the fate of cyclic volatile methyl siloxanes in the largest lake of southwest China.

Cyclic volatile methyl siloxanes (cVMS) used in personal care products are released to aquatic environments through wastewater effluent. cVMS are persistent, toxic, bioaccumulative, and have potential to cause ecological harm. In this study, the environmental behavior of octamethylcyclotetrasiloxane (D4), decamethylcyclopentasiloxane (D5) and dodecamethylcyclohexasiloxane (D6) were evaluated in the largest lake of southwest China, Dian Lake. Air, water and sediment samples were measured for three cVMS compounds in the winter (January) and summer (July) of 2017. In air, D5 exhibited the highest measured mean concentration among the three cVMS, which were 18.4 ± 8.0 ng·m-3 in winter and 5.78 ± 3.61 ng·m-3 in summer. In water and sediment, D6 was the cVMS with the highest measured mean concentration. The mean concentrations in water of D6 were 20.8 ± 5.8 ng·L-1 in winter and 20.4 ± 5.8 ng·L-1 in summer. The mean concentrations in sediment of D6 were 281 ± 45.8 ng·g-1 dw in winter and 270 ± 31.3 ng·g-1 dw in summer. A fugacity-based mass balance chemical fate model for lakes (QWASI) was used for Dian Lake to compare measurements and explore the behavior of cVMS. D6 was predicted to have the highest water column and sediment concentrations. Modeling results showed that most of the D5 and D6 partitioned into sediment and could persist for several years. Persistence was significantly influenced by the high rate of sediment burial. In an analysis of the impact of physicochemical properties and environmental parameters, KOC was identified as a key parameter for predicting cVMS behavior. This study illustrates the importance of cVMS in sediments and the potential aquatic risk that they may pose.