Reply to comments on "Volatile methylsiloxanes in personal care products - Using QuEChERS as a "green" analytical approach" published in Talanta 174 (2017) 156-157

Unraveling the distribution characteristic of cyclic volatile methylsiloxanes in various environmental media of a wastewater treatment plant

Cyclic volatile methylsiloxane (cVMS) is extensively used in consumer products and frequently detected in various environmental media, including water and air. In this study, we developed reliable and convenient methods to sample three cVMS compounds: octamethylcyclotetrasiloxane (D4), decamethylcyclopentasiloxane (D5), and dodecamethylcyclohexasiloxane (D6) in water and air samples collected from different tanks within a wastewater treatment plant (WWTP). The concentrations of D4, D5, and D6 in the water samples ranged from 0.40 to 8.0 μg L-1, 0.35 to 91 μg L-1, and 0.54 to 17 μg L-1, respectively. In the air samples, these concentrations varied from 0.34 to 20 μg m-3, 0.34 to 128 μg m-3, and 0.08 to 12 μg m-3, respectively. It is worth noting that the air-water distribution coefficient (Kaw) for these three cVMS exhibited a strong correlation with their water solubility. Moreover, fugacity fractions indicated a net evaporation process from water to the atmosphere. Furthermore, we investigated the distribution of cVMS between the gaseous and particulate phases. The results revealed a significant fraction, exceeding 72 %, of cVMS resided in the gas phase. D4 and D5 predominate in the gaseous phase, while D5 and D6 are the principal constituents within the particulate phase. The distribution coefficient characterizing the partitioning of cVMS compounds between the gaseous and particulate (Kp) exhibited a strong correlation with their corresponding octanol-air partitioning coefficients (Koa). These findings contribute to a better understanding of the distribution of cVMS in diverse environmental media and the underlying mechanism governing their dispersion.

Development of a solid-phase microextraction method for fast analysis of cyclic volatile methylsiloxanes in water

Cyclic volatile methylsiloxanes (cVMS) are widely used in consumer products and commonly detected in the environment. There are challenges in the analysis of cVMS because of their ubiquitous use which can introduce high background contamination. The current study introduces a sample preparation method based on headspace of solid-phase microextraction (SPME) for monitoring the cVMS in waters. Efforts were made to reduce the background contamination during sample preparation and instrument analysis. A laboratory prepared MIL-101 coating was prepared using polysulfone instead of polydimethylsiloxane as adhesive to avoid the contamination. The extraction performance of the MIL-101 fiber was optimized and evaluated. The optimized extraction time and temperature were 60 min and 40 °C, respectively. The method quantification limits of the MIL-101 fiber for octamethylcyclotetrasiloxane (D4), decamethylcyclopentasiloxane (D5) and dodecylcyclohexasiloxane (D6) in water were 0.15 ng mL^-1, 0.14 ng mL^-1, and 0.27 ng mL^-1, respectively. The extraction efficiency of the proposed MIL-101 fiber was comparable to the commercial polydimethylsiloxane/divinylbenzene fiber. The developed method was applied to analyze the cVMS in wastewater treatment plant and the concentrations in the barscreen and in the aeration tank ranged from 0.73 to 3.3 ng mL^-1 and 7.74-85.1 ng mL^-1, respectively. The MIL-101 fiber was also applied to study the photodegradation of the cVMS in water under simulated sunlight. Approximately 25%, 20%, and 45% of D4, D5, and D6, respectively, were degraded after 10 h exposure.