Presence, behaviour, and risk assessment of volatile methylsiloxanes in wastewater: A year-long comprehensive study within a wastewater treatment plant.

The awareness of possible environmental hazards caused by the widespread global use of volatile methylsiloxanes (VMSs) in personal care products (PCPs) and industrial processes has been increasing. Sewage containing these compounds may reach wastewater treatment plants (WWTPs), which are hotspots of their release into the environment. The levels, distribution, and potential risks of VMSs were studied in an unprecedently comprehensive sampling strategy (four seasonal campaigns) along the water line of a WWTP: the main influent entrance (SA1), after the preliminary treatment (SA2), after the primary treatment (SA3) and after the secondary treatment (the treated effluent; SA4). This WWTP was selected as a representative of the conventional set up based on a secondary treatment, allowing a similar approach in numerous facilities worldwide. Seven VMSs (L3, L4, L5, D3, D4, D5, D6) were analysed in wastewater samples by a small-scale liquid-liquid extraction (LLE) protocol, followed by gas chromatography-mass spectrometry (GC-MS), and the cyclic VMSs were dominant at all sampling sites and in all seasons. Considering the whole year, the total VMSs ranged from 0.4 to 22.5 μg L for SA1, 0.03 to 33.7 μg L for SA2, below method detection limit (MDL) to 13.2 μg L for SA3 and <MDL to 0.8 μg L for SA4. D5 prevailed, together with D6 and D4. The mean VMS mass flows dropped from 119 g day in SA1 to 1.9 g day in SA4, resulting in high removal efficiencies from the water line (>98 %). According to the risk quotients (RQ), only 18 SA4 samples (32 %) presented a minimal risk to the receiving media (0.01 ≤ RQ < 0.1). However, considering the absence of a secondary treatment or a direct discharge without treatment, there may be a risk to the environment.