Cyclic methylsiloxanes in wastewater treatment plants: Occurrence, emissions, environmental distributions, and occupational exposure.

Cyclic methylsiloxanes (CMSs), widely found in wastewater treatment plants (WWTPs), are potentially hazardous to the environment and human health. In this study, the environmental behavior and human exposure risks of three CMSs (D4-D6) were evaluated in WWTPs located in Beijing and Kunming, Yunnan province. D5 had the highest concentrations in air, water, and sludge, with seasonal variation that consisted of a high concentration in summer and low concentration in winter. The CMS concentrations in air were 3-4-fold higher in the A/O (Anaerobic-Anoxic-Oxic) treatment units than in the other units. CMS emissions to air, soil, and water from the Beijing WWTP were in the ranges of 3.4 × 10-5.0 × 10 kg·a, 4.5 × 10-7.5 × 10 kg·a, and 2.5 × 10-2.9 × 10 kg·a, constituting 98 %, 1.3 %, and 0.7 % of the total emissions, respectively. Total daily inhalation exposure doses of CMSs (ADD) associated with four different jobs in WWTPs showed that wastewater treatment technicians had the highest ADD (51 μg/kg/day), indicating that these people had the highest occupational exposure risk in WWTPs. Therefore, this study identified that atmospheric emission was the main environmental fate of CMSs in WWTPs, and provide a basis for the improvement of WWTP process and risk management decisions. ENVIRONMENTAL IMPLICATION: Assessing the environmental fate and occupational exposure risk of cyclic methylsiloxanes (CMSs) found in wastewater treatment plants (WWTPs) is crucial. This is the first study to identify that atmospheric emission was the main environmental fate of CMSs in WWTPs, especially D5; the inhalation exposure doses of CMSs were all significantly higher in the occupational population working in WWTPs. The results described in our study will help enhance the understanding of current knowledge base of environmental fate and exposure risk of CMSs in WWTPs, and provide a basis for the improvement of WWTP process and risk management decisions.