Methylsiloxanes in petroleum refinery facility: Their sources, emissions, environmental distributions and occupational exposure

Abstract

High concentrations (1.08 ng/g-3.61 mg/g) of methylsiloxanes, including cyclic analogs [octamethylcyclotetrasiloxane (D4), decamethylcyclopentasiloxane (D5) and dodecamethylcyclohexasiloxane (D6)], and linear analogs with 3–14 silicon atoms (L3-L14), have been detected in crude oil, additives and petroleum products from one petroleum refinery facility in China. Overall, the total mass load of Σmethylsiloxanes (1320 kg/day) in crude oil and additives was 1.5 times higher than that in petroleum products (857 kg/day), indicating their potential emissions in this facility, which were further confirmed by the find of their obvious emission through exhaust-gas (89.4 kg/day) and wastewater (4.70 kg/day). Σmethylsiloxanes emission from exhaust-gas discharge outlets of deep catalytic cracking units (60.6 kg/day) took up 68% of their total emission from all gas outlets. Overall, Σmethylsiloxanes in air (17.1–743 μg/m3) and soil samples [311 ng/g dw (dry weight) − 34.2 μg/g dw] from this facility were up to four orders of magnitude greater than those from surrounding areas, and plasma concentrations of Σmethylsiloxanes in current workers from this facility (7.4–609 ng/mL) were up to two orders of magnitude larger than those from reference group (<LOQ-21.2 ng/mL). Furthermore, concentration ratios (0.09–0.58) of total cyclic methylsiloxanes to their hepatic metabolites for workers were 2.3–17 times lower than those (1.32–1.56) for reference group, indicating that refinery workers may be exposed to more unknown methylsiloxane analogs than general population.