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

[Display omitted] •Siloxanes were widely found in crude oil, additives and petrochemical products.•Deep catalytic cracking unit had the largest siloxane emission in oil-refinery.•Siloxanes had more apparent distribution in refinery facility than reference area.•Plasma levels of siloxanes and metabolites in refinery workers were much elevated. 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 (