Propylene oxide

Propylene oxide (PO) is produced at about 7 billion pounds per year globally, primarily as an intermediate in polyurethane polyol production [1]. Polyurethane foam — used in furniture, mattresses, carpet backing, automotive seats, and building insulation — begins as polyols reacted with isocyanates, and most polyols are made from propylene oxide. PO is also used to make propylene glycol and as a fumigant for nuts, spices, and dried fruits [2]. Industrial production facilities are located primarily in the Gulf Coast and industrial Midwest. PO is a reactive, highly flammable compound that requires careful handling and has been involved in industrial accidents [3].

Occupational inhalation in PO production facilities, polyurethane manufacturing plants, and fumigation operations is the primary high-level exposure route [1]. Community air near PO production facilities and fumigation operations is a secondary route. Dietary exposure from fumigated foods — nuts, dried fruits, and spices treated with PO — is a minor but documented pathway [2]. Consumer exposure from outgassing of polyurethane foam products is generally considered very low once the foam has cured, as PO is consumed in the polymerization reaction [3].

Propylene oxide is classified as a probable human carcinogen (IARC Group 2A), with evidence from rodent studies for tumors at the site of contact (respiratory tract and nasal passages with inhalation exposure) and in the liver [1]. It is a reactive electrophile that directly alkylates DNA, forming adducts that drive mutagenesis and carcinogenesis. Acute exposure causes irritation of the eyes, skin, and respiratory tract; at high concentrations, CNS depression [2]. Worker cohort studies in PO manufacturing show elevated rates of cancer, though the statistical power of most studies is limited [3].

Workers in propylene oxide production, polyurethane manufacturing, and fumigation operations face the highest occupational risks [1]. Communities near large PO production facilities have elevated ambient air exposures. Frequent consumers of PO-fumigated nuts (almonds are commonly treated) receive dietary PO [2].

Choose steam-pasteurized almonds over propylene oxide-treated almonds — labeling in the US does not always distinguish, but raw almonds from farmers' markets or organic sources use alternative treatments [1]. Workers in PO environments must use local exhaust ventilation, NIOSH-approved supplied-air respirators for high-concentration operations, and impermeable chemical gloves [2]. Monitor air concentrations to maintain below the OSHA PEL of 100 ppm. Annual health monitoring including respiratory function testing should be part of occupational health programs [3].