Biological monitoring of aromatic diisocyanates in workers exposed to thermal degradation products of polyurethanes

Abstract

Exposure to diisocyanates was assessed by biological monitoring among workers exposed to the thermal degradation products of polyurethanes (PURs) in five PUR-processing environments. The processes included grinding and welding in car repair shops, milling and turning of PUR-coated metal cylinders, injection moulding of thermoplastic PUR, welding and cutting of PUR-insulated district heating pipes during installation and joint welding, and heat-flexing of PUR floor covering. Isocyanate-derived amines in acid-hydrolysed urine samples were analysed as perfluoroacylated derivatives by gas chromatography mass spectrometry in negative chemical ionisation mode. The limits of quantification (LOQs) for the aromatic diamines 2,4- and 2,6-toluenediamine (2,4- and 2,6-TDA) and 4,4′-methylenedianiline (4,4′-MDA) were 0.25 nmol l⁻¹, 0.25 nmol l⁻¹ and 0.15 nmol l⁻¹, respectively. The LOQ for the aliphatic diamines hexamethylenediamine (HDA), isophoronediamine (IpDA) and 4,4′-diaminodicyclohexyl methane (4,4′-DDHM) was 5 nmol l⁻¹. TDA and MDA were detected in urine samples from workers in car repair shops and MDA in samples from workers welding district heating pipes. The 2,4-TDA isomer accounted for about 80% of the total TDA detected. No 2,6-TDA was found in the urine of non-exposed workers. The highest measured urinary TDA and MDA concentrations were 0.79 nmol mmol⁻¹ creatinine and 3.1 nmol mmol⁻¹ creatinine, respectively. The concentrations found among non-exposed workers were 0.08 nmol mmol⁻¹ creatinine for TDA and 0.05 nmol mmol⁻¹ creatinine for MDA (arithmetic means). Exposure to diisocyanates originating from the thermal degradation of PURs are often intermittent and of short duration. Nevertheless, exposure to aromatic diisocyanates can be identified by monitoring diisocyanate-derived amines in acid-hydrolysed urine samples.