Determination of N-nitrosodiethanolamine in urine by gas chromatography thermal energy analysis: application in workers exposed to aqueous metalworking fluids.

Abstract

The aim of this study was to describe a detailed and validated methodology designed for the analysis of carcinogenic N-nitrosodiethanolamine (NDELA) down to sub-microgram/l levels in urine and its application to a number of workers exposed to NDELA-contaminated aqueous metalworking fluids (MWF). Following a work-up procedure based on solid-phase extraction of NDELA, the urinary extracts were analysed without derivatization by gas chromatography on a polar wide-bore column with chemiluminescent detection using a thermal energy analyser (TEA). N-Nitroso-(2-hydroxypropyl)amine was used as an internal standard. The method was applied to 12 workers using "nitrite-free" or "nitrite-formulated" MWF and to 15 unexposed subjects. The NDELA content of the MWF was also determined using a similar, but simpler method able to easily quantify NDELA down to at least 0.1 mg/l. Contamination by NDELA traces of some chemicals used for the sample preparation, particularly ethyl formate, must be carefully checked since it can give rise to false-positive results of up to 1 or 2 micrograms/l. The response was linear in the range of 0-500 micrograms/l. Between 0.5 and 10 micrograms/l, the recovery rate was close to 95%, while repeatability ranged from 12.5 to 6.4% (n = 5). The detection limit was 0.3 microgram/l (Signal/noise = 3). No detectable NDELA could be observed in the control workers. There was no significant increase in NDELA levels at the end of shift spot samples from an exposed worker over 1 week. Higher NDELA concentrations were found in two workers (4.3 and 10.7 micrograms/l) exposed to "nitrite-formulated" fluids (contaminated with 65 and 18 mg NDELA per 1, respectively) than in nine workers (range, 0.4-1.3 micrograms/l exposed to "nitrite-free" fluids with lower levels of NDELA (range, 0.5-6.6 mg/l). The detailed methodology described in this work and applied to a limited industrial situation was found to be suitable for monitoring NDELA in the urine of workers exposed to aqueous MWF. A much larger screening has been undertaken with the aim of obtaining better information on the real exposure of workers sometimes exposed to "nitrite-formulated" fluids that are still used.