Isocyanates continue to be one of the leading causes of occupational asthma in the UK and biological monitoring (BM) is a valuable tool in assessing exposure to them. BM for toluene diisocyanate (TDI) is based on the measurement of toluene diamine (TDA) in urine after acid hydrolysis of any conjugates (‘total TDA’). The work described here has shown some progress in being able to differentiate between TDA and TDI exposures through the analysis of urine samples. Although none of the outcomes are conclusive, there are some tests that can be applied to positive ‘total TDA’ samples to determine the most likely exposure source. Detection of free TDA is likely to indicate TDA exposure rather than TDI exposure. This technique is limited to samples where the ‘total TDA’ level exceeds about 30 nmol/l. Where a more definitive assessment of exposure to TDI is required, the measurement of TDI-specific lysine conjugates is possible. Currently this would require blood samples to achieve the necessary sensitivity although we have detected this metabolite in urine. This is an area for further work. These techniques also have application for other isocyanate exposures.
This report and the work it describes were funded by the Health and Safety Executive (HSE). Its contents, including any opinions and/or conclusions expressed, are those of the author alone and do not necessarily reflect HSE policy.
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