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Although reliable methods are available to monitor the concentrations of TDI in workplace air, some investigators use urine testing methods to determine if a worker has been recently exposed to TDI. This method relies on sophisticated analytical techniques in which various metabolic or breakdown products of TDI present in urine are converted in the laboratory to a derivative, toluene diamine (TDA). The total amount of converted TDA measured in the urine has been proposed as an estimate of exposure to TDI, assuming that an individual has not been exposed to another source of TDA. Results of TDI biomonitoring may be difficult to interpret and the following points must be considered: 1) The pathway for TDI elimination has not been fully investigated in humans, a direct correlation between TDI air monitoring and urine TDA levels is not feasible; 2) Studies of TDI exposures in the workplace have not consistently shown a good correlation between air exposure levels and biomonitoring results; 3) Biomonitoring for TDI exposure by measuring converted TDA in urine does not identify peak exposures which may be more relevant to pulmonary sensitization; 4) Urine monitoring results for TDI exposure have not been correlated to adverse health effects and no biological monitoring limit has been established for TDI; 5) The detection of converted TDA in laboratory assays on processed urine samples does not necessarily reflect the presence of free TDA in the body, therefore it may unintentionally introduce concerns related to airborne TDI exposures. Data generated from urine biomonitoring for exposure toTDI must be interpreted with caution and significant questions remain regarding the relevance of these studies for quantitative TDI exposure assessment.

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