Respiratory Effects of Toluene Diisocyanate in the Workplace: A Discussion of Exposure-Response Relationships

Abstract

Toluene diisocyanate (TDI) is an important industrial intermediate used in manufacturing flexible polyurethane (PUR) foams, surface coatings, cast elastomers, sealants, and adhesives. In this review long-term trends in workplace exposures to TDI are assessed in both the producing and using industries, and respiratory health effects of TDI are evaluated in relation to workplace TDI concentrations. The key respiratory health effects associated with repeated or long-term TDI exposure are bronchial asthma and an accelerated rate of decline in lung function. In the early years of the industry, annual incidence rates of occupational asthma (OA) due to TDI ranged from 1% to as high as 5 to 6%, depending on the extent of engineering and work practice controls in the various workplaces. Since the mid-1970s, annual OA incidence rates have been <1%, where 8 h TDI concentrations have been maintained below 5 ppb as determined by personal monitoring, even where short-termTDI concentrations above 20 ppb and less frequently above 40 ppb were routinely detected. In these latter settings, there is evidence that the majority of OA cases may be attributable to TDI concentrations well above 20 ppb associated with overexposure incidents. Further study is needed regarding the role of such incidents in inducing respiratory sensitization. Cross-sectional and longitudinal studies of lung function have indicated that continued exposure after development of work-related respiratory symptoms can lead to transient or accelerated fixed declines in forced expiratory volume in 1 sec (FEV1). These findings are congruent with the FEV1 declines demonstrated in general population studies of persons with persistent bronchial hyperresponsiveness or nonoccupational asthma. More recent longitudinal studies in settings with ongoing medical surveillance have provided no consistent evidence of accelerated FEV1 loss among employees exposed up to 5 ppb TDI on an 8 h time-weighted average basis.

Eye and airway symptoms in low occupational exposure to toluene diisocyanate

“…In western industrialized countries, the incidence of isocyanate-induced asthma has decreased (6,23,24). In recent years, at most, a handful of cases per year have been registered in Sweden.…”

“…Apart from asthma, symptoms such as cough, wheezing, and dyspnea are commonly reported (1)(2)(3)(4). Other effects are hypersensitivity pneumonitis and an accelerated decline of lung function (2,(5)(6)(7). Moreover, exposure to diisocyanates also often causes symptoms of the upper airways and eyes (1)(2)(8)(9).…”

Biological monitoring of exposure to toluene diisocyanate

“…TDI is a respiratory irritant and may also cause chronic disorders of the airways, such as occupational asthma (2)(3)(4), and, hence, it is essential to monitor the occupational exposure for workers. Such surveillance has mainly been performed by air monitoring.…”

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“…For TDI, concentrations have ranged from 0.1 to 2 percent [22]. As an example of the difficulty of interpreting patch testing results, one case has been reported to have a negative result with TDI at 0.1 percent while at 0.5 percent concentration a positive result was seen [16]. Therefore, it is not always possible to differentiate between irritant and allergic contact dermatitis through patch testing [16,20,21].…”

“…On the other hand, exposure to volatile solvents like toluene, may be caused by an occupational exposure in industrial settings or a volatile substance abuse [14]. Toluene diisocyanate (TDI) is a very toxic volatile substance that is an aromatic hydrocarbone [15], and it is also a Th2 skin sensitizer [13] and is a weak skin irritant [16]. There are many report about the effect of chemicals on skin sensitization response [17,18].…”