Occupational asthma due to toluene diisocyanate among velcro-like tape manufacturers

The relationship between toluene diisocyanate exposure and respiratory health problems: A meta-analysis of epidemiological studies

Human epidemiological studies have shown inconclusive results over the effects of diisocyanates on respiratory health problems. A meta-analysis combined evidence on the association between occupational asthma (OA), respiratory function, and toluene diisocyanate (TDI) inhalation exposure. Sixty-one articles on occupational toluene diisocyanate exposure were identified via two databases. Fourteen studies were included in the meta-analysis. The Newcastle-Ottawa Scale (NOS) was used to assess the quality of the studies. Odds ratios (OR_asthma) for the association between TDI exposure compared to non-exposure and OA were calculated. The difference in mean differences (MD) of forced expiratory volume in 1 s (FEV₁) and forced vital capacity (FVC), and the annual mean change differences-in milliliters per year (mL/yr)-in FEV₁ and FVC pulmonary function between TDI exposed and non-exposed, were calculated. When applicable, a random effects meta-analysis was performed. The overall summary OR_asthma for TDI exposed versus non-exposed was 1.18 (95% CI = 0.78-1.79). The summary of the predicted mean percentage difference (MD_%predicted) between exposed versus non-exposed was 2.96% for FEV₁ and 3.75% for FVC. A very small decrease of 5 mL/yr for FEV₁ and 10 mL/yr for FVC, respectively, was observed between the exposed and the non-exposed groups. There was moderate to low heterogeneity between study results, and most studies were evaluated as high-quality. This meta-analysis found no statistically significant adverse association between TDI occupational exposure and OA. No meaningful differences in lung function were detected between exposed and unexposed groups.

Risk Assessment for Toluene Diisocyanate and Respiratory Disease Human Studies

BACKGROUND

Toluene diisocyanate (TDI) is a highly reactive chemical that causes sensitization and has also been associated with increased lung cancer. A risk assessment was conducted based on occupational epidemiologic estimates for several health outcomes.

METHODS

Exposure and outcome details were extracted from published studies and a NIOSH Health Hazard Evaluation for new onset asthma, pulmonary function measurements, symptom prevalence, and mortality from lung cancer and respiratory disease. Summary exposure-response estimates were calculated taking into account relative precision and possible survivor selection effects. Attributable incidence of sensitization was estimated as were annual proportional losses of pulmonary function. Excess lifetime risks and benchmark doses were calculated.

RESULTS

Respiratory outcomes exhibited strong survivor bias. Asthma/sensitization exposure response decreased with increasing facility-average TDI air concentration as did TDI-associated pulmonary impairment. In a mortality cohort where mean employment duration was less than 1 year, survivor bias pre-empted estimation of lung cancer and respiratory disease exposure response.

CONCLUSION

Controlling for survivor bias and assuming a linear dose-response with facility-average TDI concentrations, excess lifetime risks exceeding one per thousand occurred at about 2 ppt TDI for sensitization and respiratory impairment. Under alternate assumptions regarding stationary and cumulative effects, one per thousand excess risks were estimated at TDI concentrations of 10 - 30 ppt. The unexplained reported excess mortality from lung cancer and other lung diseases, if attributable to TDI or associated emissions, could represent a lifetime risk comparable to that of sensitization.

Frequency and trends of occupational asthma due to toluene diisocyanate: a critical review

In recent years, occupational asthma has become the most frequent occupational lung disease in many countries. Reports and statements on the frequency of occupational asthma due to isocyanates are quite contradictory. In order to clarify the issue, a critical review of the medical literature of the past half century worldwide has been performed, with special emphasis on toluene diisocyanate (TDI) as the main representative of the isocyanate family. Nine longitudinal workplace studies of 2,751 persons under risk allow calculation of incidences of occupational asthma due to toluene diisocyanate. Annual incidences had repeatedly been above five percent before 1980, and have decreased to zero to 0.7 percent since 1980. There is a downward trend during the last half century that clearly parallels the downward trend of toluene diisocyanate exposure in some studies. Prevalences of occupational asthma due to toluene diisocyanate can be estimated from 10 cross-sectional studies, based on 788 persons. Prevalences had repeatedly been above 10 percent before 1985, and have been mostly between zero and 10 percent in recent years.

Occupational asthma, lung function decrement, and toluene diisocyanate (TDI) exposure: a critical review of exposure-response relationships

An extensive amount of clinical/epidemiological literature exists regarding the effects of toluene diisocyanate (TDI) exposure on respiratory health. This review presents an evaluation and synthesis of that literature with an emphasis on assessing exposure-response relationships in the workplace. The key respiratory disorders examined are bronchial asthma and an accelerated decline in lung function. In the early years of the industry, annual incidence rates of TDI-induced occupational asthma (OA) were as high as 5-6 percent. In settings where mean TDI concentrations have been maintained below 5 ppb based on 8-hr personal samples, OA incidence rates have declined to < 1 percent annually. Recent data also suggest that overexposure incidents may play an important role in inducing OA, particularly in work environments engineered to minimize routine ambient air concentrations. Fourteen studies were reviewed that examined lung function decrement. Early studies from the 1960s and 1970s provided evidence of transient or fixed lung function loss (measured as a decline in forced expiratory volume in one second [FEV1]) during periods of ongoing exposure among employees experiencing high rates of work-related symptoms of OA. Such findings would not be unexpected in that modest FEV1 declines have been demonstrated in general population studies of persons with bronchial hyperresponsiveness or persistent non-occupational asthma. More recent workplace studies have provided no consistent evidence of accelerated FEV1 loss among employees exposed up to 5 ppb TDI (8-hr TWA) even with documented routine short-term TDI concentrations exceeding 20 ppb TDI.

Respiratory health surveillance in a toluene di-isocyanate production unit, 1967-97: clinical observations and lung function analyses

OBJECTIVES

To characterise irritant and allergic airway responses and assess changes in forced vital capacity (FVC) and forced expiratory volume in 1 second (FEV1) relative to exposure to toluene di-isocyanate (TDI).

METHODS

Employees (n = 313) ever assigned to a TDI production unit for > or = 3 months (1967-92) were identified from personnel records along with 158 frequency matched referents without known exposure to TDI. Reports made during visits to the occupational clinic of incidents related to exposure to TDI and annual periodic examination results (questionnaire, physical findings, and spirometry) were abstracted and assessed relative to industrial hygiene estimates of exposure to TDI.

RESULTS

Mean 8 hour time weighted average estimates of TDI concentrations ranged from 9.9 ppb in jobs with potentially high exposure during the early years of plant operations to 0.5 ppb in jobs with potentially low exposure in more recent years. The corresponding rates of visits to the clinic due to incidents of exposure to TDI (including both irritant and allergic airway responses) declined from 20.5 to 1.0 visits per 100 years of employment at the unit. The annual incidence of asthma induced by TDI declined from 1.8% before 1980 to 0.7% afterwards. Neither cross sectional nor longitudinal analyses of FVC and FEV1 showed significant dose-response findings relative to exposure to TDI across the total exposed population. Among cases of occupational asthma there was an apparent initial decline in FEV1 within 2 years of first reporting symptoms, but not an accelerated rate of decline in follow up tests from 4-30 years after induction of asthma.

CONCLUSIONS

Occurrences of both asthma induced by TDI and irritant airway responses due to exposure to TDI were found in this cohort, but there was no relation between cumulative exposure to TDI and irreversible airflow obstruction as assessed by spirometry.

From conjecture and refutation to the documentation of occupational diseases in Taiwan

The documentation of occupational diseases in a developing country like Taiwan is a challenge to an occupational physician. For lack of a system including material safety data sheet (MSDS), workers are usually not aware of what chemicals they are exposed to. Since many occupational diseases have long latencies and do not show any specific symptoms and signs, recognition and identification of the occupational origin are often very difficult. Using databases which provide a relatively complete list of industrial chemicals and a set of specific signs and/or symptoms, combined with the epidemiologic approach of conjectures and refutations--i.e., considering and ruling out all possible alternative explanations--we have documented eight kinds of occupational diseases and an outbreak of botulism. We recommend that a similar approach be applied to any other country with a similar situation, and that a system involving an identification sheet (e.g., MSDS) for each chemical be advocated and implemented in such countries as one means to enable prompt recognition and prevention of occupational diseases.