Short-term respiratory changes in polyurethane foam workers exposed to low MDI concentration

Exposure to isocyanates and organic solvents, and pulmonary-function changes in workers in a polyurethane molding process

The extent of adverse health effects of isocyanates when combined with other chemicals is not well documented. This study was conducted as a 2.5-year follow-up as well as to determine daily and weekly effects of exposure to isocyanates and organic solvents on pulmonary function. The concentrations of chemicals sampled were below the recommended exposure criteria. No daily or weekly reduction in the subjects' pulmonary function was observed. The isocyanate/solvent-exposed subjects showed significant long-term reduction in their forced vital capacity (P < 0.05) and expiratory volume in 1 second (P < 0.001). No such changes were observed in non-exposed subjects or in those exposed only to organic solvents. The proportion of subjects who developed respiratory symptoms in the isocyanate-exposed group was not significantly greater than that of the non-exposed group. The results of this study indicate that long-term exposure to isocyanates, even in very low concentrations, may contribute to impaired pulmonary function.

Hemoglobin adducts and urine metabolites of 4,4'-methylenedianiline after 4,4'-methylenediphenyl diisocyanate exposure of rats

4,4'-Methylenediphenyl diisocyanate (MDI) is a very important component in the production of polyurethane. In a long-term experiment, designed to determine the carcinogenic and toxic effects of MDI, rats were exposed chronically for 3 and 12 months, to 0.0 (control), 0.26, 0.70 and 2.06 mg MDI/m3 as aerosols. Hemoglobin adducts and urine metabolites of MDI were determined at the different doses in order to develop methods to biomonitor workers exposed to MDI and to assess a risk resulting from such exposure. Hemoglobin adducts and urine metabolites of 4,4'-methylenedianiline (MDA) were found in all rats, including controls. MDA and N-acetyl-MDA (AcMDA) were quantified by GC-MS after derivatization with heptafluorobutyric anhydride. The dose-response relationships for hemoglobin adducts and urine metabolites were non-linear over this dose range. In urine, free AcMDA and MDA were found after base extraction. The amount of MDA present in urine and to a lesser extent the AcMDA found in urine correlate well with the corresponding amount determined as hemoglobin adducts for all dose groups. In order to release MDA from possible conjugates of MDA and AcMDA, urine was treated under strong acidic conditions. Following this procedure higher MDA levels were found than the sum of MDA and AcMDA from mild base hydrolysis. Similar results were obtained with the rats exposed for 3 and 12 months, indicating that a steady state had been reached by 3 months. In order to perform further investigations of the bronchoalveolar lavage fluid one group of animals was given a 1 week recovery period before sacrifice. Hemoglobin adducts from these animals showed a decrease of approximately 40% for all dose groups. According to the lifetime of rat erythrocytes the levels of hemoglobin adducts should have decreased by only 22%. This suggests that the erythrocytes with modified hemoglobin have a shorter lifespan. In order to exclude the possibility that hemoglobin adducts may have resulted from ingestion of hydrolyzed MDI via licking of the fur, a single dose experiment with rats exposed through the nose only or with the whole body was carried out. The only difference observed between these two exposure regimes was that the hemoglobin adduct levels of AcMDA after nose only exposure were significantly higher than after total body exposure. The presence of AcMDA in urine and as a hemoglobin adduct indicates that MDA was bioavailable after MDI exposure. The presence of MDA may contribute significantly to the carciongenic potential of MDI, since MDA has been shown to be carcinogenic in animals.

Short-term respiratory function changes in relation to workshift welding fume exposures

The forced vital capacity (FVC), the forced expiratory volume in one second (FEV1) and the transfer factor for the lung (TL) were measured before and after the 8-h work shift in groups of welders and non-welder controls in a shipyard. For each subject, full-shift average concentrations of welding fume constituents were evaluated. On the average, the lung function indices in both groups of welders and controls decreased from morning through afternoon. The welders demonstrated more reduction in the indices than the control group. In general, there was no significant association between the acute changes in the lung function and the daily amount of exposure to welding fume constituents or the welding environmental factors. However, the overall difference of mean diurnal variations in TL between the groups working under different ventilation condition was significant (P < 0.01). On the average, welders who did not use any ventilation system showed maximum reduction in TL value. Acute reduction of FEV1 was positively correlated (P < 0.05) with the levels of iron oxide produced during welding.