Exposure-response relationships in rhinitis and conjunctivitis caused by methyltetrahydrophthalic anhydride

To examine exposure-response relationships in the occurrence of symptoms of the eyes and airways in workers exposed to methyltetrahydrophthalic anhydride (MTHPA).

A population of 111 workers from 2 condenser plants (A and B) using epoxy resin with MTHPA underwent a questionnaire survey and serology investigations, and data obtained on 95 subjects in assembly and inspection lines were analyzed for this study.

In all, 24 (65%) of 37 workers in plant A and 38 (66%) of 58 workers in plant B had positive MTHPA-specific IgE. The air levels of MTHPA detected in assembly and inspection lines were higher in plant A than in plant B (geometric mean 25.5-63.9 and 4.93-5.49 microg/m3, respectively). IgE-sensitized workers in each plant had significantly (P < 0.05) more complaints regarding the eyes and nose than did unsensitized workers, suggesting that there is an IgE-mediated mechanism in most of these symptoms. The sensitized workers in plant A had higher frequencies for symptoms of the eyes, nose, and pharynx than did those in plant B (P < 0.02). Furthermore, only 15% of persons often displayed work-related symptoms among the 20 symptomatic workers in plant B as compared with 73% of the 26 symptomatic workers in plant A (P < 0.0001). These results can be explained by the difference in the MTHPA levels measured in the lines between the two plants. In plant B the minimal level of MTHPA that was associated with work-related symptoms was 15-22 microg/m3, which was lower than the geometric mean levels detected in assembly and inspection lines in plant A.

These results suggest that MTHPA exposure at levels above 15 microg/m3 should be avoided to prevent the development of occupational allergic diseases in most workers.