Skin exposure to aliphatic polyisocyanates in the auto body repair and refinishing industry: a qualitative assessment

Abstract

Objectives: Although respiratory exposures have been the primary concern with isocyanates, skin exposure also can occur and may contribute to sensitization and asthma. Methodologies to assess isocyanate skin exposure in the workplace are limited and skin exposure data scarce. The goals of this study were (i) to evaluate and validate the isocyanate colorimetric indicators against a quantitative assay, (ii) to evaluate the extent of isocyanate surface contamination and skin exposure among auto body shop workers and (iii) to evaluate isocyanate skin exposure determinants.

Methods: The colorimetric indicators were compared with a high-performance liquid chromatography (HPLC) quantitative assay based on the National Institute for Occupational Safety and Health Method 5525 using paired laboratory sampling. The colorimetric indicators were then used to assess surface contamination and skin exposure to aliphatic isocyanates in 35 auto body shops and 124 workers as part of an epidemiologic study. The positive sample rate was calculated for various surfaces, body parts and tasks. The color intensity of the colorimetric indicators was rated on a scale 0 (yellow color) to 5 (deep red). Side-by-side comparisons of the qualitative method with the quantitative HPLC assay were also performed in the field using paired samples.

Results: Laboratory and field evaluation validated use of the colorimetric indicators. The rate of positive surface samples for isocyanates was 46% (n = 145/313). Thirty-four percent (73/216) of samples were positive for unprotected skin and 20% (n = 22/111) for skin under latex gloves. The highest positive rate observed on skin samples was obtained after paint mixing and spraying tasks. The colorimetric indicators were highly specific for isocyanates, but false negatives occurred when compared with the more sensitive HPLC quantitative assay. The presence of surface contamination and the performance of paint-related tasks were the major determinants of isocyanate skin exposure.

Conclusions: This study documents extensive surface contamination and skin exposure, including under gloves, to aliphatic polyisocyanates during painting and paint mixing tasks in auto body shop workers. Contaminated surfaces and aerosol deposition during spray painting may both contribute to skin exposure. The colorimetric indicator is a quick, practical and low-cost, but not highly sensitive, industrial hygiene tool to detect isocyanate surface contamination and skin exposures following the use of isocyanate-containing products.