Quantification and Statistical Modeling—Part II: Dermal Concentrations of Monomeric and Polymeric 1,6-Hexamethylene Diisocyanate

Abstract

We conducted a quantitative dermal and inhalation exposure assessment of monomeric and polymeric 1,6-hexamethylene diisocyanates (HDI) in 47 automotive spray painters from North Carolina and Washington State. We report here the use of linear mixed modeling (LMM) to identify the primary determinants of dermal exposure. Dermal concentrations of HDI, uretidone, biuret, and isocyanurate were significantly higher in 15 painters who did not wear coveralls or gloves (N = 51 paint tasks) than in 32 painters who did wear coveralls and gloves (N = 192 paint tasks) during spray painting. Regardless of whether protective clothing was worn, isocyanurate was the predominant species measured in the skin [geometric mean (GM) = 33.8 ng mm(-3)], with a 95% detection rate. Other polyisocyanates (GM < or = 0.17 ng mm(-3)) were detected in skin during <23% of the paint tasks. According to marginal R(2) statistics, mixed models generated in this study described no <36% of the variability in dermal concentrations of the different polyisocyanates measured in painters who did not wear protective clothing. These models also described 55% of the variability in dermal concentrations of isocyanurate measured in all painters (N = 288 paint tasks). The product of analyte-specific breathing-zone concentration (BZC) and paint time was the most significant variable in all the models. Through LMM, a better understanding of the exposure pathways governing individual polyisocyanate exposures may be achieved. In particular, we were able to establish a link between BZC and dermal concentration, which may be useful for exposure reconstruction and quantitatively characterizing the protective effect of coveralls and gloves. This information can be used to reduce dermal exposures and better protect automotive spray painters from potential adverse health effects.

Hemoglobin adducts in workers exposed to 1,6-hexamethylene diisocyanate

“…Breathing-zone and dermal exposure measurements among these occupationally exposed spray painters have been published elsewhere (Fent et al 2009a, 2009b). Briefly, a personal air sample in the worker’s breathingzone was collected during each spray painting operation of HDI-containing paint.…”

“…HDI on the skin was collected using three consecutive tape-strips (10 cm 2 ) applied to six different sites on the worker’s body (e.g., right and left forearms, hands, and neck) after each paint task. Air and skin samples were analyzed by LC-MS as previously described by Fent and colleagues (2009a, 2009b). Work diaries and questionnaires about workers’ physical characteristics (e.g., age, height, weight), PPE use (e.g., coveralls, respirator, gloves), and work environment (e.g., paint booth type, duration of paint tasks) were completed during each visit.…”

Factors affecting variability in the urinary biomarker 1,6-hexamethylene diamine in workers exposed to 1,6-hexamethylene diisocyanate

“…However, dermal exposure as measured by the tape-strip method reflected the effect of PPE protection since the tape-strip samples were taken from the areas that had been covered during painting. 17 Thus, the dermal exposure measured accounted for the protectiveness of the gloves or coverall. However, the measured dermal exposure may have been underestimated due to the possible rapid absorption of HDI through the stratum corneum and/or conjugation of HDI to macromolecules in the skin.…”

“…16 The collection and analyses of the breathing-zone and dermal tape-strip samples have been published previously. 15,17 On each sampling visit, breathing-zone air samples were collected during each HDI-containing painting task, and tape-strip samples were collected immediately following each task. The painter was observed during the paint tasks to note the duration of exposure and the type of respirator worn.…”

“…Methods for performing the multiple imputation of the exposure data have been described previously. 3,15,17 Briefly, we applied logarithmic transformation to all exposure variables to make them normally distributed before imputation and imputed from truncated multivariate normal distributions with an upper truncation at the logarithmic transformed limit of detection for HDI or MDL for HDA. PROC MIANALYZE was used to combine the results of the analyses carried out on the 10 imputed datasets and to obtain valid estimates and statistical inferences.…”