Predictors of airborne exposures to polycyclic aromatic compounds and total organic matter among hot-mix asphalt paving workers and influence of work conditions and practices.

ABSTRACT

OBJECTIVES: We evaluated personal airborne exposures to polycyclic aromatic compounds (PACs) and total organic matter (TOM) among hot-mix asphalt (HMA) paving workers. The primary objectives of this study were to identify predictors of airborne PAC exposures, identify PAC exposure sources, and characterize how work practices may affect personal airborne exposure to PACs. METHODS: Four workers were recruited from each of three asphalt paving crews (12 workers) and were monitored for three consecutive days over 4 weeks for a total of 12 sampling days per worker (144 worker-days). Three sampling weeks were conducted while maintaining standard working conditions with regard to airborne exposures. The fourth week included the substitution of biodiesel for diesel oil used to clean tools and equipment. Linear mixed-effects models were used to evaluate predictors of airborne exposures including weather parameters (air temperature, wind speed, and relative humidity), worksite conditions (HMA application temperature, work rate, asphalt grade, and biodiesel use), and personal factors (minutes sampled, minutes of downtime, and smoking status). RESULTS: Concentrations of the 33 individual PACs measured in personal air samples were generally below detection limits under all conditions with the exception of fluorene [geometric mean (GM) = 65 ng m(-3)], naphthalene (GM = 833 ng m(-3)), phenanthrene (GM = 385 ng m(-3)), and pyrene (GM = 57 ng m(-3)). The summary measures of TOM (GM = 864 µg m(-3)) and four- to six-ring PAC (GM = 0.13 µg m(-3)) were detected in the majority of air samples. Although task was not a predictor of airborne exposures, job site characteristics such as HMA application temperature were found to significantly (P ≤ 0.001) affect summary and individual PAC exposures. Based on the results of multivariate linear mixed-effects models, substituting biodiesel for diesel oil as a cleaning agent was associated with significant (P ≤ 0.01) reductions in TOM, four- to six-ring PACs, and naphthalene and pyrene concentrations that ranged from 31 to 56%. Using multivariate linear mixed-effects models under standard conditions, reducing the application temperature of HMA from 149°C (300°F) to 127°C (260°F) could be expected to reduce airborne exposures by 42-82%, varying by analyte. CONCLUSIONS: Promising strategies for reducing airborne exposures to PACs among HMA paving workers include substituting biodiesel for diesel oil as a cleaning agent and decreasing the HMA application temperature.