A task-based analysis of black carbon exposure in Iowa farmers during harvest

ABSTRACT

Diesel exhaust has been associated with adverse human health effects. Farmers are often exposed to diesel exhaust; however, their diesel exposure has not been well characterized. In this descriptive study, we measured black carbon concentrations as a proxy for diesel exhaust exposure in 16 farmers over 20 sampling days during harvest in southeast Iowa. Farmers wore a personal aethalometer which measured real-time black carbon levels throughout the working day, and their activities were recorded by a field researcher. Black carbon concentrations were characterized for each farmer, and by activity, vehicle fuel type, and microenvironment. Overall, 574 discrete tasks were monitored with a median task duration of 5.5 min. Of these tasks, 39% involved the presence of a diesel vehicle. Farmers’ daily black carbon geometric mean exposures ranged from 0.1–2.3 µg/m³, with a median daily geometric mean of 0.3 µg/m³. The highest black carbon concentrations were measured on farmers who used or worked near diesel vehicles (geometric mean ranged from 0.5 µg/m³ while harvesting to 4.9 µg/m³ during animal work). Higher geometric means were found for near vs. far proximity to diesel-fueled vehicles and equipment (2.9 vs. 0.3 µg/m³). Indoor, bystander proximity to diesel-operated vehicles resulted in the highest geometric mean black carbon concentrations (18 µg/m³). Use of vehicles with open cabs had higher mean black carbon concentrations than closed cabs (2.1–3.2 vs. 0.4–0.9 µg/m³). In summary, our study provided evidence that farmers were frequently exposed to black carbon associated with diesel-related activities at levels above urban ambient concentrations in their daily work during harvest.

KEYWORDS:

• Aethalometer
• black carbon
• diesel exhaust
• exposure
• farmers
• harvest

Acknowledgments

We gratefully acknowledge Amy Miller, Pabitra Josse, Kate Torres, Emily Tristani, Linda Gowen, Himanshi Singh, Marsha Dunn and other staff at Westat, Inc. (Rockville, MD) for study coordination and data management. We thank Charles Lynch, Debra Lande, Debra Podaril, and Jennifer Hamilton from the field research team in Iowa for their efforts on this study. The ongoing participation of the Agricultural Health Study participants is indispensable and sincerely appreciated.

Additional information

Funding

This work was supported by the Intramural Research Program of the National Cancer Institute of the National Institutes of Health, and by NIH P30 ES005605.