Hoppin JA, Umbach DM, London SJ, Alavanja MCR & Sandler DP. 2004. Diesel Exhaust, Solvents, and Other Occupational Exposures as Risk Factors for Wheeze among Farmers. American Journal of Respiratory and Critical Care Medicine 169:1308-1313.

With this study, Hoppin et al. add to the growing body of evidence that exposure to diesel fumes and solvents have adverse effects on lungs. They report that farming activities that entail exposure to diesel fumes and solvents are associated with higher risks of wheezing. Wheezing is a common respiratory symptom of asthma, a disease that is becoming increasingly widespread in the general population.

What did they do?

Hoppin et al. used data from the Agricultural Health Study, a large survey of farmers in North Carolina and Iowa. In the survey, 20,898 farmers completed a series of questionnaires regarding farming practices and history of respiratory disease. Detailed information was gathered regarding the type and frequency of farm activities performed, type of tractor used, maintenance tasks and types of solvents used. The outcome, a history of wheezing in the past year, was determined by asking whether the farmers had experienced an episode of wheezing or “whistling in the chest” in the previous 12 months. Information was also obtained about smoking practices and history of asthma and/or atopy and these potentially confounding variables were controlled for in the statistical analyses of the data.

What did they find?

Nineteen percent of the farmers surveyed (3,922) by the Agriculture Health Study reported at least one episode of wheeze in the prior year. Of them, 16% had over 12 wheezing episodes (figure to left).

Five percent of the farmers reported a history of asthma.

A significant increased risk of wheezing was associated with a series of farming activities, for example: driving diesel tractors, driving trucks, painting and using solvents for cleaning and repairing brakes and pesticide equipment.

 

Farm Activity

Odds ratios
 for Wheeze

Drive diesel tractor

1.31

(1.13-1.52)

Drive gas tractor

1.11

(1.02-1.21)

Drive truck

1.20

(1.10-1.31)

Use gasoline as cleaning agent

1.33

(1.23-1.43)

Replace asbestos brakes

1.22

(1.10-1.34)

Repair pesticide equipment

1.25

(1.15-1.35)

Paint

1.20

(1.11-1.29)

Hand pick crops

1.24

(1.13-1.35
Chemical fertilizer
1.04
(0.94-1.14)
Natural fertilizer
1.15
(1.06-1.25)

95%confidence limits for odds ratios in parentheses;
Statistically signicant ORs in red

  

Hoppin et al. also examined the health records of asthmatics separately, comparing them to non-asthmatics for the various activities. With gasoline tractors and using gasoline as a solvent, asthma sufferers were more likely to wheeze than non-asthmatics. But for diesel tractor use, asthma history didn't matter: the likelihood of wheezing was the same for people with or without asthma.

To search for indications of a dose-response relationship, Hoppin et al. also looked at whether farmers who engaged in these activities more often was had higher risks of wheezing. They found that some activities showed significant trends. For example, as the frequency of driving a diesel tractor increased from monthly to daily, the odds ratio for wheezing grew from 1.23 to 1.38. Similarly, farmers were more likely to wheeze the more often they engaged in painting, used solvents or gasoline to clean, or used natural fertilizer. This trend was not seen for gasoline tractor driving.

What does it mean?

Data from the Agricultural Health Study have provided a unique opportunity to evaluate the occupational factors associated with respiratory illness in farmers. The one large sample size and detailed information on a variety of exposures allowed the research team to pose very specific questions about farming tasks and their links to adverse effects.

The results indicate that exposure to diesel exhaust and solvents on a continual basis increases the risk of wheezing: more exposure leads to higher risk. And while the study focused on farmers, the exposures are of types that many people encounter daily outside the farm environment, from truck fumes and other sources.