Ongoing health research on soybean white mold

White mold (Sclerotinia sclerotiorum) is a pathogenic soybean fungus that can dramatically reduce yield. At the University of Iowa's Institute for Rural and Environmental Health, investigation is underway to determine the potential health effects of breathing dusts generated while combining soybeans. Dusts generated on the farm are different from many other kinds of dusts in that they contain a variety of microorganisms, plant and insect allergens, and in some cases, chemical residues. Breathing these "organic dusts" provides an avenue for microorganisms and their products to enter the lungs where they can cause disease. Because white mold has emerged in Iowa within the past 6 years, its presence in organic dusts may represent a new health hazard to Iowa's farmers.

With funding from the Iowa Center for Health Effects of Environmental Contamination, exposure levels to white mold and other agents were measured during the 1997 soybean harvest. Air samples were collected on 10 farms in northwestern Iowa in Clay County and on 8 farms in northeastern Iowa in Floyd and Mitchell counties. White mold was identified on 8 of the 18 farms studied (44 percent), with the major incidence being in northeastern Iowa. Dust levels during combining were recorded both inside and just outside of the combine cab. The average dust level outside the combine cab was 5.7 milligrams per cubic meter of air (mg/m3) whereas the average inside dust level was 0.67 mg/m3. Although the dust levels inside the combine cabs were lower than outside the cabs, the average particle size of the dust inside the cabs was smaller and therefore better able to penetrate deeper into the lungs.

Dust samples from the air also were tested for their microbiological content. Results showed that the air both inside and outside of the combine cab was relatively high in bacteria and fungi and their components, endotoxin and glucans, when compared with air at other operations such as hog confinements or composting facilities.

White mold sclerotia in a soybean stem.

In addition to assessment of exposures, University of Iowa researchers are performing toxicology studies in laboratory mice to determine the pulmonary effects of white mold exposure. In these studies, white mold is grown in the laboratory from samples collected on an experimental Iowa State University farm in Humboldt County. The mold is ground and delivered at controlled concentrations into specially designed exposure chambers housing the mice. After the animals breathe the white mold-contaminated aerosol for a set time, their lungs are examined for early biological markers of disease. Preliminary results of this testing show that white mold effects the lungs differently than typical agricultural exposures to organic dust. Through these studies, researchers expect to learn more about the biological mechanisms of white mold lung toxicity.

Exposures to organic dusts on the farm, whether contaminated with white mold or not, can cause illness. It makes sense to minimize exposures when combining, cleaning out bins, and loading or unloading corn or soybeans. Use of closed cabs with clean air filters, automating farm tasks where possible, and use of properly fitted respirators can help reduce exposures and improve the health of Iowa farmers.

This article originally appeared on page 67 of the IC-480 (8) -- May 4, 1998 issue.

Updated 05/03/1998 - 1:00pm