Study links household exposure to endotoxin with recurrent wheeze

A portrait of Peter Thorne of the Department of Occupational and Environmental Health at the University of Iowa College of Public Health.
Peter Thorne

Researchers at the University of Iowa recently reported the results of the largest study to date on the relationship between exposure to endotoxin and incidences of wheeze and asthma in children and adults. The study was a collaboration with researchers at the National Institute of Environmental Health Sciences and the National Center for Health Statistics.

Endotoxins are immune-modulating molecules found in the outer membrane of common bacteria that elicit inflammation in the airways of animals and humans.

According to research team leader Peter Thorne, professor and head of occupational and environmental health at the University of Iowa College of Public Health, the study showed that higher levels of endotoxin in dust samples were positively associated with an increased prevalence of active wheezing requiring medication and health care utilization.

“Everyone is exposed to some endotoxin,” Thorne says, “however, in this nationwide representative sample we showed that higher exposure would be expected to produce more severe wheezing in people both with and without allergy, producing more medication use and requiring more medical care.”

It was noteworthy that the relationship between endotoxin and wheezing did not exhibit a threshold, but showed a positive association over the entire range of values measured.

Thorne’s group tested endotoxin in bed and bedroom floor dust samples from almost 7,000 U.S. households using a novel approach that included unprecedented quality control measures. The participants were enrolled in the National Health and Nutritional Examination Survey (NHANES).

According to Thorne, endotoxin was found at higher concentrations in lower-income households and in households with carpet, children, pets, vermin, and smokers.

“The study shows the importance of improving the U.S. housing stock and educating people about the importance of controlling vermin, keeping a clean home. and eliminating indoor smoking.”

Results of the study were published in the December 2015 edition of the American Journal of Respiratory and Critical Care Medicine with an accompanying editorial. The full article is available here:

Researchers study air quality, heaters in livestock buildings

A current research project based in the Great Plains Center for Agricultural Health (GPCAH) is investigating methods to improve air quality in swine farrowing buildings1. The research team developed models to estimate room concentrations of multiple indoor contaminants [ammonia, dust, hydrogen sulfide, carbon monoxide, and carbon dioxide (CO2)] and conducted field monitoring to evaluate the effectiveness of using ventilation and engineering controls.

In both modeling and field work, the researchers found that CO2 concentrations exceeded recommended workplace limits for swine workers2 (1540 ppm) over the entire winter season and also exceeded one-half the Occupational Safety and Health Administration (OSHA) permissible exposure limit (PEL=5000 ppm), which is based on exposure to a single contaminant (unlike what exists in swine buildings). Sources of CO2 in livestock production include both animal respiration (exhaled breath) and combustion products from heaters.

Since controlling animal breathing is infeasible, the team evaluated whether the unvented heaters commonly used throughout the Midwest (e.g., LB White heaters) were a significant contributor to high CO2 levels measured in livestock buildings. In fall 2014, researchers installed new gas-fired heaters, the Effinity93 (60K BTU, approximately $500 more than equivalent LB White unit), in a test barn. The team measured concentrations throughout the following winter, comparing them to that of the previous winter with traditional unvented heaters.

To protect the unit from dust, fresh air intake to the combustion device was from outside the farrowing building, and combustion gases were exhausted from the unit to outside the building. The investigators identified that CO2 was reduced by 800 ppm with the new heaters.

Another 200 ppm difference in CO2 between seasons was attributed to colder outdoor temperature and larger in-room animal population in the winter with the older unvented heaters. Other vented gas-fired heaters are available, and the researchers recommend substituting unvented heaters with vented units that have stainless steel internal components, which should improve the lifespan of the heater when used in livestock environments containing ammonia.

1. See for more details on this larger project.
2. Donham K, Haglind P, Peterson Y, et al. (1989) Environmental and health studies of farm workers in Swedish swine confinement buildings. Brit. J. Industr. Med. 46:31–37.

This story originally appeared in the September 2015 issue of Farm Families Alive & Well

UI researchers study public health impact of Iowa City landfill fire

An aerial view of the 2012 Iowa City landfill fire, with smoke primarily from the burning shredded tire drainage layer.
An aerial view of the 2012 Iowa City landfill fire, with smoke primarily from the burning shredded tire drainage layer.

On May 26, 2012, a fire broke out at Iowa City’s municipal landfill. While more than 8,000 landfill fires occur annually in the United States, the Iowa City fire was unusual in that the ignition involved the landfill’s lining system, a three-foot layer of shredded tires designed to protect underlying soil and water.

Over the next 18 days, while fire fighters and contractors worked to extinguish the blaze, a column of black smoke was visible for miles as an estimated 1.3 million tires burned.

Researchers at the University of Iowa, including associate professor of occupational and environmental health Tom Peters, an expert in inhalation exposures, joined the Johnson County Department of Public Health and state agencies in responding to the crisis.

UI researchers monitored emissions from the fire at two stationary sites located 6.5 miles east and 2.5 miles northeast of the landfill. A mobile sampling trailer was also moved as needed to capture the tire fire smoke. The investigators created models of how pollutants were likely to disperse and affect local air quality, and made measurements available to the incident command group so they could advise the public on necessary safety precautions.

A portrait of Thomas Peters of the Department of Occupational and Environmental Health at the University of Iowa College of Public Health.
Tom Peters

“Tire fires are relatively rare, and there is not a consensus as to what compounds should be monitored for the best public health response,” says Peters.

The UI team took the opportunity to determine potential improvements to the air quality response in terms of how to monitor such fires. They developed a unique tire fire irritant air quality index to interpret the measured pollutants and rank them by acute and cancer hazard ratios. These measures help responders determine when they should take precautions such as closing schools and canceling outdoor events.

Fortunately, the impact of the 2012 fire was episodic, and much of the smoke plume was dispersed by winds. However, all locations within one mile of the fire experienced at least one hour of unhealthy air during the 18-day period. Unhealthy conditions extended up to 11 miles downwind for short periods of time. While several toxic substances had been measured in laboratory simulations of tire fires, the UI results determined their strength under real-world burn conditions.

One UI recommendation from the tire fire is to shift focus away from the most-commonly recognized tire fire emissions, which include metals and the toxic gas benzene. Instead, overall levels of smoke particles, the gas sulfur dioxide, and the chemical components of the smoke particles may be more important in terms of health effects.

The UI team concluded that the landfill fire constituted a serious public health concern. They offered recommendations for future emergency air quality responses, including better preparation, monitoring, modeling, and interpretation of results. The team’s findings were published in the journal Atmospheric Environment.