The steroid growth hormones given to cattle on factory farm operations have long been of interest to environmental scientists. Because these drugs pose the most serious risk to aquatic life, past studies have focused mainly on their transport to bodies of water via surface runoff. However, a recent study confirms the viability of a vector no one had ever considered before – dust.

Researcher Brett Blackwell setting up monitoring equipment.
Credit: Jerod Foster
Cattle given drugs such as steroids do not break them down completely. The compounds are excreted in their manure, which can then dry and be pulverized into airbourne dust.

Researcher Philip N. Smith, an ecotoxicologist at Texas Tech, first considered the possibility when he was out duck hunting downwing from a cattle feed yard. The dust in the air was so thick that it coated his teeth, and he began to wonder what was in it.  He and colleages at the Environmental Protection Agency set up sampling equiptment at five feed yards in Texas and Oklahoma, which remained collecting samples and taking measurements for two years. 

After analysis was complete, they determined that the most abundant hormone was the estrogen 17α-estradiol, which appeared on 94% of filters with a mean concentration of 21-ng/g particulate matter.

The biggest risk posed by such airbourne contaminants is to aquatic life. The particles were large enough that people are unlikely to inhale them, as they would not travel very far. Only those people working on feedlots or living very nearby would be exposed to appreciable quantities, but the health impacts of such exposures are not well-understood.

The largest feed yard in the study was found to emit 63 mg of 17α-estradiol per day in dust alone. This amount is comparable to what might be transported each day in runoff, making dust a significant source of potential environmental harm.

By: Aisling Williams


Lockwood, Deirdre. “Cattle Feed Yard Dust Can Transport Steroids Into Environment.” Chemical & Engineering News: (2015) n. pag. 7 July. Web. 25 July 2015.