Vegetarians and concerned carnivores alike have long protested the way livestock is raised at many large farms. But it’s taking some time for Americans to view this not only as an animal-mistreatment issue but one that directly affects human health. The Union of Concerned Scientists has taken the issue up, and is driving its point home by citing a recent event in which rural Minnesotans actually fled their homes as a result of animal crowding’s side-effects.

According to reporting by Minnesota Public Radio, the fumes from a northwestern Minnesota dairy operation, Excel Dairy, recently became so noxious that the state’s Health Department declared they “posed an immediate health threat.” At issue is hydrogen sulfide, which causes respiratory complaints even at very low levels but has allegedly been high enough lately that residents have seen “neighbors throw up in their driveways.”

The state’s initial monitoring device, set up by the Minnesota Pollution Control Agency after repeated citizen requests, showed no pollution – because it was placed upwind of the farm, which is licensed for about 1,500 head of cattle. Once a monitor was placed downwind, there were some days in which hydrogen-sulfide levels actually reached the maximum the device was capable of measuring, 90 parts-per-billion (or 90 ppb).

UCS points out this Occupational Health and Safety article which cites research finding that “symptoms such as headache, nausea, and eye and throat irritation were found in communities with ambient levels as low as 7 to 10 ppb.”

The dangerous gas, according to UCS, is being “generated by low-oxygen conditions in manure pits” that are a distinguishing feature of confined animal feeding operations, or CAFOs. CAFOs are the focus of an in-depth report by the organization (both a summary and the full report can be downloaded here), which argues that mass confinement is not, as many would assume, the inevitable result of market forces – but is “largely the result of misguided public policy that can and should be changed.”

Representatives from Excel Dairy and its owner, The Dairy Dozen, based in Veblen, S.D., have not publicly responded to the issue, except to plead not guilty to a misdemeanor nuisance charge. No one could be reached for comment at the Dairy Dozen for this story.