Modeling hydrogen sulfide emissions: are current swine animal feeding operation regulations effective at protecting against hydrogen sulfide exposure in Iowa?

Confined farm animals generate large amounts of excrement on-site. Many toxic substances emitted from Concentrated Animal Feeding Operations (CAFOs) emanate from that manure including hydrogen sulfide. There is growing concern that these pollutants, including hydrogen sulfide, may lead to adverse health effects among people living close to these operations. Iowa law mandates that separation distances be established from CAFOs to residences, public areas, and public buildings to protect human health. The primary objective of this study was to assess the adequacy of current separation distance requirements established in Iowa to protect for the Health Effects Standard (HES) and Health Effects Value (HEV) of hydrogen sulfide concentrations emanating from swine CAFOs in Iowa. Specifically, the research examined: 1) the characteristics of swine weight dense areas, 2) if current CAFO setback distance regulations in Iowa protect for the HES and HEV of hydrogen sulfide nearest the largest swine weight CAFO, and 3) if current CAFO setback distance regulations in Iowa protect for the HES and HEV of hydrogen sulfide for an area of Iowa which has the greatest swine weight density. The results suggest that the highest swine weight dense areas generally have a greater median and average swine weight per CAFO than is observed for all active swine CAFOs in Iowa. The high swine weight areas are also generally influenced greatly by a few very large swine CAFOs. Additionally, these areas tend to have a high CAFO density but are not located in the highest CAFO dense areas of Iowa. The HEV level of hydrogen sulfide is estimated to be exceeded in a total area of 423,568 m2 beyond the associated separated distance for the largest active swine CAFO alone in 2004. This indicates that the 914.4 m (3,000 ft) separation distance does not protect against the HEV of hydrogen sulfide for the largest swine CAFO in Iowa. The HES of hydrogen sulfide was not exceeded in this area. Additionally, the estimated concentrations of hydrogen sulfide in the highest swine weight dense area did not exceed the HES or HEV beyond the minimum separation distances.