A research project was conducted from May 2004 through mid-September 2005 to investigate the concentration of hydrogen sulfide (H2S) at the perimeter of nine swine operations across the state of Iowa, and, to investigate the ammonia (NH3) and H2S concentrations near and inside residences located in the community of swine operations and in one area of the state not associated with animal agriculture. The nine sources monitored ranged from sites that housed 1,200 to 4,800 finishing animals. The results indicated that at the perimeter of all nine sources monitored, the overall average H2S concentration ranged from a low of 1.9±2.7 ppb to a high of 26.3±32.3 ppb. If a sampler was determined to be in the downwind plume, or the meteorological conditions were calm, the average measured results ranged from a low of 7.4±6.9 ppb to a high of 45.8±31.8 ppb. In both cases, the maximum H2S concentration was recorded at a finishing site where an earthen basin and a concrete formed below-grade basin existed in close proximity to the livestock housing. As a frame of reference, the State of Iowa is currently considering a Health Effects Value (HEV) for H2S of 30 ppb at a residence located at or beyond the regulated separation distance, not to be exceeded more than seven 1-hour averages per year (the Health Effects Standard, HES).
Measurements of H2S and NH3 were also collected at five residences, four of which were located near four of the sites monitored for perimeter H2S levels, with one located in an urban setting far removed from animal agriculture. The results, based on the daily averages, indicate that the overall average NH3 concentration measured inside the homes ranged from a low of 28.6±12.8 ppb to a high of 94.7±28.1 ppb. The overall average NH3 concentration measured in the ambient air outside the homes ranged from a low of 11.7±5.3 ppb to a high of 55.1±20.6 ppb. The NH3 concentration inside the homes were significantly higher than in the ambient air outside of the homes (p<0.01). H2S concentration inside the homes ranged from a low of 0.7±0.2 ppb to a high of 2.5±1.5 ppb. H2S concentration in the ambient air outside the home ranged from a low of 0.4±0.2 ppb to a high of 2.4±2.4 ppb. The highest ambient air average for H2S (2.4±2.4 ppb) and NH3 (55.1±20.6 ppb) was recorded for a residence located 251 ft to the east of a 4,800-hd deep-pit finishing site and served as the home for the tenants of the farm. For the residence monitored in an urban setting far removed from animal agriculture, the overall average H2S concentration outside the home was 0.4±0.2 ppb with the inside home averaging 0.7±0.2 ppb. The highest average inside home concentration for NH3 and H2S was 94.7±28.1 ppb and 2.5±1.5 ppb, respectively, both from a residence where the occupants smoked and in which cats were kept inside. The next highest inside home NH3 concentration was 85.7±15.3 ppb. For this residence the occupants did not smoke but cats were kept inside. The two inside home NH3 levels specified above are close to the currently recommended Minimum Risk Level (MRL) for NH3, established by the Agency for Toxic Substances and Disease Registry (ATSDR), where a chronic MRL of 100 ppb for NH3 has been established. If the levels recorded for the two residences specified above would persist for 365 days or more, the ATSDR guidelines for the protection of sensitive populations would be very close to exceeding the ATSDR MRL for ammonia. The results from the residence ambient air monitoring indicate that the concentration and duration for either NH3 or H2S fall well below the MRLs as defined by the ATSDR. This was true even for the residence located 251 feet from the nearest swine source.