Operator Exposure to Hydrogen Sulfide from Dairy Manure Storages Containing Gypsum Bedding

Abstract

Dairy manure storages containing gypsum-based bedding have been linked anecdotally with injury and death due to presumed dangerous levels of gases released. Recycled gypsum products are used as a cost-effective bedding alternative to improve animal welfare and provide agronomic benefits to manure recycled back to the land. Sulfur contained in gypsum (calcium sulfate) can contribute to hydrogen sulfide (H2S) gas formation under the anaerobic storage conditions typical of dairy manure slurry. Disturbance of stored manure during agitation releases a burst of volatile gases. On-farm monitoring was conducted to document conditions during manure storage agitation relative to gas concentration and operator safety. One objective was to document operator exposure to H2S levels; therefore, each operator wore a personal gas monitor while performing tasks associated with manure storage agitation. Data from three dairy bedding management categories on ten farms were compared: (1) traditional organic bedding, (2) gypsum bedding, and (3) gypsum bedding plus a manure additive thought to reduce H2S formation and/or release. Portable meters placed around the perimeter of dairy manure storages recorded H2S concentrations prior to and during 19 agitation events. Results show that farms using gypsum bedding produced higher H2S concentrations during manure storage agitation than farms using traditional bedding. In most cases, gypsum-containing manure storages produced H2S levels above recognized safe thresholds for both livestock and humans. Farm operators were most at risk during activities in close proximity to the manure storage during agitation, and conditions 10 m away from the storage were above the 20 ppm H2S threshold on some farms using gypsum bedding. Although H2S concentrations rose to dangerous levels, only two of 18 operators were exposed to >50 ppm H2S during the first 60 min of manure storage agitation. Operators who are aware of the risk of high H2S concentrations near gypsum-laden manure storages can reduce their exposure risk by working upwind and away from the H2S plume within a closed tractor cab.

Invited review: Compost-bedded pack barns for dairy cows

“…Inorganic materials have been shown to be unsuitable for use in CBP because they do not promote composting (Galama et al, 2011). Gypsum from wallboard produces hydrogen sulfide under anaerobic conditions and consequently can have health effects on operators during removal of the anaerobic layer during cleanout (Fabian-Wheeler et al, 2017). An active microbial aerobic compost layer can act as a biofilter throughout the year to oxidize the hydrogen sulfide gases diffusing from the anaerobic layer.…”

Development of a “Turn-on” Fluorescent Probe-Based Sensing System for Hydrogen Sulfide in Liquid and Gas Phase

“…These experiments revealed that the fluorescence response after 5 min of exposure to an atmosphere containing 11 ppm H 2 S is distinctly higher compared to a reference sample which was exposed to synthetic air for 30 min. 11 ppm H 2 S is a concentration that for instance workers involved in manure storage or handling on farms are frequently exposed to (Fabian-Wheeler et al, 2017). For the hydrogel film format used here, we determined that approximately 1 h is needed to achieve complete saturation of the system.…”

Markers for the Comparison of the Performances of Anoxic Biotrickling Filters in Biogas Desulphurisation: A Critical Review

“…At low concentrations (0.01-0.3 ppm v ) H 2 S produces foul smells and the effects of H 2 S on human health at different concentrations are summarized in Table 1. Thus, the maximum exposure concentration permitted in the industry is 10 ppm v , with peaks of 50 ppm v accepted for a duration of 10 min [4,5]. Table 1.…”