Hydrogen Sulfide Concentrations in Mushroom Farm Operations

1669 

Student Poster 

T Washington¹, L Cena²

¹West Chester University, West Chester, PA, ²West Chester University of PA, West Chester, PA

Tristan Washington  
West Chester University

Lorenzo Cena  
West Chester University of PA

Chester County, Pennsylvania is home to the largest region of mushroom farming in the United States which is credited with producing more than half of all fresh mushrooms in the US annually. Mushrooms are grown on a substrate made of fermented ingredients including animal manure. The bacterial decomposition of the growth substrate releases hydrogen sulfide (H2S), a toxic gas that can be lethal at concentrations above 100 ppm. The environmental sampling conducted by our research group found elevated and irregular H2S concentrations occurring on residential properties located near mushroom production facilities. In several instances, these readings were found in exceedance of Pennsylvania's ambient air quality standards. Concentrations are elevated enough to cause recognizable health symptoms in exposed groups and corrosion of outdoor metals and electrical equipment. The elevated exposure levels are a concern for the workers and the general public.

Chester County Pennsylvania is home to the largest region of mushroom farming in the United States which is credited with producing more than half of all fresh mushrooms in the US annually. The 2022-2023 growing season reached a market share of $1.0 billion (Gorgo-Simcox, 2024). A nutrient rich substrate is required for mushrooms to grow. Chester County mushroom farming operations produce the substrate that is needed for large scale farming in mushroom houses (Ab Rhaman et al., 2021; CoAS, 2008). With little regulatory requirements for mushroom production facilities in land development, the growth of this industry in Chester County is uniquely surrounded by residential regions with distances between substrate production facilities, composting piles, and homes being as little as 100 feet away. Mushroom growth substrate production starts with composting ingredients such as straw, horse and chicken manure, gypsum (calcium sulfate), and ground corn cobs (Beyer, 2023). For decades, residents living near these facilities have lodged complaints and concerns about their health, safety, noxious odors, respiratory irritation, and reported enhanced metal corrosion rates of metal equipment on their properties. Little research exists on evaluating the sources of these persistent issues. Hydrogen sulfide (H2S) is a known byproducts of composting processes and a recognized toxic gas (CoAS 2008; ATSDR, 2016). Velusami et al., (2013) identified that concentrations of H2S released after disturbing composting piles and spent substrate used for mushroom farming depend on moisture content, temperature, airflow and other environmental parameters. Further, they show that concentrations have the potential to exceed 2000 ppm, which would cause instantaneous death if inhaled (OSHA, 2024). Occupational regulations and ambient air quality standards have conflicting exposure tolerances due to the variability in health status of the general public compared to a healthy worker. The Pennsylvania Department of Environmental Protection (DEP) establishes a limit for H2S of 0.1 ppm averaged over an hour (DEP, 2024), while the OSHA PEL is 20 ppm. Our previous pilot research revealed that H2S concentrations in residential areas near the farms exceed the PA DEP regulations and are close to the OSHA PEL. This study is a larger investigation to evaluate the degradation of ambient air quality and plausibility of exposure to toxic gases for mushroom farm workers and the local residents.

Seven area monitors (G7-EXO, Blackline Safety, Calgary Canada) were strategically placed within 100-600 feet of suspected point sources associated with mushroom farming operations and substrate production facilities. Samplers were placed from April 2025 through April 2026 to record concentrations of hydrogen sulfide (H2S) in the ambient environment. The devices were calibrated
within manufacturer specifications of 180 days. The samplers continuously logged environmental concentrations of the gas within the limits of detection, 0.5 ppm – 500.0 ppm. Data was recorded in 10 second intervals. Gas concentrations were analyzed to obtain descriptive statistics and time weighted averages and compared to federal and state regulations including OSHA and DEP ambient air quality standards.

H2S concentrations, followed elevated and irregular patterns of concentration during the sampling period. Concentrations of H2S reached its highest peak of 37 ppm during the sampling period and were
often in exceedance of the DEP's ambient air quality standard of 0.1 ppm averaged over the course of an hour. Concentrations exceeded the Occupational Safety and Health Administration permissible exposure limit of 20 ppm. Further analysis identified that elevated concentrations of H2S were predominantly found between the hours of midnight and 8:00 AM. Outdoor air concentrations are susceptible of changes in temperature, pressure, wind direction, and other atmospheric conditions. Limitations of this study prevented us from sampling closer than 100 ft from the sources; however, based on our findings, workers on the mushroom farms are suspected to be exposed to concentrations above those measured by our samplers. The workers' proximity to the fermenting compost and drainage lagoons puts them at higher risk for exposure. Concerns are especially geared towards the predominantly migrant workers on the farms who are less likely to report symptoms and lodge concerns with their supervisors or state and federal agencies.
The environmental sampling data demonstrates elevated and irregular H2S concentrations occurring near mushroom production facilities. In several instances, these readings were found in exceedance of Pennsylvania's ambient air quality standard and OSHA's PEL. Concentrations are elevated enough to cause recognizable symptoms in exposed groups. This research did not directly correlate the symptoms described by the residents with the exposure levels, but the symptoms are in line with the exposures and ultimately demonstrate the need for a health-focused study in the area. The growth of the mushroom industry and proximity of residents to point-sources of H2S will need further evaluation for future land development planning. Symptoms of H2S exposure have been studied primarily through animal exposure modeling and sub-chronic studies in humans. Our findings inform future research perspectives to consider the health impact for irregular H2S exposures over several years and decades. Additionally, it highlights the need to understand the process of making the growth substrate and mushroom fertilizer to determine specific sources of H2S so that they can be addressed directly.

Exposure Assessment

Chemical Hazards

Community Exposure