Hydrogen sulfide gas emissions during disturbance and removal of stored spent mushroom compost

 Spent mushroom compost (SMC) is a by-product of the mushroom industry that is used as an agricultural fertilizer. In Europe its storage and use are governed by the EU Nitrates Directive 91/676/EEC to protect waterways against pollution by nitrates. A health and safety risk was identified during the removal and spreading of stored SMC onto land whereby stored SMC released high levels of toxic H2S gas into the atmosphere when disturbed. Emissions of H2S were monitored at two outdoor and two indoor locations where stored SMC was being removed for spreading on land. A repeating peak-trough pattern of H2S emissions was detected at all sites with peaks corresponding to periods of active disturbance of SMC. The highest H2S concentrations (10 s average) detected at the SMC face were: 680 and 2083 ppm at outdoor Sites 1 and 2; and 687 and 89 ppm at indoor Sites 3 and 4, respectively. Higher concentrations of H2S were released from older SMC compared to younger material. Indoor-stored SMC had lower moisture content (53% to 65%) compared to outdoor-stored material (66% to 72%) while the temperature of indoor-stored SMC was higher (33 ºC to 51ºC) compared to outdoor-stored material (24ºC to 36ºC). The current Short Term Exposure Limit (STEL) of 10 ppm was exceeded at all sites except Site 4, which was smaller than the others, indicating a significant health and safety risk associated with working in the vicinity of stored SMC when it is being actively disturbed. Results suggest that SMC stored in small heaps (600 m3) under cover, emits less H2S during disturbance and removal compared to SMC stored in large heaps (>1500 m3) outdoors. This should be taken into consideration in the design, construction and management of SMC storage facilities. Health and safety protocols should be in place at SMC storage facilities to cover the risks of exposure to toxic H2S gas during disturbance of stored SMC.