Recent incidents involving the deaths of humans and cattle due to poisonous toxic fumes has highlighted the need to continue with strict protocols on how slurries are mixed and handled. Additional concerns are now emerging on the potential risks of mixing bedding products such as gypsum with slurries. Preliminary evidence suggests the mixing of gypsum with slurry may increase the amounts of poisonous toxic fumes generated during slurry mixing.
It is illegal to use waste gypsum as a bedding material for livestock. This includes its use in both slurry and dry bedding systems.
The agitation and mixing of manures and slurries in livestock sheds releases hydrogen sulphide (H2S) which is a toxic gas that affects the nervous system causing a range of symptoms including discomfort, disorientation, collapse or sudden death. Hydrogen sulphide will produce an odour but at concentrations above 140 parts per million, the human sense of smell becomes unable to detect the odour. Gypsum contains sulphur and mixing it with slurries may increase the total amount of hydrogen sulphide gas that is produced.
Waste gypsum has also been used in dry bed systems since it is perceived by many farmers to have animal health benefits. It had been assumed by farmers that there would be little if any risk to human and cattle health arising from the use of gypsum in a dry bed system. Due to the potential risks waste gypsum reprocessors decided that further examination was required.
SAC Consulting Environment and Design was contracted in September 2012 to conduct an air quality assessment on a farm where gypsum had been mixed in with straw to produce Farm Yard Manure (FYM). The purpose was to determine if detectable levels of hydrogen sulphide (H2S) gas could be found during the removal of the FYM from the building in which gypsum has been used in with straw in a dry bedding system. Results showed alarming levels being recorded.
The building consisted of an open sided roofed bedded court with a central feed passage. A gas analyser was used to take readings outside the building and then inside before any disturbing of the FYM. As soon as the FYM was disturbed hydrogen sulphide was detected at levels up to 2705 parts per million which is seen as very high when taken into context that The World Health Organisation indicates fatalities can occur when the count goes over 700 parts per million. Carbon Dioxide readings also increased.
Waste gypsum poses a risk to both humans and animals and is not approved for use as a bedding material for livestock.
Farmers can use waste gypsum that complies with SEPA’s April 2010 Gypsum Position Statement (which includes a requirement to meet the PAS 109:2008 specification) as a soil conditioner without having to register the end use with SEPA. But each farm has to be clear what this entails and ensure that the gypsum is not allowed to mix with organic wastes during storage or application.
Copies of SEPA position statements supporting the use of waste gypsum as a soil conditioner, and making clear its position on the use in animal bedding systems, are available on the SEPA website:
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