This work aimed to determine whether composting reduced concentrations of plant toxins (grayanotoxins) present in rhododendron leaves. Bags of shredded R. ponticum leaves and twigs were buried in a commercial compost windrow during a 12-week composting process. Samples of R. ponticum tissue were tested for toxic grayanotoxins prior to the composting process. Further samples were removed eight times during the process and were analysed for grayanotoxins. Grayanotoxins-I and III were present in the R. ponticum material prior to composting, but were found to degrade during the composting process and were not detected in samples removed for testing 11 weeks after the start of composting. Similar degradation was not recorded in R. ponticum material stored outside at ambient temperatures. Degradation of the grayanotoxins present in rhododendron is likely to occur during composting, and the amount of rhododendron material present in typical green waste compost windrows is likely to be low. For these reasons, there is no need to exclude rhododendron from feedstock accepted on to UK PAS 100 accredited composting sites. The risk to livestock from grayanotoxin poisoning through grazing grassland treated with PAS 100 green waste composts is likely to be negligible.
- Grazing grassland
- Windrow composting