AimsTo determine the persistence of Clostridium difficile spores in biosolids during composting or when amended into soil and held under natural environmental climatic conditions. Methods and ResultsFivelogCFUg(-1)Cl.difficile spores (ribotypes 027 or 078) were inoculated into agricultural soils (sandy loam or loam) amended with 10% w/w anaerobically digested biosolids. The inoculated soil:biosolids mixture was then placed into sentinel vials which were introduced at a depth of 15cm within the field plot consisting of the corresponding soil type. Two trials were performed, the first of which started in late spring (May 2013 through to August 2014) and second from November 2013 through to October 2014 (fall trial). Ribotype 078 endospores in loam or sandy loam soil decreased during the summer but then increased in numbers towards the fall. At the end of the trial, levels of ribotype 078 spores had decreased by 1.5logCFUg(,)(-1) with 027 spores decreasing by <1logCFUg(-1) over the same time period. Windrow composting of biosolids decreased Cl.difficile levels from 3.7logCFUg(-1) down to 0.3logCFUg(-1) with the greater reduction occurring during the curing phase. In comparison, Cl.perfringens decreased from 6.3logCFUg(-1) down to 2.4logCFUg(-1) but mainly in the thermal phase of the composting process. ConclusionsComposting of biosolids is a more effective means of inactivating Cl.difficile compared to land application. Significance and Impact of the StudyWindrow composting represents an effective method to reduce the environmental burden of Cl.difficile associated with biosolids.