Biological risks to food crops fertilized with Ecosan sludge

摘要

This paper presents the microbial effects of using Ecosan sludge in agriculture. Sludge from KwaZulu Natal in South Africa having a helminth ova content of around 30 HO/gTS, faecal coliforms of 106 CFU/gTS, faecal streptococi of 106 CFU/gTS and Salmonella spp. of 105 CFU/gTS were applied to soils to grow carrots and spinach at different rates. Results showed that helminth ova content in crops was always greater in leaves than in stems, with a content varying from 2 to 15 HO/gTS for spinach and sludge application rates of sludge of 0–37.5 ton/ha and from 2–8 HO/gTS in carrots crops for sludge application rates varying from 0 to35 ton/ha. Health risks resulting from crop consumption were calculated using the b-poisson and the single-hit exponential models for Salmonella and helminths eggs, respectively. For Salmonella, no risks were found when consuming carrots for all the sludge rates studied while for spinach, risks were high but results were not deemed conclusive due to the technical methods used to measure bacteria. Concerning helminths, it was found that the morbidity rate will increase by 9% for the higher sludge application rates. To increase regional risks by 1% the egg content in crops needs to be less than 0.2 HO/gTS.