Application of Helminth ova infection dose curve to estimate the risks associated with biosolid application on soil.

Helminth ova (HO) are the main biological concern when reusing sludge for agricultural production. Worldwide sludge regulations consider a permissible range of 0.25-1 HO/gTS. Such limits are unaffordable to most developing countries, due to high helminth ova content in sludge, and the lack of viable technology to inactivate them as needed. The quantitative microbial risk assessment (QMRA) is a useful tool to estimate the risk of treated sludge, considering feasible and viable limits. QMRA, however, has not been applied before for HO because no dose-infection curve was available. Therefore, the objectives of this paper are: to build up a risk-based model designed for untreated wastewater exposure (i.e., land irrigation) using Ascaris lumbricoides eggs as indicators for HO, and apply the results to assess health risk (i.e., Ascaris lumbricoides infection) associated with consumption of crops grown on biosolid-enriched soil. Data showed that it may be feasible to update HO threshold in biosolids from developing countries without significantly increasing risks. To reduce health risk from HO, it may be wiser to achieve feasible and evidence-based standards, than to set unaffordable limits in these countries. QMRA data suggested additional protection measures, such as biosolid application rates, crop restriction, and produce better washing practices.