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.

No abstract

Helminth ovum (HO) is the main biological concern when reusing sludge for agricultural production. Worldwide sludge norms consider a maximum allowable value for this pathogen of 0.25-1 HO/gTS. Such a threshold may be unaffordable to most developing countries, due to: (a) a very high original content of a wide variety of helminth ovum in sludge, and (b) the lack of technology to inactivate up to 2-3 log. This paper presents the actual risk caused by the use in agricultural land of treated sludge at the US-EPA and WHO limits, as well as the achievable content in sludge treated with affordable technology in developing countries, by using a quantitative microbial risk assessment (QMRA). This research developed a dose response curve for the Ascaris lumbricoides infection (Beta-Poisson model), to estimate the risk due to the ingestion of carrots grown in biosolids-amended soil and eaten raw. Using @Risk, risk estimates were constructed. The results indicated that the daily risk of infection was between 9.0 x 10-5 and 5.0 x 10-2. The QMRA proved to be a useful tool to determine that the risk not only is not considerably higher but also can be managed in different ways, other than only by sludge treatment. The pollution of crops by helminths could be controlled by using different sludge application rates, limiting the kind of crops to be grown and introducing efficient produce washing methods.