For public health, the hazard is mostly associated with microorganisms related to waterborne diseases, usually represented by indicators of fecal contamination.In the case of irrigation for agricultural purposes, chemical constituents such as compounds of emerging concern can be absorbed by crops in the irrigation process, with this absorption being greater in foliage and roots than in fruits.However, despite still being studied, it is suggested that most contaminants of emerging concern, as well as heavy metals, may not present major health risk concerns.Furthermore, according to ISO 16075-1:2020, to date, there is a lack of evidence of adverse effects of contaminants of emerging concern on human health or the environment from RW irrigation or consumption of irrigated crops with RW.Thus, the hazards inherent to the RW to be made available for irrigation are mainly related to the microbiological content, especially pathogens.The exposure routes considered are ingestion, inhalation, or dermal adsorption, are assumed with direct or indirect contact, to different receptors, such as humans, animals , landscape vegetation or crops.The receptors and their respective susceptibilities to hazard are always different in each water reuse project in the irrigation of different types of crops.The scenarios should portray, in the greatest possible detail, the potential situations of exposure of receptors to RW.For this reason, it is the most critical stage, which involves subjectivity and uncertainties.The risk characterization consists of quantifying and prioritizing the risk for human health resulting directly from the factors associated with the hazard, exposure routes, applicable scenarios, and the applied multiple barriers.The World Health Organization suggests several risk assessment approaches that can respond to different management needs.These are qualitative and semi-quantitative models or quantitative mathematical methods, in addition to sanitary inspection, which involves a simple and effective approach for small systems.All approaches,nft hydroponic in different ways, estimate the possible risks associated with the practice of reuse, to reduce them to a minimum level considered acceptable.

Quantitative assessment, known by the acronym QMRA combines scientific knowledge about the presence and nature of pathogens, their potential fate and transport in the water cycle and exposure scenarios referring to the receptor and their health effects that result from such exposure.Qualitative or semi-quantitative assessment is based on the approach of the risk matrix that allows assessing different risks associated with water quality, involving an appraisal of the likelihood of occurrence of exposure to a given hazard and its severity or consequence, if it happens.Among the different risk assessment methodologies, those that use quantitative mathematical models, similar to QMRA, are complex and have a high uncertainty as they require extensive local data that are not always available for non-potable uses.Besides that, the data limitation ends up requiring many assumptions during the process, absorbing great uncertainties for the result.The quantitative model, due to the characteristics already described, and not because it is difficult to apply in reclaimed water scenarios, has great applicability for risk assessment in potable reuse.In the context of reuse, the quantitative method should only be used for potability purposes.On the other hand, the QMRA can be used to assess risk at a specific point in the reuse system, such as the delivery point between the RW production system and the farmer but does not allow the quantification of the risk beyond that.For non-potable uses, it was developed a Semiquantitative model, based on the qualitative methodology presented by the ISO 20426:2018 in order to deal with the limitations of quantitative microbiological risk assessment.This, along with parts 1 and 2 of the 16075 serie of standards form the basis of the Portuguese legislation and the European Union Regulation.The Semiquantitative Microbiological Risk Assessment comprises the use of an empirical qualitative judgmental approach to assess the relative importance of hazards, exposure routes and contact scenarios, and multi-barriers in place.For this, instead of dealing with complex input data such as those required for the application of QMRA, in the semi-quantitative methodology, the input data can be the possible quality standards that indirectly represent the eventually tolerable doses.

According to this, the regulations that legally enable the practice of water reuse should be taken into account, not only the water quality standards, but also a risk management plan, specifically associated with the project in question, according to a fit-for-purpose approach.This is the purpose indicated by ISO 16075-1:2020, i.e., the use of RW with a quality suitable for the purpose for which it is intended without jeopardizing public health or the environment.In this approach, is possible to combine physical, chemical, or biological barriers to minimize contact between hazards and receptors, and consequently minimize risk.To control microbiological risk, the concept of accredited barrier can also be used, which is a measure that produces a result equivalent to a certain microbiological reduction measured in logarithmic scale.The receptors involved must be identified according to the main characteristics of the analyzed project, such as the irrigation method and systems, culture typology, area location, neighborhood, among others.Potential receptors are those that are susceptible to exposure, especially humans, animals, and vegetation.In the present study, only human receptors were adopted.The human beings can be separated by age group, by function in the production chain, and by adherence to the project.In the case of age group, children, adolescents and the elderly are usually more vulnerable than adults.Regarding the role in the production chain, farmers and system operators are more vulnerable than merchant, because the first group is closer to the irrigation event and, consequently, to the RW.Merchants, a group of intermediaries between collection and distribution, must be adopted according to the specificities of each project.In relation to adherence to the project, consumers and neighbors have different degrees of susceptibility, related to the distance of the irrigation systems and the type of consumption of the crop by consumers.

For instance, ingestion can occur directly, and can be intentional, accidental, by lack of information about the non-potability of water, inadvertently due to the ingestion of micro-droplets during sprinkler irrigation, hand to mouth, among others.Inhalation by human beings occurs directly by inhalation of the RW, for example, in cases of sprinkler irrigation; and indirectly, through domestic animals that carry the droplets to these environments.Adsorption, on the other hand, occurs through contact with wet or damp surfaces,either directly or indirectly.The highest risk exposure routes about RW are ingestion and inhalation, especially in situations where aerosols are produced, as in the case of sprinkler irrigation.Regarding dermal adsorption, less evidence of infection is known, although a few cases have been identified in some studies, in Southeast Asia, of dermatitis, urticaria, and fungal infections of the fingers or nails in workers of untreated or just partially treated wastewater systems.For each exposure scenario, it is important to take into account the specific characteristics of the location and regional habits, as well as the operational criteria for applying the RW.For each type of receptor, the value assigned should vary depending on the understanding of greater or lesser exposure in each situation and the evidence described in the literature, related to the infection associated with the scenarios.This step may involve a certain degree of uncertainty due to the absence of data demonstrating infections related to non-potable use.Important factors , related to the probability of infection, are attributed to the different receptors, for each established scenario, with values ranging from 1 to 9, due to an empirical qualitative approach to judgment.The use of this scale allows dealing with the complexity of the problem through its decomposition into clear and scalable factors, facilitating the establishment of comparative relationships for the construction of hierarchies and the definition of priorities.To reduce uncertainties, the analysis should always consider the worst-case perspective; scenarios that present exposure routes with high importance of infection should initially be considered with the highest fi.For the attributions of fi, justifications that are consistent and adequate for each situation must be pointed out.This justification, based on constructed hierarchies and defined priorities, provides the minimization of uncertainties, besides intensifying the risk assessment,nft system ensuring a higher confidence on the process.Table 2 shows the fi related to exposure scenarios and exposure routes.

In the first case, for intermediate levels between two judgments, values of 2, 4, 6, or 8 can be assigned according to the need.In the second, the following variations are allowed: for the route of ingestion, the value 9 is always assigned; for inhalation, 5 or 9; and for dermal adsorption, the value 3.Vulnerability estimation is performed for each receptor by applying the equations presented in Table 3.Equation 1 characterizes a sum of the individual relationships between the exposure route and the number of scenarios for each situation.In Equation 2 the sum of the product of the fi of the exposure route with the fi of the exposure scenario is performed.In Equation 3, there is the calculation of the normalization factor, where the maximum importance factor is equal to 9 since it is considered the highest importance value.The use of normalization factors in hierarchical analytical method allows the reduction and adequacy of the work scale.Through Equation 4, the vulnerability of each receptor is estimated.To minimize the contact of receptors with RW, through exposure routes of ingestion, inhalation and dermal adsorption, the concept of physical or chemical barriers is introduced.In this way, a barrier can be defined as the means of reducing and preventing risks associated with health and the environment, avoiding contact with RW and/or improving its quality.Thus, water quality is not the only parameter to guarantee health protection in reuse projects.Other options, such as irrigation type and schedule, crop characteristics or harvesting options may limit contact between receptors and pathogenic organisms present in RW.Some barriers, called accredited barriers, play a role of equivalence to the pathogenicity of RW, even if it still presents values higher than the maximum acceptable for the standard indicator of fecal contamination for the end-use.When considering these options, lower quality RW can be used for different purposes in the context of multiple barriers.In this case, the risk is minimized, as the probability of failure of multiple barriers is lower than the probability of failure of a single barrier.The basic principle of multiple barriers is that the failure of one barrier can be compensated for by the effective operation of the remaining barriers in place, to make the project more reliable.Table 4 shows the types of accredited barriers, their corresponding reductions in logarithmic units of pathogens and the associated number of accredited barriers.At this point, the damage severity versus the failure probability of each barrier associated with the project, defined in Step 1, is analyzed.The generalized application model for this type of analysis, called a prioritization matrix, whose cells, grouped in a certain number of classes, represent values, relating the probability of the occurrence of the events with the consequence of the respective impacts.Similarly, the damage matrix was adapted and presented in Fig.2, from the ISO 20462:2018.Damage estimation is performed by applying the equations presented in Table 5.Firstly, the sum of partial damages , referring to each barrier associated with the project, must be performed.Subsequently, we proceed with the calculation of the normalization factor.And, finally, the damage is calculated from the two previous ones.The Hazard was previously established in Table 1 , the Damage was calculated using Equation 5 , and the Vulnerability of each receptor using Equation 4.The Global Risk presents values that vary between a value above zero to nine, depending on the characteristics involved in each project.Prioritization is achieved by converting the RGlobal into a three-level qualitative scale, as shown in Table 7 and adopted by other authors.In case of an unacceptable Global Risk, it is necessary to repeat the entire process, to reassess the stages, with new actions such as changing the level of the hazard and/or application of new barriers to achieving an acceptable or despicable risk.If is not possible to obtain a minimal acceptable level, the project implementation is considered unfeasible.Once the appropriate risk level for a specific project is reached, the previously established hazard used in the risk characterization can be validated as the quality standard be applied to the RW.The SqMRA was applied to rice farming, considering that rice production occupies 25% of the total irrigated area in Brazil and demands 40% of the entire volume of water abstracted in the national territory.It is also noteworthy that other low and middle-income countries such as China, India, Indonesia, and the Philippines are also major rice producers, contributing to the consumption of water for irrigation worldwide.