Water reuse is a feasible alternative for non-potable and potable needs, e.g., irrigation. Nonetheless, this option is associated with environmental and public health risks. Therefore, a microbiological health risk assessment was carried out regarding the application of agricultural reuse of water in the neighborhood of Wastewater Treatment Plants (WWTP). This study was carried out in cities in the central region of Brazil, using a semiquantitative methodology. Escherichia coli density in treated wastewater was used as an input, which was obtained from the city wastewater utility. The same exposure scenario was defined for two crops – sugarcane and pasture – at the surroundings of four WWTP under study. As receptors, the following were adopted: farmers; water reuse transport workers; the local community; and sugarcane industry workers. The estimated risks for all groups were considered acceptable. Furthermore, such risks should be reduced to despicable (despicable risk should be understood as low risk) if improvements in the wastewater treatment system and more efficient configurations of barriers are adopted. It can be concluded that risk assessment clarifies the options for system-management, allowing for better informed decision-making and encouraging public confidence in the safe application of water reuse.

  • The reclaimed water showed E. coli above the limits recommended by the WHO and the Brazilian guidelines.

  • Acceptable risk was obtained for agricultural reuse of sugarcane and pasture.

  • Farmers had the greatest health risk.

  • The risk becomes despicable by increasing the treatment of recycled water and adopting more barriers.

  • The most suitable for Brazil is to adopt standards based on a fit-for-purpose approach supported by risk assessment.

Graphical Abstract

Graphical Abstract
Graphical Abstract

Although Brazil has about 12%–16% of the total amount of water available in the world (Avins 2015), this availability is not evenly distributed across the territory (Lima et al. 2021). Urban centers in the central region of Brazil have pressure on water resources classified as high, in addition to extensive land use and land cover for agriculture (SEMAD 2020). Therefore, water reuse from treated wastewater comes as an alternative way to meet the demands for non-potable purposes in the region, such as irrigation.

However, due to the constituents present in wastewater after treatment, there is an associated risk for the health of workers, consumers, local population and the environment (Shoushtarian & Negahban-Azar 2020). To assess the hazard related to microbiological constituents when reusing water, fecal contamination indicators are used, such as bacteria of the coliform group (Rebelo et al. 2020; Zhiteneva et al. 2020).

Water reuse must be managed to minimize and eliminate the risks of exposure to the hazard (WHO 2006). Hazard is understood as chemical, biological or physical agents with the potential to cause damage (Vuppaladadiyam et al. 2019). The risk is obtained by the relationship between the hazard, the receptor vulnerability and the possible damage (Rebelo et al. 2020).

Risk assessment is developed to achieve acceptable levels of risk, with different approaches being possible depending on needs and data availability (WHO 2016). Risk assessment involves the likelihood that human exposure to one or more pathogens will result in an adverse health effect (Seto et al. 2018). In cases of non-potable water reuse, methodologies with a semiquantitative or qualitative approach are more suitable (Zhiteneva et al. 2020), such as the model developed by Rebelo et al. (2020), based on the recommendations of ISO 16075-1:2015. Therefore, the aim of this research is to carry out a semiquantitative microbiological health risk assessment regarding theoretical application of agricultural reuse.

Among the cities in the southwest of Goiás (Brazil) that have Wastewater Treatment Plants (WWTP) and for which the final quality data of treated wastewater were made available are (Figure 1): Aparecida do Rio Doce (18°18′08″S 51°09′15″W), Caçu (18°34′03″S 51°06′49″W), Lagoa Santa (19°11′12″S 51°23′27″W) and Quirinópolis (18°28′10″S 50°28′02″W). Land use around the WWTPs of the selected cities is mainly based on sugarcane for industry and irrigated pasture (SEMAD 2020). For the transport of reclaimed water, it was considered to be by tank truck and for the irrigation system, the sprinkler grid method.
Figure 1

Localization scheme for the cities under study.

Figure 1

Localization scheme for the cities under study.

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To check safety of agricultural reuse, the semi-quantitative microbiological health risk assessment methodology developed by Rebelo et al. (2020) was used, based on the recommendation of ISO 16075-1:2015. The methodology follows the steps: identification of hazards, identification of exposure routes and receptors, exposure scenarios and risk characterization, as well as risk management, as shown in the flowchart in Figure 2.
Figure 2

Methodological flowchart. Vrec = vulnerability of receptor; fiPath = factor exposure route; fiScen = factor exposure scenario; fnormal v = normalization factor of vulnerability; fimax = higher value of the importance scale (9); nScen = number of scenarios considered by exposure route; D = damage; di = partial damage (matrix for damage, view Rebelo et al. (2020)); ni = number of barriers; fnormal D = normalization factor of damage; Rrec = risk for each receptor; H = hazard.

Figure 2

Methodological flowchart. Vrec = vulnerability of receptor; fiPath = factor exposure route; fiScen = factor exposure scenario; fnormal v = normalization factor of vulnerability; fimax = higher value of the importance scale (9); nScen = number of scenarios considered by exposure route; D = damage; di = partial damage (matrix for damage, view Rebelo et al. (2020)); ni = number of barriers; fnormal D = normalization factor of damage; Rrec = risk for each receptor; H = hazard.

Close modal

For the hazard, the input data is the treated wastewater Escherichia coli density and the treatment level, given away by the Saneamento de Goias S/A – SANEAGO (water and wastewater utility). The utility performs punctual collection at the exit of the WWTP and bimonthly monitoring of the parameter. The analysis was performed according to the Standard Methods for the Examination of Water and Wastewater (SMEWW), method SMEWW 9223 B. The E. coli density data used to determine the hazard of each city represent the 2019 annual geometric mean, and the raw data is in the Supplementary Material.

The microbiological risk assessment methodology developed by Rebelo et al. (2020), predicts, in the first place, the use of E. coli as input, however, it allows for other parameters to be used, and it is enough to develop a new scale of relationship between the parameter concentrations or densities and the equivalent hazard importance factor, as well as is performed in the Table in Figure 2.

According to Rebelo et al. (2020), the risk is classified as despicable (0<risk<3), acceptable (3≤risk<7) or unacceptable (7≤risk<9). Despicable risk should be understood as low risk. If the risk is unacceptable, it is necessary to adopt mitigation measures, such as hazard reduction by adopting more advanced levels of treatment than the first ones, or damage reduction, with the use of a greater number of barriers or more efficient barriers.

Hazard identification

Data on the treatment system in the WWTP of each city and the treated wastewater E. coli density, in Colony Forming Units (CFU) per millilitre (mL), are presented in Table 1.

Table 1

Data for hazard identification (source: water and wastewater utility)

WWTP of the cityTreatment systemE. coli (CFU/100 mL)
Geometric meanStandard deviation
Aparecida do Rio Doce Anaerobic lagoon, facultative lagoon and maturation lagoon 3.1×104 3.8×104 
Caçu Facultative lagoon 2.5×106 1.1×106 
Lagoa Santa Facultative lagoon 2.2×105 2.6×105 
Quirinópolis UASB reactor, facultative lagoon 4.8×106 1.4×106 
WWTP of the cityTreatment systemE. coli (CFU/100 mL)
Geometric meanStandard deviation
Aparecida do Rio Doce Anaerobic lagoon, facultative lagoon and maturation lagoon 3.1×104 3.8×104 
Caçu Facultative lagoon 2.5×106 1.1×106 
Lagoa Santa Facultative lagoon 2.2×105 2.6×105 
Quirinópolis UASB reactor, facultative lagoon 4.8×106 1.4×106 

Raw data is in the supplementary material.

Based on the E. coli density data (Table 1) the hazard importance factor used was 9 (E. coli >104 CFU/100 mL, as shown in Figure 2).

Brazil does not have legislation on standards for water reuse, but there are national guidelines, Interaguas and the recommendations from the World Health Organization (WHO). INTERÁGUAS (2017) indicates a maximum E. coli density of 103 CFU/100 mL for restricted agricultural reuse (irrigation of crops not intended for human consumption). However, Santos & Vieira (2020) argue that the proposed limits are too restrictive for the Brazilian reality. For restricted low-tech and labor-intensive agriculture reuse, WHO (2006) recommends an E. coli density of 104 CFU/100 mL, determined by a Quantitative Microbiological Risk Methodology (QMRA). QMRA is an assessment based on local characteristics (WHO 2016). In other words, the WHO use general data that might not portray the conditions in Brazil.

Several countries such as Spain, France and Italy have quality standards for water reuse at the national level (European Commission 2016), while other countries such as the United States of America have legislation at the local level (Angelakis et al. 2018). According to Santos & Vieira (2020), in Portugal, in addition to defining standards for E. coli, the legislation bases the quality requirements on a fit-for-purpose approach, recommended by ISO 16075-1:2015. This approach considers the adoption of multiple barriers, which can effectively promote a microbiological reduction or only represent this reduction through barriers. Therefore, the quality limits established according to the fit-for-purpose approach are adaptable to the local reality, being more consistent than the guidelines proposed by WHO (2006) and INTERÁGUAS (2017). It is important to highlight that reuse patterns in agriculture in general, defined by regulations, vary depending on the type of crop and irrigation method.

Identification of routes and receptors

For the safe practice of agricultural reuse, the following must be considered: workers and farmers exposed to reclaimed water; food consumers; those involved in the marketing and processing of irrigated products; and the population located close to the irrigation site (Shoushtarian & Negahban-Azar 2020).

The receptors theoretically considered for the risk assessment were (Figure 2):

  • Farmers who work in the pasture and sugarcane areas to be irrigated;

  • Water reuse transport workers by tank truck;

  • Local community that inhabits or circulates in the vicinity of the irrigated area.

For sugarcane irrigation, the following were also analyzed:

  • Sugarcane industry workers.

The classic exposure routes for water reuse are ingestion, inhalation and dermal adsorption. The first two assume a factor of absolute importance (9) as they are demonstrably harmful to human health. On the other hand, dermal adsorption assumes a factor of weak importance (3) as there is little evidence of damage to health (Russo et al. 2020).

Exposure scenario

The same exposure scenarios were defined for the neighborhood of the four WWTP analyzed, as well as for the two crops. The importance factors of exposure scenarios are initially assigned according to available data on the related route. Therefore, scenarios associated with the ingestion route assume values in the range of 7 to 9; those associated with inhalation, from 5 to 9; and those related to dermal adsorption, from 1 to 5 (Rebelo et al. 2020).

It should be noted that water ingestion can occur intentionally, due to lack of information about water potability, or unintentionally, such by as ingestion of microdroplets during sprinkler irrigation (Russo et al. 2020). Both situations are considered in the scenarios of the research.

The exposure routes and scenarios, as well as the assigned importance factors and the respective vulnerabilities of each receptor, are presented in Table 2, for pasture crop.

Table 2

Route, exposure scenarios and vulnerability by receptor for pasture

Transport worker
Local community
Pasture farmer
ScenariofiPathfiScenJustificationfiScenJustificationfiScenJustification
Intentional water ingestion Receptor is aware that water is inappropriate Receptor is not aware that water is inappropriate Decreases the possibility with training and releases 
Unintentional ingestion of microdroplets during irrigation/water handling It is possible when handling water in the water truck Restricted area, but depends on human behavior It is possible when handling the irrigation system 
Irrigated crop ingestion – Not applicable There is a possibility for the receptor to enter the area and consume the irrigated crop Non-food crops 
Soil ingestion – Not applicable There is a possibility for the receptor to enter the area and consume the irrigated crop It is possible when handling the irrigation system 
Inhalation of microdroplets during irrigation – Not applicable Restricted area, but depends on human behavior There is a possibility of the receptor entering the area during irrigation 
Dermal adsorption by contact with reclaimed water It is possible when handling water in the water truck Restricted area, but depends on human behavior It is possible when handling the irrigation system 
Dermal adsorption by contact with an irrigation system Little contact with the irrigation system Restricted area, but depends on human behavior It is possible when handling the irrigation system 
Dermal adsorption by contact with the irrigated crop – Not applicable Restricted area, but depends on human behavior It is possible when handling the irrigation system 
∑ (fi Path × fi Scen162  360  396 
Fnormal Vfimax = 9 216  486  486 
Vrec 0.75  0.74  0.81 
Transport worker
Local community
Pasture farmer
ScenariofiPathfiScenJustificationfiScenJustificationfiScenJustification
Intentional water ingestion Receptor is aware that water is inappropriate Receptor is not aware that water is inappropriate Decreases the possibility with training and releases 
Unintentional ingestion of microdroplets during irrigation/water handling It is possible when handling water in the water truck Restricted area, but depends on human behavior It is possible when handling the irrigation system 
Irrigated crop ingestion – Not applicable There is a possibility for the receptor to enter the area and consume the irrigated crop Non-food crops 
Soil ingestion – Not applicable There is a possibility for the receptor to enter the area and consume the irrigated crop It is possible when handling the irrigation system 
Inhalation of microdroplets during irrigation – Not applicable Restricted area, but depends on human behavior There is a possibility of the receptor entering the area during irrigation 
Dermal adsorption by contact with reclaimed water It is possible when handling water in the water truck Restricted area, but depends on human behavior It is possible when handling the irrigation system 
Dermal adsorption by contact with an irrigation system Little contact with the irrigation system Restricted area, but depends on human behavior It is possible when handling the irrigation system 
Dermal adsorption by contact with the irrigated crop – Not applicable Restricted area, but depends on human behavior It is possible when handling the irrigation system 
∑ (fi Path × fi Scen162  360  396 
Fnormal Vfimax = 9 216  486  486 
Vrec 0.75  0.74  0.81 

The exposure routes and scenarios, as well as the assigned importance factors and the respective vulnerabilities of each receptor, are presented in Table 3, for sugarcane.

Table 3

Routes, scenarios exposure and vulnerability by receptor for sugarcane

Transport workerLocal communitySugarcane farmer
Industry worker
ScenariofiPathfaiScenfiScenafiScenJustificationfiScenJustification
Intentional water ingestion Decreases the possibility with training and releases – Not applicable 
Unintentional ingestion of microdroplets during irrigation/water handling It is possible when handling the irrigation system. Crops far from the ground level – Not applicable 
Irrigated crop ingestion – Food crops. Decreases the possibility with training and releases Decreases the possibility with training and releases 
Soil ingestion – It is possible when handling the irrigation system Decreases the possibility with training and releases 
Inhalation of microdroplets during irrigation – There is a possibility of the receptor entering the area during irrigation – Not applicable 
Dermal adsorption by contact with reclaimed water It is possible when handling the irrigation system – Not applicable 
Dermal adsorption by contact with an irrigation system It is possible when handling the irrigation system – Not applicable 
Dermal adsorption by contact with the irrigated crop – It is possible when handling the irrigation system Decreases the possibility with training and PPE 
∑ (fi Path × fi Scen162 360  432  135 
fnormal Vfimax = 9 216 486  486  189 
Vrec 0.75 0.74  0.89  0.71 
Transport workerLocal communitySugarcane farmer
Industry worker
ScenariofiPathfaiScenfiScenafiScenJustificationfiScenJustification
Intentional water ingestion Decreases the possibility with training and releases – Not applicable 
Unintentional ingestion of microdroplets during irrigation/water handling It is possible when handling the irrigation system. Crops far from the ground level – Not applicable 
Irrigated crop ingestion – Food crops. Decreases the possibility with training and releases Decreases the possibility with training and releases 
Soil ingestion – It is possible when handling the irrigation system Decreases the possibility with training and releases 
Inhalation of microdroplets during irrigation – There is a possibility of the receptor entering the area during irrigation – Not applicable 
Dermal adsorption by contact with reclaimed water It is possible when handling the irrigation system – Not applicable 
Dermal adsorption by contact with an irrigation system It is possible when handling the irrigation system – Not applicable 
Dermal adsorption by contact with the irrigated crop – It is possible when handling the irrigation system Decreases the possibility with training and PPE 
∑ (fi Path × fi Scen162 360  432  135 
fnormal Vfimax = 9 216 486  486  189 
Vrec 0.75 0.74  0.89  0.71 

aFactors in the exposure scenario present the same justifications as for pasture scenarios.

Risk characterization

ISO 16075-1:2015 presents possible barriers to be used in agricultural reuse, as well as the microbiological density reduction and number of equivalent barriers (concept related to a barrier that produces a microbiological reduction to an acceptable level). Based on the ISO 16075-1:2015, US EPA (2012) and WHO (2006) technical standards, the barriers used were defined to determine the damage of each analyzed crop (sugarcane and pasture), as shown in Table 4.

Table 4

Adopted barriers and damage

Pasture barriersnidiJustification
Failure probabilitySeverity of damage
Farmer access restriction for at least 24 h after irrigation Likely. It depends on human behavior. Strong. If the receptors fail, they may come into contact with the reclaimed water, which can cause illnesses. 
Training and use of PPE Likely. It depends on human behavior. Severe. If it fails, it would have a very serious effect on human health. 
∑ (di × ni17   
Fnormal Dfimax = 9 18   
D 0.94   
Justification
Sugarcane barriernidiFailure probabilitySeverity of damage
Discontinue irrigation in a period prior to harvest Likely. It depends on human behavior. Strong. If the receptors fail, they may come into contact with the reclaimed water, which can cause illnesses. 
Peeling fruits and roots Unlikely. Crops destined for industrial production. However, in case of consumption, it takes place without the skin. Strong. If it fails, there will be direct contact with the surface of the crops irrigated with reclaimed water, which may cause diseases. 
Training and use of PPE Likely. It depends on human behavior. Severe. If it fails, it would have a very serious effect on human health. 
∑ (di × ni29   
fnormal Dfimax = 9 36   
D 0.81   
Pasture barriersnidiJustification
Failure probabilitySeverity of damage
Farmer access restriction for at least 24 h after irrigation Likely. It depends on human behavior. Strong. If the receptors fail, they may come into contact with the reclaimed water, which can cause illnesses. 
Training and use of PPE Likely. It depends on human behavior. Severe. If it fails, it would have a very serious effect on human health. 
∑ (di × ni17   
Fnormal Dfimax = 9 18   
D 0.94   
Justification
Sugarcane barriernidiFailure probabilitySeverity of damage
Discontinue irrigation in a period prior to harvest Likely. It depends on human behavior. Strong. If the receptors fail, they may come into contact with the reclaimed water, which can cause illnesses. 
Peeling fruits and roots Unlikely. Crops destined for industrial production. However, in case of consumption, it takes place without the skin. Strong. If it fails, there will be direct contact with the surface of the crops irrigated with reclaimed water, which may cause diseases. 
Training and use of PPE Likely. It depends on human behavior. Severe. If it fails, it would have a very serious effect on human health. 
∑ (di × ni29   
fnormal Dfimax = 9 36   
D 0.81   

For farmers to use Personal Protective Equipment (PPE), training and capacity building are necessary, in order to make these workers aware of the risks to which they are subjected. Data indicate that farmers do not usually use PPE even for pesticide application, which can lead to health problems such as acute and chronic poisoning (Yarpuz-Bozdogan 2018).

The risk for each receptor and global risk obtained for the application of agricultural reuse in areas around the WWTP in the cities for the analyzed crops are presented in Table 5.

Table 5

Receptor and global risk for pasture and sugarcane irrigation

CropsReceptorHVrecDRrecRisk levelRglobal
Pasture Transport worker 0.75 0.94 6.4 Acceptable risk 6.5 
Local community 0.74 6.3 Acceptable risk Acceptable risk 
Pasture farmer 0.81 6.9 Acceptable risk 
Sugarcane Transport worker 0.75 0.81 5.4 Acceptable risk 5.6 
Local community 0.74 5.4 Acceptable risk 
Sugarcane farmer 0.89 6.4 Acceptable risk Acceptable risk 
Industry worker 0.71 5.2 Acceptable risk 
CropsReceptorHVrecDRrecRisk levelRglobal
Pasture Transport worker 0.75 0.94 6.4 Acceptable risk 6.5 
Local community 0.74 6.3 Acceptable risk Acceptable risk 
Pasture farmer 0.81 6.9 Acceptable risk 
Sugarcane Transport worker 0.75 0.81 5.4 Acceptable risk 5.6 
Local community 0.74 5.4 Acceptable risk 
Sugarcane farmer 0.89 6.4 Acceptable risk Acceptable risk 
Industry worker 0.71 5.2 Acceptable risk 

The estimated risk for all receptors is in the acceptable category, with sugarcane and pasture farmers being the most at risk (Table 5). Rebelo et al. (2020), when applying the same methodology of the present research to assess the microbiological risk of the application of agricultural reuse in wineries, also obtained the highest risk for the receptor farmer.

The numerical value of the risk, both by receptor and global, was close to the acceptable risk limit, 7, which could lead to unacceptable risk. In this case, possible minimization measures can be adopted, involving the terms hazard, vulnerability and/or damage.

Risk management

It is possible to reduce the hazard importance factor by promoting improvements in the reclaimed water treatment system. According to Rebelo et al. (2020), an importance factor for hazard equal to 3 is equivalent to a density of E. coli in the order of 101 to 102 CFU/100 mL, which is achievable with secondary treatment associated with disinfection and chlorination (Figure 2).

The adoption of a hazard importance factor of 3 or less results in despicable risk for the same vulnerability configurations (receptors, scenarios and factors) and damage (barriers), as shown in Table 6.

Table 6

Receptor and global risk for pasture and sugarcane irrigation modifying the hazard = 3

CropsReceptorHVrecDRrecRisk levelRglobal
Pasture Transport worker 0.75 0.94 2.1 Despicable risk 2.2 
Local community 0.74 2.1 Despicable risk Despicable risk 
Pasture farmer 0.81 2.3 Despicable risk 
Sugarcane Transport worker 0.75 0.81 1.8 Despicable risk 1.9 
Local community 0.74 1.8 Despicable risk 
Sugarcane farmer 0.89 2.1 Despicable risk Despicable risk 
Industry worker 0.71 1.7 Despicable risk 
CropsReceptorHVrecDRrecRisk levelRglobal
Pasture Transport worker 0.75 0.94 2.1 Despicable risk 2.2 
Local community 0.74 2.1 Despicable risk Despicable risk 
Pasture farmer 0.81 2.3 Despicable risk 
Sugarcane Transport worker 0.75 0.81 1.8 Despicable risk 1.9 
Local community 0.74 1.8 Despicable risk 
Sugarcane farmer 0.89 2.1 Despicable risk Despicable risk 
Industry worker 0.71 1.7 Despicable risk 

Note: Despicable risk should be understood as low risk.

Figures 3 and 4, for pasture and sugarcane respectively, show the vulnerability associated with the numerical value of the risk and its classification, keeping the same hazard configurations (factor 9), damage (barriers) and scenarios used previously (Table 5). The despicable risk level is equivalent to vulnerabilities lower than 0.35 for pasture (Figure 3) and 0.41 for sugarcane (Figure 4), however, these values cannot be reached for the analyzed scenarios. This is because the scenarios' importance factors used to estimate vulnerability have values according to the route (Rebelo et al. 2020): intake from 7 to 9; inhalation from 5 to 9 and dermal adsorption from 1 to 5. But, according to the same authors, higher or lower values than those initially assigned are due to greater or lesser probability of occurrence of the scenario.
Figure 3

Risk variation with vulnerability for pasture.

Figure 3

Risk variation with vulnerability for pasture.

Close modal
Figure 4

Risk variation with vulnerability for sugarcane.

Figure 4

Risk variation with vulnerability for sugarcane.

Close modal

It is possible to obtain despicable risk by changing the damage to values less than 0.43 (for sugarcane and pasture), for the same hazard and vulnerability configurations in Table 5, by adopting more barriers and considering a scale of partial damage (di) based on demonstrated evidence of damage to health in the event of a barrier failure.

Table 7 presents the risk for each receptor and global risk altering the damage, and Table 8 presents the details of the changes in the damage, with the adoption of less rigid factors and inclusion of a barrier related to bacteriological decay. Such decay was provided by the adoption of a reservoir to store the water used in agricultural reuse. Despite the modifications in the damage, sugarcane farmers continued with an acceptable risk, since it presents higher vulnerability values.

Table 7

Receptor and global risk for pasture and sugarcane irrigation modifying the damage

CropsReceptorHVrecDRrecRisk levelRglobal
Pasture Transport worker 0.75 0.39 2.6 Despicable risk 2.9 
Local community 0.74 2.6 Despicable risk Despicable risk 
Pasture farmer 0.81 2.9 Despicable risk 
Sugarcane Transport worker 0.75 0.41 2.8 Despicable risk 2.8 
Local community 0.74 2.7 Despicable risk 
Sugarcane farmer 0.89 3.3 Acceptable risk Despicable risk 
Industry worker 0.71 2.6 Despicable risk 
CropsReceptorHVrecDRrecRisk levelRglobal
Pasture Transport worker 0.75 0.39 2.6 Despicable risk 2.9 
Local community 0.74 2.6 Despicable risk Despicable risk 
Pasture farmer 0.81 2.9 Despicable risk 
Sugarcane Transport worker 0.75 0.41 2.8 Despicable risk 2.8 
Local community 0.74 2.7 Despicable risk 
Sugarcane farmer 0.89 3.3 Acceptable risk Despicable risk 
Industry worker 0.71 2.6 Despicable risk 

Note: Despicable risk should be understood as low risk.

Table 8

Modified damage detail

Pasture barriersnidiJustification
Failure probabilitySeverity of damage
Farmer access restriction for at least 24 h after irrigation Possible Moderate 
Training and use of PPE Possible Strong 
Water tank Unlikely Strong 
∑ (di × ni14    
fnormal Dfimax = 9 36    
D 0.39    
Justification
Sugarcane barriernidiFailure probabilitySeverity of damage
Discontinue irrigation in a period prior to harvest Possible Moderate 
Peeling fruits and roots Unlikely Moderate 
Training and use of PPE Possible Strong 
Water tank or green curtain Unlikely Weak 
∑ (di × ni22   
fnormal Dfimax = 9 54   
D 0.41   
Pasture barriersnidiJustification
Failure probabilitySeverity of damage
Farmer access restriction for at least 24 h after irrigation Possible Moderate 
Training and use of PPE Possible Strong 
Water tank Unlikely Strong 
∑ (di × ni14    
fnormal Dfimax = 9 36    
D 0.39    
Justification
Sugarcane barriernidiFailure probabilitySeverity of damage
Discontinue irrigation in a period prior to harvest Possible Moderate 
Peeling fruits and roots Unlikely Moderate 
Training and use of PPE Possible Strong 
Water tank or green curtain Unlikely Weak 
∑ (di × ni22   
fnormal Dfimax = 9 54   
D 0.41   

Table 9 presents a summary of the initial risk estimate by receptor, with the hazard (H), vulnerability (V) and damage (D) values and the modifications in each term. The vulnerability values for each receptor in the term ‘modified vulnerability’ are equivalent to adopting the lowest possible values for the scenario's importance factors. Modifying only the vulnerability does not allow for a despicable risk range (between 0 and 3). Modification of hazard and damage allow for reaching risk estimates for each receptor that are lower than the initial estimate.

Table 9

Summary of initial risk estimate and modifications

Initial estimate
Modified hazard
Modified vulnerability
Modified damage
CropsReceptorHVrecDRrecHRrecVrecRrecDRrec
Pasture Transport worker 0.75 0.94 6.4 2.1 0.61 5.2 0.39 2.6 
Local community 0.74 6.3 2.1 0.63 5.4 2.6 
Pasture farmer 0.81 6.9 2.3 0.63 5.4 2.9 
Sugarcane Transport worker 0.75 0.81 5.4 1.8 0.61 4.4 0.41 2.8 
Local community 0.74 5.4 1.8 0.63 4.6 2.7 
Sugarcane farmer 0.89 6.4 2.1 0.63 4.6 3.3 
Industry worker 0.71 5.2 1.7 0.68 4.9 2.6 
Initial estimate
Modified hazard
Modified vulnerability
Modified damage
CropsReceptorHVrecDRrecHRrecVrecRrecDRrec
Pasture Transport worker 0.75 0.94 6.4 2.1 0.61 5.2 0.39 2.6 
Local community 0.74 6.3 2.1 0.63 5.4 2.6 
Pasture farmer 0.81 6.9 2.3 0.63 5.4 2.9 
Sugarcane Transport worker 0.75 0.81 5.4 1.8 0.61 4.4 0.41 2.8 
Local community 0.74 5.4 1.8 0.63 4.6 2.7 
Sugarcane farmer 0.89 6.4 2.1 0.63 4.6 3.3 
Industry worker 0.71 5.2 1.7 0.68 4.9 2.6 

Although the microbiological risk was acceptable for all receptors, according to the methodology used, there are other risks in the application of agricultural reuse. Therefore, to reduce the probability of damage to human health, based on the recommendations of the World Health Organization, International Organization for Standardization, and United States Environmental Protection Agency, the adoption of measures is suggested such as: use of a reclaimed water storage reservoir to promote microbiological decay; use of personal protective equipment; conducting training; as far as possible, use of a localized irrigation system; and access restriction during irrigation.

Restricting cattle access to pasture after irrigation, as well as cooking foods made from these cattle, reduces the likelihood of human health risk associated with dairy and meat consumption (WHO 2006).

The maximum values indicated in both non-mandatory WHO and Brazilian guidelines for the coliform standard for water reuse in agriculture are more restrictive than the density present in the application of this study. However, there was an acceptable level of risk for all receptors considered for sugarcane and pasture irrigation, with water reuse, around the WWTP in the cities of Aparecida do Rio Doce, Caçu, Lagoa Santa and Quirinópolis (Goiás, Brazil). For Brazil, the most suitable is the adoption of reclaimed water quality standards according to the fit-for-purpose approach (case by case), supported by risk assessment.

The methodology uses scenarios, receptors, barriers and data on the quality of the reclaimed water, all focused on the specifics of the project. Therefore, it allows for a closer approximation to local reality and facilitates the evaluation of options to achieve the lowest possible risk. In this sense, modifications such as improvements in the wastewater treatment system, used for agricultural reuse, were considered (which reduces the hazard), as well as the adoption of different barrier configurations (which reduces the damage). Consequently, the global risks and those for each receptor, keeping the same scenarios and receptors, went from acceptable to despicable.

Nevertheless, the adoption of preventive measures is suggested, such as restricting the access of animals, population and workers during irrigation, use of personal protective equipment, training, capacity building and modification of the sprinkler irrigation system for a localized system.

Finally, risk assessment enables better system-management, bringing information about the many scenarios for decision-making, in addition to encouraging public confidence in the safe application of water reuse.

This study was financed in part by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior – Brasil (CAPES) – Finance Code 001.

Data cannot be made publicly available; readers should contact the corresponding author for details.

The authors declare there is no conflict.

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Supplementary data