Keywords

1 Introduction

Water, sanitation, and hygiene (WASH) is a practice that reduces the chance that people are exposed to pathogens, especially those derived from human excreta. Out of the three components of WASH, sanitation plays a role in treating and disposing excreta for people’s health, which makes the living environment free from fecal contamination, and eventually reduce fecal exposure and fecal–oral infection (Fig. 8.1). Sanitation can change the fate of excreta and control the emission of fecal matter to the living and ambient environment. A sanitary toilet is the step to contain fecal matter and is a key part of sanitation. If the fate of excreta after toilets is not properly controlled, fecal matter is emitted to the living environment and sanitation will not achieve its goal.

Fig. 8.1
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Emission, transmission, and exposure of fecal matter and the role of water supply, sanitation, and hygiene (F-diagram)

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Unfortunately, a large proportion of the global population cannot successfully change the fate of fecal matter owing to improper sanitation. After excreta is emitted in an unsanitary manner with the amount above the level of an acceptable environmental capacity, the living environment will be contaminated by fecal matter and its associated microorganisms. As illustrated in Fig. 8.1, humans can be exposed to them by different environmental media (water, soil, object surface, etc.) through various pathways in daily activities (drinking, eating, and activities involving contact with fomite).

The media, pathways, and associated daily activities are, by nature, the matter of socio-culture. The fate of excreta may not be limited within the living boundary of a single person, or further even in a community. Excreta are generated in a place and can be transferred to and emitted in another place, by the movement of media carrying excreta, by a vehicle truck, and by passing through water ways and pipelines. Rivers or canals in areas with dense populations but improper sanitation potentially transfer excreta and their diluted matter to downstream areas. More generally, community X may be cleaned out by the transfer of excreta to community Y. This transfer, however, may pollute community Y, where the excreta was transferred, possibly causing the transfer of health risks derived from excreta-related (i.e., sanitation-related) microorganisms from community X. Substantial pollution and the associated health risks in community Y, transferred from community X, may change the livelihood of people in community Y to avoid contact with pollutants and further mitigate the associated health risks.

The transfer of sanitation-related health risks may also occur between people within a community. When excreta are stored, treated, and disposed of where generated, the health risks caused by the excreta will be held by the excreter. In reality, there are many types of sanitation, in which the people who excreted differ from the people who handle the excreta generated by the former. Excreta stored in an on-site sanitation facility, called fecal sludge, is often emptied and transported by someone other than the excreter; then, the excreta is transported to another place, where it is hopefully treated and disposed of by someone else. This may allocate the sanitation-related health risk from the excreter to someone who handles excreta later on. Further, even within a single family, the excreter may not be involved in handling excreta. For example, the cleaning duties of sanitation facilities are not equally allocated to each of the users of the facility, and the person responsible for cleaning may be exposed to the sanitation-related health risk more than others who transfer the risk to the cleaning person.

The health issue of sanitation is not only an issue within a certain person, but beyond a person, a family, and even a community. It is transferred and allocated to society as a socio-cultural matter. This section will demonstrate the transfer and allocation of sanitation-related health risks based on cases in Vietnam. Then, we discuss how such a transfer and allocation of health risk will affect and be affected by socio-culture.

2 Transfer of Fecal Matter from Urban Upstream Areas to Downstream Areas

2.1 Study Area

The Nhue River is a distributary of the Red River, passing through the center of Hanoi, the capital of Vietnam (Fig. 8.2). It flows down through agricultural fields and joins another larger distributary of the Red River—the Day River—nearly 80 km downstream of the intake. Hanoi, located upstream of the Nhue River, has a limited capacity for wastewater treatment. Of the city’s population, 96.8% used water flush toilets and 84% was connected to septic systems, most effluent of which was discharged into sewer systems (Brandes et al. 2016; Harada et al. 2011). In contrast, only 33% of the population is covered by wastewater treatment plants in the city (Japan International Cooperation Agency and Nippon Koei 2019), meaning that most of blackwater (toilet wastewater) generated in Hanoi reach at public water only after limited treatment in septic systems.

Fig. 8.2
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A map of Nhue River

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The upstream area of the Nhue River is characterized by urban land use with high population density but poor wastewater treatment capacity, while the downstream area is characterized by farming areas, including rice cultivation, livestock, and poultry production. Historically, the river has played an important role as an irrigation water source for farming areas as well as a place for river fishing (Pham et al. 2015; Nguyen et al. 2014). However, it has been recently contaminated by receiving a large amount of polluted water from urban Hanoi in its upstream areas (Fig. 8.3).

Fig. 8.3
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Nhue River approximately 20 km downstream from the intake. The river water was heavily polluted with dark gray color. (Photo taken by Harada, September 2017)

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2.2 Transition of Fecal Pollution Along Nhue River

To characterize the impact of upstream urban water pollution on the downstream area along the Nhue River, we conducted a series of river surveys from 2011 to 2018. Figure 8.4 shows the river water quality along the Nhue River from the intake point (S1) to 1 km downstream of the confluence with the Day River (S9). The low values of total organic carbon (TOC; an indicator of organic pollution) concentration and electrical conductivity (EC; an indicator of ionic substances) at S1 indicate less pollution of the source water of the Nhue River at the intake, which is diverted from the Red River (1.0 mg/L of TOC, 0.18 mS/cm of EC). They, however, gradually increased by passing thorough urban Hanoi and peaked right after passing urban Hanoi (S5; TOC: 134.0 mg/L, EC: 0.76 mS/cm). The concentration of Escherichia coli, a microbiological indicator of fecal pollution, was also low at the intake of Nhue River (S1; 7.0 × 102 cfu/mL). Entering urban Hanoi, it increased more rapidly than TOC and EC, and then reached near 105 cfu/100 mL at S3–S5. All these parameters started to decrease after leaving the urban areas. The pollution, however, lasted long distances. The E. coli concentration was 5.0 times higher than the intake level at S8, 35 km downstream from the border of urban and suburban areas. Even at S9, where the Nhue River flowed into the Day River, the E. coli concentration was 2.3 times higher than the intake of Nhue River, S1.

Fig. 8.4
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Transition of TOC, EC, and E. coli along Nhue River. TOC total organic carbon, EC electrical conductivity. Data are shown as geometric mean of the results from three surveys on March 9, 12, and 15, 2018 (Tanaka 2019)

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The aforementioned fecal pollution trend was further characterized by a host-specific E. coli genetic marker. E. coli can be derived not only from humans but also from warm-blooded animals. A human-associated genetic marker, H8 (Gomi et al. 2014; Harada et al. 2018; Warish et al. 2015), was tested with 120 E. coli isolates for each of the nine sampling points to obtain information on the host of each E. coli isolate. As illustrated in Fig. 8.5, the proportion of H8-positive E. coli continuously increased from the intake (23.3% at S1) and peaked immediately after urban Hanoi (56.7% at S3), and it tended to decrease after leaving the urban areas. As the sensitivity of H8 markers for sewage was 63.3% in Vietnam (n = 120), the high positive proportions (52.5–56.7% at S3–S5) indicate that most E. coli isolates at S3–S5 are expected to have a human origin. This implies that the fecal pollution strengthened within urban areas was biologically associated with human fecal pollution.

Fig. 8.5
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Positive proportion of human-associated genetic marker, H8, for 120 E. coli isolates collected at each of the nine sampling points along Nhue River. (Data originated from Tanaka (2019))

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Further, helminth eggs were investigated in the water and sediment of the Nhue River, as shown in Fig. 8.6. They were rarely detected in the sample of Nhue River water even though we increased the sample water volume up to 5 L per sample. In contrast, the eggs were detected in 100-g-wet sediment for all samples, of which 77% and 12% were Ascaris spp. and Trichuris spp., respectively. Possible hosts of Ascaris spp. are humans and pigs. Since pig raising was not a common practice in urban Hanoi at S2a–S4, human fecal pollution from urban populations caused the accumulation of helminth eggs in the river sediment. This supports the fecal contamination by human excreta, as indicated by the above results of the human-associated genetic marker of E. coli.

Fig. 8.6
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Helminth egg number of Nhue River water (upper) and sediment (lower). The numbers in the figure are the average of viable and nonviable egg numbers from the survey on October 9 and 23, 2015. (Data originated from Sakaguchi (2016))

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The transition of helminth egg concentration in sediment along the river had a different trend from that of E. coli concentration in river water. The concentration of helminth eggs in the semibent decreased more quickly after passing urban Hanoi than that of E. coli. This could be explained by the fact that helminth eggs, which settle more easily than bacteria (i.e., E. coli), accumulated in sediment but were rarely detected in water (Fig. 8.6). Still, eggs in sediment can be transferred when strong river flows occur (e.g., after heavy rain). The high number of helminth eggs at S9 was possibly caused by the pollution of the Day River, of which the watershed includes ample pig raising.

2.3 Allocation of Health Risk Along the Nhue River

The Nhue River was seriously polluted microbiologically, passing through the urban centers of Hanoi. The E. coli concentration reached approximately 105 cfu/100 mL in urban areas, and helminth eggs accumulated in the river sediment. The rapid deterioration of river water quality within urban areas is explained by the discharge of a large amount of wastewater from urban Hanoi, located upstream of the river. Furthermore, the impact of wastewater discharge in urban Hanoi continued far downstream from the urban areas. In other words, the downstream river water was contaminated by the upstream wastewater, although the downstream areas also discharged their own wastewater (Pham et al. 2017).

Downstream of S5, small-scale agricultural farmers were observed along the river, who utilized river water for irrigation. A health guideline for fecal coliform concentration in wastewater use for irrigation was set as 103 count/100 mL by the World Health Organization (Blumenthal et al. 2001; WHO 1989). As fecal coliform is a larger group including E. coli, the fecal coliform concentration of a water sample is theoretically equal to or higher than the E. coli concentration, indicating that all the sampling points except the intake would not meet the guideline concentration of fecal coliform. Furthermore, despite the gradual decrease in E. coli levels, this trend lasted far downstream areas, and the E. coli concentration still exceeded 103 cfu/100 mL at S9. These results clearly demonstrate that agriculture activities using irrigation water from the Nhue River pose a health risk, as mentioned by Fuhrimann et al. (2016), who demonstrated the serious microbial pollution of irrigation water near S5. A study also highlighted that farmers along a river in Hanoi in contact with wastewater experienced a significantly higher frequency of diarrhea than those without contact (odds ratio [OR]: 1.98, 95% confidence interval [CI]: 1.18–3.33) (Trang et al. 2007). Of people in the downstream area of the Nhue River, 47% were infected by helminth (Ascaris lumbricoides: 24%; Trichuris trichiura: 40%; and hookworm: 2%), and people in contact with river water had a higher risk of A. lumbricoides (OR: 2.1; 95% CI: 1.4–3.2) in comparison with those without contact (Pham-Duc et al. 2013).

Thus, the case of the Nhue River highlighted the microbiological contamination of the upstream areas, which affected the river water quality and the associated health of people in the downstream areas. This clearly indicates the transfer of fecal pollution and the associated health risks from the urban upstream areas to the downstream areas. In nature, water is possibly polluted after use, and the polluted water flows to another place, posing a health impact there. Sanitation definitely affects this health risk transfer because sanitation is a measure to change the fate of excreta and control the emission to the living and ambient environment. In the following section, we discuss how the livelihood has been affected by pollution with further details of fecal exposure characteristics in a community downstream of the Nhue River.

3 Fecal Exposure in Livelihood of the Downstream

3.1 Study Area

Trai hamlet is a rural community in the Phu Xuyen suburban district of Hanoi, located downstream of the Nhue River (55 km from the intake of the Nhue River from the Red River). The community had a population of 800 people in a total area of 56.1 ha as of 2010 (Pham et al. 2015). Farming, mainly rice cultivation, is a major occupation. The Nhue River is used as a major irrigation source together with reservoirs, some of which are used as fishponds. Some residents have a side job of river fishing.

A public water supply was not established as of 2010. The people in the community used three types of water for domestic purposes in a mixed manner: well water stored in a tank outside, rainwater stored in a tank outside, and drinking water stored in a pot after boiling. Of the 240 households in the community, 52% employed traditional dry toilets (Fig. 8.7) (Pham et al. 2017). Dry toilets are typically designed as high-floor toilets with a single or double chamber(s), located under the floor slab and above the ground. Excreta or feces separated from urine are stored in the chamber and treated with drying agents such as ash and dry soils. This fecal mixture is used for agriculture after several months of retention in the chamber. The remaining 48% used water flush toilets and discharged their toilet wastewater into the environment directly or after a limited treatment by a septic tank. Water flush toilets have been gradually replacing dry toilets (Pham et al. 2017).

Fig. 8.7
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A dry toilet storing excreta in a fecal chamber under the floor slab. (Photo adapted from Harada and Fujii (2020))

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3.2 Fecal Contamination in the Community

To investigate the fecal contamination in the community, a variety of environmental media such as drinking water, environmental water, soil, manure, and vegetables were sampled and tested with E. coli as a biological fecal indicator in 2014 and 2015 (Fig. 8.8). As mentioned in the previous section, high-level fecal contamination was observed for Nhue River water near the community (median = 7.4 × 104 cfu/100 mL). Similar to the discussion in the previous section, the median E. coli concentration of the irrigation water (med. = 1.0 × 104 cfu/100 mL) indicates substantial fecal contamination, considering the WHO guidelines of wastewater irrigation with a total coliform level of 103 count/100 mL (WHO 1989). As the Nhue River is a major irrigation source for the community, this fecal contamination of irrigation water can be associated with Nhue River contamination as well as poor sanitation practices of this community itself, where 48% of households used water flush toilets and discharged toilet wastewater in unsanitary manners to community channels, which is connected to irrigation water reservoirs. Water in paddy fields, where irrigation water was used, was contaminated at a high level (med. = 6.5 × 102 cfu/100 mL). Thus, the outside environment in the community was highly contaminated with fecal matter.

Fig. 8.8
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E. coli levels of various environmental media. The box indicates quartiles with whiskers extending up to 1.5 times the interquartile range from the hinge. (Figure modified from Harada et al. (2016b))

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Daily water for domestic use was also contaminated. High levels of E. coli in stored well water (med. = 60 cfu/100 mL) and stored rainwater (med. = 50 cfu/100 mL) indicate the fecal contamination of their daily water other than drinking water. Although people seemed to keep their drinking water considerably cleaner (med. = 1 cfu/100 mL) than other domestic water, 44% of drinking water was positive with E. coli from 100 mL, which is above the WHO drinking water quality guideline (no detection from 100 mL). Since drinking water is stored after boiling, drinking water contamination is likely caused during storage. As indicated by fecal contamination of rice bowls and chopsticks (62% positive with E. coli), their eating/cooking environment was contaminated by fecal matter, supporting potential contamination of boiled water during storage. These contaminations inside houses could be caused by fecal contamination outside.

Animal and human manure mostly originated in the community. Owing to its incomplete treatment, the manure in use was still contaminated at high levels (animal manure: 2.5 × 104 cfu/g-dry; human manure: 1.5 × 104 cfu/g-dry). The community has a custom to eat raw vegetables such as herbs. As contamination of irrigation water and manure implies, E. coli was frequently detected in raw vegetables at farms or stores in the community (80% positive, med. = 34 cfu/g-wet), indicating substantial fecal contamination of raw vegetables.

3.3 Fecal Exposure in the Community

Fecal contamination potentially causes fecal exposure to humans, leading to the health risk of infection by fecal pathogens. Fecal exposure through their daily life activities was estimated as E. coli exposure. The methodology of stochastic estimation is briefly explained. Exposure was obtained as follows:

$$ {E}_{\mathrm{day},i}=\sum \limits_j{F}_i\times {U}_{i,j}\times {C}_j $$
(8.1)

where Eday, i is the exposure of E. coli through activity i (cfu/day) if a person performs the activity; Fi is the frequency or duration of activity i {(count or time duration)/day}; Ui, j is the unit ingestion amount of media j during activity i {(amount of media j)/(count or unit time duration of activity i)}; and Cj is the concentration of E. coli for media j {cfu/(unit amount of media j)}.

For Fi, people’s daily activity data were investigated by an interview survey of the people conducted in 2014 and 2015, including activity types, time duration per activity event, and event frequency. Ui, j, called the exposure factor, was collected from the literature. Cj was obtained from the fecal contamination survey in the previous section. Owing to the large variability and uncertainty of the data, the exposure was estimated in a stochastic manner. Probability density functions (PDFs) were defined for variables based on the data obtained. Values of variables were obtained randomly from the PDFs, and the daily exposure of Eq. (8.1) was repeatedly calculated in a stochastic manner by a Monte Carlo simulation with 100,000 trials.

The stochastically estimated exposure is shown in Fig. 8.9 with the probability ranges of the estimates. Although a public water supply had not been established in the community, fecal exposure through drinking (20 cfu/day) and hygiene activities such as bathing and teeth brushing (33 cfu/day) was relatively small. One of the major reasons for these low exposures is the boiling of drinking water before storage. A relatively low contribution of drinking water to exposure in contexts of low- and middle-income countries was also reported in previous studies. For example, hand-to-mouth contact was a greater pathway of fecal exposure than drinking in Tanzania (Mattioli et al. 2015); diarrhea in an urban slum in Bangladesh was more attributable to housing and surrounding conditions than the water supply (Khan et al. 2014). However, this result does not indicate the reduced importance of safe domestic water because there is an infection risk of fecal pathogens through drinking and hygiene activities. Further, safe domestic water can greatly contribute to the improvement of sanitary and hygienic conditions in and around houses, potentially reducing exposure through various pathways.

Fig. 8.9
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Per-day exposure of E. coli from various pathways (12.5, 50, and 87.5 percentiles). (Figure revised from Harada and Fujii (2020))

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In this community, three major activities causing intensive per-day exposure were swimming [med. = 3.5 × 103 cfu/day (1 h/day)], eating raw vegetables [med. = 2.4 × 103 cfu/day (med. 58 g-wet eating/day)], and human manure handling [med. = 2.2 × 103 cfu/day (1 time/day)]. These high exposures were caused by accidental ingestion of strongly contaminated reservoirs where they swim, eating contaminated raw vegetables, and accidental ingestion of contaminated manure during manure handling. The fourth largest exposure activity was fishing. Fishing was conducted by walking into the water of the Nhue River to catch snails and fishes. This intensive water contact manner of fishing caused the ingestion of contaminated water from the Nhue River, resulting in the great exposure of E. coli. Among these activities, swimming and fishing are directly linked to the ingestion of the media of the surrounding environment: reservoirs and Nhue River, respectively. Considering that reservoir contamination was substantially affected by the Nhue River as the original water source, these exposures were associated with Nhue River water pollution, which was strengthened by the pollutants from urban upstream areas, as previously mentioned.

Living on the conditions of the exposure trend mentioned above, people were likely to mitigate health risks through some of the activities with intensive exposure. According to interviews with the chief of the community, people, mainly young men, used to swim almost every day from May to September (the hottest time of the year in the area). The frequency of swimming, however, has recently decreased owing to concerns about contamination of the reservoir and Nhue River. This trend was similar to that of fishing. Fishing was a common side job in the community, and people often fished (except in winter); however, the frequency has decreased. These changing trends of activities could reduce the fecal exposure, leading to less infectious risk of fecal microorganisms. In other words, strengthened by the pollution transfer from the upstream urban areas, the fecal pollution of the Nhue River caused a change in downstream livelihood, such as swimming and fishing.

Exposure through eating raw vegetables is also partly associated with fecal pollution strengthened by pollution transfer from urban areas as the vegetables were irrigated by water in the community, of which quality was affected by Nhue River water quality. Part of the health risks associated with this exposure has been mitigated by people’s efforts as people often washed raw vegetables, including washing them with disinfectants. The exposure was calculated based on the fecal contamination of vegetables at farms and stores (before washing for eating), meaning that exposure to eating raw vegetables after washing could be substantially lower than the estimates. According to the WHO (2006), washing in disinfectants and rinsing in tap water can reduce contamination by 1–2 log units (10–100 times reduction). Assuming a 2 log reduction by their food hygiene behavior, the fecal exposure through eating raw vegetables will be reduced to the same magnitude as relatively small exposure activities such as eating with contaminated bowl/chopsticks, handing animal manure by accidental ingestion, and hygiene activities with contaminated water.

Thus, a significant portion of fecal exposure and the associated health risks was linked to the fecal pollution strengthened by the fecal pollution transfer from urban upstream areas. People’s recent change in their livelihood and hygiene behavior mitigated the fecal exposure and the associated health risks to some degree. This demonstrated that the transfer of the fecal-associated health risks from the urban upstream areas contributed to the change in downstream livelihood. However, the remaining major activity causing intensive daily exposure, human manure handling, was not associated with the Nhue River or urban upstream areas. It is a matter within the community. This inner-community exposure is further characterized in the following section.

3.4 Fecal Exposure Characterization Through Excreta Use for Agriculture

Although the use of human manure for agriculture could contribute to the development of a sound material cycle, the handling of human manure was one of the major activities causing intensive exposure in the community, possibly leading to infection by fecal microorganisms. The human manure in the community was derived from stored human excreta and dry conditioning agents such as soil and ash after being kept for several months in the toilet chambers. It was removed from the chamber by farmers, and then used for agriculture; for example, soil preparation for rice fields or vegetable farms. If human manure is not completely sanitized, these activities are possible exposure activities owing to accidental contact of contaminated hands with one’s face or mouth.

From November 2015 to February 2016, first-person videography captured the human manure handling activities of 25 farmers in the abovementioned community by using small video cameras on their heads (Fig. 8.10). The videography recorded farmers’ hand movements. In total, 18.2 h of videography was collected during the period that famers took human manure out from dry toilets and used manure for vegetable farms. Collected video data were translated into a second-by-second time series data of hand contact, known as the micro-level activity time series (MLATS) (Zartarian et al. 1995). By using MLATS data, the hand contamination level and human exposure (dose) were modeled by a stochastic–mechanistic simulation. The details can be found in Julian et al. (2018). Briefly, E. coli concentration on hands at a certain time was modeled based on the initial concentration on one’s hands, the event of hand-to-object contacts (e.g., hand tool, plastic bag, soil, manure, cloth, water), E. coli concentration on the object, and a bacterial transfer coefficient from the object to the hand. Then, the dose of E. coli was modeled based on the modeled E. coli concentration on one’s hands, the event of hand-to-mouth contact, surface area of the hand in contact with his/her mouth, and bacterial transfer coefficient from the hand to the mouth. By using field data and literature, E. coli concentration on the hands of 14 farmers during the application of human manure for vegetable farms was modeled.

Fig. 8.10
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A farmer taking human manure out from a fecal chamber. A mobile video camera was mounted on her head. (Photo taken by Harada)

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The results indicated widespread E. coli contamination with a variety of objects, corresponding to the results in the previous section. The strong contamination of human manure indicates incomplete treatment of human manure in toilet chambers. The farmers contacted 342–848 objects with their left or right hand, per person, every hour. Contacted objects included shovels, plastic bags to keep manure, seeds, the toilet pit, mud, and surface water. In contrast, only four farmers contacted their mouths during the video. This frequency was surprisingly lower than other studies on hand-to-mouth contact: for example, the mean frequency of hand-to-mouth contact among US office workers was 8 times/h, which is adopted in the US Exposure Handbook (Nicas and Best 2008; United States Environmental Protection Agency 2011).

Figure 8.11 shows the simulated E. coli concentration on farmers’ hands and their E. coli dose. As indicated in frequent contact with various objects, the simulation showed strong E. coli contamination on farmers’ hands after handling human manure. Reflecting the variation of contact objects and contact frequencies by each farmer, the results showed dynamic changes and variation in E. coli concentration on the hands and E. coli dose. Out of 15 farmers, four farmers (IDs 108, 109, 112, and 117) had a dose of E. coli during land application of human manure through hand-to-mouth contact, which rarely occurs in this case. Notably, out of the four farmers, two wore masks. However, they had hand-to-mouth contact, resulting in ingestion. The estimated E. coli dose of mean [95% CI] were, for each of the four farmers, 1.2 [0.7–2], 4.2 [2.7–6.5], 3.0 [1.6–6.1], and 0.6 [0.3–1.3] cfu during each event, corresponding to 0.7 [0.4–1.3], 2.9 [1.8–4.4], 2.2 [1.2–4.4], and 0.7 [0.3–1.5] cfu/h. Assuming a 1-day activity of human manure handling happen for 8 h, the maximum 95% CI of four farmers will be between 2.4 cfu/day (0.3 cfu/h × 8 h) and 35.2 cfu/day (4.4 cfu/h × 8 h). This exposure amount is relatively small compared to the exposures through other activities, as shown in Fig. 8.9.

Fig. 8.11
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Modeled distributions for final (top) E. coli hand concentration and (bottom) E. coli dose for farmers (n = 14) applying human excreta to land. The simulation was iterated for 100 times. Boxplots indicate median and interquartile range (IQR) with whiskers extending up to 1.5 × IQR from the hinge. E. coli concentration on hands was measured for nine farmers before (red) and after (blue) video capturing. The use of personal protective equipment is marked by the gray background for gloves (top) and masks (bottom). The number between 108 and 124 indicates farmers’ ID. (Figure adapted from Julian et al. (2018))

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Thus, farmers’ hands were strongly contaminated after handling human manure. This implies that contaminated surrounding conditions caused fecal contamination on their hands. In contrast, their behavior during human manure handling was preventive; substantially less hand-to-mouth contact than other studies. In fact, despite the surrounding contamination, their behavior mitigated a substantial portion of the health risks during human manure handling. However, the simulation demonstrated that accidental and rare hand-to-mouth contacts led to the ingestion of E. coli, even though they wore personal preventive equipment such as masks.

Notably, out of the 25 farmers handling human manure in the present study, 24 (95%) were women. The removal of human manure is essential to maintain the function of dry toilets in the community. From the aspect of social allocation of health risks in sanitation, this resource-oriented sanitation was achieved at the expense of female farmers’ health risks, while they partly mitigated the risk by their preventive behavior.

4 Allocation of the Responsibility of Sanitation Service and the Associated Societal Health Risks

The above sections indicated that the impact of sanitation spreads in wide parts of society, and even affects the culture. Without sound sanitation, the risks were allocated in an unequitable manner, while people receiving the risks might try to mitigate the risk by different measures such as a change in livelihood and preventive behavior.

The case of pollutant transfer from upstream to downstream areas along the Nhue River suggests the allocation of health risks over geographical boundaries, resulting in the change of livelihood in downstream areas. Although this was severely found in areas where a large part of wastewater was not properly treated, a geographical allocation of risk potentially happens anywhere. For example, household-level polluting behavior in upstream areas generated large health externalities in downstream areas, representing 7.5% of all diarrheal deaths in targeted drainage areas in Indonesia (Garg et al. 2018). In the Citrum River basin of Indonesia, the benefit of investment in river water quality improvement was estimated to be mainly from the development of sanitation and wastewater treatment in its upstream areas, including Bandung City with a population of approximately 2.4 million (Asian Development Bank and World Bank 2013). The overall economic benefit was estimated as 2.3-fold the investment, and 45% of the benefits were derived from health improvements. Such a geographical allocation of health risk potentially occurs also in high-income countries. For example, the Lake Biwa-Yodo River basin in Japan serves water for 17 million people. Owing to water use by people in the upstream areas, it was estimated that 50% of the population in the basin uses water that was consumed equal or more than five times upstream (Sumitomo et al. 1998). Without great effort to establish 43 wastewater treatment plants in the basin, unreasonable health risks in the downstream areas would not be mitigated. A sanitation measure across upstream and downstream areas is challenging. However, it is vital to properly allocate and mitigate the risks associated with sanitation. Mutual discussion between the upstream and downstream areas is required not only for pollution control but also for health risk allocation justified by people in different contexts, leading to the concept of river basin management or watershed management.

Besides the social allocation of health risks from improper sanitation, sanitation technologies have a function in transferring the risk, except those that can completely sanitize human waste on the site of generation without the help of someone else. In the case of the Nhue River, sewerage without sufficient treatment capacity in Hanoi transferred pollutants to the river and posed the associated health risk to the downstream areas. Originally, sewerage was invented from waterways to transfer human waste to the water body. This technology can remove dirty matter immediately from their living space in the least obtrusive and offensive manner, only by flushing. This convenience was a major socio-economic reason why this system was adopted in most countries (Burian et al. 2000). Instead, nuisance sanitation works (e.g., collecting, transporting, and treating excreta) and the associated health risks, which were originally owned by the people at home, are now allocated to other people. The occupational risk of waterborne diseases by people working in wastewater treatment plants and sewers has been reported. For example, Clark et al. (1976) summarized sewer worker infections such as typhoid fever, Shigellosis, other gastrointestinal bacterial infections, and parasitic infections such as Entamoeba histolytica and Ascaris lumbricoides. An epidemiological study showed that 65.7% and 32.4% of the wastewater treatment plant workers were, respectively, infected by hepatitis A virus and hepatitis B virus at the timing or prior to the study against 32.6% and 5.8% of the control group, respectively, in Greece (Arvanitidou et al. 2004). Furthermore, the prevalence and risk of respiratory and intestinal diseases are caused by airborne microorganisms among wastewater treatment plant workers (Benami et al. 2016; Heinonen-Tanski et al. 2009; Yang et al. 2019). This evidence suggests that a group of people in the society owns the responsibility to maintain sanitation facilities and the associated health risks, and other people live a healthy life at the expense of sanitation workers’ health risks. This can be a form of allocation of health risks to sanitation in society.

Health risk allocation also occurs with on-site sanitation technologies, which accumulate fecal sludge in the facility and therefore require proper fecal sludge management (FSM). Globally, at least 1.8 million people rely on on-site sanitation requiring FSM (Berendes et al. 2017). On-site sanitation and FSM follow the sanitation service chain: excreta containment, emptying, transportation, treatment, and final disposal/reuse (Harada et al. 2016a). The health risks of sanitation are transferred and shared along the service chain. Primarily, emptying work is performed by the expense of the health risks of emptying workers. In the case of Trai hamlet, female farmers were mainly responsible for the service chain between emptying and reuse, potentially owing to health risks, although they substantially mitigated the risk by their protective behavior. However, emptying works are not conducted in a hygienic way in many cases in low- and middle-income countries. For example, in Maputo, Mozambique, 60% of emptying works are estimated to be performed in unhygienic manners (Capone et al. 2020). In addition, the sanitation service chain of FSM often fails in the middle (Peal and Evans 2015). In Mandalay, Myanmar, 67% of fecal sludge from on-site sanitation was emptied as informal business and 64% was illegally dumped (Naing et al. 2019). In other words, the allocation of the responsibility of FSM was released from sanitation workers in the middle of the chain. Although fecal sludge is stored excreta for some years, it also contains fresh excreta from the latest excretion. A variety of pathogens are found in fecal sludge (Yen-Phi et al. 2010). Although the global estimate of the proportion using on-site sanitation with proper FSM was not available owing to insufficient data (WHO and UNICEF 2017), a significant proportion expect to lack proper FSM. Besides the released responsibility of FSM in the middle of the sanitation service chain, the failure of FSM releases and transfers the associated health risk to the public through environmental fecal pollution by dumping fecal sludge. This could be a major challenge for the social allocation of health risks in on-site sanitation and FSM.

The case of Trai hamlet showed the allocation of health risks related to gender at household levels. This trend can be observed in low- and middle-income countries. Hannan and Andersson (2002) suggested that, in low- and middle-income countries, men typically construct latrines, while women usually clean them. Kwiringira et al. (2014) suggested that both women and men see the cleaning of shared latrines as women’s responsibility. Regardless of on-site and off-site sanitation, the handling excreta in households would pose a potential health risk, which is often allocated to women. Further, as suggested in the case of human manure use in Trai hamlet, on-site sanitation with resource recovery often requires additional work with more chances to contact excreta rather than sanitation without resource recovery, and these additional works were mostly done by women. In other words, resource recovery in sanitation in the community is achieved at the expense of women’s health risks. In cases of resource recovery in on-site sanitation, resource recovery work is expected to be linked to the persons who are responsible for cleaning toilets, that is, women at household levels in many cases. As the risk of sanitation workers was observed even in modern sewerage, complete mitigation of the additional health risks derived from resource recovery activities is challenging, especially in the context of low- and middle-income countries. In addition to promoting resource recovery in sanitation, it is important to understand the allocation of potential health risks to a group of people behind the resource recovery as well as to minimize the risk along with the resource recovery activities in sanitation.

5 Concluding Remarks

This chapter demonstrated the social allocation of health risks in sanitation based on examples in Vietnam. Health risks were clearly transferred among different groups in the society. The increased health risks in sanitation even changed the livelihood. As the complete elimination of the risks is fundamentally difficult owing to the nature of the risks, we should understand who owns the health risks and consider if the risk allocation is reasonable and acceptable in society. Society clearly has a responsibility to allocate health risks equitably among groups in society, and to decrease the risk to a socially acceptable level. Since sanitation possibly causes the transfer of health risks, sound social allocation and mitigation of health risks are essential to address social challenges in sanitation.