Health risk assessment along wastewater recovery and reuse systems in Kampala, Uganda and Hanoi, Vietnam

Background: Reuse and recovery of wastewater in agriculture and aquaculture has gained traction in the new millennium. In view of continued population growth, increasing scarcity of freshwater and other natural resources, the demand to boost food production and efforts to enhance wastewater reuse will increase in the years to come. Indeed, wastewater reuse and the recovery of water, nutrients and energy can generate promising business opportunities and support livelihoods in poor communities, particularly in urban and peri-urban areas of low- and middle-income countries (LMICs). Contact with untreated wastewater is associated with microbial and chemical hazards and thus might negatively affect human health. Standardised, quality-controlled methods to assess and manage health risks are available, such as those described in the World Health Organization (WHO) guidelines for the safe use of wastewater, excreta and greywater. However, the practicability and uptake of these methods have proved difficult in LMICs. There is a paucity of context-specific, quality-based environmental pollution data, epidemiological data and accurate disease burden estimates for highly dynamic environments along wastewater recovery and reuse systems in major urban settings, especially in Africa, Asia and Latin America. Moreover, discharge thresholds and health-based targets need to be reviewed to match the realities of LMICs.
Objectives: This PhD thesis aims to generate evidence of health risks among people living and working along wastewater and faecal sludge management and reuse systems in Kampala, Uganda, a low-income African city, and in Hanoi, Vietnam, a lower-middle-income Asian city. By comparing relevant conditions in these two systems, the thesis seeks to: (i) generate evidence on microbial and chemical contamination and treatment capacities along wastewater management systems; (ii) assess prevalence and risk factors of intestinal parasitic infections in different population groups exposed to wastewater and faecal sludge; (iii) estimate the burden of gastrointestinal infections due to the exposure to wastewater; and (iv) discuss and compare risk assessment approaches and their potential for application along wastewater recovery reuse systems in selected LMICs.
Research partnership: This PhD thesis is embedded in the “Resource Recovery and Reuse” (RRR) project, funded by the Swiss Agency for Development and Cooperation (SDC). Our main partner in this collaborating endeavour is WHO, while other international partners include the International Water Management Institute, the International Centre for Water Management Services, and the Department of Water and Sanitation in Developing Countries, Swiss Federal Institute of Aquatic Science and Technology. In Uganda, we closely work with the Makerere School of Public Health, the Vector Control Division of the Ministry of Health and the National Water and Sewerage Corporation. In Hanoi, our main partner is the Center for Public Health and Ecosystem Research at Hanoi School of Public Health. Moreover, we closely work with the Department of Parasitology at the National Institute of Malaria, Parasitology and Entomology, the National Institute of Hygiene and Epidemiology, and the National Institute of Veterinary Research.
Methods: Two accordant case studies were carried out along the major wastewater recovery and reuse systems in Kampala (along the Nakivubo channel) between September and December 2013 and in Hanoi (along the To Lich River) between April and June 2014. A methodological triangulation was performed, including (i) an environmental assessment; (ii) a cross-sectional survey; and (iii) a quantitative microbial risk assessment (QMRA). In brief, the environmental assessment entailed different standard analyses to observe the variance of microbial contamination (thermotolerant coliforms (TTC), Escherichia coli, Salmonella spp. and helminths (e.g. Ascaris and hookworm eggs) in water at critical control points over a period of two months. In addition, in Kampala, a range of physico-chemical parameters and heavy metal contamination in sediment, soil and plants were measured. Cross-sectional parasitological surveys were conducted to assess intestinal parasitic infections in different population groups (aged ≥18 years) exposed to wastewater and faecal sludge such as sanitation workers, urban farmers and community members living in proximity to wastewater channels. Moreover, comparison groups without exposure to wastewater were included. Stool samples were subjected to the Kato-Katz and formalin-ether concentration methods for the diagnosis of helminth and intestinal protozoa infections. A questionnaire was administered to all participants to identify self-reported signs and symptoms and risk factors for intestinal parasite infections. The QMRA methodology was applied to different scenarios of exposure to wastewater (e.g. farming, flooding of living area, living in informal communities and swimming). Pathogenic strains of norovirus, rotavirus, Campylobacter spp., pathogenic E. coli, pathogenic Salmonella spp., Cryptosporidium spp. and Ascaris lumbricoides were used to estimate annual incidence of gastrointestinal illness and the resulting disease burden.
Results: The environmental assessment revealed high concentrations of bacteria along the major wastewater channels in Kampala and Hanoi (e.g. between 105 and 107 colony forming unit (CFU) per 100 mL). In Kampala, along the Nakivubo channel, the concentration of TTC, biological oxygen demand5 (BOD5), chemical oxygen demand (COD) and total suspended solids (TSS) were 2- to 3-fold higher, when compared with data reported in 2008. Moreover, contamination of bacteria measured in water of the Nakivubo wetland, where urban farming takes place, was above national discharge standards and WHO’s tolerable safety limits for unrestricted irrigation. In Hanoi, the To Lich River water used in wastewater-fed agriculture fields in peri-urban areas showed (beside applied treatment in retention ponds) mean contamination with total coliforms (TC), E. coli and Salmonella spp. of 1.3 × 107, 1.1 × 106 CFU/100 mL and 108 most probable number (MPN)/100 mL, respectively. These values are 110-fold above the Vietnam discharge limits for agriculture reuse and even 260-fold above WHO’s tolerable safety limits for unrestricted irrigation. In both cities, the issue of faecal sludge collection is challenged by the provision of formal and adequate collection services, disposal and reuse solutions. Moreover, industrial pollution is a major issue, while registration and the source control of industries and effluents is lacking, leading to elevated concentration of various heavy metals in the environment.
The cross-sectional survey in Kampala included 915 individuals and revealed that the highest point-prevalence of intestinal parasite infections was found among urban farmers (75.9%), whereas the lowest point-prevalence was found among workers collecting faecal sludge (35.8%). Hookworm was the predominant helminth species (27.8%). Trichuris trichiura, Schistosoma mansoni, A. lumbricoides, and Entamoeba histolytica/E. dispar showed prevalence rates of 15% and above among urban farmers. For all investigated parasite infections, we found significantly higher odds for urban farmers than for the other groups (adjusted odds ratios ranging between 1.6 and 12.9). In Hanoi, the cross-sectional survey included 681 individuals and showed lower point-prevalence rates of intestinal parasite infections than in Kampala. The highest point-prevalence rate of parasitic infection was found among rural farmers (30.2%), with hookworm and T. trichiura being the predominant helminth species (24.8% and 5.4%, respectively). For intestinal parasite infections, we found significantly higher odds for rural farmers than for other groups (adjusted odds ratios 5.8, 95% confidence interval 2.5 to 13.7).
For Kampala, the QMRA estimated an annual disease burden across all 18,204 exposed people of 304,3 disability-adjusted life years (DALYs). Disease burden per person per year (pppy) was highest among urban farmers, sanitation workers and children in slum communities (0.073, 0.040 and 0.017 DALYs, respectively). For Hanoi, QMRA estimated an annual disease burden across 7,125 exposed people of 62.7 DALYs. Disease burden pppy was highest in urban farmers (0.0122 DALYs pppy), followed by sanitation workers (0.006 DALYs pppy) and rural farmers (0.0004 DALYs pppy).
Conclusions: The findings from this 3-year PhD thesis make an important contribution for a deeper understanding of the nexus of urban wastewater recovery and reuse systems, wastewater pollution and their implications for public health in the context of a major East African and Southeast Asian city. In both cities, and besides considerable differences in applied infrastructures, wastewater treatment capacities are insufficient for reducing the levels of microbial and chemical contamination to tolerable levels that would allow for safe reuse in agriculture. Major health risks were observed along both wastewater recovery and reuse systems. Children living in informal communities in Kampala are at very high risk of gastrointestinal diseases, especially due to rotavirus, and pathogenic E. coli and Salmonella spp. Epidemiological survey estimates revealed that urban farmers using wastewater were especially vulnerable for schistosomiasis and soil-transmitted helminthiasis in Kampala, whereas the high risk for urban farmers in Hanoi was only evident by means of QMRA. Indeed, for urban farmers, QMRA estimates were as high as 0.073 and 0.011 DALYs pppy in Kampala and Hanoi, respectively. These estimates are several thousand-fold above the revised WHO health-based targets and 7 and 6 times higher than the estimates made by the Global Burden of Disease study 2010 for an average Ugandan and Vietnamese, respectively. It is argued that the current health-based targets should be set according to local reference levels (e.g. to estimates made by the Global Burden of Disease study 2010). Promoting sanitation safety planning while combining evidence generated from environmental surveys, epidemiological surveys and QMRA can contribute to the understanding of existing systems and hazards along critical control points to better evaluate further investments in infrastructure and coordinate actions to protect public health. Considering the increasing attention to wastewater in the framework of the sustainable development goals (SDGs), more integrated studies using sanitation safety planning approaches are needed to generate sufficient understanding of reuse situations in rapidly changing urban contexts to minimise detrimental health effects and maximise gains from the recovered water, nutrients and energy in urban areas of LMICs.