7.3 Associated Risk and Mitigation: Health Risks
Improperly managed wastewater/effluent harms living conditions and threatens human health and ecosystems. Untreated wastewater can contaminate drinking water, enter the food chain through fruits, vegetables, and seafood, expose individuals to contaminated waters during recreational activities, and create breeding grounds for disease-carrying flies and insects. Health concerns also arise due to the limited efficacy of conventional secondary treatment techniques in removing pathogens from wastewater.
The following table presents various pathogens and the respective diseases that they can cause.
| Type | Pathogen | Diseases |
|---|---|---|
| Bacteria | Salmonella typhi | Typhus |
| Shigella sp | Bacterial dysentery | |
| Enteropathogenic Escherichia coli | Enteritiden, enterotoxäemien | |
| Pseudomonas aeruginosa | Dermatitis, Otitis | |
| Vibrio cholerae | Cholera | |
| Virus | Poliovirus | Meningitides |
| Hepatitis A | Hepatitis Epidemic | |
| Protozoa | Entamoeba histolytica | Amoebic dysentery |
| Giardia lamblia | Lamblia dysentery | |
| Worms | Ascaris lumbricoides | Reel worm infestation |
| Taenia sp | Tapeworm infestation |
In agricultural reuse, the primary groups at risk are:
- Farmers that use wastewater or excreta-based products for irrigation.
- Consumers of crops that are treated with these products, especially raw-eaten vegetables.
- People who are living near agricultural sites.
The following table provides a summary of health risks by group associated with the use of wastewater for irrigation:
| Group exposed | Helminths infections | Bacterial/Virus Infections | Protozoal infections |
|---|---|---|---|
| Consumers | Significant risk of Ascaris infection for both adults and children due to untreated wastewater | Cholera, typhoid, and shigellosis outbreaks were reported from use of untreated wastewater Seropositive responses for Helicobacter pylori Increase in non-specific diarrhoea if water quality >104/100mL thermotolerant coliforms | Evidence of parasitic protozoa was found on wastewater-irrigated vegetable surfaces, but no direct evidence of disease transmissions |
| Farm workers and their families | Significant risk of Ascaris infection for both adults and children with untreated wastewater Risk remains, especially for children, when wastewater treated to <1 nematode egg per litre Increased risk of hookworm infection in workers | Increased risk of diarrhoeal disease in young children with wastewater contact if water quality >104/100mL thermotolerant coliforms Elevated risk of Salmonella infection in children exposed to untreated wastewater; Elevated corresponds to norovirus in adults exposed to partially treated wastewater | No data |
| Nearby Communities | The risk of Giardia intestinal infection was found insignificant for both treated and untreated wastewater An increased risk of amoebiasis was observed with contact with untreated wastewater | Sprinkler irrigation with poor water quality 106 – 108 TC/100mL and high aerosol exposure was associated with an increased rate of infections Use of partially treated water 104 – 105 TC/100mL or less found to be not associated with increased viral infection rates | No data |
The primary pathways for agricultural wastewater reuse entail various potential points of exposure:
- Direct Contact: Farm workers may come into direct contact with reclaimed wastewater, warranting stringent safety measures.
- Unplanned Public Access: The inadvertent exposure of the public to reclaimed wastewater is a concern that necessitates vigilance in controlling access and maintaining security.
- Indirect Infections: There is a risk of indirect infections by consuming food products irrigated with reclaimed wastewater, underlining the importance of maintaining high-quality irrigation practices.
- Aerosol Contamination: The release of contaminated aerosols during irrigation operations can contribute to spreading pathogens, posing a health hazard.
- Contamination of Freshwater Sources: Furthermore, the infiltration and runoff of reclaimed wastewater into surface and groundwater can contaminate downstream freshwater sources, requiring strict monitoring and protection measures.
Addressing these potential exposure pathways is paramount in ensuring reclaimed wastewater’s safe and responsible agricultural reuse.
Mitigating Health Risks
Most of the health risks can be effectively mitigated through cost-effective measures, such as implementing suitable occupational health precautions.
For comprehensive protection, a multi-barrier approach is recommended as follows:
- Wastewater/Effluent Treatment: Reducing pathogen concentrations through effective wastewater treatment. Secondary or tertiary treatment is required depending on the irrigation method and crop category.
- Crop Restrictions: Limit reclaimed wastewater to fodder crops and/or crops that are typically cooked or processed before consumption.
- Irrigation Method: Prioritise drip/trickle irrigation over sprinkler or furrow irrigation. This approach conserves water and helps avoid issues like salt-related leaf damage and salt accumulation in the root zone.
- Irrigation Scheduling: Implement restrictions on the timing of reclaimed water application before the harvest.
- Location Restrictions: Establish buffer zones to maintain a safe distance between areas of reclaimed water discharge and dwellings, surface water and groundwater infiltration points.
- Human Exposure Control: Ensure measures such as protective clothing, hygiene practices, washing of harvested produce before sale, cooking crops, clear signage indicating the use of reclaimed wastewater, and considering immunisation.
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