The risk of using sewage effluent for irrigation purposes


Although sewage effluent contains high levels of essential plant nutrients and minerals that stimulate growth, the use of effluent however also poses several short-and long-term health threats to the user. Effluent is mostly applied for irrigation during dry seasons with rapid evaporation of water, leaving behind high concentrations of non-biodegradable chemicals, which gradually drain into the groundwater and remain active for long periods of time, rendering it unfit for use.

The practice of re-using treated sewage effluent in times of great water scarcity and drought conditions is recognised internationally. This is mainly evident in the agricultural sector where sewage is diverted for irrigation of crops, orchards or even on recreational sport fields. This practice has now been extended to the irrigation of local household gardens. Local entrepreneurs are exploring this trade of distribution of sewage effluent. With the current water scarcity situation, this trade may be seen as an alternative water source as opposed to fresh water from the municipal distribution system. Section 24 of the CONSTITUTION OF REPUBLIC OF SOUTH AFRICA, (ACT NO. 108 OF 1996), states that everyone has the right to an environment that is not harmful to their health or well-being.

Relative health risk from sewage effluent usage

According to the World Health Organization (WHO), there are significant health implications associated with the use of sewage for irrigation. These “sewage chemicals” contain domestic, industrial, pharmaceutical and hospital waste discharges. The following chemicals may typically be found: salts, minerals, heavy metals, pesticide residues and synthetic compounds such as disinfection by-products, pharmaceutically active chemicals such as endocrine disrupters and various acids. Some chemicals, for example, bromodichloro-methane, may be associated with miscarriages in women, while heavy metals may accumulate in the leaves or roots of many vegetables, posing risks to human health when consumed.

Furthermore, sewage effluent (especially when inadequately treated) also contains high levels of micro-organisms such as bacteria, viruses and parasites, of which the majority may pose a serious health threat after exposure/ingestion. Bacteria such as Salmonella, Shigella, Clostridium, several strains of Eschericia coli, and Vibrio cholera, as well as entero-viruses such as polio-, echo and coxsackie viruses are recognised human pathogens. Parasites or their microscopic ova, such as hookworms, roundworms, tapeworms and bilharzia are commonly found. The majority of these micro-organisms have the ability to remain viable and infective for periods up to 30 days and some even as long as several months.

While the reuse of sewage effluent seems to be sensible in times of water scarcity and may even look good as a long term solution, contact exposure to this water source or soil and plants or irrigated playgrounds and lawns may pose a serious health risk to keen gardeners and recreational sport field users. Symptoms may include diarrhoea, fever, generalised infections, infections of skin abrasions, malnutrition from worm infestation, to more serious long term effects from ingestion of aforementioned chemicals and heavy metals. Whilst the serious water shortage in the Garden Route region is recognised, the continued use of sewage effluent as source of irrigation for household gardens and crops is not recommended.

Please contact the Municipal Health Section of the Garden Route District Municipality for further information at 044- 803 1300.