An assessment of the public health hazard potential of wastewater reuse for crop production. A case of Bulawayo city, Zimbabwe

Wastewater reuse is one possible way in which food production can be improved especially in developing countries where food is often scarce. However, the potential public health risks associated with wastewater use is of major concern. Health concerns are centered on pathogens and other health related pollutants that normally occur in the effluent. This research was conducted in Bulawayo, Zimbabwe during the period December 2005–May 2006. Bulawayo is a semi-arid area, with an average rainfall of 460 mm/annum and experiences frequent droughts. The study aimed at assessing the potential health impacts of effluent reuse for irrigating crops. Some 110 farmers are using wastewater for irrigation of vegetable crops on plots of about 500 m2 each. Samples were collected from the effluent, the fields and vegetables and analyzed for selected quality parameters of health significance. Results were compared to national and international guidelines for effluent use in irrigation. Farmers’ knowledge on potential risks and practices were investigated through interviews.The results show that 70% of the respondents were aware of related health risks of using wastewater for irrigation. Respondents reported no major disease outbreaks. Mean values of pH were 8.1 and 7.3 for effluent and field soil and were within the FAO range of 6.5–8.5 for irrigation. Average temperature was 22.6 °C, while electrical conductivity ranged from 784 to 957 μS/cm and was less than the guideline value of 2000 μS/cm. Total coliforms in the effluent were found to be 7291 cfu/100 ml, while faecal coliforms were 5836 cfu/100 ml compared to the WHO limit of 1000 cfu/100 ml for irrigation. For effluent, cadmium were 0.04 mg/l and exceeded the long-term threshold limit of 0.01 mg/l, while lead was within the limit of 20 mg/l, with an average of 7.2 mg/l. No cadmium and lead were detected in the vegetables. It can be concluded that there is some health risks related to use of the effluent in the field, while for consumption of the vegetables there appears to be no risk. It is recommended that appropriate wastewater treatment mechanisms such as maturation ponds be put in place to reduce the coliform levels. Farmers must minimize direct contact with the effluent. The long-term impact of the irrigation on the soil for about 30 years and the seasonal impact to see variations on results need further studies.