HEALTH AND ENVIRONMENTAL RISKS OF USING WASTEWATER IN VEGETABLE PRODUCTION IN URBAN AND PERI- URBAN AREAS OF NAIROBI CITY, KENYA

Abstract

The use of wastewater for farming results in excessive accumulation of heavy metals in soils leading to elevated levels of metal uptake by crops, which in turn affects food safety. The identified knowledge gap in vegetable production using wastewater in urban and peri-urban areas of Nairobi City relates to inadequate awareness concerning associated health and environmental risks occasioned by quality of wastewater used for irrigation and vegetable produce, which the study sought to fill. Cross-sectional, correlational and evaluation research designs were used based on the research objectives. Qualitative and quantitative data was collected using interview guide, questionnaire, observation checklist and visual aids. Quantitative data was also generated by carrying out laboratory analysis of wastewater and vegetable samples. Generated data was analysed using descriptive and inferential statistics. The study findings were presented using tables, pie charts and graphs. The findings showed vegetable farmers use raw influent, the treated effluent, and wastewater-polluted Nairobi River. Farmers used wastewater for irrigation because it is the only source of water, contain plant nutrients, reliable and without restrictions of access. Irrigation methods used are surface irrigation (basin and flood), and spray. Petrol-powered water pump generators are used for pumping and applying wastewater. The most challenging source of wastewater is the raw influent in view of the bad odour and need for dilution to facilitate flow in the channels leading to farmlands. Wastewater used for vegetable production did not meet the Environmental Management and Coordination (Water Quality) Regulations 2006 standards for irrigation water and microbiological quality guidelines for wastewater use in irrigation. Titanium, zinc, lead, chromium, cadmium, cobalt and copper concentrations in the sampled vegetables exceeded the FAO/WHO safe limits in leafy vegetables. Total coliforms and Escherichia coli in the wastewater samples exceeded <1000/ 100ml recommended for total coliforms and nil/ 100 ml recommended for Escherichia coli. Health risks associated with wastewater use in vegetable production include breeding grounds for mosquitoes, bioaccumulation of heavy metals and illnesses such as skin and waterborne diseases like typhoid and cholera. Environmental risks are bad odour, river bank erosion, and resultant pollution. In order to mitigate risks of using wastewater in irrigation, the study recommends sensitization of farmers on the potential risks of using wastewater, carrying out periodic assessment of wastewater to confirm its suitability for irrigation, development and implementation of policy guidelines for safe use of wastewater in irrigation. Theoretical significance of the study is the added body of knowledge on the potential of wastewater reuse in urban and peri-urban areas. The generated data can provide baseline information for the proposed further research, namely; carrying out a similar study in both seasons for comparison purposes; monitoring contamination levels in vegetable produce before and after harvest; and gathering large data set of farmers and consumers and where possible their blood samples and other health indicators be taken to see the impact of wastewater.