Assessment Of Effectiveness Of Non-Treatment Interventions In Reducing Health Risks Associated With Consumption of Wastewater – Irrigated Cabbage
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Date
2009-07-15
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Abstract
Health risks associated with consumption of wastewater irrigated cabbage can be greatly reduced by treating the wastewater before its use. But wastewater treatment facilities are prohibitively expensive. The World Health Organization (WHO) in 2006 proposed alternative guidelines called non – treatment interventions for low – income countries for reducing health risk associated with wastewater irrigated vegetables. This study focused on the assessment of the effectiveness of non-treatment interventions in reducing potential health risks along production – consumption chain. The first phase of the study was a preliminary component that established the appropriate day for the cessation of irrigation before harvesting of cabbage, and post - harvest handling practices in the market and their contribution to the overall contamination. The study assessed post - harvest handling practices including places of display of cabbage during marketing, removal of outer leaves, and cutting of cabbage in the market for sales. Thermotolerant coliforms and helminth eggs levels were used as indicator organisms for health risk assessment. In this study, four-day cessation of irrigation before harvesting was identified as an acceptable on-farm non-treatment intervention. The four – day cessation of irrigation before harvesting could reduce thermotolerant coliforms by 0.83 log units and 0.6 helminth eggs per 100 g cabbage representing reduction rate of 0.21 log units and 0.15 helminth eggs per day. These reductions were both significant (P ≤ 0.05). Removal of one outer leaf and display of cabbage on table covered with clean sack as intervention at the market reduced thermotolerant coliforms significantly by 0.97 log units (P = 0.000) and 0.2 helminth egg counts which was not significant (P = 0.753). Treatment of cut cabbage with vinegar reduced thermotolerant coliforms significantly by 2.11 log10 units and helminth eggs insignificantly (P = 0.909) by 0.6. Furthermore, treating cut cabbage with salt solution reduced both thermotolerant coliforms and helminth eggs significantly by 1.27 log10 units and 0.7 respectively. Overall cumulative reduction of 3.91 log10 units thermotolerant coliforms and 1.4 helminth eggs were achieved when cabbage pieces were treated with vinegar, and 3.07 log units thermotolerant coliforms and 1.5 helmith eggs for samples treated with salt solution. These figures are however, lower than the 6-7 log units’ reduction proposed in the WHO guideline. The main species of helminth eggs isolated in the irrigation water and on the cabbage were Ascaris lumbricoides, Schistosoma species, Strongyloides stercoralis, Taenia species and Trichuris trichiura. The combinations of the non – treatment interventions have a potential of considerably reducing health risks associated with wastewater irrigated cabbage.
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A Thesis submitted to the Department of Theoretical and Applied Biology,
Kwame Nkrumah University of Science and Technology in partial fulfillment of the requirements for the degree of Master of Science (Environmental Science)