Abstract:
The use of wastewater to produce food crops particularly vegetables is very prevalent within and outside the urban centers of developing countries. In the capital city of Ethiopia, Addis Ababa, where irrigation water for cultivation of vegetables is commonly derived from the polluted Akaki River, the practice has often been blamed for causing negative externalities to public health and the environment. To address these issues, the studies of this doctoral dissertation mainly focused on five aspects of wastewater and dried faecal matter biochar use in vegetable cropping system of Addis Ababa. In the first study, data were collected on farm through 263 individual interviews and 12 focus group discussions. The difference in perception to quality consideration of Akaki River/irrigation water is highlighted by the result of Kruskal-Wallis H test analysis which shows significant mean value (1.33) of positive perception towards the water quality by male farmers. Among the perceived health risks, skin problems were top-rated health risk while eye burn, sore feet and abdominal pains were rated low across the farming sites. Irrespective of the farming site and gender differences, the most accepted health risk reduction measures were health promotion programs and cessation of irrigation before harvesting. The requisite quantitative data on contamination levels of irrigation water and selected leafy vegetables and potential health implications were covered in study II and III. Lettuce was used as a test crop in study II compared to additional two leafy vegetables (Swiss chard, and Ethiopian kale) in study III. At this stage, an assessment was done to determine the faecal coliform, helminth eggs and heavy metal levels of irrigation water and vegetables harvested from 10 urban vegetable farming sites. Attempts were also made to assess the efficacy of common green salads washing methods and potential health risk associated with the consumption of the analyzed vegetables via computing estimated daily intakes (EDIs) and target hazard quotients (THQs) of heavy metals. The mean faecal coliform levels of irrigation water ranged from 4.29-5.61 log10 MPN 100 ml−1, while on lettuce, the concentrations ranged from 3.46-5.03 log10 MPN 100 g−1. Helminth eggs and larvae were detected in 80% of irrigation water and 61% of lettuce samples. The helminth eggs identified included those of Ascaris lumbricoides, Hookworm, Enterobius vermicularis, Trichuris trichiura, and Taenia. Compared with the WHO recommendations and international standards, the faecal coliform and helminth eggs levels in irrigation water and lettuce samples exceeded the recommended levels. Irrespective of the tested washing methods, faecal coliform and helminth eggs levels were significantly (p
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