Health risk assessment by consumption of vegetables irrigated with reclaimed waste water: A case study in Thika (Kenya)

Current study was conducted to assess remediation efficiency of heavy metals in Thika waste water treatment plant, human health risk posed by consumption of vegetables irrigated with its reclaimed waste water, and vegetables supplied at Makongeni market. Concentration of Cu, Zn, Cr, Ni and Pb was investigated in the sludge, waste water and vegetables, spinach (Spinacea oleracea), kales (Brassica oleracea var. acephala) and coriander (Coriandrum sativum). Thika waste water treatment plant was efficient in heavy metal remediation. Effluent heavy metal concentration was within recommended concentration for irrigation. Dietary intake of heavy metals and target hazard quotient were used to evaluate health risk posed to consumers. Heavy metals concentrations of vegetables sampled and analyzed were within world health organization permissible limit. Thika waste water treatment plant was found to be efficient; however, regular dredging is essential to reduce accumulated heavy metals in the sludge. Moreover, the study outcome revealed that besides reclaimed waste water that may be perceived to pose great health risk to consumers, the whole food production and distribution chain should be monitored to guarantee food safety.