Health Risk Assessment Of Selected Essential And Non-Essential Elements In Food Crops Grown In Kibra Slum, Nairobi-Kenya

Peri-urban agriculture of food crops is practiced in many cities in developing countries, often involving the use of contaminated water and soils, thereby posing health risks for the consumers. Chemical pollutants such as metals present in minute quantities become part of the food chain through occupational exposure in industrial activities, biomagnification and bioaccumulation. In Nairobi City, peri-urban agriculture is practiced in many slum areas, including Kibra slum. Kibra slum, is a densely populated slum with poor drainage systems. Peri-urban agriculture in Kibra slum involves the growing of kales, amaranthus, arrowroots, and spinach food crops which contain high proportions of elements, some of them exceeding allowed limits by WHO. However, high levels of elements in food crops do not necessarily cause health risks, requiring that health risk assessment is done. The study, therefore, determined the levels of selected essential (Mn, Mg, Cu, Fe, Zn and Al) and non-essential (Cr and Pb) elements and assessed the health risks associated with the consumption of the food crops grown in Kibra slum in Nairobi County. Health risk assessment was done using daily intake of metals (DIM), target hazard quotient (THQ) and incremental lifetime cancer risk (ILCR). A randomized block design was used to obtain a representative sample from the six gardens including the control for the study. Analysis of essential and non-essential elements was performed using atomic absorption spectroscopy (AAS) and results obtained used to calculate the health risk assessment indices. ANOVA was used to measure significant differences in levels between gardens at 95% confidence limits. The levels of essential elements ranged as follows; Mn 91.04-374.44, Mg 261.28-532.96, Fe 350.74-1273.68, and Zn 1.18-6.3 µg/g were found to be below the recommended limits by FAO/WHO, implying no health risk. Ranges of the non-essential elements were; Cr 1.15-4.32 and Pb 0.14-0.91 µg/g these were found to be above the EU recommendation, implying a health risk. DIM of Fe 5.81-27.61 and Mn 1.97-8.12 µg/g were above the recommended daily intake amounts, implying a health risk. THQ values for Mn and Fe were more than unit, implying a potential health risk. THQ values for non-essential elements were below unit except for Pb in arrowroots in garden U002 (THQ > 1). ILCR showed that from lead alone 73 people are likely to develop cancer this translates to 0.043% of 0.17M residents. The result of DIM and THQ suggests that consumption of arrowroots, amaranthus, kales, and spinach grown in Kibra slum poses a potential health risk to the consumers. There is need for measures to be put in place to de contaminate the water and soils in a bid to eliminate the health risks.