Informations et ressources scientifiques
sur le développement des zones arides et semi-arides

Titre : Naturally occurring potentially harmful elements in the Makueni County environment, South-Eastern Kenya : health implications and community awareness

Auteur : GEVERA Patrick Kirita

Université de soutenance : University of Johannesburg

Grade : Doctor of Philosophy (PhD) Medical Geology 2022

Résumé
The geological environment is the source of nutrients for all biota, including human beings. A complex web of interactions takes nutrients from rocks into drinking water as groundwater percolates through aquifers ; from soils to food crops grown on farms ; and through the air we breathe. However, this supply includes both essential and potentially harmful elements, and depending upon the concentration, it can be beneficial and deleterious. To maximise the benefits and limit the detriments, there is a need to understand the occurrence and movement of naturally occurring potentially harmful elements (NOPHEs) in the geological environment and main pathways, address their potential health implications, and make sure affected communities are well informed of their risk mitigations. Makueni County is a rural region of south-eastern Kenya that faces health threats from NOPHEs. Despite reports of some NOPHEs in groundwater in the area, risk factors based on element concentrations in the source material, all the main pathways, and health implications are not well understood. Additionally, the efficiency of any mitigation measures cannot be established since the level of community awareness of the risk factors of these NOPHEs is unknown. This thesis addresses this knowledge gap by employing multidisciplinary research. The approach determines the concentrations of NOPHEs in farm soils, the main drinking water sources, and selected food crops grown and consumed in the southern region of Makueni County. The agricultural effects of NOPHEs in irrigation water were also established. Furthermore, through an interview-based survey, the health implications and the local community awareness of the health risk factors of NOPHEs were determined. The process involved field investigations, including determination of background geology and hydrogeology, sampling and analysis of farm soil, drinking water and food crops, as well as interviews, and data processing. The outcomes of this research presented in this thesis show that high fluoride (F) in drinking water, farm soil, and food crops, in addition to high salinity in drinking and irrigation water present the main health and agricultural concerns in the study area. Among the drinking water sources analysed (tap water, boreholes, shallow wells, and streams), F concentrations ranging from 0.6-7.17 mg/L were recorded. More than 50% of the water sources had higher than the World Health Organisation (WHO) and Kenya Bureau of Standards (KEBS) recommended F value of 1.5 mg/L in drinking water. Similarly, salinity ranged from very high to extremely high (900-4224 mg/L) in 55% of the analysed water sources. Spatial analysis revealed that the northern region of the area had the highest F and salinity concentrations. The evaluation of the water sources for agricultural suitability revealed that 60% of the water sources presented salinity, Na, and Mg hazards if used for a prolonged time as the sole water source

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