Naturally Occurring Potentially Harmful Elements in Groundwater in Makueni County, South-Eastern Kenya: Effects on Drinking Water Quality and Agriculture

Makueni County is located in the semi-arid south-eastern Kenya region characterized by unreliable rainfall and limited surface water resources. This necessitates a high reliance on groundwater for domestic and agricultural use. In this paper, we report on the physico-chemical characteristics of 20 drinking water sources (boreholes, shallow wells, streams, and tap water) collected during the dry season (November 2018), the geochemical processes controlling their composition, and their suitability for drinking water and irrigation. Of all the physico-chemical parameters analysed, the concentrations of total dissolved solids, hardness, electrical conductivity, magnesium, calcium, chloride, and fluoride exceeded the permissible drinking water limits set by both the World Health Organization (WHO) and Kenya Bureau of Standards (KEBS) in up to 55% of the samples. The dominant ions reflect the high salinity in the water that ranged from very high to extreme in up to 50% of samples. The northern region shows the highest concentrations of the dominant parameters. The water type is predominantly Ca-Mg-HCO3 with a trend to Ca-Mg-Cl-SO4. Rock weathering and evaporation are suggested to be the primary controls of groundwater geochemical characteristics. High salinity and fluoride, which are associated with reported undesirable taste and gastrointestinal upsets, as well as cases of dental fluorosis are some of the effects of consuming groundwater in the region. These two parameters can be attributed to the weathering of biotite gneisses, granitoid gneisses, migmatites, and basaltic rocks that occur in the area. The high salinity and alkalinity of most of the samples analysed, renders the water unsuitable for irrigation in the study area

Potential fluoride exposure from selected food crops grown in high fluoride soils in the Makueni County, south-eastern Kenya

Makueni County, located in south-eastern Kenya, faces challenges such as limited potable water and restricted food supplies as the result of semi-aridity. High fluoride (F) concentrations have been reported in drinking water with resultant dental fluorosis affecting the local population. To determine the potential F exposure through the consumption of food crops grown in the area, F concentration was assessed in the main five locally grown and consumed crops. Additionally, the water-soluble F fraction was determined from 30 soil samples with mineralogical determination of 20 samples. Mean F concentration in the food crops was in the order; 700, 288, 71.2, 36.6, and 29 mg/kg in kale, cowpeas leaves, green grams, cowpeas (legume portion), and maize, respectively. The F concentration in farm soils ranged from 0 to 3.47 mg/kg (mean of 0.87 mg/kg) and showed a significant strong positive correlation (p = 0.03, r = 0.89) with F values in the crops. Apatite, muscovite, and biotite were identified as the F-rich minerals present. While considering two hypothetical F absorption fractions (75 and 100%), the estimated average daily dose (EADD) of F from consuming the crops ranged between 0.004 and 65.17 mg/kg/day where the highest values were from the vegetables. Most of these values were higher than the F reference dose (RfD) of 0.06 mg/kg. The estimated EADD values of several hypothetical meals prepared from the analyzed crops revealed that steamed kale and maize porridge pose the highest health risk of F associated diseases to the local population, whereas boiled cowpeas pose no health risk. Children, due to their higher daily energy requirement and low body weight, were the most vulnerable group at risk of high daily F intake relative to the RfD. These results suggest that consumption of the analyzed food crops in Makueni County may significantly contribute to F related diseases in the local population. This creates a food security issue for the area because of the potential health risks associated with these crops which are highly relied upon in the semi-arid area with a limited selection of food crops available and viable to grow

Public Knowledge and Perception of Drinking Water Quality and Its Health Implications: An Example from the Makueni County, South-Eastern Kenya

Due to the semi-arid nature of Makueni County in South-Eastern Kenya, there is a high dependence on groundwater resources for domestic use. Reliance on this source of potable water may have health implications for the population, given the presence of several naturally occurring and potentially harmful elements reported from aquifer source rocks, soil, and water in the area. A survey involving questionnaires and focus group discussions (FGDs) was conducted with 115 individuals to determine the local population’s knowledge, attitude, and perceptions of their drinking water quality and its health impacts. The results show that most respondents (67%) preferred piped water because it was pre-treated and not saline. Only 29% of the respondents were very satisfied with the taste of their drinking water, while the rest complained about varying salinity levels, ranging from slightly salty to very salty. This low satisfaction might have influenced the low daily drinking water consumption (1–2 L) by most respondents. Health issues reported by many (43%) respondents in the area include diarrhoea and gastrointestinal upsets, which may be associated with the saline nature of the drinking water. Elevated fluoride (F−) in the local groundwater was reported, and the health effects remain a concern. Although 91% knew someone with dental fluorosis, 53% did not know the deleterious effects of high F− in drinking water. Most respondents (59%) associated the salty nature of the water with dental fluorosis, and as a result, 48% avoided drinking the salty water to prevent the condition. Despite the high prevalence and known psycho-social effects, most people did not perceive dental fluorosis as a severe health threat. The increased health risks associated with high salinity and high F− in drinking water in Makueni County are poorly understood by most residents, regardless of their education, gender, or age. This warrants an immediate public health education programme and detailed epidemiological studies to determine all the health effects associated with naturally occurring, potentially harmful elements in groundwater in the area

A review on the occurrence of some potentially harmful elements in the natural environment and their health implications: examples of fluoride, iron and salinity in the South-Eastern Kenya Region

Makueni, Machakos and Kitui Counties, located in the Arid and Semi-Arid land (ASAL) region of south-eastern Kenya, receive low and unreliable rainfall which necessitates a high dependence on groundwater for potable, domestic and agricultural purposes. The geology of the region is dominated by metamorphic rocks of the Precambrian Mozambique Mobile Belt and Tertiary-Pleistocene volcanic rocks both of which are known to have highly variable concentrations of diverse naturally occurring potentially harmful elements. The geochemical composition of local soils and groundwater reflect the chemistry of the parent geological material and this constrains the type and concentrations of elements and nutrients in drinking water and locally produced food. This review reports the occurrence of some commonly reported potentially harmful elements, fluoride (F−), iron (Fe) and salinity, in groundwater, farm soil and commonly consumed food crops in parts of south-central Kenya and considers their potential health implications. Drinking water issues are documented. The presence high F− in drinking water is associated with dental fluorosis in Machakos and Makueni Counties. Iron in Makueni and Kitui Counties is associated with an undesirable brown colour and taste in drinking water. Salty water is a common drinking water problem in most parts of Kitui and Makueni Counties that has led to the abandonment of shallow wells. Groundwater and spring water analysis show elevated F− (max. 9.30 mg/l), Fe (max. 7.60 mg/l) and salinity (max. hardness, chloride (Cl−) and magnesium (Mg) of 950 mg/l, 260 mg/l and 122.40 mg/l, respectively). In soils, elevated F− levels were reported in Kitui County while acidity and salinity in soil were reported throughout the region. The effects of high F− soils are not reported, but acidic and saline soils were found to be unproductive for maize and green grams farming. Chemical and nutritional analyses of food crops grown in the area are essential to determine overall health implications on the local population. Detailed soil and groundwater geochemical databases are required in the region in order to assess the potential health implications of the natural environment on the local population