Abstract
All living organisms, including humans, obtain and use nutrients from the geological environment, including rocks, surface and groundwater, soil-grown crops, and even from the air. However, exposure to elements originating from both natural and human-influenced sources may be beneficial or detrimental, depending on their concentration levels. Therefore, understanding the occurrence, distribution and mechanisms of potentially harmful elements (PHEs) in the geoenvironment, the potential health outcomes, and communicating with communities about related risks and mitigation strategies is crucial.
The studied area in Bertoua and its environs is an urban and peri-urban area in the eastern region of Cameroon and is susceptible to geoenvironmental contamination. Despite a limited hydrogeochemical study conducted only during the dry season in Bertoua, there remains a scientific gap concerning a broader geochemical composition and spatial distribution of elements in source materials, water, and food crops, as well as the suitability of water for drinking and irrigation in Bertoua and its surrounding areas. This data scarcity also extends to the assessment of health risks associated with consuming contaminated water and food crops. Furthermore, there is a general lack of community-wide awareness regarding the risks posed by these PHEs in the community. This thesis aims to address these gaps by adopting an integrated multidisciplinary approach.
This research was accomplished through systematic field sampling, geochemical analysis of rocks, soils, surface/groundwater sources, and staple food crops. Health data on the prevalence of diseases in the area, along with community practices and knowledge regarding the health implications associated with PHEs from the geoenvironment, were collected through structured interview surveys. Laboratory methods used in this thesis were the Ion chromatography (IC) and the Inductively Coupled Plasma Mass Spectrometry (ICP-MS). Various geochemical and statistical methods were applied for comprehensive data analysis and interpretation. For water studies, the Piper, Langguth, Durov, Gibbs, ionic ratios, Pearson correlation analysis, hierarchical cluster analysis, spatial variation maps and USEPA health risk assessment model were employed. For soil studies, computation of rock chemical alteration, soil pollution indices, correlation, hierarchical cluster analysis, geospatial analysis, bioaccumulation factor and human health risk analysis were employed. For irrigation suitability studies, irrigation parameters and various agricultural models used
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in irrigation were employed. For the community health-based study, statistical tests such as regression and cross-tabulation analysis were employed. The research employed various software platforms such as: Global Mapper® and Surfer®, SPPS®, and Excel® among others.
The research findings indicate that for water samples (n=30), aluminium (Al) concentrations (0.004–0.12 mg/L in surface water; 0.02–1.79 mg/L in groundwater) and NO3- concentrations (surface water: 152.71–188 mg/L wet season, 143.3–166.5 mg/L dry season; groundwater: 0–643.5 mg/L wet season, 0–705.4 mg/L dry season) exceeded their respective World Health Organization guidelines of 0.01 mg/L and 50 mg/L across all water sources. Rock-water interaction was identified as the dominant hydrogeochemical process, with additional contributions from anthropogenic activities. Water types followed a decreasing order of abundance: Na+-K+-SO42- > Ca2+-HCO3- > Ca2+-SO42- > Ca2+-Cl-. Spatial distribution maps showed high NO3- levels throughout the study area and elevated Al concentrations in the southern, south-eastern, north-eastern, and northern zones of the study area. Human health risk assessment indicated high oral hazard quotients (HQoral >1) for Al, NO3-, Fe, and Se, with no dermal exposure.
Water quality for irrigational suitability revealed that groundwater EC ranged from 39–750 μS/cm, and TDS from 19–380 mg/L, while surface water EC ranged from 13–361 μS/cm, and TDS from 6–181 mg/L, all within World Health Organization guideline limits (EC: 400 μS/cm, TDS: 1000 mg/L), thus suitable for irrigation. Also, the Na+ and K+ concentrations contributing to water hardness were below their permissible thresholds. Only NO3- exceeded the FAO (1985) recommended safe limit for irrigation water. The Sodium Adsorption Ratio (SAR) (<10) and Residual Sodium Carbonate (RSC) (<1.25) classified all water samples as excellent for irrigation use. The Permeability Index (PI) (50 – >75) and Magnesium Adsorption Ratio (MAR) (<50) indicated that 93.3% of the samples were suitable, whereas 6.7% were unsuitable (PI: <25 – >25, MAR: >50). The Kelly Ratio (KR) (<1) showed; 40% suitability and 60% unsuitability (KR >1). Finally, the FAO, Wilcox, and USSL diagrams classified 90% of the samples as suitable and 10% as unsuitable for irrigation. The Integrated Water Quality Index (IIWQindex) was 1524.96 for the wet season and 1295.76 for the dry season, making the water excellent for irrigation (class ≥ 80).
Soils (n=10) and staple food crops (n=6) generally exhibited high concentrations of Al, NO3-, F-, Fe, Ba, Cu, Cr, Mn, Co, Ni, Pb, As, Zn, and Se, surpassing their respective Food and Agriculture Organization/World Health Organization guideline values. The daily metal intake (DMI) of PHEs was highest for NO3-, Al, and Fe in both adults and children. The
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total hazard risk index (THRI) ranged from 0 to 10.63 for adults (with values <1 only for Cr, Co, and Se) and 0 to 16.43 for children (with values <1 for Ni, Se, and Ba). Carcinogens such as Cr, As, and Pb were found at concerning levels in all staple food crops, with Cr posing the highest risk to both demographic groups. Children were identified as the most vulnerable group to the consumption of these contaminated crops. Correlation analyses showed that PHEs in soils and water sources originate from a combination of geogenic processes and anthropogenic activities.
A health survey with 196 respondents examined community perceptions, practices, and knowledge regarding drinking water quality, food safety, and associated health risks. Due to an inadequate municipal water supply, most respondents (76%) preferred groundwater. Additionally, 83.2% reported not boiling their water, and 81.2% did not filter it. Fertilizer use was minimal, with only 9% using NPK and 10% using cow dung. The most common symptoms related to waterborne PHEs included fever, memory loss, and dizziness (71% in children, 69% in adults). Symptoms linked to NO3- included headaches, difficulty swallowing, and abdominal discomfort. Contaminants such as Se, Fe, F-, Ba, Pb, As, Cr, Zn, and Cu in food crops were associated with symptoms like loss of coordination, diarrhoea, and paralysis. Chronic illnesses commonly linked to PHEs included gastrointestinal challenges in children and hypertension in adults. Health data from the district revealed the most common disease prevalence in decreasing order: gastroenteritis, hypertension, anaemia, flaccid paralysis, and dementia. Furthermore, demographic analysis revealed that 81% of respondents lacked awareness regarding the health issues associated with harmful elements in contaminated food and water, despite reported health concerns within the study population.
The research outcomes demonstrate that, while drinking water is an established pathway for PHEs (including Al and NO3-), some staple food crops cultivated and consumed in this region are also significant contributors to human exposure to multiple PHEs, including F-, Fe, Ba, Cu, Cr, Mn, Co, Ni, Pb, As, Zn, and Se. Additionally, although most water sources were suitable for irrigation, the high NO3− concentrations in the water sources may adversely affect plants, crops, and livestock.
These findings underscore the urgent need for integrated public health interventions, comprehensive environmental monitoring, and evidence-based policy development to empower populations with the knowledge required to mitigate PHEs exposures, risks and protect public health in PHEs-impacted areas like Bertoua and its environs, Cameroon, as
well as in other regions worldwide facing similar challenges.