HUMAN HEALTH RISKS TO POTENTIALLY HARMFUL ELEMENTS EXPOSURE IN ARTISANAL AND SMALL-SCALE GOLD MINING IN KENYA

Abstract

Despite frequent safety concerns regarding artisanal and small-scale gold mining (ASGM) activities, comprehensive investigations are uncommon. This study filled a critical research gap by holistically quantifying exposure to potentially harmful elements (PHEs) from ASGM activities and the subsequent effect on public health in Kenya. Ores, soil, sediment, water, staple food crops, human hair, nails, and urine samples from 19 ASGM villages were collected and analysed for trace and major elements using ICPQQQ-MS. Soil bioaccessibility and the mineral composition of ores were examined. This thesis focuses on PHEs, for which exposure risk factors and potential health effects among 144 ASGM workers and 25 residents were investigated using questionnaires. The ore elemental and mineral composition analysis results revealed natural geological enrichment of major and trace elements in the gold belt, with ASGM activities being the primary mode of dispersing the elements. Pollution indices indicated significant PHE enrichment and pollution of soils, sediment, and water in decreasing order of As>Cr>Hg>Ni>Pb>Cd. Soil As, Cr, and Ni concentrations were 154, 9, and 4 times higher than background concentrations. Soil samples from mining and ore processing sites (96%) had As concentrations up to 7937 times higher than the USEPA 12 mg kg−1 standard for residential soils. Soil Cr, Hg, and Ni concentrations in 98%, 49%, and 68% of the samples exceeded USEPA and CCME standards, with 1–72% bioaccessibility. Total As concentrations in 18% of community drinking water sources exceeded the WHO guideline (10 µg L-1) by up to 36 times. Human exposure to PHEs was predominantly via inhalation of Hg vapours and contaminated dust, consumption of drinking water from mine shafts, springs, and shallow wells (for As>Pb>Cr>Al), and locally grown staple food crops (for As>Ni>Pb>Cr>Cd>Hg>Al) and incidental ingestion of soils via hand-tomouth transmission. Human biomonitoring data revealed ASGM workers’ and residents’ exposure above bioequivalents and reference upper thresholds for Al, As, Cr, Cd, Hg, Ni, and Pb with neurological, respiratory, cancers, skeletal, and cardiovascular health implications. Urinary As, Cr, Hg, Ni, Pb, and Sb in over 76% of ASGM workers and residents exceeded bioequivalents and reference upper thresholds, with median concentrations of 12.3, 0.4, 1.6, 5.1, 0.7, and 0.15 µg L-1, respectively. Overall, increased risks of non-cancer health effects (98.6) and cancer in adults (4.93×10−2) and children (1.75×10−1) were found in ASGM villages. In addition to observed exposure differences between ASGM workers, residents, and controls, positive associations were established between PHE concentrations in environmental, dietary, and human biomonitoring matrices. Urine As concentrations, for example, showed a strong positive correlation with As in drinking water (coeff. +0.958). This thesis highlights the importance of a multidisciplinary approach in integrating environmental, dietary, and public health investigations to inform exposure pathways, better characterise the risks associated with ASGM, and better understand the trade-offs associated with ASGM activities relating to public health and environmental sustainability. The study's findings have been shared with Kenyan medical services and public health authorities for intervention, including technological improvements in ASGM processes, industrial hygiene, and policy formulation to safeguard residents' and workers' health.