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Geochemistry


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      1.3.1 Occupational Exposure

      Toxic contaminants in serpentinitic geological systems may occur in various environmental compartments, including soils, wild plants, crops, and animals. Once in these environmental compartments, toxic contaminants may enter the human body via occupational and non-occupational exposure [4]. Occupational exposure to toxic contaminants may occur via inhalation in industrial production systems [36]. Typical industries promoting occupation exposure are: (1) mining and mineral processing, including quarries; (2) production of frictional materials such as brake pads, textiles, gas masks, cement, and asbestos; (3) agriculture; (4) construction; and (5) sculpturing, engraving, and carving [4, 37, 38]. Occupational exposure to chrysotile asbestos has been linked to human health risks such as kidney and ovarian cancers, respiratory diseases, and mesothelioma [38].

      1.3.2 Non-Occupational Exposure Routes

       1.3.2.1 Inhalation of Contaminated Particulates

       1.3.2.2 Ingestion of Contaminated Geophagic Earths

      The deliberate ingestion of geophagic earths such as clays and termite mounds, which is referred to as geophagy, may contribute to non-occupational exposure. Geophagy, which is practiced for various cultural and perceived health reasons, is common in several communities in Africa [10, 43]. For example, in Kenya, it is estimated that women consume 40 g per day of geophagic earths, contributing to iron intake of at least about nine times the maximum permissible daily intake [43]. High intake of toxic metals via geophagy has also been reported in other studies [44]. Although data pertaining to geophagy in serpentinitic geological systems are still missing, the intake of toxic contaminants could be higher in such environments compared to non-serpentinitic environments. This risk could be particularly higher among pregnant women and their unborn babies. This is because pregnant women have a high intake of geophagic earths, which is perceived to reduce anemia and nausea [45].

       1.3.2.3 Ingestion of Contaminated Drinking Water

      Toxic contaminants including chrysotile and toxic metals such as Cr and its highly toxic form Cr(VI) have been reported in aquatic systems in serpentinitic geological environments as early as the 1980s [46–48]. Cr(VI) exceeding the maximum permissible drinking water limit of 50 μg/L WHO [49] has also been detected in several aquatic systems, including groundwater, and surface water systems [50–52]. Thus, the consumption of untreated contaminated drinking water, a common practice in most developing countries may constitute a human exposure route to toxic contaminants.

       1.3.2.4 Ingestion of Contaminated Medicinal Plants

       1.3.2.5 Ingestion of Contaminated Wild Foods

      Edible wild plants and animals foods such as mushrooms and honey harvested from serpentinitic geological environments have been reported to have high concentrations of toxic contaminants [4]. For example, wild edible mushroom species (e.g., Russula delica) harvested from serpentine had higher Cd, Cr, and Ni than those from volcanic sites [55]. Higher Al, Zn, and Pb were also observed in edible mushrooms in the Great Dyke (Zimbabwe), a well-known serpentinitic geological system than those from non-serpentinitic environment [56]. Wild honey harvested from the wild and apiaries in serpentinitic environments had high concentrations of toxic metals compared to that from the control [57, 58]. In Kosovo, the concentration of nickel in honey from serpentinitic flora (3.71 mg/kg) was twice that of the non-serpentine one (1.66 mg/kg) [58]. The same authors concluded that the high Ni in honey originated from Ni in dust from serpentine soils, and nectar collected by honeybees from Ni accumulating plants growing on serpentine soils.

      As Gwenzi [4] pointed out, food crops, livestock products such as meat and milk, and edible rodents and insects derived from serpentinitic geological environments may also contain high concentrations of toxic contaminants. For example, paddy rice from serpentine soils had high total Ni concentration of 472 mg/kg and posed human health risks [59]. In Galicia (Spain), forage growing on serpentines accumulated Cr, Cu, and Ni, resulting in toxic concentrations of Ni in kidneys (1.296–1.765 mg/kg) and liver (257 mg/kg) [60]. In the same study, the concentrations of Ni and Cu in animal tissues were significantly correlated to concentrations in the soils and forage (r2 = 0.71–0.87). Insects and rodents occurring on metal contaminated environments have been reported to accumulate toxic contaminants such as metals [61–63]. Although data on toxic contaminants in edible insects and rodents on serpentinitic geological environments are still lacking, one may infer that such edible insects and rodents may also accumulate toxic contaminants [4]. Hence, the consumption of wild foods is a non-occupational exposure route for toxic contaminants.

      1.4.1 Health Risks

       1.4.1.1 Chrysotile Asbestos

      The human health risks of chrysotile asbestos are the most documented among the three groups of toxic contaminants occurring in serpentinitic geological systems. Chrysotile is considered as a carcinogen and has been linked to incidences of human health conditions. High incidences of asbestosis, lung and ovarian cancers, and mesothelioma have been associated with chrysotile asbestos [4, 38]. Specifically, increased incidences of cancer in human populations inhabiting serpentinitic geological environments have been reported in Calabria in Southern Italy) [21, 22]. The toxicity mechanisms and carcinogenicity of chrysotile are quite complex and depends on the physico-chemical properties of the chrysotile [64, 65]. The toxicity mechanisms include (1) breakage of the deoxyribonucleic acid or gene structure and (2) the generation