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===Excessiveness of Arsenic (As)===

===Excessiveness of Arsenic (As)===

'''Geochemistry of Arsenic:''' Arsenic is a metalloid and has high affinity for sulphide-bearing minerals. One of such minerals is pyrite, hence the formation of arsenopyrite (FeAsS). In the tropics, oxidative weathering leads to the formation Arsenite (As3+) and Arsenate (As4+).<ref name=Adeyinka>Adeyinka, O., N. M. Miranda, P. T. Raymond, Y. Abubakar, and C. A. Edafetano, 2013, Arsenic in Rocks of Kaltungo Area, Upper Benue Trough, Nigeria. Earth Resources, 1(1), 5-11.</ref>

'''Geochemistry of Arsenic:''' Arsenic is a metalloid and has high affinity for sulphide-bearing minerals. One of such minerals is pyrite, hence the formation of arsenopyrite (FeAsS). In the tropics, oxidative weathering leads to the formation Arsenite (As3+) and Arsenate (As4+).<ref name=Adeyinka>Adeyinka, O., N. M. Miranda, P. T. Raymond, Y. Abubakar, and C. A. Edafetano, 2013, Arsenic in rocks of Kaltungo Area, Upper Benue Trough, Nigeria: Earth Resources, v. 1, no. 1, p. 5–11.</ref>

'''Mechanism of Toxicity:''' Due to its affinity for sulphur, arsenic in biological systems, attacks sulphur-bearing enzymes by binding and blocking them. Soon, it makes its way through the digestive tract to the liver, spleen and lungs. Although most arsenic is excreted, some are still retained in the skin, hair, legs, nails and teeth.<ref name=Fnklman2010a>Finkelman, R. B., H. E. Belkin, and B. Zheng, 2010a, Health Impacts of Domestic Coal Use in China: Proceedings National Academy of Science, (USA), 96, 3427-3431.</ref> As the concentration increases, adverse health effects result leading to carcinogenic or non-cancer problems. Prolonged exposure to arsenic induces peripheral arteriosclerosis, hair fall-out, retarded nail growth and various types of skin conditions such as hyperkeratosis, hyper- pigmentation and skin malignancies. These levels of disorders are prominent in places with arsenic concentrations of 100−1000μg/l in their groundwater as against 50μg/l stipulated by WHO in 1993.<ref name=Htton>Hutton, M., 1987, Human Health Concerns of Lead, Mercury, Cadmium and Arsenic. John Wiley & Sons Ltd, Uk, 68p.</ref> However, the presence of selenium reduces the toxic effects of arsenic.

'''Mechanism of Toxicity:''' Due to its affinity for sulphur, arsenic in biological systems, attacks sulphur-bearing enzymes by binding and blocking them. Soon, it makes its way through the digestive tract to the liver, spleen and lungs. Although most arsenic is excreted, some are still retained in the skin, hair, legs, nails and teeth.<ref name=Fnklman2010a>Finkelman, R. B., H. E. Belkin, and B. Zheng, 2010a, Health Impacts of Domestic Coal Use in China: Proceedings National Academy of Science, (USA), 96, 3427-3431.</ref> As the concentration increases, adverse health effects result leading to carcinogenic or non-cancer problems. Prolonged exposure to arsenic induces peripheral arteriosclerosis, hair fall-out, retarded nail growth and various types of skin conditions such as hyperkeratosis, hyper- pigmentation and skin malignancies. These levels of disorders are prominent in places with arsenic concentrations of 100−1000μg/l in their groundwater as against 50μg/l stipulated by WHO in 1993.<ref name=Htton>Hutton, M., 1987, Human Health Concerns of Lead, Mercury, Cadmium and Arsenic. John Wiley & Sons Ltd, Uk, 68p.</ref> However, the presence of selenium reduces the toxic effects of arsenic.