Human Exposure to Arsenic and Other Potentially Toxic Metals in Some Waters of Biu Volcanic Province

The Biu Volcanic Province is one of the largest Volcanic Provinces in Nigeria covering an area of 5000 km2 with a thickness of 250m. Geochemical analysis of the volcanic soil revealed the complete leaching of the major elements (CaO, K2O, MgO, MnO, and TiO2) from the surface soil probably into water sources. This may explain the extremely high Ca and K levels especially in the stream water where they display values of 348mg/l and 36 mg/l as against 200mg/l to 12 mg/l respectively of WHO admissible limits for drinking water. The accumulation of transition metals in the soil (Co 84-111ppm; Cr: 230-441ppm); Ni: 169-237ppm) is geogenic derived from the weathering of the host basaltic rock. Cr, Ni, and Cu do not easily form soluble ions in solution explaining why they display lower levels below their respective WHO admissible limits for drinking water. The absence in the soil profile and the extremely higher values of potentially harmful elements (PHEs) (As, Se, Sb, and Pb) in the spring and stream water as opposed to the lower values in the wells and borehole water suggest their extreme solubility, direct leaching and transportation of these elements from the surrounding rocks into the surface water, which may be source of exposure to the inhabitants.



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Chapter, 1.1.0 Introduction:

Through physical and chemical weathering processes, rocks break down to form the soils on which the crops that constitute the food supply are raised for humans and animals consumption. Drinking water travels through rocks and soils as part of the hydrological cycle and in the process leached elements in solution (Lar, 2009).

Volcanism and related igneous activities are the principal processes that bring elements to the surface from deep inside the Earth. For example, the volcano Pinatubo ejected on the 2nd of June 1991, about 10 billion tonnes of magma and 20 million tonnes of SO2 and the resulting aerosols influenced the global climate for 3 years (Selinus, 2004). This event alone introduced 800,000 tonnes of zinc, 600,000 tonnes of copper, and 1,000 tonnes of cadmium to the surface environment. In addition to this, 30,000 tonnes of nickel, 550,000 tonnes of chromium, and 800 tonnes of mercury were also added to the Earth's surface environment. Volcanic eruptions redistribute some of the harmful elements, such as arsenic, beryllium, cadmium, mercury, lead, radon, and uranium. It is also important to realize that there is an average of 60 sub aerial volcanoes erupting on the surface of the Earth at any given time, releasing various elements into the environment. Submarine volcanism is even more significant than that at continental margins, and it has been conservatively estimated that there are at least 3,000 vent fields on the mid ocean ridges (Selinus, 2004). Almost all metals present in the environment have been biogeochemically cycled since the formation of the Earth. Human activity has introduced additional processes that have increased the rate of redistribution of metals between environmental compartments, particularly since the industrial revolution. However, over most of the Earth's land surface the primary control on the distribution of metals is the geochemistry of the underlying local rocks. Fundamental links between chemistry and mineralogy lead to characteristic geochemical signatures for different rock types. As rocks erode and weather to form soils and sediments, chemistry and mineralogy again influence how much metal remains close to the source, how much is translocated greater distances, and how much is transported in solutions that replenish ground and surface water supplies. In addition, direct processes such as the escape of gases and fluids along major fractures in the Earth's crust, and volcanic related activity, locally can provide significant sources of metals to surface environments, including the atmosphere and sea floor. As a result of these processes the Earth's surface is geochemically inhomogeneous. Regional scale processes lead to large areas with enhanced or depressed metal levels that can cause biological effects due to either toxicity or deficiency if the metals are, or are not, transformed to bioavailable chemical species (Selinus, 2004). Many elements are essential to plant, human and animal health, but this depends on the dose. Most of these elements are taken into the human body via food, water, in the diet and in the air we breathe. The naturally occurring elements are not distributed evenly across the surface of the Earth, and problems can arise when element abundances are too low (deficiency) or too high (toxicity). The inability of the environment to provide the correct chemical balance can lead to serious health problems. Approximately 25 of the naturally occurring elements are known to be essential to plant and animal life in trace amounts, including Ca, Mg, Fe, Co, Cu, Zn, P, N, S, Se, I, and Mo. On the other hand, an excess of these elements can cause toxicity problems. Some elements such as As, Cd, Pb, Hg, and Al have no or limited biological function and are generally toxic to humans (Selinus, 2007).

Those living on lands with heavily impoverished soils, have such a low intake of essential elements that a very large percentage of the population suffers from a variety of diseases caused by severe mineral imbalances. Likewise, in areas, where there is excess intake of elements due to the abundance of certain minerals in the environment, may leads to high incidences of toxicity.

Environmental pollution arising from the distribution elements by natural or anthropogenic processes distorts geochemical systems. The natural geochemical composition of rocks and soils that make up the environment where we live may become direct risks to human health and may be the underlying cause of element deficiency and toxicity (lar, 2008).

Because of the increasing concern on the negative effects of excess or lack of trace elements to Humans and Animals an attempt will be made to study trace elements concentration in the soils, surface and underground waters of some part of Biu volcanic province.

1.2.0, Location, Extent and Accessibility:

The study area covers some parts of the Biu Plateau. The area is located in the standard sheet 133SW. Lying between longitude 12 ̊ 07ˈE and 12 ̊ 15ˈE and latitude 10 ̊ 31ˈN and 10 ̊ 38ˈN. Biu Town is located at the centre of the Plateau. The towns bordering the area include Damaturu to the North, Mubi to the South and Damboa to the East and Gombe to the West figure1.

The area is fairly accessible and has relatively good network of roads and foot paths. There is a trunk ‘A’ road in the area that stretches from Biu-Damboa road and Biu-Garkida road that give good access for sample collection.



Mr Adamu Usman Muhammad is an exploration Geologist with National Steel Raw Materials exploration Agency, Kaduna, Nigeria. He earned his First Degree in Geology from University of Maiduguri and Master’s in Hydrogeology and Engineering Geology from University of Jos, Nigeria. He also earned an International e-learning course on Introduction to Remote Sensing Technology for Educators organised by Committee on Earth Observation Satellites (CEOS) and International Institute of Research, Brazil (INPE). Mr Usman is registered Geoscientists with council of Nigeria Mining Engineers and Geoscientists (COMEG). He is member Nigerian Mining and Geosciences Sciences Society (NMGS), Nigeria Association of Hydrogeologist (NAH), International Medical Geology Association (IMGA) and International Association of Geochemistry