IMPACT OF SOLID MINERALS MINING ON SELECTED SOIL AND WATER PROPERTIES IN ENYIGBA, EBONYI STATE NIGERIA

CHAPTER ONE Introduction

It is well established that one of the primary anthropogenic sources of heavy metals is mine (Goyer, 1996). Thus mines have significant negative environmental impacts such as pollution of water bodies and farmlands as well as changes of the landscape with subsequent typical changes in flora and fauna (Aremu et al., 2010). Uncontrolled  mining activities have left behind devastated landscape and abandoned mine pits (Plate  1), leading to soil and water erosion. Such activities might have also exposed fertile lands, wells, ponds, streams, rivers and food crops grown around the area to lead (Pb) and other mineral contamination. In most cases, the water from the mining pit is pumped out and sprayed on the surface soil with pipes, thus  exposing  the  surface  soils  and   agricultural  crops  to  higher  metal  contamination (Fakayode and Olu-Owolobe, 2003).

During mining, a fine grind of the ore is often necessary to release metals and minerals, so the mining industry produces enormous quantities of the fine rock particles, in sizes ranging from sand-sized down to as low as a few microns (USEPA, 1994). These fine-grained wastes, known as ‘‘tailings’’, are rich in heavy metals. When introduced into the soil, these heavy metals are absorbed by plants which are consequently consumed by man and livestock, thus leading  to  human  health  risk  and  physiological  disorder  in  plants.  Toxic  heavy  metals entering the ecosystem may lead to a higher accumulation of the heavy metals above critical levels.  This could  cause “silent  epidemic”  of environmental  poisoning  (Jimoh,  2001).  In small  concentrations,  the  traces  of  the  heavy  metals  in  plants  or  animals  are  not  toxic (Kabata-Pendias and Pendias, 2001), but lead, cadmium and mercury are exceptions; they are toxic even in  low concentrations (Galas-Gorcher,  1991). Heavy metals bioaccumulation  in the food  chain can be especially  highly dangerous  to human health (Udom et al., 2003). Contaminated  soils  may constitute  a health hazard  if the metals  are  transferred  to  other reservoirs (Ano et al., 2007). Traditionally, lead, zinc, copper, cadmium, nickel and arsenic are associated with Pb-Zn mineralization.

Cadmium is a heavy metal of major environmental concern because of its high mobility and ability  to  adversely  affect  plants  and  animal  metabolism  even  at  small  concentrations. Furthermore, it has adverse impact on soil biological activity (Kabata-Pendias and Pendias,

1984).

Lead has an average range in soils of 17-26 mg/kg (Stoessel, 2004). It is the most immobile of all the common heavy metals. Lead introduced  at the soil’s surface will  complex with organic matter causing lead to be bound in the soil within the top few centimetres, where organic  matter  content  is  highest  (National  Environmental  Policy  Institute,  2000).  Lead poisoning has dominated the environmental agenda for several decades, with the recent lead poisoning in Zamfara State in 2010 becoming an issue of major concern to environmentalists (Adelekan and Abegunde, 2011).

In soils the natural levels of arsenic are dependent on the source rock type, and the  normal range is 1-40 mg As/kg, with most soils being in the lower half of this range (Alloway, 1995). Levels  may  be  elevated  due  to  mineralization,  contamination  from  industrial  activity (especially Cu smelters) and the use of As-based pesticides.  Some anthropogenic activities including mining and smelting of metal ores, agricultural fertilizers and pesticides have led to assimilation of high As levels (10000 to 20000 mg/kg) in some agricultural areas and human habitats (Adriano, 2001).

Zinc is an essential trace element for both animals and humans. The distribution and transport of Zn in water, sediment and soil are dependent upon the species present and characteristics of the environment. Increased levels can be attributed to natural occurrence of Zn-enriched ores, to anthropogenic sources or even to abiotic and biotic processes.

Anomalous  copper concentration in soils is generally from mineralisation.  Copper is  very mobile in weathering environment (Alloway, 1995), and this is the reason why it can hardly be found in excess in soils. Cu deficiency in soils can generally lead to serious reduction in yield in cereals (Thornton, 1981).

Heavy metals such as lead, cadmium, copper, and zinc are therefore important environmental

pollutants, particularly in areas with high anthropogenic pressure, while it has generally been assumed that these metals are immobile in managed agricultural soils (McBride 1995). Some factors that enhance their mobility can result in more plant uptake or leaching of these metals to ground  water. These factors include  the properties of the  metals,  soil texture, pH and competing cations in the soil solution (Dowley and Volk, 1984). Their presence in the soil, water and atmosphere, even in traces can cause serious problems to all organisms, thus heavy metal accumulations  in surface  and subsurface  soils  is of serious  concern  in agricultural production due to the adverse effects on soil nutrient availability, water and food quality and environmental health (Fergusson, 1990; Ma et al., 1994). Heavy metals get accumulated in time in soils and plants and would  have a negative influence on physiological activities of plants  (e.g.  photosynthesis,  gaseous  exchange  and  nutrient  absorption)  determining  the

reduction  in plant  growth,  dry matter  accumulation  and  yield  (Suciu  et al., 2008).  It  is noteworthy that Ebonyi State is an agrarian state and has a severe problem of reduced quality of portable water. Enyigba is an agrarian community in Abakaliki Local Government Area of Ebonyi State and is richly endowed with solid minerals (lead, zinc, quartzite etc) as well as favorable weather and fertile land for agricultural production (figure 1). The inhabitants of Enyigba which is one of the major communities where mining is heavily done in the state are historically  farmers.  Activities  of small-scale  miners  have left behind  numerous  artificial ponds and pits, which form sources of drinking water and water for agricultural purposes for the inhabitants  especially  during  periods of water  scarcity.  Thus,  soils,  plants  and  water bodies within the vicinity of the mines might have been contaminated by potentially toxic elements from tailings through wind and water.

The major objective of this study was to investigate soil and water contamination in the vicinity of Enyigba mine as impacts of solid minerals mining. The specific  objectives were to:

i)         determine  the  physico-chemical  properties  of  the  surface  (0-15  cm)  and  sub- surface (15-30 cm) soils of the mine site at specified intervals;

ii)        assess the distribution of heavy metals (Pb, Cd, Zn, Cu and As) in the surface (0-

15 cm) and sub-surface (15-30 cm) soils;

iii)       determine the concentration levels of Pb, Cd, Zn, Cu and As in the water bodies within the area;

iv)       assess the pollution status of the soils and water bodies by comparing their metal concentration with WHO standards of 1993.

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