Assessment of Surface Water Qualities in Ihetutu Mining Areas of Ishiagu, Nigeria, using Water Quality Index Model

Benibo AG^* and Sha’ato R
^*Correspondence: Benibo AG, Department of Chemistry and Centre for Agrochemical Technology & Environmental Research (CATER), Federal University of Agriculture, Makurdi, Nigeria, Email:

Keywords

Contamination • Index • Mining • Quality • Surface water

Introduction

Water is the most important, abundant and useful natural resources on the earth; and without it life cannot exist. It is the basic necessity of human lives and thus should be at an optimal level in quality. Water quality, which refers to the chemical, physical and biological characteristics of water [1] is more important in water supply planning than its quantity just as its purity is also important for the purpose of drinking [2]. Water quality is a measure of the condition of water with respect to the needs of biotic species and or to any human need or purpose [3].

Ihetutu is located in Ishiagu, Ebonyi State of Nigeria, within the Lower Benue trough where Pb- Zn mining has been going on for several decades now. There are a good number of rivers, streams, ponds dotting the area, and that are used by the inhabitants for various purposes including drinking, bathing, irrigation, and washing. The prolonged mining activities in the area, despite the huge economic benefits, were suspected to have serious negative impacts on the environment, especially the qualities of the surface water resources. The mining operations and associated industries generate large volumes of wastewater, drainage wastes and tailings, which plunders the landscape and contaminate the surrounding environment with inorganic pollutants, particularly heavy metals [4].

Various chemicals used during ore processing cause high degree of pollution of surface and groundwater bodies, mostly through wrong application, faulty disposal system, poor storage system and several other conditions prevalent at the time of operations, and these chemicals used at mine sites could also cause intense pollution of the environment [5]. Water pollution increases also in response to human population size, industrialization, the use of fertilizers in agriculture and man-made activity [6], which include mining operations, artisan activities, etc. Some important factors that determine growth of living organisms in a water body include temperature, turbidity, nutrients, hardness, alkalinity, dissolved oxygen, etc. [7].

The suspicion that the qualities of the surface water resources in the study area are seriously deteriorate by wastes from point and non-point sources, mostly the mining processes have made it imperative to carry out this study. Toxic chemical substances constantly being discharged into surface water bodies have become sources of contamination and threat to aquatic biota, as they deteriorate the water qualities. Availability of quality drinking water is of utmost importance to all humans; hence the significance of this research to ascertain the quality of the available surface water resources around Ihetutu. The objective of the study was therefore to assess the suitability of the surface water resources in the study area especially for drinking, using the Water Quality Index (WQI) model.

Materials and Methods

Sample collection and analysis

Samples were collected in four seasons; rainy season, late rainy season, dry season, and late dry season from both study and control areas (12 km away from the study area). Five surface water samples were collected in each season from the river, stream or pond, about 10 cm below the water surface to collect about 500 mL of water sample; and labeled as: SSW3, SSW6, SSW7, SSW8, and CSW1 (Table 1). Collected surface water samples were digested and analyzed for the various physico- chemical parameters using standard methods [8]. Temperature, pH, turbidity, and electrical conductivity were determined in-situ. NESREA [9] regulatory values for surface water were used as standard values to determine the WQI values.

Estimation of Water Quality Index (WQI)

This is a mathematical model that provides a single number that expresses the overall quality of water at a given location and time, based on several water quality parameters; and it can be applied in comparing the quality of water from different sources [10]. WQI also gives the public a general idea of the possible problems with water in a particular area or place. WQI, which is one of the most widely used water quality tool among the existing ones, is defined as a rating reflecting the overall influence of different the various water quality parameters [2].

Water Quality Index (WQI) is calculated using the model proposed by Horton and further developed by Brown et al. [11]; and is expressed arithmetically as:

(1)

Where, n is the number of parameters; and wi which is the unit weight of the i^th water quality parameter, is inversely proportional to the recommended standards for the corresponding parameters, and is expressed as:

wi = K/Si (2)

where K (Constant) = 1/(1/S1+1/S2+1/S3+......+1/Sn)

Saxena and Sharma expressed as the inverse of the sum of inverses of standard parameters used [2], in order to make the parameters expressed by large numbers to weigh less in the final formula (Equation 1) [12]; and S_i = Standard values for different water quality parameters, qi is the water quality rating of the ith parameter, and is expressed as:

(3)

where Vactual is the observed (measured) value of the ith parameter; S_i is the standard permissible value of the ith parameter; Videal is the ideal value of the ith parameter in pure water, and are taken as zero for drinking water except for pH and DO which are 7.0 and 14.6 mg/L respectively [2,10,13].

The calculated Water Quality Index (WQI) values are used to express/ assess the status of the water quality at the given location and time on the scale (Table 2) [10].

Environmental Standards and Regulations Enforcement Agency [9] standard surface water values (s_i), unit weights (w_i), water quality ratings (q_i) and wiqi of the selected physico-chemical parameters in the various surface water samples.

Assessment of quality parameters

•pH: Mean pH ranged from 6.52–7.49 with SSW3 having the lowest value while SSW7 has the highest (Table 8). The lower pH at the mine pit (SSW3) was due to the presence of sulfides such as pyrites (FeS2) which when exposed to water and atmospheric air were oxidized to sulfuric acid and formed Acid Mine Drain (AMD). The generated AMD infiltrated the surface water body and therefore reduced the pH [14].

•Calcium and Magnesium: Range of Ca²⁺ concentration was 6.56–130.44 mg/L (SSW7– SSW3) while that of Mg²⁺ was 2.06–20.89 mg/L (SSW8–SSW6) (Table 8). Calcium availability in water is directly related to hardness of the water [15], as the sum of the levels of Ca²⁺ and Mg²⁺ gives the total hardness of thewater. The high level of calcium could be due to weathering of limestone in the surrounding rocks/soils and underground water beds. Concentrations of magnesium in the surface water were generally found to be lower than the levels of calcium, though both are associated with each other in all kinds of water [2].

•Chloride: Mean concentrations of Cl- ranged from 13.70 mg/L at SSW8 to 795.25 mg/L at SSW3 (Table 8). The presence of chloride in the surface water was related to the agricultural and industrial activities, and chloride rich rocks in the area [16]. High chloride content in water causes eye and nose irritation, stomach discomfort, and increase in corrosive character of the water [17].

•Sulphate: SO₄²- mean concentrations ranged from 19.28 mg/L at SSW8 to 229.25 mg/L at SSW3 (Table 8). The high sulphate concentration in surface water at SSW3, SSW6 and SSW7 could be related to the constant excavation, discharge and dumping of mine wastes containing sulphate salts such as pyrites (FeS) in the surface water bodies.

•Nitrate: Mean NO₃- concentrations ranged from 0.33 to 3.72 mg/L (Table 8). The low nitrate levels in the surface water could be due to its constant utilization by plankton and aquatic plants for metabolic activities [6].

•Dissolved oxygen: DO levels ranged from 5.72–8.76 mg/L (SSW8–SSW6) (Table 8). The low level of DO at SSW3 could be due to chemical and biochemical activities going on in the water body which depended mostly on the dissolved oxygen [18]. Also, the increased water temperature in the semi-closed mine pit due to the concentration of solar energy on the small surface area [19], could hinder the dissolution of oxygen in the water.

•Biochemical oxygen demand: BOD₅ mean levels ranged from 12.19–18.20 mg/L (SSW8– SSW3) (Table 8). This is the amount of oxygen required by microorganisms to decompose organic matter present in the water body [20].

Increase in BOD in could be due to increase in effluent discharge and dumping of organic waste to the stream/river [21]. This includes fertilizers and other organic wastes materials from the farmlands and domestic sources.

•Potassium: K+ concentrations ranged from 4.51 mg/L at SSW8 to 32.93 mg/L at SSW6 (Table 8). The high K+ level could be due to discharge of agricultural wastes including fertilizers containing potassium, from surrounding farmlands [22]. It could also occur naturally in feldspar, micas and clay minerals in the surrounding rocks/soil [18], from where it could leach/sip into the water bodies.

Estimation of WQI in surface water

Average and seasonal WQI values and status of surface water from various sampling stations in the control and study areas are also presented in Tables 8 and 9. The WQI values, which indicated the overall status or qualities of water at the sampling stations, depending on selected quality parameters were determined, using Equation 1. NESREA (2011) regulatory values for surface water were used as standard values [9], and mean values of the physico- chemical parameters used as observed values. The trend of deterioration of surface water qualities at different sampling stations, based on average WQI values was in the order of Pb-Zn mine downstream/run-off (SS6)>Pb-Zn mine site (SS3)>NNPC pipeline (SS7)>Iyiogwe stream (SS8). WQI values for all sampling stations in the study area were higher than that of the control station (CSW1) (Table 8). This confirmed a deterioration of the water qualities. Generally, the status of surface water samples from the study area were “Unsuitable for drinking” with average WQI values >100 [10] in all stations (Table 8). Also, status of surface water from the study area in the various seasons indicated unsuitability for drinking, as the respective seasonal WQI values for all the samples were >100 [10], exception of the late dry season (LDS) surface water status at Iyiogwe stream (SSW8), with WQI value of 98.00 (very poor) (Table 9). The extremely poor (unsuitable) quality/status of the surface water in the study area was due majorly to the high levels of toxic chemical substances discharged into the water bodies (rivers, streams and ponds/pits) both from point and non-point sources such as mine waste dumps, tailings, mine drains, washouts, and surface run-offs, especially in the rainy seasons. These toxic chemical species heavily contaminate/pollute the surface water in the area and thus drastically deteriorate their qualities, and also render them unsuitable for drinking and other domestic purposes.

Conclusion

Results from the study revealed that most of the physico-chemical parameters of surface water in Ihetutu mining areas of Ishiagu were higher than those of the control (background) samples, thereby indicating a deterioration of the water quality in the study area. Average and seasonal WQI values were found to be above 100 which also indicated that the surface water resources in the area were unsuitable for drinking. WQI value for Iyiogwe stream was 98 in the late dry season which also indicated a very poor quality of its water in the season. The results revealed that untreated mine wastewater, dumps, and other contaminants discharged from point and non-point sources into the rivers, streams, and ponds/pits were responsible for the poor qualities of the surface water. Both government and mining companies operating in the area must treat these available surface water resources and make them suitable for drinking and other domestic purposes, and to avoid prevalence water related ailments when consumed. Measures must be taken by the companies operating in the area to ensure that their wastes and other toxic chemical substances generated are not carelessly discharged into the water bodies. Regulatory bodies must also ensure proper monitoring of the activities of these mining companies in the area, and also enforce strict compliance with laid down standards/regulations, to safeguard the surface water in the rivers from being contaminated. This study only covers the status of surface water in the area. Similar studies should therefore be carried out on groundwater status/ qualities in the area.

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