Water physicochemical properties and quality assessment pH
According to Fakayode (2005), the pH of a water body determines the quality because it affects the solubility and toxicity of metals. The pH of both ground and surface water in the study area is slightly acidic. During the present investigation, the mean pH of the water samples (well) was observed to be less than the WHO (2004) permissible range of 6.5 and 9.2 units. However, the pH level of surface water (6.57 ± 0.21) was within the WHO permissible range. It is important to note that the groundwater sample in the control area is more acidic than the study area. This may be attributed to the composition of rocks and sediments. Furthermore, the high acidity may be linked to the high concentration of CO2 due to more human activities in the control area (Osinbajo 2012). Acidic water has been shown to lower the pH of water, hence, increasing the concentration of heavy metals such as lead, copper, and zinc (SON 2007).
Electrical conductivity (EC) measures the ability of water to conduct electricity, which is related to the amount of dissolved minerals in the water without an indication of which element is present or absent. A high value of EC is an indication of the presence of sodium, potassium, chloride, or sulfate contaminants (Orebiyi et al. 2010). EC conductivity is a good way to measure the total dissolved ions as it has a direct relationship with the total amount of solids in the water samples. This then means that a high number of dissolved ions in water translate to a greater number of ions in water (Adewoye et al. 2013). Analysis of the results of this research shows that the EC of all the water sampled were below the WHO (2004) permissible limit of 1000 μS/cm (Table 2).
Total dissolved solid (TDS)
Total dissolved solids refer to the inorganic and small amounts of organic matter present in solution in water (WHO 2006). There are no known possible health effects associated with the ingestion of drinking waters with high total dissolved solids. Rather, the result of an early epidemiological study shows that low concentrations of TDS in drinking water have beneficial effect. However, the presence of high TDS may be unacceptable to consumers due to the taste and scaling of pipes, boilers, heaters, and household appliances (WHO 2006). All the water samples analyzed in the study area were found to be below the WHO (2004) permissible limits of 500 mg/L. However, the control area has a higher amount of TDS. In the control area, agricultural activity is intensive as well as industrial activities. This may be responsible for the higher values.
Water turbidity is very important because high turbidity is often associated with a higher level of disease-causing organisms such as bacteria and other parasites (Shittu et al. 2008). The turbidity values of all the water samples analyzed were above the WHO (2006) permissible limit of 5 NTU. This may be due to the presence of a large amount of inorganic particulate matter, suspended minerals, bacteria, and plankton, as well as dissolved organic and inorganic substances. The high turbidity values obtained, therefore, indicate that the water located in the study area is unhealthy for human use and consumption. Besides, the high turbidity of the water decreases the concentration of oxygen in the water and the photosynthetic activity of plants and algae (Teng et al. 2007).
Dissolved oxygen (DO)
Dissolved oxygen is one of the most important parameters used to measure water quality and to determine the degree of freshness of a river (Fakayode 2005). It is also used to indicate the level of organic pollution in a water body (Wetzel and Likens 2006). It is important to note that there is a direct relationship between the amount of dissolved oxygen and temperature as well as biological activities (Chapman and Kimstach 1992). The maximum DO level recorded at the mining ponds was (3.5 ± 0.3 mg/L) while 3.1 ± 0.3 mg/L was the minimum recorded in Mararaban-Edege. The high value recorded in surface water may be attributed to the open-source of the water and is highly enriched with oxygen from the atmosphere. For all the water samples analyzed, the values were below the 5-mg/L minimum standard limit (WHO 2006). These low values of DO might retard the biochemical reactions in all the water samples.
Water contamination by heavy metals (Ni, Mn, Pb, Cd, and Fe) was evaluated by comparing their concentrations with the guidelines for drinking water and surface water established by the Standard Organisation of Nigeria (SON). The surface and groundwater resource in the study area plays an important role in the supply of water resources for human consumption, agricultural, and mining activity. Standard Organisation of Nigeria (SON) served as the primary guideline against which to evaluate the heavy metal contamination (Table 3).
The result of heavy metals in the study area shows that the level of nickel in all the water samples was above the recommended level by the Nigerian standard (Table 4) except for well water in Edege-Mbeki. This could pose a serious health challenge to the inhabitants of the study area. Research shows that contact with nickel or nickel compounds has adverse effects such as contact dermatitis, lung fibrosis, cardiovascular, and kidney disease as well as cancer of the respiratory tract. Other health effects include nausea, vomiting, cough, giddiness, headache, abdominal problems, diarrhea, and visual disturbance (El Safty et al. 2018).
The level of manganese in all the water samples analyzed was below the maximum desirable limit as specified in the national and international standards. This means the people may not suffer from the problem of manganese, because excess manganese can increase bacterial growth, interfere with the ingestion of dietary iron, and cause hypertension in patients older than 40 years (Adewoye et al. 2013).
The most significant of all heavy metals are lead (Pb) owing to its toxicity and abundance in the earth’s crust (Gregoriadou et al. 2001). Lead is harmful even in the minutest quantity (Adewoye et al. 2013). Children are more susceptible to Pb exposure than adults; it has been shown to impair children’s physical growth and lowering their intelligence (Agency for Toxic Substance and Disease Registry 2007). Exposure to lead has been associated with attention deficit, hyperactivity disorder, antisocial behavior, an endocrine disorder, and hormonal dysfunction. Furthermore, lead is a known carcinogen and a neurotoxin substance (Bellinger 2008). All the water samples analyzed showed lead (Pb) concentration above the maximum permissible limit as specified by the SON standard, indicating Pb contamination. The high concentration of Pb may result in metallic poisoning that manifests in possible human carcinogens (Bakare-Odunola 2005).
Cadmium is a known carcinogen, especially for lung cancer. It also causes kidney, intestinal, and lung damage. Cadmium is associated with behavioral and learning defects, low fetal weight, and skeletal deformation in pregnant animals. Research also suggests that low sperm count and low birth weight are caused by cadmium (EPA 2007). In the study under review, cadmium was above the national and international permissible limit, meaning there was cadmium contamination.
Fe is a necessary element found in nearly all living organisms and is considered at the border between macro and microelements. Iron-containing enzymes and proteins often contain heme-prosthetic groups that participate in many biological oxidations and transport (Chandra et al. 2009). The concentration of iron ranged from a minimum of 0.608 ± 0.540 mg/L to a maximum of 6.99 ± 6.06 mg/L. The iron (Fe) content of all the water samples was found to be below the WHO (2004) maximum permissible limit of 1 mg/L except for surface water in Edege-Mbeki (6.99 ± 6.06). Though an important component of human dietary requirement required by hemoglobin, a high concentration of iron is stored in the pancreas, heart, spleen, and the liver. This may end up damaging these vital organs. Furthermore, the presence of excess iron in water affects the taste as well as promotes the growth of iron bacteria that increases the rate of rusting (Chukwu et al. 2008).
From the foregoing, the result of the water quality in Edege-Mbeki mining district was within the permissible limit values concerning the physicochemical parameters. However, the water samples were contaminated with alarming levels of Ni, Cd, and Pb. Therefore, the water quality is not good, and it is contaminated; hence, appropriate measures need to be put in place to avoid an outbreak of diseases.
The results of the contamination factor (CF), modified contamination degree (mCd), and enrichment factors (EF) of the water samples are shown in Tables 5 and 6.
All the water samples analyzed showed very high contamination (CF > 6) for Pb and Cd, while the remaining samples showed low to medium contamination. Mining pond water in Edege-Mbeki recorded the highest contamination degree of 11.29 for all the heavy metals analyzed. The well waters of both Edege-Mbeki and Mararaban-Edege recorded moderately low to high values of contamination degree (5.53−8.71).
The enrichment factors (EF) calculated for nickel (Ni) and manganese (Mn) for all the water samples was lower than 2 except for nickel in Mararaban-Edege, thus highlighting their natural origin in the water samples. However, except Edege-Mbeki surface water (mining pond), the enrichment factor for lead (Pb) and cadmium (Cd) in the water samples was found to be greater than 2. On the whole, the presence of lead (Pb) and cadmium (Cd) in the water samples of the study area may be due to anthropogenic origin and artisanal tantalite/columbite mining probably.