Calibration of the instrument
Calibration of the instrument (ARCOS FHS12) was done by the standards prepared before the determinations were done. Because the qualities of results obtained for heavy metals analysis using ICP-OES are seriously affected by the calibration and standard solution preparation procedures. Calibration curves of the metals (Cd, Pb, Cr and Mn), were plotted and validated with their corresponding R2 values for the determination of each metal (Fig. 1). The correlation coefficients of all metals are higher than 0.999, indicating good relationship between concentration and intensity in the range. The values of R2 of the curves were 0.99996, 0.99979, 0.99936 and 099967 for Cd, Pb, Cr and Mn respectively. The respective calibration curve was given in Fig. 1(A-D).
Temperature is a basic water quality variable. It determines the suitability of water for various forms of aquatic life (Chirag 2017). Cool water is generally more usable than hot water, and temperature will impact on the acceptability of a number of other inorganic constituents and chemical contaminants that may affect taste. High water temperature increases the growth of microorganisms and may increase taste, odour, colour and corrosion problems (WHO 2011).
The temperature (oc.) of all sample station was shown in Fig. 2. The temperatures of all sampling station range between 18.9 and 19.2°c (Table 3). As indicated in graph below, the temperature was 19.1, 18.9, 19.2, 19 and 19.2°c in sample 1, 2, 3, 4 and 5 respectively. The World Health Organization (WHO) guidelines recommend a maximum temperature limit of 25°c in the domestic drinking water. The average temperature in this study was 19.08°c, which was found within permissible limit of WHO standards.
Hydrogen Ion Concentration (pH)
pH of water is a measure of amount of hydrogen ions that is present in the water. We measure the pH of the water to determine wither the water is alkaline or acidic in nature. The pH scale is logarithmic and ranges from 0 (very acidic) to 14 (very alkaline). The permissible value of pH for drink water is 6.5 to 8.5 (WHO 2017). The result of pH was shown in Fig. 3. The maximum pH of 7.11 was reported in sample 2, and the least pH of 6.54 was reported in sample 4. Acidic nature of sample 4 may result from carbonic acid deposit formed via reaction of carbon dioxide with rainwater. On the other hand, there are a large number of plants growing around these three sampling station, they release carbon dioxide when they die and decompose. When the CO2 mixes with the water, a weak carbonic acid is formed; this can then cause the pH of the water body to decrease.
Slightly alkalinity of water in sample 2 may be attributed to the presence of bicarbonates into the soil and percolated into the water by runoff. In addition, biological degradation of waste in the soil may be a major influence of this observation. The mean Hydrogen Ion Concentration in Abzana water was found to be 6.86 and it is within the desired limit of WHO standards.
Electrical conductivity (EC)
The electrical conductivity (EC) can be defined as it is a numerical expression that shows the ability of water to hold an electrical current and it is related to ionic forces of the solution and the number of salts dissolved in water (Algamal 2015). Electrical conductivity is used to indicate the total ionisable constituents of water. It is directly related to sum of the cations and anions. As most of the salts in water are present in ionic forms, they make water capable for conducting current (Adhena et al. 2015). According to WHO standards, EC valueshould not exceeded 400 µS/cm (WHO, 2011).
The experimental analysis for electrical conductivity (EC) was carried out for all samples. The result was shown in Fig. 4 above. The EC of all Abzana water samples is varied between 174.5µS/cm to 206µS/cm. This is in the range of WHO standards. The high value of EC in sample 4(206 µS/cm) indicates the presence of a high amount of dissolved inorganic substances in the ionized form at that location. The average value of EC in Abzana water was 191.3µS/cm. The overall result indicates that the water samples in all sampling station of Abzana are within the desirable and suitable range.
Total dissolved solid (TDS)
Total dissolved solids (TDS) are the term used to describe the inorganic salts and small amounts of organic matter present in solution in water. The water with high TDS value indicates that water is highly mineralized. The TDS result in present study was shown in Fig.5. Desirable limit for TDS is 500 mg/l and maximum limit is 1000 mg/l prescribed for drinking purpose (WHO, 2017).
As shown in Fig. 5 above, the total dissolved solids concentration for all samples in present study was observed in the range of 131.4 and 140.1ppm. The highest TDS values of 140.1 ppm and the lowest TDS values of 131.4ppm correspond to samples 4 and sample 1, respectively. The highest TDS value in sample 4 shows the existence of inorganic salts and organic matter and the reason is due to sewage and urban and agricultural run-off. Water containing high total dissolved solid may cause laxative or constipation effects. Potable water should not contain more than 500 ppm of total dissolved solids (TDS) (Sasikaran et al. 2012). The average TDS value of Abzana water was 136.74 ppm which was found within the safe limit of WHO-standards.
Heavy metal analysis
The amount of heavy metal micro contaminants in five water samples was analysed with Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES). Four heavy metals like cadmium (Cd), lead (Pb), chromium (Cr) and manganese (Mn) were observed in all five sampling station.
Cadmium is highly toxic non-essential heavy metal and it does not have a role in the biological process in living organisms. Thus even low concentration, Cadmium could be harmful to living organisms ( Ambedkar and Muniyan 2012). The permissible value of cadmium concentration for drink water is 0.003mg/L (WHO 2017).
Cadmium was reported in water samples of all sampling stations. As shown in Fig. 6, the concentration of Cadmium is varied from 0.00557 to 0.00712 mg/L. High concentration of Cadmium in sample point 4 and 5 which was 0.00712, and 0.00701 mg/L respectively, may be due to the increase mixing of agricultural runoff from agricultural fields to Abzana. The cultivated areas are more concentrated around these two sampling point. Therefore, the increasing consumption of pesticides and herbicides and chemical fertilizers in addition to soil contamination transfer these materials by water irrigation or rainfall (runoff) resulting in the contamination of adjacent surface water (Abzana). The mean concentration of Cadmium in Abzana water sample was 0.00664 mg/L. The result shows the concentrations of Cadmium in all samples are higher than the recommended value of drinking water by WHO. Therefore, the quality Abzana water is not recommended for drinking due to heavy Cadmium stress.
Lead serves no useful purpose in the human body. Even though Lead does not dissolve easily into the environment, it can mix with soil particles or dust and enter underground water or drinking water following rain and surface water runoff. Exposure of Lead can occur when eating food cultivated on soil with high Lead concentrations, drinking contaminated water, breathing polluted air and so on (Abdul-Wahab et al. 2012). The permissible value of Lead concentration in drink water is 0.01mg/L (WHO, 2017)
As shown on Fig. 6, the concentration of Lead in water of all five sampling stations ranged between 0.00761 mg/L to 0.00854 mg/L. The concentration of Lead in station four (0.00854mg/L) was high compared to other sampling station. Slightly high concentration of Lead in station 4 is may be due to disintegration/breakdown and leaching of Lead from Abzana mountain rocks dumps. The mean Lead concentration in Abzana water was 0.008098 mg/L. Thus, the overall result indicates that, in the Abzana stream water Lead content are within the permissible limit. So the level of Lead obtained in the present study does not indicate a potential health hazard to consumers.
Chromium is an essential trace nutrient that is required in small amounts for carbohydrate metabolism, but becomes toxic at higher concentrations. The permissible value of chromium concentration for drink water is 0.05 mg/L (WHO, 2017).
As shown in Fig. 6 above, Chromium was observed in all Abzana sampling station. The concentrations of Chromium were found between 0.02642mg/L and 0.04240mg/L. High concentration of chromium was observed in sampling station 3 and 5. Slightly high concentration of Chromium in station 3 and 5 may be due to the sensitivity of the site for runoff and human activities. The mean concentration of Chromium in this study was 0.03544 mg/L. This value is lower than the maximum permissible limit of Chromium concentration recommended for dinking purpose.
Manganese is essential trace element required for various biochemical processes. The kidney and liver are the main storage places for the Manganese in the body. Manganese is essential for the normal bone structure, reproduction and normal functioning of the central nervous system. Its deficiency causes reproductive failure in both male and female (Saraf and Samant 2013). The permissible value of Manganese concentration for drink water is 0.1 mg/L (WHO 2017).
As shown on Fig. 6 above, the concentration of Manganese over the surface of Abzana water varies between 0.06126mg/L and 0.09053mg/L. However, higher concentration of Manganese was recorded in sampling station 3 and 5 which was 0.08513mg/L and 0.09053mg/L respectively, indicating that the sites are highly polluted areas. High amounts of Manganese in these two sampling sites is may be due to dumping of dead organisms, aquaculture input, low level of water, plant life and animals. The arithmetic average concentration of Manganese obtained from Abzana water sample was 0.076082mg/L and it was higher than the permissible value of WHO standards for drinking purpose. The increments in the concentration were due to the effects of natural and human activities diluted by hot springs bulk waters. Manganese concentration in water may be toxic to a number of crops at a few-tenths, it’s above permissible limit was 0.2 mg/L for long term irrigation as well as available for livestock (Tamiru 2005). In general, the concentration of Manganese was found below the permissible level in all water sample of Abzana and the water quality is safe for drinking and other activities