Assessment of the level of some selected heavy metals and physicochemical in Abzana water samples, Kibet woreda, Ethiopia

This study was conducted to investigate the contamination level of Abzana water in Asano district. Five water samples were collected from different point of Abzana water. Some physicochemical parameters and four heavy metals (Cd, Pb, Cr and Mn) concentration were analyzed using standard procedures, and the results were compared with World Health Organization guideline values. The results of the present study have shown the temperatures of all sampling station range between 18.9 and 19.2 °C. The pH was found to be of range from 6.54 to 7.11, whereas the electrical conductance was 1.745 × 102 to 2.06 × 102 (µS/cm). In addition, the lowest value of total dissolved solids was 1.314 × 102 mg/L and the highest was 1.401 × 102 mg/L. In contrast, four heavy metals were analyzed and compared with standards of drinking water. The results indicate that the mean concentration of Cd (6.64 × 10−3 mg/L) exceeded the standards, but the mean concentration of Mn, Pb and Cr was founds within the standard limit at 7.608 × 10–2, 8.10 × 10–3 and 3.5442 × 10–2 mg/L, respectively. The concentrations of the investigated metal (Cr, Pb and Mn) and all physicochemical result of Abzana water from Asano kebele were found below the guidelines for drinking water. However, the concentration of Cd in Abzana water sample was found above the permissible limit of World Health Organization standards. Therefore, it was not safe for drinking and health effect according metals what we have studied here.


Introduction
Water plays an important role in the world economy, as it functions as a universal solvent, which has the ability to dissolve many substances of organic or inorganic compounds, industrial cooling and transportation (Bernard and Ayeni 2012;Kinuthia et al. 2020). Water is obtained from a variety of sources like; wells, stream, rivers, lakes, reservoirs etc., which support drinking water supply, livestock needs, irrigation, industrial and many other commercial and domestic purposes (Alemu et al. 2015). The quality of these water source may be affected by; a rise in anthropogenic activities, a raise in population, urbanization, global climate change and any pollutant either physical or chemical (Aremu et al. 2011). Chemical contaminants of water mainly consist of heavy metals, fertilizers and thousands of toxic organic compounds (Jackson et al. 2001). Metal pollution can result from direct atmospheric deposition (Shanbehzadeh et al. 2014), geologic weathering or through the discharge of agricultural, municipal or industrial waste products (Gerenfes and Teju 2018). Heavy metals in water occur only in trace level but are damaged central nervous function, blood irregularity and also badly effect vital organs such as kidneys and liver (Baroni et al. 2007;Malsiu et al. 2020).
In developing countries, like Ethiopia, have suffered from a lack of access to safe drinking water from improved sources and to adequate sanitation services (Supply and Programme 2015). As a result, people are still dependent on unprotected water sources such as rivers, streams, springs and hand dug wells. Since these sources are open, they are highly susceptible to flood and birds, animals and human contamination (Addisie 2012;Mebrahtu and Zerabruk 2011). Over 60% of the communicable diseases in Ethiopia are due Editorial responsibility: Samareh Mirkia.
to poor environmental health conditions arising from unsafe and inadequate water supply and poor hygienic and sanitation practices (Peletz et al. 2016).
In Ethiopia, much research has been carried out with regards to assessment of heavy metal concentrations in different river and lakes like in; drinking water from selected areas in Gurage Zone (Sage et al. 2018), Hawassa and Ziway lakes (Gebremedhin and Berhanu 2015), Lake Baseka (Abduro 2017), Rebu river in Oromia region (Tadesse et al. 2018), Abaya and Chamo Lakes (Mebrahtu and Zerabruk 2011), Chilga drinking water (Lijalem et al. 2015). All these findings give conclusive evidence that water quality problems are rampant both with small-scale and large-scale water delivery systems in the country. This may pose high health risks to users unless prompt intervention is undertaken. Abzana is also one of the stream water located in Kibet woreda Asano district and often used as a drinking and other domestic activities for the people of Asano district. There is no study conducted to prove and asses the quality of Abzana water before. Therefore, the present study was conducted on Abzana water to check the quality and generate baseline data for further studies. This study was conducted from September 10, 2020 to April 20, 2021 in Werabe, Ethiopia.

The study area
The study was conducted in Kibet woreda Asano kebele, which was located in 30 km north direction from the town of Werabe and about 150 km south of Addis Ababa, Ethiopia's capital city. Abzana stream water is located in Kibet woreda Asano kebele. The people around Asano use Abzana water for farmlands, drink, other domestic activities, etc. The areas are under continuous cultivation throughout the year and have been supplying significant portion of a wide variety of vegetables.

Apparatus and chemicals
Apparatus such as; different size beakers, measuring cylinders, volumetric flasks, burettes, funnel, test tubes, hydrometer, thermometer, oven, electronic-mill, plastic bags, stirrer, Erlenmeyer flask (different sizes), refrigerator, filter paper are used. All chemicals of high purity analytical grade reagents were employed; 69% nitric acid (HNO 3 ) and 35-38% hydrochloric acid (HCl) (35-38%) were used for both extraction and acid digestion procedures. Distilled water was used for preparation of stock standards and intermediate standard solutions of manganese (Mn), chromium (Cr), cadmium (Cd), and lead (Pb) metals.

Instrumentation
Digital analytical balance used for all measurements of samples and chemicals, Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES) was to determine the concentrations of Mn, Cr, Cd and Pb. Thermometer, digital pH meter, Conductivity meter and TDS meter are used to measure the temperature, pH, electrical conductivity (EC) and total dissolved solid of the water sample respectively.

Sample collection
The present study has carried out at five sampling stations on Abzana stream water. Sampling sites for water were selected purposely, which represents the entire water bodies having ecological significance. To avoid any kind of contamination during sampling extra care was taken and the bottles were rinsed several times with the water being collected or filled. The bottles are filled and then sealed tightly to avoid headspace that causes loss of samples because of oxidation. However, on-site analyses were comprised for temperature, EC, pH and TDS were urgently determined when receive the sample in the laboratory because of their unstable nature. All analyses were carried out at a standardized laboratory using international regulatory methods.

Water sample digestion
100 ml of the water sample was measured with a measuring cylinder, and 5 ml of concentrated hydrochloric acid was added to it. The solution was then transferred into a conical flask and a few boiling chips were added into the flask and heated on the hot plate for one hours at 95 °C to 50 ml. Digestion is complete as shown by a light color clear solution. Then transferred into 100-ml volumetric flask and distilled water was added to fill up to the mark where it was filtered and transferred into the pre-cleaned sample bottle and taken for further Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES) analysis.

Heavy metal analysis
Four trace elements were analyzed from the diluted digests of water samples using Inductively Coupled Plasma Optical Emission Spectroscopy (ARCOS FHS12) using aqueous calibration standards prepared from stock standard solutions of the respective elements. The instrument parameters optimized according to the manufacturers were provided. Finally, the data were statistically analyzed using Excel 2007 and Origin 8.1 software.

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 R 2 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 R 2 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. 1A-D

Temperature
Temperature is a basic water quality variable. It determines the suitability of water for various forms of aquatic life (Shah 2017). Cool water is generally more suitable than hot water, and temperature will affect 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, odor, color and corrosion problems (WHO 2011). As shown in Table 1 above the temperatures were 19.1, 18.9, 19.2, 19 and 19.2 °C in sampling station one, two, three, four and five, respectively. The temperatures of all sampling station range between 18.9 and 19.2 °C and the average temperature in this study was 19.08 °C. The World Health Organization (WHO) guidelines recommend a maximum temperature limit of 25 °C in the domestic drinking water. Therefore, the temperature in present study was found within permissible limit of WHO standards. pH pH of water is a measure of amount of hydrogen ions that is present in the water(El Morhit and Mouhir 2014; Ma et al. 2020). 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 Table 1. The maximum pH of 7.11 was reported in sampling station two, and the least pH of 6.54 was reported in sampling station four. Acidic nature of sampling station four 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 CO 2 mixes with the water, a weak carbonic acid is formed and this can cause the pH of the water body to decrease. Slightly alkalinity of water in sampling station two may be due 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
The electrical conductivity 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;Yasin et al. 2015). Electrical conductivity is used to indicate the total ionisable constituents of water (Rahmanian et al. 2015). As most of the salts in water are present in ionic forms, they make water capable for conducting current (Werkneh et al. 2015). According to WHO standards, EC value should not exceeded 400 μS/cm (WHO 2011). The experimental analysis for EC was carried out for all samples. As shown in Table 1, the EC of all Abzana water samples was varied between 1.745 × 10 2 to 2.06 × 10 2 µS/cm. This is in the range of WHO standards. The high value of EC in sampling station four (2.06 × 10 2 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 1.913 × 10 2 µS/cm. The overall result indicates that the water samples in all sampling station of Abzana are within the desirable and suitable range.

Total dissolved solids
Total dissolved solids 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. Desirable limit for TDS is 5 × 10 2 mg/L and maximum limit is 1 × 10 3 mg/L prescribed for drinking purpose (WHO 2017). As shown in Table 1, the TDS concentration for all sampling station in present study was observed in the range of 1.314 × 10 2 and 1.401 × 10 2 mg/L. The highest TDS values of 1.401 × 10 2 mg/L and the lowest TDS values of 1.314 × 10 2 mg/L correspond to sampling station four and sampling station one. The highest TDS value in sample four 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 5 × 10 2 mg/L of TDS (Sasikaran et al. 2012). The average TDS value of Abzana water was 1.3674 × 10 2 mg/L, 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 analyzed with Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES). Four heavy metals (Cd, Pb, Cr and Mn) were observed in all five sampling station of Abzana water.

Cd
Cd is highly toxic non-essential heavy metal and it does not have a role in the biological process in living organisms (Rafati Rahimzadeh et al. 2017). Thus even low concentration of Cd could be harmful to living organisms  (Ambedkar and Muniyan 2012). The permissible value of Cd concentration for drink water is 3 × 10 −3 mg/L (WHO 2017). As shown in Fig. 2, the concentration of Cd was varied from 5.57 × 10 -3 to 7.12 × 10 -3 mg/L. High concentration of Cd was observed in sampling station four and five, which was 7.12 × 10 -3 , and 7.01 × 10 -3 mg/L, respectively. This may be due to the increase mixing of agricultural runoff from agricultural fields to Abzana. In 2019 (two years ago), the area was badly affected by flood disaster which affect the life of both plants and animals and also cultivated areas are more concentrated around Abzana water. Therefore, the increasing consumption of pesticides and herbicides and chemical fertilizers in addition to soil contamination transfer these materials by water irrigation or runoff resulting in the contamination of adjacent surface water (Abzana). In general, natural and human activities are the main reason to the increments in the concentration of Cr in Abzana water. The mean concentration of Cd in Abzana water sample was 6.64 × 10 -3 mg/L. The result shown us the concentrations of Cd in all samples are higher than the recommended value of drinking water by WHO. Therefore, the quality Abzana water was not recommended for drinking due to heavy Cd stress.

Pb
Pb serves no useful purpose in the human body. Even though Pb 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 (Payne 2008). Exposure of Pb can occur when eating food cultivated on soil with high Pb concentrations, drinking contaminated water, breathing polluted air and so on (Abdul-Wahab and Marikar 2012). The permissible value of Pb concentration in drink water is 1 × 10 -2 mg/L (WHO 2017). As shown on Fig. 2, the concentration of Pb in water of all five sampling stations ranged between 7.61 × 10 -3 to 8.54 × 10 -3 mg/L. The concentration of Pb in station four (8.54 × 10 -3 mg/L) was high compared to other sampling station. Slightly high concentration of Pb in station four is may be due to disintegration/breakdown and leaching of Pb from Abzana mountain rocks dumps. The mean Pb concentration in Abzana water was 8.098 × 10 -3 mg/L. Thus, the overall result indicates that, in the Abzana stream water Pb content are within the permissible limit. Therefore, the level of Pb obtained in the present study does not indicate a potential health hazard to consumers.

Cr
Cr is an essential trace nutrient that is required in small amounts for carbohydrate metabolism, but becomes toxic at higher concentrations (Tumolo et al. 2020). The permissible value of Cr concentration for drink water is 5 × 10 -2 mg/L (WHO 2017). As shown in Fig. 2, Cr was observed in all Abzana sampling station. The concentrations of Cr were found between 2.642 × 10 -2 mg/L and 4.24 × 10 -2 mg/L. High concentration of Cr was observed in sampling station three and five. Slightly high concentration of Cr in these two stations may be due to the sensitivity of the site for runoff and human activities. The mean concentration of Cr in this study was 3.544 × 10 -2 mg/L. This value is lower than the maximum permissible limit of Cr concentration recommended for dinking purpose.

Mn
Mn is essential trace element required for various biochemical processes. The kidney and liver are the main storage places for the Mn in the body. Mn 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 Mn concentration for drink water is 0.1 mg/L (WHO 2017). As shown on Fig. 2, the concentration of Mn in Abzana water varies between 6.126 × 10 -2 mg/L and 9.053 × 10 -2 mg/L. However, higher concentration of Mn were observed in sampling station three and five which was 8.513 × 10 -2 mg/L and 9.053 × 10 -2 mg/L, respectively, indicating that the sites are slightly polluted areas when we compare with that of other station. Slightly high amounts of Mn 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 Mn obtained from Abzana water sample was 7.6082 × 10 -2 mg/L and it was lower than the permissible value of WHO standards for drinking purpose. Mn concentration in water may be toxic to a number of crops at a few-tenths, its above permissible limit was 0.2 mg/L for long term irrigation as well as available for livestock (Abduro 2017). In general, the concentration of Mn was found below the permissible level in all water sample of Abzana and the water quality is safe for drinking and other activities.

Conclusion
The main goal of this paper was to assess the status of Abzana water quality in Asano located southern Ethiopia, with special emphasis on trace heavy metals and physicochemical analysis. Five water samples were collected from different points of Abzana stream water. All of the samples were analyzed for four heavy metals (Cd, Pb, Cr & Mn,) and physicochemical (temperature, pH, EC and TDS) using standard procedures. The results of the samples vary among the samples because of the anthropogenic factors like disposal of effluent from the municipals and natural processes such as precipitation inputs, erosion, weathering of crustal materials, dilutions of rocks by hot ground waters. The concentrations of the investigated metal (Cr, Pb and Mn) and physicochemical analysis result of Abzana water were found below the guidelines for drinking water given by the WHO. However, the concentration of Cd in Abzana water sample was found above the permissible limit of WHO standards. Therefore, it was not safe for drinking and health effect according metals what we have studied here. To ensure that public health is better protected, future study is needed on effects of multiple heavy metals on human health and removal of heavy metals and on other physical, chemical and biological parameters of significant health concern and on identification of potential sources of the contaminants.