Level of selected heavy metals in drinking water of assosa district, assosa zone, benishangul gumuz regional state, south west Ethiopia

Abstract

Heavy metals are identified as one among a wide ranges of drinking water contaminants. They enter to human body mainly through drinking water and food. Therefore, knowing the status of heavy metals in drinking water is important to monitor the quality of water.This research dealt with determination of the levels of five heavy metals namely: Fe, Cu, Zn, Cd and Pb in the groundwater of 11 different Kebeles of Assosa district,Benishangul Gumuz regional state, Ethiopia. Samples from each Kebele were collected for four consecutive days from May 22-26/2017 and transported to Jimma university chemistry department research laboratory. EPA 3005A method was used for digestion of the water samples.Accordingly 50 mL of triplicate samples were digested by mixing with 1 mL concentrated (69%) HNO3 , 2.5 mL concentrated (37%) HCl and 4 drops of (30%) H2O2 until the volume was reached 15 mL.. Calibration curve for each metal was prepared by plotting the emission intensity as a function of metal standard concentration. The correlation coefficients of the calibration curves were 0.999 for Fe, Zn, Cd, and Pb whereas 0.996 for Cu. The recoveries for almost all metals analyzed were in the range of 70% - 130% except Pb which had 66% in Alubo. Thus, all the results are in the acceptable range. The levels of these metals were determined by analyzing the digested samples using Inductivly coupled plasma- optical emmision spectrometry (ICP-OES). All samples analyzed contained one or more of the five metals under determination each in varying concentration. Fe concentration varied from 0.367 ± 0.19 to 1.36 ± 0.39 mg/L,Cu varied from 0.072 ± 0.09 to 0.096 ± 0.17 mg/L, Zn varied from 0.142 ± 0.48 to 0.519 ± 0.77 mg/L.The observed results showed that the concentrations of Fe, Cu and Zn were not detected in some samples similarly, Cd was also not detected in two samples and its concentration was below LOQ in all other samples whereas Pb was not detected in all cases. Statistical data analyses showed that concentration of Fe, Cu, Cd and Zn were significantly diffrent at 95% confidence level in the water samples..The overall mean concentration of metals in the analyzed water sources followed the order of Fe > Zn >Cu . In general, the result obtained in this study indicated that Cu, Zn, Cd and Pb metals are in their safe level in all water samples. But the concentration of iron is above the WHO limit. Accordingly, it is recommended to follow up the content of heavy metals in the well waters of the study area.