Sources and level of heavy metal contamination in the water of Awetu watershed streams, southwestern Ethiopia

Abstract

The present study aimed to investigate the contamination source, level, and spatial distribution of globally alarming trace metals from Awetu watershed streams, southwestern Ethiopia. Surface water samples were collected from 20 sampling sites in December 2019. Water samples were collected in 500 ml polyethylene bottles previously washed with deionized water and rinsed with the sample to be collected from different stretches and acidified with 5 ml concentrated nitric acid. The samples were digested with open acid digestion and the contents of the metal were analysed using inductively coupled plasma optical emission spectrometry (ICP-OES) ranged from 18 - 351 μg/L for As, 5-19 μg/L for Cd, 232-421 μg/L for Cr, 314-920 μg/L for Pb and 10-16 μg/L for Hg. The highest concentrations of As were detected at K3, Cd at K2, Pb and Cr at D4, and Hg at D5. Analysis of variance results revealed that the Cd concentrations were statistically significant among all the streams except for Boye. Streams found at the center of Jimma city with effluents emanated from Jimma University, garage maintenances, car-wash and agricultural areas had higher values than the streams in the periphery. This study concluded that a higher concentration of trace elements is associated with the type of waste entering the streams. Trace elements concentration in the watershed is to the level that can pose a risk to downstream users. Public awareness creation to establish waste management systems and river quality monitoring should be implemented to minimize the public health risk and deterioration of the aquatic ecosystem.

Keywords: Heavy metals; Pollution distribution; Surface water pollution; Watershed streams.

Figure 1

Sampling points along streams at Awetu watershed (Generated from ArcGIS 10.3 (ESRI, Redlands, California, USA)).

Figure 2

Spatial distribution of trace element concentrations (μg/L) in surface water samples in the Awetu watershed streams.

Figure 3

Tukey HSD test output showing the 95% stream-wise confidence level of the contaminants.

Figure 4

Dendrogram of hierarchical clustering analyses showing the relevant association among the parameters in waters of the study area.

Figure 5

PCA biplot of trace metal and physicochemical characteristics of water samples from Awetu Watershed, Southwestern Ethiopia. The color bar indicates the variable contribution (degree of loading) to the plot.