Assessment of Heavy Metal Concentration in Irrigation Water, Soil and Cabbage in the Awetu Watershed, Jimma Town, Southwest Ethiopia

Abstract

Heavy metals are introduced in the environment during natural weathering of bedrock. Currently, environmental pollution by heavy metals is a global problem. Excessive level of heavy metal pollution in the environment could cause harm. It is necessary to accurately determine heavy metal concentrations in different environmental samples. This study investigated several physicochemical parameters, and the levels of selected heavy metals (Cr, Cd and Pb) were determined in selected cabbage, soil and Awetu River at Jimma town, southwestern Ethiopia. For this purpose, seven samples (three from water, two from vegetable (cabbage) and two from soil) were analyzed. The cabbage, soil and irrigation water samples were randomly collected from the farmlands around Awetu River. The samples were digested using properly optimized digestion procedures. The physicochemical parameters and heavy metal concentrations were determined using Multimeter parameter probe and flame atomic absorption spectroscopy (FAAS). The results of the physicochemical analysis were obtained in the following ranges: pH (6.8-7.02), temperature (21-23 °C), conductivity (336-399 μS/cm), dissolved oxygen (6.17-6.705 mg/L) and biological oxygen demand (2.345-2.88 mg/L),which were found to be below the maximum permissible levels set by the WHO/FAO. In this study, the levels of selected heavy metals (Cr, Cd and Pb) in cabbage, soil and irrigation water were investigated. Cd and Cr were not detected in any of the samples. The mean concentration (mg/kg) of Pb in the soil downstream was 0.115 ± 0.035. However, Cr and Cd were not detected. For irrigation water, only lead was detected downstream and its mean concentration (mg/L) was 0.033 ± 0.019. For vegetables (cabbage), the levels of all heavy metals were found to be below the detection limit. The metal concentrations determined on the farm were compared to the standards, and the Pb concentrations in the soil and irrigation water were still below the permissible limits. This study concluded that the concentration of lead detected in soil and downstream water is associated with the waste discharged to the river as a sink.