Abstract

In areas where rainfall is insufficient to meet crop water requirements, irrigation is especially important for increasing agricultural production. However, a number of contaminants, particularly heavy metals, are constantly affecting the quality of irrigation water. In this study, seasonal variation and ecological risks of heavy metals (Cd, Cr, Cu, Fe, Pb, Zn, As, Ni, Mn and Co) in irrigation water from three sites of Omi Dam irrigation field were detected by Atomic Absorption Spectrometry (AAS). The concentration of Cd (0.006 – 0.109 mg/l), Cr (0.01 – 0.238 mg/l), Cu (0.002 – 0.499 mg/l), As (0.06 – 0.312 mg/l), Mn (0.017 – 3.07 mg/l) and Co (0.024 – 0.579 mg/l) were above the Food and Agricultural Organization standard limits of heavy metals in irrigation water while Fe (2.263 – 3.933 mg/l), Pb (0.233 – 1.484 mg/l), Zn (0.046 – 0.174 mg/l) and Ni (0.05 – 0.104 mg/l) do not exceed the standard limit. The dry season concentration of all the metals was higher than the wet season concentration except for Fe and Ni. All the sites under examination exhibited low levels of ecological risk with the exception of Cd which exhibited moderate to considerable ecological risk. Geological sources, other agrochemicals and runoff from agricultural land treated with phosphate fertilizer may be the primary cause of elevated cadmium contamination in irrigation water. The principal component analysis indicated a positive correction between cadmium, chromium, zinc, lead, and manganese suggesting a common origin. These findings indicate that remediation strategies are essential to enhance the heavy metal quality of irrigation water due to its adverse impacts on human health.

Key words: heavy metals, irrigation water, Omi Dam, ecological risk