Accumulation of heavy metal in onion (Allium cepa) plants irrigated with treated wastewater under field conditions

Abstract

Accumulation of heavy metals in edible parts of crops irrigated with treated wastewater could create a health hazard. The objective of the study was to assess the distribution of heavy metals in edible and non-edible parts of onion (Allium cepa) plants irrigated with treated wastewater under field conditions. A 15-ha field was established for onions irrigated with centre pivot using commercial cultural practices. At harvest, 1 ha among the 15 ha was selected at random and demarcated into eight blocks for sampling five plants at random during two different seasons. Plants were separated into root, bulb and leaf, which were separately dried, ground and quantified for heavy metals using ICP-OES. In Experiment 1, plant organ treatments were significant (P<0.05) on Arsenic (As), Manganese (Mn), Cadmium (Cd), Cobalt (Co), Chromium (Cr), Copper (Cu) and Lead (Pb), contributing 73, 84, 80, 76, 95 and 81% in total treatment variation (TTV), of the respective treatments. In Experiment 2, treatments were significant on As, Mn, Cd, Cr, Cu and Pb, contributing 83, 88, 80, 74, 96 and 78% in TTV of the respective variables, with no significant effects on Co. Relative to root tissues, the accumulation of heavy metals increased (32–35%) and decreased (20–87%) in leaf and bulb tissues, respectively. In conclusion, onion bulbs were relatively safe for consumption in plants irrigated with treated wastewater.