An appraisal of copper and zinc as Contaminants of Potential Ecological Concern (COPEC) on onions (<i>Allium cepa</i> L.)

Abstract

This research estimated the phyto-toxic effects of two heavy metals (copper and zinc) on onion (Allium cepa L).The effective concentration (EC₅₀) for copper and zinc following a 96 hour exposure was estimated at 1.04 mg/L ± 0.14 mg/L and 1.94 ± 0.17 mg/L respectively. The results indicated that at concentrations of 1.04 mg/L, copper may be considered as Contaminant of Potential Ecological Concern (COPEC) on the growth of onion (Allium cepa L) i.e. harmful effects of copper cannot be ruled out but may probably be a threat at concentrations ≤ 1.04 mg/L. However, zinc may not be considered as COPEC at concentration less or approximately < ≈ 2 mg/L (1.94 mg/L) i.e. zinc alone is not likely to cause ecological risk at concentrations lower than 2 mg/L. The lower the EC₅₀ value, the more toxic the contaminant and vice versa. Similarly, if exposure to copper and zinc is likely to occur frequently in areas with heavy anthropogenic activities, then Allium cepa L would be able to absorb significant concentration of the toxicants and this could have multiplier effects on humans who daily consume significant quantity of the crop in their delicacies as a rich source of anti-oxidants.

Keywords: copper and zinc, contaminant of potential ecological concern (COPEC), growth inhibition, onions.