Zinc and copper uptake by silver beet grown in secondary treated effluent

The study was conducted in a hydroponics set-up to determine the suitability of zinc (Zn) and copper (Cu) contaminated wastewater as a growth medium for edible crops; to identify accumulation of Zn and Cu in different parts of the plants and to understand their effects on plant growth. Silver beet was found to produce adequate yields in the Zn (1.7 mg/L and 2.0 mg/L) and Cu (0.35 mg/L and 1.1 mg/L) spiked medium but not in the secondary treated domestic effluent. The plants grown in secondary treated effluent showed stunted growth and accumulated Zn and Cu to a high level in their shoots. In all other mediums Zn and Cu accumulated more in the roots. The stunted growth of silver beet in secondary treated wastewater and uptake of Zn in particular was considered to be due to the deficiency of nitrogen and other plant nutrients rather than the effect of heavy metals. The study also revealed that if there was adequate amount of macronutrients available for growth, silver beet could be grown in domestic effluent without the risk of Zn or Cu contamination to the undesired level through hydroponics.