Metal element uptake in vegetables and wheat after biosolids application

Metal element concentrations were measured in the edible portions of silverbeet, potato and wheat grown in a glasshouse experiment after application of lime amended biosolids (LAB) and digester sludge. Biosolids were mixed into soil for the replicated pot experiment at rates of 1, 2 and 5 times the N requirement of each crop grown. No significant effect was found of different biosolids application rates on uptake of As, Hg or Se. The concentration of As was less than the maximum permitted limit (ML) of 1mg/kg in all crops grown. The ML for lead (0.1 mg/kg in vegetables) was only exceeded at the greatest LAB treatment rate in silverbeet. No significant differences in the concentration of Cd were found at different application rates of LAB or digester sludge in potato, wheat fodder or wheat grain. Silverbeet was found to contain much higher concentrations than potato or wheat fodder of Al, Fe and Zn and higher concentrations of Cu, Ni, Cd, and Co and the concentration of Cd in silverbeet exceeded the ML (0.1 mg/kg) in most treatments including the control, which may be due to species specific bioaccumulation. Correlation of soil pH and EC to rate and type of biosolids applied are likely explanations for different metal element concentrations due to contrasting bio-availability resulting from pH or EC effects. An increased plant uptake of metal elements associated with the greatest biosolids application rates applied in this glasshouse experiment are unlikely under realistic field conditions in Tasmania. Keywords: Heavy metals, potato, silverbeet, wheat