Copper, nickel and zinc accumulations in lettuce grown in soil amended with contaminated cattle manure vermicompost after sequential cultivations.

The Cu, Ni and Zn accumulations in leaves and roots of lettuce (Lactuca sativa L) grown in soil amended with natural and contaminated cattle manure vermicompost were evaluated. The vermicompost residues containing relatively high metal concentrations used in this work were obtained from a previous experiment, in which vermicompost was applied to removing metals from electroplating wastes. Sequential lettuce cultivations were conducted in pots containing the residual substrates from the first cultivation by adding metal-enriched vermicompost residues. In general, the Cu, Ni and Zn concentrations in leaves and roots of lettuce plants grown in vermicompost enriched with these metals were higher than in the treatment using the natural vermicompost. The metal concentrations in leaves from treatments with natural vermicompost were below the critical concentrations of toxicity to plants. However, the metal concentrations in leaves of the third cultivation in which metal-enriched vermicompost was applied were greater than the upper limit that causes plant toxicity, but no visual damage was observed in the plants. Treatment with Zn-enriched vermicompost resulted in toxicity symptoms, but plant damage did not result in the death of the plant. The chemical fractionation of Cu, Ni and Zn in residues from lettuce cultivation was evaluated by using a sequential extraction procedure and metal concentrations were increased in the different chemical fractions according to the increase of vermicompost dose.

Speciation of cadmium, cooper, lead and zinc in compost from a Brazilian urban solid waste treatment plant

A compost sample from a solid waste treatment plant of a Brasilian city, Araraquara, SP, was submitted to a sequential extraction procedure to evaluate the contamination and to asses the bioavailability of some heavy metals. The metal concentrations obtained by acid digestion (HNO3/HF/HCIO4) in the compost were (in mug.g-1): Cd=2.8; Cu=295; Pb=244 and Zn=1,481. The fraction of available metals, as extracted by magnesium chloride, was approximately 1 per cent for each of the metals Cu, Pb and Zn, and 16 per cent for Cd. The remaining amounts were sequentially leached off with increasingly stronger extractans, namely, sodium acetate, hydroxylamine hydrocloride and hydrogen peroxide. The bulk amounts found by this sequence were: Cd=46 per cent; Cu=74 per cent; Pb=21 per cent and Zn=79 per cent. Finally, the residual matrix was digested by a HF/HCIO4 treatment.