Essential oil quality and heavy metal concentrations of peppermint grown on a municipal sludge-amended soil

Potentially hazardous heavy metals accumulated in soil may present a long-term problem for plant growth and human health, If nonfood crops are grown on heavy metal-contaminated soils, the potential for food chain transfer of hazardous heavy metal elements from contaminated soils to consumers may be reduced. In a pat experiment, peppermint (Mentha X piperita L.) was grown on sewage sludge-treated soils that had metal concentrations 3 to 60 times higher than those of the control soil. The plants were harvested before anthesis, approximately 100 d after transplanting. The metal contents of plant tissue and essential oil extracted from leaves were determined; organic chemical compositions of the extracted oils were also analyzed. The results of the experiment indicated that the biomass production was not affected by the presence of metals up to 6.1, 256, 182, 86, 173, and 601 mg kg(-1) dry weight for Cd, Cr, Cu, Ni, Pb, and Zn, respectively. The concentrations of Cd, Cr, Cu, Ni, and Pb in peppermint grown on sewage sludge-treated soils were not significantly different from those grown on control soil. Plant tissue Zn concentrations were significantly higher when the Zn concentration of the soils exceeded 260 mg kg(-1) dry weight, The metal concentrations of the extracted oils of the control and the sewage sludge treatments were not significantly different and were always < 1 mg L-1. The chemical composition of oil was not affected by the presence of metals in sludge-treated soils.