Phytoremediation of a soil contaminated by heavy metals and boron using castor oil plants and organic matter amendments

Phytoremediation is a sound alternative to soil decontamination, as it has lower costs and is more environmentally friendly than other practices. The need to handle contaminated biomass after harvesting and the search for new renewable energy sources have shifted research interests from typical edible or scenic plant species to those that can be used to produce biofuels. The castor oil plant (Ricinus communis L.) is a fast growing plant with high biomass production and is a potential phytoaccumulator of several metals. In recent years, the federal government of Brazil has encouraged castor oil plant cultivation for biodiesel and bioethanol production. The aim of the present work was to evaluate the phytoextraction potential of R. communis L. and the effect of organic matter addition (peat vs. filter cake) to a soil contaminated with scrap metal residue containing heavy metals and boron. The experiment consisted of a completely randomized block design with two organic matter sources and four rates of amendment (0, 20, 40 and 80 Mg ha− 1 organic carbon). Treatments were replicated three times. The castor oil plants were harvested 74 days after sowing. No accumulation of Cr, Ni, Cd, Cu, Pb or Zn was observed in the plants, but the concentration of B increased to 626 mg kg− 1 upon filter cake addition in castor oil shoots. Peat addition reduced by 2.7 years the time needed for removal of 50% of soil B content compared to the treatment with no organic matter addition. The transfer factor and transference index values obtained for B with castor oil plants in the present study were comparable to those obtained for hyperaccumulator species. Although our results are promising, further studies should be conducted to prove the usefulness of plants grown in contaminated areas for remediation purposes and for biofuel production.

► Phytoremediator tested for heavy metals and B phytoextraction.
► Castor oil plant was able to phytoextract B from soil.
► B phytoextraction was improved with peat addition.