Production of oil crops for bioenergy under heavy metal contaminated soils

Several crops species can be cultivated for energy production, being an auspicious option for the partial substitution of fossil fuels. In addition to energy production, some crops have also the ability to remove contaminants from the soil, potentiating soil remediation. Due to limitations in the availability of arable land, the hypothesis of introducing such crops on marginal soils, such as heavy metals contaminated soils, should be explored. In this context, this work aims to assess the effects of soils contaminated with zinc or lead on the productivity and quality of biomass of four oil crops Thlaspi arvense L., Brassica carinata A. Braun and Camelina sativa L. Crantz, spring and winter varieties, in the phytoremediation of soils artificially contaminated with Zn (450/900 mg.kg^-1) or Pb (450/900 mg.kg^-1). This work was carried out in pots, under controlled conditions, with the duration of one vegetative cycle. B. carinata was the most productive crop (600 g/m²), followed by T. arvense (350 g/m²). Both camelina’s showed lower yields (average 110 g/m²). B. carinata and C. sativa (both winter and spring varieties) can be considered tolerant to the heavy metals in study (tolerance index, yields in contaminated soils/yields in control soils, higher than 0.75) contrasting with the low tolerance displayed by T. arvense (tolerance index lower than 0.50). All oil crops exhibited high phytoextraction potential for zinc, but B. carinata showed the greatest accumulation index (metal content in the biomass from contaminated pots/metal content in the biomass from control pots), while the remaining oil crops, showed lower accumulation index. B. carinata and the spring variety of C. sativa showed the highest zinc accumulation in the leaves, while the winter variety of C. sativa, in the stems, and T. arvense, in the roots fraction. Contrasting, all these crops showed low phytoextraction potential for Pb, and the highest accumulation was observed in the roots fraction. Nevertheless, the metals content in the siliquae fraction of all oil crops tested was minor.