Opportunities and risks associated with the production of crambe oil when cultivated in soils contaminated with heavy metals

Several crop species can be cultivated for the production of bioproducts, biomaterials, bioenergy and biofuels, representing an auspicious option for the partial substitution of fossil based feedstocks. In addition, some crops have also the ability to tolerate and remove contaminants from the soil, potentiating soil remediation. Moreover, the production of industrial crops in soils contaminated with heavy metals contribute to reduce land use competition with food crops and land use change controversies. Oilseed crops represent a source of medium-chain fatty acids and medium-chain polymer building blocks that can be used for the production of plastics, surfactants, detergents, lubricants, plasticizers and other products. In this context, this work aims to assess the potential of crambe (Crambe abyssinica) for the production of oil for the bioeconomy along with the phytoremediation of heavy metals contaminated soils. Therefore, Crambe abyssinica were sowed in different soils artificially contaminated with Zn: 450 mg/kg; Pb: 450 mg/kg; Cd: 4 mg/kg; or Ni: 110 mg/kg. This work was carried out in pots, under semi-controlled conditions, with the duration of two vegetative cycles. Over the two growing cycles, yields of Crambe abyssinica were on average 190 g/m² and the crop presented high tolerance index to the different heavy metal contaminated soils (> 0.75). Yet, the oil content in the seed was slightly affected by the level of contamination in the soil. A small increment was observed in protein content and ash content, of the seeds, with a lower content in oil. In terms of phytoremediation, highest phytoextraction potential was observed for zinc and cadmium, and reduced potential for nickel and lead. Nonetheless, metals content in the siliquae fraction of all oil crops tested was minor and linked with the protein fraction of siliquae and not to the oil fraction of the siliquae. Based on those results, environmental and socio-economic opportunities and risks were assessed. For this evaluation the agronomic production of crops and the extraction and refinement of vegetable oil were addressed. The reduction in the yields due to contamination, increases the production cost of the vegetable oil, which might compromise its industrial application. Yet, the introduction of a vegetative cover to the contaminated soil, improves the soil quality, namely in terms of organic matter, structure, and contaminants phytostabilization. Socially, it contributes to restore the soil ecosystem function and services, thus reducing human and environment exposure to pollutants. And in rural areas, it may represent an increment in employment (12h/ha/year), compared with permanent degraded land (0-2 h/ha/year).