Phytoremediation of low-concentration Cr(VI)-contaminated soil from a superfund site using sunflower (Helianthus annuus L.) with concurrent biodiesel production from harvested seeds

Abstract

The purpose of this study was to evaluate the feasibility of using sunflower (Helianthus annuus L.) for simultaneous phytoremediation of low-level hexavalent chromium [Cr(VI)]-contaminated soil and biodiesel production. Soil was collected from a remediated superfund site where the residual Cr(VI) concentration was low (0.16 ± 0.04 mg/kg) due to prior cleanup, and controlled pot experiments were conducted under two amendment conditions—low-nitrogen chemical fertilizer and biosolids—to assess plant growth, Cr(VI) uptake, biodiesel quality, and microbial responses. In addition, bioaccumulation factor and translocation factor were assessed to evaluate the efficiency of chromium uptake and movement within the plant. Results showed that Cr(VI) was absorbed by the roots and translocated to shoots, leaves, and seeds, with both amendments achieving comparable phytoextraction efficiencies. Biosolids amendment significantly enhanced plant biomass compared to chemical fertilizer, while no visible phytotoxicity symptoms were observed, indicating that sunflower tolerated the low-level Cr(VI) contamination. Biodiesel extracted from the seeds met the American Society for Testing and Materials (ASTM) standards for acid value and density, confirming its potential as a renewable fuel. Moreover, microbial biomass carbon and nitrogen in the rhizosphere increased after phytoremediation, suggesting a beneficial role of soil microbes in supporting plant growth and remediation. Overall, this study demonstrates that integrating sunflower-based phytoremediation of low-level Cr(VI) with biodiesel production provides a sustainable and cost-effective strategy for addressing residual contamination while contributing to renewable energy generation.

^⁎Corresponding author at: School of Civil, Environmental and Infrastructure Engineering, Mail Code 6603, Southern Illinois University, 1230 Lincoln Dr., Carbondale, Illinois 62901, USA.