Selecting effective plant species for the phytoremediation of persistent organic pollutants and multielement contaminated fibrous sediments

Background

Wastewater discharges from the old pulp and paper industry led to the accumulation of contaminated wood pulping fibers and debris—referred to as fiberbanks (FB)—in the Baltic Sea and freshwater bodies across Sweden and other pulp-producing countries. These anthropogenic sediments are polluted with toxic metal(oid)s and persistent organic pollutants, and their decomposition releases greenhouse gases. Phytoremediation offers a nature-based solution for the ex-situ treatment of these fibrous sediments, but they present unique challenges due to the abundant and unstable organic matter and aged pollution. This study aims to identify potential plant candidates and to address the limitations of fiberbanks as a plants growing media for phytoremediation.

In a greenhouse experiment, we assessed the performance of five plant species (Brassica juncea, Brassica napus, Helianthus annuus, Hordeum vulgare, and Poa annua) grown in substrates formulated with fiberbank. The evaluation included plant growth parameters, bioconcentration and uptake efficiency of metal(oid)s (V, Cr, Co, Ni, Cu, Zn, As, Cd, and Pb), and the degradation of polycyclic and linear hydrocarbons.

Results

Despite initial concerns, fiberbanks displayed favorable physical characteristics and a degree of fertility conducive to plant growth. Even though all tested species seeds could cope with fiberbanks acute toxicity, H. vulgare and P. annua showed better tolerance to the fiberbanks substrates and superior aerial biomass development, which promoted a highest toxic metal(oid)s uptake efficiency, regardless of lower bioconcentration factors for most of the target elements. Zn (17.16–23.25 mg/kg of FB), Cu (4.18–6.48 mg/kg of FB) and Cr (1.05–1.36 mg/kg of FB) were most effectively taken up by these plants. The uptake of Co (0.04–0.18 mg/kg of FB) and Ni (0.05–0.17 mg/kg of FB) was lower. As (0.01–0.02 mg/kg of FB), Cd (0.02–0.06 mg/kg of FB), Pb (0.02–0.04 mg/kg of FB) and V (0.02–0.03 mg/kg of FB) phytoextraction was not significant. None of the species exhibited a significant removal of targeted organic pollutants.

Conclusions

Phytoremediation, either on its own or in combination with other strategies, shows promise for the remediation of fiberbanks. However, further research is needed to understand how the organic matrix and long-term underwater aging of fiberbanks affect pollutants bioavailability.