Assisted phytoremediation of mixed metal(loid)-polluted pyrite waste: Effects of foliar and substrate IBA application on fodder radish

Exogenous application of plant-growth promoting substances may potentially improve phytoremediation of metal-polluted substrates by increasing shoot and root growth. In a pot-based study, fodder radish (Raphanus sativus L. var. oleiformis Pers.) was grown in As–Zn–Cu–Co–Pb-contaminated pyrite waste, and treated with indolebutyric acid (IBA) either by foliar spraying (10 mg L−1), or by direct application of IBA to the substrate (0.1 and 1 mg kg−1) in association, or not, with foliar spraying. With the exception of foliar spraying, IBA reduced above-ground biomass, whilst direct application of IBA to the substrate surface reduced root biomass (−59%). Trace element concentrations were generally increased, but removals (mg per plant) greatly reduced with IBA application, together with greater metal leaching from the substrate. It is concluded that, in our case, IBA had a negative effect on plant growth and phytoextraction of trace elements, possibly due to unsuitable root indoleacetic acid concentration following soil IBA application, the direct chelating effect of IBA and the low microbial activity in the pyrite waste affecting its breakdown.

► Substrate (but not foliar) IBA application caused root and shoot biomass losses.
► IBA increased specific root length and metal concentration in fodder radish.
► Metal removals were not increased by IBA.
► In polluted pyrite waste IBA showed a chelating effect.
► Need to investigate into suitable plant density to maximize biomass yield.