Effect of citric acid and bacteria on metal uptake in reeds grown in a synthetic acid mine drainage solution

The effect of citric acid (CA), rhizosphere acidophilic heterotrophs and/or Fe(II) oxidizing bacteria (Fe(II)OB) on plaque formation and metal accumulation in Phragmites australis L. (common reed) from acid mine drainage (AMD) solution were investigated. Reeds were grown in different hydroponic solutions that contained AMD, CA and/or rhizosphere bacteria for three months. Triplicate experiments were conducted for each experimental condition. Fe(II)OB enhanced the formation of Fe plaque which decreased Fe and Mn uptake in reeds, while it had no significant influence on Al accumulation. CA inhibited the growth of Fe(II)OB, decreased the formation of metal plaque and increased Fe and Mn accumulation in reeds. Acidophilic heterotrophs consumed CA and made the environment more suitable for the growth of Fe(II)OB. Reeds are a good candidate for phytoextraction while CA is a useful chelator to enhance metal uptake in plants. More research may be needed to investigate the influence of CA on microbial community. Further investigations are required to study the effect of CA on phytoremediation of AMD contaminated fields.