Potential of citric acid to alter pH and metal uptake in reeds in acid mine drainage solutions

Phragmites australis (common reed) is often used to treat acid mine drainage (AMD) sites contaminated with high concentrations of heavy metals and low pH. This study investigated the effects of different levels (low 0.34 g/L, middle 17.86 g/L and high 33.62 g/L) of the biodegradable chelator citric acid (CA) on pH change, metal (i.e. Fe, Al and Mn) accumulation and translocation in reeds cultured in aqueous AMD contaminated media for 4 and 12 weeks. The results indicated that CA inhibited further deceases in AMD pH as well as increased Fe and Mn accumulation in both belowground and above ground tissues of reeds. As expected, increasing CA dosage and treatment time increased metal accumulation in plants. By 12 weeks, 0.18 +/- 0.01 mg Mn/g, 56.78 +/- 7.63 mg Fe/g and 0.60 +/- 0.01 mg Al/g were accumulated in roots; while 0.06 +/- 0.01 mg Mn/g; 6.38 +/- 0.06 mg Fe/g; and 0.19 +/- 0.01 mg Al/g were sequestered in stems of reeds treated with 33.62 g/L CA. Further research is needed to study the application of CA to enhance the phytoremediation efficiency of AMD contaminated field.