Potential for the phytoremediation of arsenic-contaminated mine tailings in Fiji

The objectives of this study were (1) to compare the bioavailability of arsenic (As) to plants in an As-spiked agricultural soil and a naturally contaminated mine tailings, (2) to compare the theoretical ability of various chemical amendments to solubilise As in naturally contaminated mine tailings, and (3) to examine the ability of Brassica juncea (Indian mustard) plants to remove the solubilised As from the soil and tailings. The growth media used for this study included mine tailings from a gold mine in Fiji contaminated with As (683 As mg/kg) due to the presence of arsenopyrite in the mined rock, and a pasture soil from New Zealand (Manawatu sandy loam) amended with lime and/or As. Brassica juncea was grown in these substrates in a glasshouse. In a separate batch experiment, we examined the theoretical ability of several chemical extractants to solubilise As from the mine tailings. Of the tested extractants, only hydrochloric acid (HCl) and a mixture containing ammonium oxalate (NH4)2C2O4, oxalic acid, and ascorbic acid were effective in extracting As from the tailings. In the plant growth experiment, solutions of these 2 chemicals were used as soil amendments at 2 different concentrations to increase As uptake by 6-week-old, actively growing B. juncea plants. Arsenic bioavailability as a function of the growth media influenced the germination rate of B. juncea, the As concentration in the plants, and the water-soluble As concentration in the media. There was approximately a 3-fold reduction in the germination of seeds, and a 64- and 380-fold increase in As concentration in plant and soil solution, respectively, in the spiked Manawatu soil compared with the naturally contaminated Fiji mine tailings. The spiking of soil with As did not mimic naturally contaminated tailings in this experiment. The total amount of As taken up by B. juncea plants increased approximately 9 fold with the addition of the amendments. However, the phytoremediation capacity of B. juncea for As extraction in Fiji mine tailings was too low for efficient remediation even in the presence of solubilising chemicals.