Phytoremediation of Mine Tailing – Potential of Chrysopogon Zizanioides and Andropogon Gayanus in a Sahelian Climate

Abstract

The pollution of soil and, by extension, water resources by pollutants from mining operations is a major threat to Burkina Faso due to the lack of waste treatment. Phytoremediation is an alternative way of cleaning up soil contaminated by pollutants from mining waste. The ability of Chrysopogon zizanioides and Andropogon gayanus to accumulate iron (Fe) and zinc (Zn) was studied in mine tailings in Burkina Faso in a Sahelian climate. The phytoremediation efficacy of the two plant species was studied in 30-litre pots containing mine tailings from the artisanal gold processing site in the rural commune of Nimbrogo in the Centre-Sud region of Burkina Faso. The pot experiments involving unpolluted (PN) and polluted (P) modalities were arranged randomly under an experimental greenhouse. The phytoremediation efficiency was evaluated by comparing the growth, biomass and capacity of these two herbaceous plants to extract Fe and Zn from mine tailings. Analysis of the rate of appearance of green leaves and new leaves of A. gayanus and C. zizanioides grown in mine tailings showed no significant difference between the polluted and unpolluted conditions, either within the same plant or between the two species during the experiment. The same applies to changes in the height and circumference of the plant species studied, i.e. no significant differences were observed. However, C. zizanioides showed a significantly different tolerance index (TI) compared to A. gayanus during the sampling campaigns, with the exception of campaign C3 where TI_AG (90.6%) was much higher than TI_CZ (70.9%). After six months of cultivation in mine tailings, the two herbaceous plants showed a potential to accumulate Fe and Zn, unlike Hg and As. Root biomass showed a more significant accumulation than above-ground biomass for both grasses. Although the BCF values for both plants were low (<1), the elimination efficiencies for Fe and Zn were 36.5% and 22.6% respectively in 6 months of experimentation with C. zizanioides. However, for the same period, A. gayanus gave an efficiency rate of 34.3% and 21.3% for Fe and Zn. The results indicate that the plant species studied have phytoremediation potential, although that of A. gayanus is relatively low compared with that of C. zizanioides. On the basis of these results, A. gayanus, an indigenous plant, can be described as a phytoremediator for the treatment of mine tailings.