Capacity of Lemna gibba L. (Duckweed) for Uranium and Arsenic Phytoremediation in Mine Tailing Waters

ABSTRACT

The potential of Lemna gibba L. to clean uranium and arsenic contamination from mine surface waters was investigated in wetlands of two former uranium mines in eastern Germany and in laboratory hydroponic culture. Water and plants were sampled and L. gibba growth and yield were monitored in tailing ponds from the field study sites. Contaminant accumulation, growth and yield experiments were conducted in the laboratory using synthetic tailing water. Mean background concentrations of the surface waters were 186.0 ± 81.2 μg l⁻¹ uranium and 47.0 ± 21.3 μg l⁻¹ arsenic in Site one and 293.7 ± 121.3 μg l⁻¹ uranium and 41.37 ± 24.7 μg l⁻¹ arsenic in Site two. The initial concentration of both uranium and arsenic in the culture solutions was 100 μg l⁻¹. The plant samples were either not leached, leached with deionized H₂O or ethylenediaminetetracetic (EDTA). The results revealed high bioaccumulation coefficients for both uranium and arsenic. Uranium and arsenic content of L. gibba dry biomass of the field samples were as follows: nonleached samples > deionized H₂O leached (insignificant ANOVA p = 0.05) > EDTA leached. The difference in both arsenic and uranium enrichment were significantly high between the nonleached and the other two lead samples tested at ANOVA p > 0.001. Estimated mean L. gibba density in surface water was 85,344.8 ± 1843.4 fronds m⁻² (∼1319.7 g m⁻²). The maximum specific growth rate was 0.47 ± 0.2 d⁻¹, which exceeded reported specific growth rates for L. gibba in the literature. Average yield was estimated at 20.2 ± 6.7 g m⁻² d⁻¹, giving approximately 73.6 ± 21.4 t ha⁻¹ y⁻¹ as the annual yield. The highest accumulations observed were 896.9 ± 203.8 mg kg⁻¹ uranium and 1021.7 ± 250.8 mg kg⁻¹ arsenic dry biomass for a 21-d test period in the laboratory steady-state experiments. The potential extractions from surface waters with L. gibba L. were estimated to be 662.7 kg uranium ha⁻¹ yr⁻¹ and 751.9 kg arsenic ha⁻¹ yr⁻¹ under the above conditions.

Keywords:

• bioaccumulation
• extraction potential
• growth rate
• immobilization
• plant density
• yield.

ACKNOWLEDGEMENTS

This study was financed through BMBF (German Federal Ministry for Education and Research) project grant No. 02WB0222. We thank members of our research group, mainly Carsten Brackhage, Holger and Claudia Dienemann, Yelena Lyubun, Jan-Henning Ross, Andreas Wallukat, and Jan Winderlich for participation in field sampling; Arndt Weiske for chemical analyses; and Karin Klinzmann and Annet Jost for laboratory assistance. Carsten Brackhage read the manuscript and contributed tremendously to the quality of the language of this article. We are also sincerely indebted to two anonymous reviewers for their criticisms and comments that helped us to reshape this article

Notes

*p ≤ 0.05, p ≤ 0.01, and Implies p ≤ 0.001.