Chrysotile dissolution in the rhizosphere of the nickel hyperaccumulator Leptoplax emarginata

Our plain-English summary of Chrysotile dissolution in the rhizosphere of the nickel hyperaccumulator Leptoplax emarginata, by V. Chardot-Jacques, C. Calvaruso, B. Simon, et al (Environmental Science & Technology, 2013).

The study

• Authors: V. Chardot-Jacques, C. Calvaruso, B. Simon, M.P. Turpault, G. Echevarria, J.L. Morel
• Journal: Environmental Science & Technology
• Published: 2013;47(6):2612-20
• Cited by: 11 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Ni phytoextraction processes need further understanding of the interactions between Ni availability in soils and its absorption by plant roots. The large metal uptake and root exudation by hyperaccumulator species could accelerate the weathering process of Ni-bearing phases in the rhizosphere. The aim of this work was to quantify the weathering of a Ni-bearing mineral phase in the rhizosphere of the Ni-hyperaccumulator Leptoplax emarginata. The studied mineral was chrysotile which was characterized by a low Ni solubility. Column experiments were performed to assess the effect of the Ni-hyperaccumulator L. emarginata and the contribution of rhizobacteria on the dissolution rate of chrysotile. Mineral weathering was monitored by measuring Ni and Mg transferred to leachates or plants throughout the experiment. Results showed that L. emarginata increased chrysotile dissolution by more than 2-fold . The hyperaccumulator L. emarginata accumulated 88% on average of total mobilized Ni. Inoculation with Ni-resistant bacteria in the rhizosphere of L. emarginata had no significant effect on chrysotile dissolution or plant accumulation of Ni in this context. Finally, after 15 weeks of culture, 1.65% of total Ni in the system was mobilized in the planted treatments compared with 0.03% in the unplanted treatments.

In plain English

This laboratory experiment, run in a growth chamber, tested whether a nickel-accumulating plant, Leptoplax emarginata, speeds up the breakdown (dissolution) of chrysotile. The chrysotile came from raw asbestos ore in waste heaps at Dobšiná, eastern Slovakia. It was the only source of nickel, magnesium and iron in small columns of chrysotile mixed with quartz sand. Four treatments, each with six replicate columns, ran for 15 weeks: no plant, the plant alone, and the plant inoculated with one of two nickel-resistant bacterial strains. Columns with plants released more than twice as much magnesium as unplanted columns, and their chrysotile dissolution rate was more than double. On average 1.65% of the nickel in the planted columns was released, compared with 0.03% in unplanted columns. The plants took up on average 88% of the released nickel. The bacteria had no statistically significant effect on dissolution or nickel uptake. X-ray diffraction detected no mineralogical difference in the chrysotile before and after the experiment, and electron microscopy found no new minerals or transformation. The authors concluded that the plant's strong nickel uptake could drive chrysotile dissolution.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Laboratory column experiment with plants grown in a growth chamber (a study of plants and mineral weathering, not a human health study)
• Who was studied: Seedlings of the nickel hyperaccumulator plant Leptoplax emarginata, one seedling per column. The seeds were collected in 2002 at Katara Pass, northern Greece. There were four treatments (unplanted; plant alone; plant plus bacterial strain B1; plant plus bacterial strain B2), each with six replicates, grown for 15 weeks.
• Exposure: Nickel-bearing chrysotile (20 to 40 μm particles, 3 g per column mixed with 30 g quartz) prepared from raw asbestos ore from waste heaps in Dobšiná, eastern Slovakia. It was the only source of nickel, magnesium and iron in the columns. Some columns were also inoculated with nickel-resistant bacteria from New Caledonia.
• Main results:
  • Leached magnesium was on average 2-fold higher in all treatments with L. emarginata than in the unplanted, uninoculated treatment.
  • Total magnesium released was more than 2-fold higher with L. emarginata. The authors report that nickel released was more than 50-fold higher.
  • Of the initial nickel in the chrysotile, 1.65% was released (in leachates or taken up by plants) on average in the planted treatments, compared with 0.03% in the unplanted treatment.
  • The plants accumulated on average 88% of the total nickel released but only 9% of the total magnesium released.
  • The chrysotile dissolution rate was 9.3 × 10^-14 mol per square metre per second in unplanted columns, compared with 2.2 to 2.3 × 10^-13 in planted columns. The unplanted rate was less than 50% of the planted rates.
  • Bacterial inoculation had no statistically significant effect on the total magnesium and nickel released from chrysotile. Strain B1 did significantly increase root biomass.
  • X-ray diffraction found no mineralogical difference between the chrysotile before and after the experiment in any treatment. Scanning electron microscopy found neither new mineral phases nor transformation.
  • Only 10.5% of the nickel in the chrysotile was isotopically exchangeable within the duration of the experiment.
• The authors' conclusion: The authors suggested that L. emarginata's strong ability to hyperaccumulate nickel could drive chrysotile dissolution by sharply lowering water-soluble nickel around the roots. They also suggested that such a process could be optimized for nickel phytomining on soils with limited nickel availability.
• Limitations the authors state:
  • The authors could not exclude that the plant's need for iron and magnesium, which were also supplied only by the chrysotile, influenced the initial weathering.
  • The inoculated bacterial strains may not have established. The authors suggest this may have been because of unsuitable experimental conditions or competition with bacteria already on the seeds.
  • Bacteria from outside contamination appeared in the unplanted columns during the experiment.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Chrysotile.

Medical terms in this study, explained in our Lexicon: Chrysotile.

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