Siderophore-mediated iron removal from chrysotile: Implications for asbestos toxicity reduction and bioremediation

Our plain-English summary of Siderophore-mediated iron removal from chrysotile: Implications for asbestos toxicity reduction and bioremediation, by S.K. Mohanty, C. Gonneau, A. Salamatipour, et al (Journal of Hazardous Materials, 2018).

The study

• Authors: S.K. Mohanty, C. Gonneau, A. Salamatipour, R.A. Pietrofesa, B. Casper, M. Christofidou-Solomidou, J.K. Willenbring
• Journal: Journal of Hazardous Materials
• Published: 2018;341:290-296
• Cited by: 24 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Asbestos fibers are highly toxic (Group 1 carcinogen) due to their high aspect ratio, durability, and the presence of iron. In nature, plants, fungi, and microorganisms release exudates, which can alter the physical and chemical properties of soil minerals including asbestos minerals. We examined whether exudates from bacteria and fungi at environmentally relevant concentrations can alter chrysotile, the most widely used asbestos mineral, and lower its toxicity. We monitored the release of iron from chrysotile in the presence of organic acid ligands and iron-specific siderophores derived from bacteria and fungi and measured any change in fiber toxicity toward peritoneal macrophages harvested from mice. Both fungal and bacterial siderophores increased the removal of iron from asbestos fibers. In contrast, organic acid ligands at environmentally relevant concentrations neither released iron from fibers nor helped in siderophore-mediated iron removal. Removal of plant-available or exchangeable iron did not diminish iron dissolution by both types of siderophores, which indicates that siderophores can effectively remove structural iron from chrysotile fibers. Removal of iron by siderophore lowered the fiber toxicity; fungal siderophore appears to be more effective than bacterial siderophore in lowering the toxicity. These results indicate that prolonged exposure to siderophores, not organic acids, in the soil environment decreases asbestos fiber toxicity and possibly lowers the health risks. Thus, bioremediation should be explored as a viable strategy to manage asbestos-contaminated sites such as Brownfield sites, which are currently left untreated despite dangers to surrounding communities.

Copyright © 2017 Elsevier B.V. All rights reserved.

In plain English

This was a laboratory experiment, not a study of people. The authors purified chrysotile asbestos fibers from Arizona ore and exposed them to substances that soil bacteria and fungi release. These were a bacterial siderophore (desferrioxamine B, DFO), a fungal siderophore (ferrichrome, FC), and oxalic, malonic and citric acids, at concentrations the authors described as environmentally relevant. Both siderophores removed iron from the fibers, in similar amounts. They did so even after the exchangeable, 'plant-available' iron had first been removed with a chemical called DTPA. Oxalic acid alone released no detectable iron. Oxalic and malonic acid did not change siderophore iron release, but citric acid increased it. To gauge toxicity, the treated fibers were placed on immune cells (peritoneal macrophages) from mice, and the reactive oxygen species the cells produced were measured. Siderophore treatment reduced this signal. For DTPA-treated fibers, only the fungal siderophore lowered it significantly. The authors concluded that bioremediation of asbestos fibers is feasible. They noted that siderophores may not eliminate the risk completely and that they used purified rather than soil-derived fibers.

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 experiment: chemical treatment of chrysotile fibers followed by a cell-based toxicity test using mouse immune cells
• Who was studied: Purified chrysotile fibers from Arizona ore, tested on peritoneal macrophages harvested from mice (number of mice not stated); no human subjects
• Exposure: Chrysotile fibers (iron content measured at 2.3% by weight) treated with the bacterial siderophore DFO at 1 or 10 µM, the fungal siderophore ferrichrome (FC) at 1 µM, and oxalic, malonic or citric acid at 100 µM, with or without DTPA pretreatment to remove plant-available iron
• Main results:
  • DFO released iron from the chrysotile fibers, and more iron was released at 10 µM DFO than at 1 µM
  • With 1 µM DFO, iron release levelled off within 24 h; with 10 µM DFO, this was delayed to at least 120 h
  • Oxalic acid alone (100 µM) released no detectable iron (below the 1 µg/L detection limit)
  • Citric acid increased the iron released by 1 µM DFO, whereas oxalic and malonic acid appeared to have no effect
  • Pre-exposing fibers to the organic acids for 48 h did not change the amount of iron released by 1 µM DFO
  • The fungal and bacterial siderophores released similar amounts of iron, reported as 172 µM of Fe per g of fiber per µM of siderophore
  • Removing plant-available iron with DTPA did not reduce either siderophore's ability to remove iron from the fibers
  • In control samples without a siderophore, DTPA treatment significantly lowered reactive oxygen species generated by the mouse macrophages (p less than 0.05)
  • For fibers with plant-available iron, treatment with either siderophore reduced reactive oxygen species generation compared with control
  • For DTPA-treated fibers, the fungal siderophore significantly lowered reactive oxygen species generation compared with control, but the bacterial siderophore did not
• The authors' conclusion: The authors concluded that bioremediation of asbestos fibers is feasible
• Limitations the authors state:
  • The chrysotile was purified before use, removing coatings that might hinder iron removal; the authors said future studies should use fibers isolated from the environment
  • Fiber toxicity also depends on physical properties, so siderophores may not eliminate the risk completely
  • DTPA left on the fibers could have contributed a small amount of the iron released
  • The iron measurement method did not distinguish ferrous from ferric iron

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, Aspect Ratio (Length-to-diameter ratio), Exudate, Asbestos, Macrophage.

Related studies

• Iron removal from raw asbestos by siderophores-producing Pseudomonas — S.R. David, D. Ihiawakrim, et al. (2020)
• Iron-loaded synthetic chrysotile: a new model solid for studying the role of iron in asbestos toxicity — E. Gazzano, F. Turci, et al. (2007)
• Engineering siderophore production in Pseudomonas to improve asbestos weathering — M. Lemare, H. Puja, et al. (2022)
• Biodeterioration of asbestos cement by siderophore-producing Pseudomonas — S.R. David, A. Jaouen, et al. (2021)
• Phospholipase A2-mediated superoxide production of murine peritoneal macrophages induced by chrysotile stimulation — T. Nakajima, M. Ito, et al. (2000)
• N-acetyl L-cysteine attenuates oxidant-mediated toxicity induced by chrysotile fibers — F. Afaq, P. Abidi, et al. (2000)

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