Traffic-related distribution of antimony in roadside soils

Our plain-English summary of Traffic-related distribution of antimony in roadside soils, by C. Földi, S. Sauermann, R. Dohrmann, et al (Environmental Pollution, 2018).

The study

• Authors: C. Földi, S. Sauermann, R. Dohrmann, T. Mansfeldt
• Journal: Environmental Pollution
• Published: 2018;237:704-712
• Cited by: 31 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Vehicular emissions have become one of the main source of pollution of urban soils; this highlights the need for more detailed research on various traffic-related emissions and related distribution patterns. Since the banning of asbestos in the European Union, its substitution with antimony (Sb) in brake linings has led to increased inputs of this toxic metalloid to environmental compartments. The objective of this study was to provide detailed information about the spatial distribution patterns of Sb and to assess its mobility and bioavailability. Roadside soils along an arterial road (approx. 9000 vehicles per day) in Cologne (Germany) were studied along five transects, at four soil depths and at seven sampling points set at varying distances from the road (n = 140). For all samples, comprehensive soil characterization was performed and inverse aqua regia-extractable trace metal content was determined being pseudo-total contents. Furthermore, for one transect, also total Sb and a chemical sequential extraction procedure was applied (n = 28). Pseudo-total Sb for all transects decreased significantly with soil depth and distance from the road, reflecting a distribution pattern similar to that of other trace metals associated with brake lining emissions. Conversely, metals associated with exhaust emissions showed a convex distribution. The geochemical fractionation of Sb revealed the following trends: i) non-specifically sorbed Sb was <5%; ii) specifically sorbed Sb was only detected within 1 m distance from the road and decreased with depth; iii) Sb associated with poorly-crystalline Fe oxides decreased with distance from the road; and iv) content of Sb bounded to well-crystalline Fe oxides, and Sb present in the residual fraction remained relatively constant at each depth. Consequently, roadside soils appear to inhibit brake lining-related Sb contamination, with significant but rather low ecotoxicological potential for input into surface and groundwater.

Copyright © 2017 Elsevier Ltd. All rights reserved.

In plain English

This was an environmental field study of antimony, a toxic metalloid, in roadside soil in Cologne, Germany. It did not measure asbestos. The article's background states that antimony replaced asbestos in brake linings after the European Union ban. The authors took 140 soil samples along five lines running away from a road carrying about 9000 vehicles a day. Samples came from seven distances, from the road edge out to 10 m, and from depths down to 30 cm. Antimony ranged from 0.513 to 6.19 mg per kg, and 90% of samples exceeded the local background value of 0.80 mg per kg. Antimony fell significantly with distance and depth. Copper and molybdenum, also found in brake linings, showed a similar pattern, while lead and cadmium peaked about 1 m from the road. Some unusually high spots were assumed to come from construction material. In one line of samples, under 10% of the antimony was in more easily available forms. The authors concluded that the antimony came mostly from brake lining wear and that leaching risk was rather low, but that risk was likely underestimated.

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: Environmental field study: soil sampling along transects next to a road, with chemical analysis and a sequential extraction procedure
• Who was studied: Roadside soil on the east side of Berrenrather Street, Cologne, Germany. There were 140 samples from five transects, each with seven points from the road edge to 10 m away, at four depths down to 30 cm. A subset of 28 samples from transect III was used for total antimony and sequential extraction. The sampling date is not given.
• Exposure: Road traffic emissions (about 9000 vehicles per day) as a source of antimony and other trace metals (copper, molybdenum, lead, cadmium, zinc) in soil. Asbestos itself was not measured.
• Main results:
  • Soil pH in the 140 samples ranged from 5.7 to 7.8.
  • Pseudo-total antimony in the soil samples ranged from 0.513 to 6.19 mg per kg. The mean was 2.11 mg per kg and the median 1.69 mg per kg.
  • 90% of samples exceeded the background value of 0.80 mg per kg, and 10 samples exceeded it more than five-fold.
  • Antimony was significantly related to depth and distance from the road (p less than 0.001), decreasing as both increased.
  • Copper and molybdenum, which are found in brake linings, showed relatively strong correlations with antimony.
  • Lead and cadmium showed a different, convex pattern, peaking about 1 m from the road.
  • Some isolated high antimony values were assumed by the authors to come from construction material rather than traffic.
  • In transect III samples, non-specifically sorbed antimony stayed below about 5% in all samples.
  • In transect III samples, specifically sorbed antimony was found almost only within 1 m of the road.
  • In the top 5 cm, antimony associated with poorly-crystalline iron oxides fell from 64.2% at the road edge to 54.4% at 10 m.
• The authors' conclusion: The authors concluded that antimony in these soils came mostly from brake lining abrasion. They judged that leaching of traffic-related antimony from roadside soils carried rather low risk, though higher traffic could raise inputs to water, and that environmental risk was likely underestimated.
• Limitations the authors state:
  • Sequential extraction results may be affected by phase overlap and re-adsorption, and should be interpreted with care.
  • The extraction scheme, originally designed for arsenic, did not separate organically bound antimony, so environmental risk was likely underestimated.
  • X-ray diffraction could not rule out non-crystalline or low-concentration mineral phases at the hot spots.
  • It was uncertain which chemical fraction holds the antimony from brake lining wear.

Topics

Medical terms in this study, explained in our Lexicon: Brake Lining, Crystalline.

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