Effective radium concentration in topsoils contaminated by lead and zinc smelters Frédéric Girault a, ⁎, Frédéric Perrier a , Charles Poitou a , Aude Isambert a , Hervé Théveniaut b , Valérie Laperche b , Blandine Clozel-Leloup c , Francis Douay d a Institut de Physique du Globe de Paris, Sorbonne Paris Cité, Université Paris Diderot, CNRS, Paris, France. b Bureau de Recherches Géologiques et Minières, Orléans, France. c Bureau de Recherches Géologiques et Minières, Villeurbanne, France. d Laboratoire Génie Civil et géo Environnement, ISA Lille, Lille, France. HIGHLIGHTS • Effective radium concentration (EC Ra ) is used to study trace element pollution. • EC Ra is measured in 186 contaminated topsoils near smelters in the north of France. • Soil EC Ra values are spatially organized and depend on the geographical units. • EC Ra helps to identify the natural spatial variability of magnetic susceptibility. • EC Ra provides a novel index to identify soils able to fix leached components. abstract article info Article history: Received 27 January 2016 Received in revised form 26 March 2016 Accepted 2 May 2016 Available online xxxx Editor: F.M. Tack Trace elements (TE) are indicative of industrial pollution in soils, but geochemical methods are difficult to imple- ment in contaminated sites with large numbers of samples. Therefore, measurement of soil magnetic susceptibil- ity (MS) has been used to map TE pollutions, albeit with contrasted results in some cases. Effective radium concentration (EC Ra ), product of radium concentration by the emanation factor, can be measured in a cost-effec- tive manner in the laboratory, and could then provide a useful addition. We evaluate this possibility using 186 topsoils sampled over about 783 km 2 around two former lead and zinc smelters in Northern France. The EC Ra values, obtained from 319 measurements, range from 0.70 ± 0.06 to 12.53 ± 0.49 Bq·kg -1 , and are remarkably organized spatially, away from the smelters, in domains corresponding to geographical units. Lead-contaminated soils, with lead concentrations above 100 mg·kg -1 b 3 km from the smelters, are characterized on average by larger peak EC Ra values and larger dispersion. At large scales, away from the smelters, spatial variations of EC Ra correlate well with spatial variations of MS, thus suggesting that, at distance larger than 5 km, variability of MS contains a significant natural component. Larger EC Ra values are correlated with larger fine fraction and, possibly, mercury concentration. While MS is enhanced in the vicinity of the smelters and is associated with the presence of soft ferrimagnetic minerals such as magnetite, it does not correlate systematically with metal concentrations. When multiple industrial and urban sources are present, EC Ra mapping, thus, can help in identifying at least part of the natural spatial variability of MS. More generally, this study shows that EC Ra mapping provides an indepen- dent and reliable assessment of the background spatial structure which underlies the structure of a given con- tamination. Furthermore, EC Ra may provide a novel index to identify soils potentially able to fix leached components. © 2016 Elsevier B.V. All rights reserved. Keywords: Radon-222 Radium-226 Topsoils Lead contamination Environmental magnetism Magnetic susceptibility Science of the Total Environment 566–567 (2016) 865–876 ⁎ Corresponding author. E-mail address: girault@ipgp.fr (F. Girault). http://dx.doi.org/10.1016/j.scitotenv.2016.05.007 0048-9697/© 2016 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Science of the Total Environment journal homepage: www.elsevier.com/locate/scitotenv