title: Thallium-rich rust scales in drinkable water distribution systems: A case study from northern Tuscany, Italy.
abstract: Following the detection of a severe thallium contamination of the drinkable water from the public distribution system of Valdicastello Carducci-Pietrasanta (northern Tuscany, Italy), and the identification of the source of contamination in the Molini di Sant'Anna spring (average Tl content≈15μgL-1), the replacement of the contaminated water with a virtually Tl-free one (Tl<0.10μgL-1) caused an increase in Tl concentration in the drinkable water. This suggested that the pipeline interior had become a secondary source of Tl contamination, promoting its mineralogical and geochemical study. Rust scales samples taken from several pipeline segments, as well as leaching products obtained from these samples, were investigated through scanning electron microscopy, X-ray fluorescence chemical analyses, inductively coupled plasma - mass spectrometry, X-ray diffraction, and X-ray absorption spectroscopy. Thallium-rich rust scales (up to 5.3wt% Tl) have been found only in pipeline samples taken downstream the water treatment plant, whereas the sample taken upstream contains much less Tl (~90μgg-1). The Tl-rich nature of such scales is related to the occurrence of nano- and micro-spherules of Tl2O3and less abundant nanocrystalline μm-sized encrustations of TlCl. Leaching experiments on Tl-rich rust scales indicate that a fraction of the available Tl is easily dissolved in tap water; X-ray absorption spectroscopy suggests that monovalent thallium occurs in water equilibrated with the rust scales, probably related to the dissolution of TlCl encrustations. Therefore, Tl dissolved as Tl+only in the water from the Molini di Sant'Anna spring was partially removed through oxidative precipitation of Tl2O3and precipitation of TlCl. This highlights the critical role played by the addition of chlorine-based oxidants in water treatment plants that could favour the deposition of Tl-rich coatings within the pipelines, giving rise to unexpected secondary sources of contamination.
authors.affiliation: Dipartimento di Scienze della Terra, Università di Pisa, Via S. Maria 53, 56126 Pisa, Italy. Electronic address: biagioni@dst.unipi.it.
authors.forename: Cristian
authors.initials: C
authors.lastname: Biagioni
authors.affiliation: Dipartimento di Scienze della Terra, Università di Pisa, Via S. Maria 53, 56126 Pisa, Italy.
authors.forename: Massimo
authors.initials: M
authors.lastname: D'Orazio
authors.affiliation: CNR-IOM-OGG, 71 Avenue des Martyrs, F-38043 Grenoble, France.
authors.forename: Giovanni O
authors.initials: GO
authors.lastname: Lepore
authors.affiliation: CNR-IOM-OGG, 71 Avenue des Martyrs, F-38043 Grenoble, France.
authors.forename: Francesco
authors.initials: F
authors.lastname: d'Acapito
authors.affiliation: Dipartimento di Scienze della Terra, Università di Pisa, Via S. Maria 53, 56126 Pisa, Italy.
authors.forename: Simone
authors.initials: S
authors.lastname: Vezzoni
mesh_terms: D060766:Drinking Water / Q000737:chemistry*; D004784:Environmental Monitoring; D007558:Italy; D013793:Thallium / Q000032:analysis; D014874:Water Pollutants, Chemical / Q000032:analysis*
chemical_list: D060766:Drinking Water; D014874:Water Pollutants, Chemical; D013793:Thallium
keywords: Drinkable water; Emerging pollution; Thallium; Water treatment; X-ray absorption spectroscopy