Clay mineralogy insights and assessment of the natural (Ra-228, Ra-226, Pb-210, K-40) and anthropogenic (Cs-137) radionuclides dispersion in the estuarine and lagoon systems along the Atlantic coast of Portugal

• Type: Article in International Scientific Journal
• Date: 2021

Authors

Bobos, I (Author) FCUP; Madruga, MJ (Author) Other; Reis, M (Author) Other; Esteves, J (Author) Other; Guimaraes, V (Author) Other

Journal

Title: Catena

Vol. 206

ISSN: 0341-8162

Publisher: Elsevier

Indexing

ISI Web of Knowledge - 7 Citations

Scopus - 8 Citations

Other information

Authenticus ID: P-00V-4SA

DOI: 10.1016/j.catena.2021.105532

Abstract (EN): The activity concentrations of natural (Ra-228, Ra-226, Pb-210, K-40) and anthropogenic (Cs-137) radionuclides were measured by gamma spectrometry on sediments collected from aquatic systems. The mineralogy of clay fractions identified by X-ray diffraction (XRD) is composed by an illitic material (detrital mica, illite/smectite, and illite/ smectite/vermiculite mixed-layers) +/- kaolinite and illite. The Mg2+-saturated clay fractions show three distinct illitic populations within the illitic material: detrital mica, illite/vermiculite mixed-layers, and illite/smectite. Transmission electron microscopy (TEM) images show illitic material aggregates with a flaky- and lath-shapes, pseudohexagonal platy kaolinite and lath-shape illite. The Ra-228 activity concentration values range from 30.1 to 403 Bq Kg(-,) the Ra-226 from 24.6 to 290 Bq Kg(-1) and from 44 to 368 Bq Kg 1 for Pb-210. The Ra fluxes suggest a unique source where the mixing process and radioactive decay equilibrated the losses of short- (Ra-228) and long-lived (Ra-226) isotopes. The Pb-210/Ra-226 ratio shows an average value of 2.165, indicating that the radioactive secular equilibrium (similar to 1) was reached. A decrease of the natural radionuclide (Ra-228, Ra-226, Pb-210) activity concentrations was observed in estuaries and near shore coastal sediments from north to south of Atlantic Portuguese coast. Higher Pb-210 and Ra-226 activity concentrations were obtained in samples composed by illitic material + kaolinite and organic matter. The illite/smectite mixed-layers and kaolinite are suitable sorbents for Ra and Pb-210 isotopes. Higher 40K values (473-1001 Bq K-1) were measured on feldspar, mica and clay sediments provided from granite weathering (north region). The Cs-137 activity values range from 1.25 to 10.1 +/- 1.9 Bq Kg(- 1) for samples collected from the northern and central part of estuarine areas. A higher Cs-137 activity (31.2 +/- 3.5 Bq Kg(- 1)) was measured in the southern part of the Atlantic coast, corresponding to a sediment with a higher amount of illite.

Language: English

Type (Professor's evaluation): Scientific

No. of pages: 13