Thorium content in soil, water and sediment samples and fluvial sediment-associated transport in a catchment system with a semiarid-coastal interface, Brazil
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Thorium (Th) is one of the main sources of natural radiation to ecosystems. However, data regarding Th concentrations in rocks, soil, water and sediments are currently scarce. Accordingly, this study aimed to establish background concentrations and quality reference values (QRVs) for Th in the environmentally impacted Ipojuca River catchment in Brazil, where the weathering of granites releases Th into the environment. Additionally, the study aimed to calculate Th fluxes in water, and both bed and suspended sediment. The mean Th concentration in the study catchment soils was 28.6 mg kg−1. The QRV for Th was estimated to be 21 mg kg−1 and 86.3 Bq kg−1. Bed and suspended sediment–associated concentrations ranged from 2.8 to 32.9 mg kg−1. Suspended sediment–associated discharge (3.42 t year−1) accounted for more than 99% of the total Th flux, while the dissolved phase transport was negligible in comparison. At the downstream cross section in the study catchment, suspended sediment samples exhibited Th concentrations similar to those observed in rivers impacted by mining activities. The discharge of sediment to the ocean from the study area is mainly triggered by soil erosion processes in the hotspot region (middle-inferior course). It is essential to identify Th hotspots before establishing environmental policies regarding human health and environmental protection.
KeywordsQuality reference values Environmental quality Watershed Th hotspot Sediment-associated transport Soil erosion processes
We would like to thank the editor and anonymous reviewers for their insightful and constructive comments that greatly contributed to the improvement of the original manuscript.
This research was supported by the Brazilian Government, MEC/MCTI/CAPES/CNPq/FAPs EDITAL No. 61/2011-Science Without Borders Program, project number (402603/2012-5), and by FACEPE process number (IBPG-0889-5.01/11). ALC was funded by the UK Biotechnology and Biological Sciences Research Council (BBSRC) via grant award BBS/E/C/000I0330 – Soil to Nutrition.
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