Investigation of chemical partitioning of 7Be, 210Pb and 137Cs and novel dating of road sediment by 210Po:210Pb disequilibrium method

• Published in: The Science of the total environment 2023-09, Vol.892, p.164738-164738, Article 164738
• Main Authors: Denny, M., Baskaran, M.
• Format: Article
• Language: English
• Subjects: 210Po-210Pb disequilibrium; Atmospheric fallout of 7Be, 210Po and 210Pb; Geochemical behavior of 210Po, 210Pb and 7Be in terrestrial environment; Road sediment dating using 210Po/210Pb activity ratio; Sequential leaching of road sediment
• ISSN: 0048-9697; 1879-1026
• DOI: 10.1016/j.scitotenv.2023.164738

A suite of road sediment and soil samples from a post-industrial city (Detroit, MI) were collected and analyzed for atmospherically-delivered 210Pb, 210Po, 7Be along with 226Ra and 137Cs in the bulk and size-fractionated solid samples. From the measured atmospheric depositional fluxes of 7Be, 210Po, and 210Pb, the initial 210Po/210Pb activity ratio was quantified. In all samples, there is disequilibrium between 210Po and 210Pb, with a 210Po/210Pb activity ratio (AR) of 1 year. Results from a subset of samples that were sequentially extracted for exchangeable, carbonate, Fe-Mn oxide, organic and residual phases indicate the Fe-Mn oxide fraction was found to contain the largest fraction of 7Be and 210Pb; however, the largest fraction of 210Pb was associated with the residual phase and is attributed to complexation of 210Pb with recalcitrant organic matter. This study shows that the natural tagging of 7Be and 210Po-210Pb pair via precipitation provides insights on the time scale of their mobility and adds a new dimension of time information on the pollutant-laden road sediment. Model-predicted activity ratio of excess (210Po/210Pb) in road sediment. [Display omitted] •First dating of road sediment based on 210Po:210Pb disequilibrium•Average ‘apparent age’ of sediment 146 ± 62 days (n = 43) compared to 19 ± 10 days (n = 7) of aerosol•Largest fractions of 7Be and 210Pb in road sediments are associated with Fe-Mn oxides.•The model predicts a (210Po/210Pb)xs ratio reaching a dynamic equilibrium of ~0.59 in >1.0 year.