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Access Type

WSU Access

Date of Award

January 2021

Degree Type

Thesis

Degree Name

M.S.

Department

Geology

First Advisor

Mark Baskaran

Abstract

Road dusts (<63 µm) are known to commonly contain elevated levels of many pollutants especially heavy metals such as Pb, Cd, and Cr. The timescale of their movement in the urban environment remains elusive. Use of particle-reactive radionuclides as tracers and chronometers to quantify environmental processes is well established in terrestrial, aquatic, and atmospheric systems. This is the first study to evaluate the application of naturally occurring and atmospherically delivered radionuclides to estimate timescales associated with the uptake of 210Pb, 7Be, 210Po by road dusts. This study investigates the spatial variations and distribution of 210Pb, 210Po, 226Ra, 7Be, and 137Cs activities in bulk precipitation, soil, and road dusts in and around Detroit, MI. The present study includes investigations of the distributions of these nuclides in different size fractions of road dust samples as well as in 5 different species that were sequentially extracted. Estimates of composite/apparent age were determined from the disequilibrium between 210Po and 210Pb. A new numerical modeling is developed to simulate the measured 210Po/210Pb activity ratios under different fractions of radionuclides uptake. From the analysis of a suite of heavy metals on road dust samples, four metrics of metal enrichment and metal contamination status of road dust were assessed: i) Enrichment Factor; ii) Pollution Index, iii) Geoaccumulation Index, and iv) Pollution Load Index. In addition, statistical analyses were conducted on trace metal data for the identification of contamination profiles common among road dusts. From the analysis of these diverse datasets, higher 7Be/210Pbxs activity ratios, yet lower (210Po/210Pb)xs activity ratios were found in road dusts compared to soils. A major fraction of 7Be and 210Pb sorbed onto road dust was found to be associated with Fe-Mn oxide fraction. Replication of measured (210Po/210Pb)xs activity ratios in road dusts via numerical modelling suggest the conditions under which the transfer of atmospherically-delivered radionuclides from precipitation to road dust takes place can be simulated. Contamination of Cr, Zn, and Ba in road dusts, and three contamination profiles that together explain >70% of variance in concentration of eleven trace metals.

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