Graduate Thesis Or Dissertation


Spatial and Temporal Variability of Heavy Metals (Lead, Copper, and Zinc) in Stormwater, Moss, and Street Dust in Portland, OR Public Deposited

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  • Lead (Pb), copper (Cu), and zinc (Zn) are known to have detrimental effects on aquatic and terrestrial ecosystems, and to human health both in rural and urban areas. Heavy metal contamination enters stormwater by atmospheric deposition and by the collection of surface particles during overland flow. Stormwater runoff in urban areas has multiple fates including urban yards, Underground Injection Control (UIC) wells, waterways such as rivers, streams, and lakes, and coastal environments. Monitoring atmospheric deposition in urban areas can be expensive and recently researchers have been using mosses as biomonitors of atmospheric deposition. Terrestrial epiphytic moss species are useful when monitoring atmospheric deposition as they intake all moisture and nutrients from the atmosphere and only use the plant as their physical host. Similarly, street dust is useful when determining the levels of pollution in urban areas due to atmospheric deposition on local and regional scales. All three media types are interconnected and together can elucidate the distribution of heavy metal contamination in urbans areas. The research presented in this thesis examines the spatial and temporal variability of unfiltered and filtered (dissolved) stormwater, epiphytic moss (Orthotricuum lyyeli), and street dust at 21 sampling sites randomly selected throughout Portland, OR. Along with concentration data, Pb isotope signatures (a geochemical tool) were used to identify potential regional and global sources and compare their signatures to other samples from various media types in the local region. The breadth of known Pb isotopic endmembers restricted the confidence of source identification using Pb isotope fingerprinting. In all media types, concentrations were generally lowest for Pb, followed by Cu, then Zn. Concentrations of all three analytes were very heterogeneous around the city and had elevated levels occurring in various zoning types which spanned residential, industrial, and business districts. Stormwater concentrations were higher in fall relative to the spring due to the buildup of particles on city surfaces during the prolonged dry periods between the limited storm events occurring during the summer. In unfiltered stormwater, Cu had the greatest number of sites with levels above the 1200-Z benchmark levels followed by Zn, and Pb. In filtered samples, Cu had the highest affinity for the dissolved state followed again by Zn, and Pb. Seasonally, moss concentrations increased in all 3 analytes from spring to summer, and summer to fall with the exception for Pb decreasing from summer to fall. On average, street dust concentrations increased from the beginning (June) to the end (September) of summer. This increase in metal concentrations in all sample medias from either before to after, or from the beginning to the end of summer shows the influence of dry days on metal pollution in urban areas. Small-scale industrial emissions are known to influence stormwater, moss, and street dust in Portland by high positive Fisher-Pearson skewness coefficients in stormwater (Pb, Cu, and Zn in spring, and Cu in fall), and moss (Pb in spring and summer) and from the variability of Pb isotope ratios in all three media types extending out of the general Portland stormwater, moss, and street dust trend. Pb isotope ratios from this study as well as numerous other studies conducted in Portland overlap to form a unique Portland Pb isotopic signature across all media showing the interconnection between different sample types with the local, regional, and global sources of Pb pollution in Portland.
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