Browsing by Subject "lead"

Now showing 1 - 9 of 9
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    Assessment of Lead and Beryllium Sorption To Exposed Stream Channel Sediment Under Varying Freshwater Channel Conditions
    (2019-06) Pawlowski, Ethan
    Purpose: Beryllium (Be) and lead (Pb) sorption is important to the utility of the radioisotopes of these elements for sediment fingerprinting. I examined the sorption of Be and Pb to exposed fluvial sediment under varying chemical conditions representative of freshwater streams draining two distinct Critical Zone environments in the eastern United States: the mid-Atlantic piedmont and heavily glaciated Great Lakes region. Materials and Methods: Batch experiments were completed using well-characterized in-stream deposit sediments collected from these two systems and varying solutions to reflect background and elevated levels of iron oxide in the form of goethite across times ranging from 0.25 to 360 h. The mid-Atlantic piedmont sediment had further treatments testing dissolved organic carbon (up to 11.86 mg L-1) and increased sediment to solution ratio (up to 8000 mg: 1 L) effects on Pb and Be sorption. Results and Discussion: Beryllium partition coefficients (Kd) ranged from a log Kd of 1.46 to 3.48 L kg-1 and Pb ranged from 0 to 5.03 L kg-1 across all treatments displaying several noticeable patterns. Two-stage sorption was observed such that sorption increased over time across all treatments and substrates. Goethite additions either enhanced or reduced sorption relative to the base treatment depending on the original sediment and mixing time. Lead sorption with the addition of 100 mg of goethite increased during shorter mixing times before being surpassed by the base treatment at longer mixing times for both the mid-Atlantic piedmont and glaciated Great Lakes sediment. Beryllium sorption was increased with the mid-Atlantic piedmont sediment whereas it was primarily decreased with the glaciated Great Lakes sediment. The 1 mg of goethite generally showed equal to or slightly enhanced sorption relative to the base treatment of both Pb and Be with the exception of Pb sorption to the Great Lakes sediment. The highest DOC concentration that I tested (11.86 mg L-1) retained a greater amount of Be and Pb in solution compared to other treatments after 360 h. Increasing the sediment to solution ratio showed decreased partition coefficients across all analogous times for Be compared to the base treatment whereas Pb sorption surpassed the unaltered treatment after 24 h. Conclusions: It is not recommended to use either 7Be or 210Pb in fluvial systems with high background concentrations of DOC because the DOC was shown to inhibit sorption to sediment surfaces and it could produce erroneous results in sediment fingerprinting studies unless that inhibition or loss is accounted for. The goethite treatments produced mixed results and further research is needed to parse out conditions that enhance or inhibit the sorption of fallout radionuclides in the presence of stream sediments with varying amounts of organic matter occlusion of surface binding sites. Increased sediment to solution ratios increased sorption of Pb suggesting that Pb would be a conservative tracer in fluvial systems with high sediment delivery. These results suggest that fluvial sediment mineralogy, organic matter concentration, and biogeochemical cycling of common stream chemical constituents may play a role in the mobilization or retention of these two trace metals and alter their utility for sediment fingerprinting.
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    Environmental Lead Risk in the Twin Cities.
    (Center for Urban and Regional Affairs, University of Minnesota, 1989) Mielke, Howard W.; Adams, John L.
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    Evaluation of the Utility of Deterministic Models for Dermal Exposure Assessment of Solids and Investigation of the Potential Influence of Repeated Contacts and Skin Hydration on Quantitative Dermal Loading and Transfer
    (2021-02) Elliott, Jennifer
    Exposure assessment is an important tool for occupational, environmental and consumer health professionals to evaluate the level of risk associated with various scenarios. While exposure assessment methods have been well defined for inhalation exposures for many decades, dermal exposure assessment methods are often lacking in quality and accuracy. A number of deterministic models have been developed to evaluate the potential for dermal exposure and uptake or ingestion in the absence of substance-specific or scenario-specific dermal loading measurement data. These models typically use default assumptions regarding the quantity of loading on the skin surface, frequently requiring the use of data with unknown relevance. Further, these models routinely incorporate an assumption of additive transfer with each successive or routine contact with the substance of interest. Overall, however, relatively few data are available to characterize the factors or determinants most likely to influence the accurate estimation or calculation of dermal exposure potential for specific substances. The purpose of the research in this dissertation was therefore to quantitatively consider the influence of current loading-related assumptions used in deterministic dermal exposure models available to exposure assessment practitioners and to explore these influences further. This research included several specific aims. First, a study of the accuracy of exposure assessment practitioners when using available deterministic, scenario-specific dermal exposure assessment models was performed. Second, the outcomes of this analysis were used along with a comprehensive literature review to identify determinants with the greatest potential to influence dermal loading and transfer. Two specific determinants, repeated dermal contacts and skin hydration, were noted to have a statistically-significant influence on quantitative dermal loading in the literature and were reported to have potentially complex relationships with dermal loading and transfer. These two determinants were therefore identified for additional quantitative analysis with respect to their potential to influence dermal loading and transfer. To assess the influence of repeated contacts on dermal loading, a study design based on a dermal conceptual model was developed for human skin in vivo to characterize the different pathways and compartments and their contributions to dermal loading following repeated contacts with a dermal test substance (elemental metallic lead). To assess the influence of skin condition and hydration, first, different measurement methods were quantitatively compared for multiple skin sites and were evaluated for their utility in skin surface sampling studies. The quantitative influence of normal skin hydration on dermal loading was then also investigated for the same test substance. Overall, the results suggested that, contrary to the general acceptance and use of additive loading principles for many dermal exposure assessment models, the application of this assumption for repeated contact scenarios in dermal exposure modeling resulted in overestimates or substantial overestimates of dermal exposure by exposure assessment practitioners. When tested using experimental measurements for scenarios including source-to-skin, skin-to-skin, and skin-to-gloves, repeated transfer tests appeared to approach a steady state loading on the skin between five and ten contacts with the test substance, consistent with other data in the literature. The results also suggested that substantial variability exists in skin hydration characteristics between different skin sites, and that skin hydration may influence quantitative dermal loading and transfer. Although additional data are needed for other substances, the measurement data collected point to a need to reconsider the way that influences on dermal loading and transfer, and particularly the additive loading assumption, are used in current deterministic dermal exposure assessment models.
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    From Soil to Squirrel: The Legacy of Lead Pollution & Its Effects on Urban Wildlife Behavior
    (2024-04-18) Schulz, Rachel K; Devitz, Amy-Charlotte; Snell-Rood, Emilie C
    Urbanization increasingly threatens wildlife through the introduction of novel threats and pollution. Animals can use behavior to adapt to urban environments and urban pollutants drive changes in behavior, leading to populations of urban wildlife with some behaviors that are distinct from rural populations. Lead (Pb) pollution is ubiquitous in urban areas, but there can be significant local variation in soil lead levels. In this study, I examined the relationship between soil lead, hair lead, docility, and aggressive and social behavior in eastern gray squirrels (Sciurus carolinensis) and eastern chipmunks (Tamias striatus) in Minneapolis and Saint Paul, Minnesota. Docility was measured through a struggle test and aggressive and social responses were measured in a mirror image stimulation trial. Soil lead and hair lead were significantly positively correlated in gray squirrels and chipmunks, and there was no difference in hair lead based on species or sex. Chipmunks had significantly longer struggle times than gray squirrels, but struggle time did not vary based on hair lead or sex. Only six of 235 animals displayed aggression in the mirror image stimulation trial, and frequency of contacting the mirror in a nonaggressive way was not correlated with hair lead, species, or sex. These results provide correlational evidence of lead transfer from soils to gray squirrels and chipmunks, though the magnitude of lead accumulation does not seem to depend on the distinct life histories of these two species. At the levels currently present in these urban environments, lead does not affect aggressive or social behavior in gray squirrels or chipmunks. Future studies should examine aggression through direct observation rather than a mirror image stimulation trial to better quantify aggression in these species that have low territorial aggression.
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    Health and Safety at Deconstruction Services.
    (1999) Thompson, Faye and Diana Wolf
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    A Method for the Detection of Lead in Bovine Blood and Liver
    (Minnesota Agricultural Experiment Station, 1956-12) Hammond, Paul B.; Wright, Harold N.; Roepke, Martin H.
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    Standards for Soil Lead Limitations in the United States.
    (1986) Chaney, Rufus L.; Mielke, Howard W.