Award Date
12-15-2025
Degree Type
Dissertation
Degree Name
Doctor of Philosophy (PhD)
Department
Civil and Environmental Engineering and Construction
First Committee Member
Erica Marti
Second Committee Member
Daniel Gerrity
Third Committee Member
Haroon Stephen
Fourth Committee Member
Sajjad Ahmad
Fifth Committee Member
Patricia Cruz
Number of Pages
235
Abstract
The increased use of chemical markers in water analysis has gained attention due to their effectiveness in identifying sources of contaminants. These markers help identify pollution sources such as those from sewage, treated wastewater, and urban runoff. Advances in chemical and biological marker techniques have expanded their scope, allowing both qualitative and quantitative information about population activities. Consequently, environmental epidemiology based on runoff monitoring has emerged as a valuable approach to indirectly estimate the consumption of legal and illicit substances within a given population. This study focused on evaluating the utility of chemical markers and water quality parameters in linking contamination sources at different locations along the Las Vegas Wash. Additionally, leveraging environmental epidemiology, the research explored illicit drug markers in the Las Vegas Wash, focusing on contributions from areas with homeless encampments and treated wastewater discharges. The objective was to better understand how these sources contributed to water pollution and to characterize the presence and relative loads of drug-related compounds. Beyond chemical loads, there was a need to address fecal contamination from tributaries like urban runoff and treated wastewater, which can carry significant pathogen loads. Therefore, the final goal was to model the probability of illness due to exposure to human adenovirus (HAdV) using quantitative microbial risk assessment (QMRA). Two non-pathogenic viruses, the human gut bacteriophage cross-assembly phage (crAssphage) and the food virus pepper mild mottle virus (PMMoV), were used for this purpose. The objective was to quantify the potential risk of illness associated with HAdV for individuals coming into contact with urban water sources under two distinct scenarios: urban water sources influenced by the presence of a significant unsheltered homeless population and urban water bodies where flows from contaminated tributaries converge. Across the three research objectives, the findings demonstrated clear differences in contamination sources, chemical inputs, and public-health risks along the Las Vegas Wash. The principal component analysis showed that trace organic compounds (TOrCs) alone could distinctly separate treated wastewater effluents from urban runoff, with persistent compounds such as carbamazepine, sucralose, tramadol, oxycodone, lidocaine, ecgonine, and MDMA characterizing WWTP discharges, while caffeine, morphine, and methamphetamine were most strongly associated with human-impacted runoff. The inclusion of water-quality parameters further strengthened this separation, increased variability along a principal component axis, and revealed refined gradients among individual sites, highlighting the unique chemical signatures of WWTPs, the influence of homeless encampments at the FAT tributary, and the mixing effects at downstream confluence locations. Building on these source distinctions, back-calculation of drug residues from runoff demonstrated that unsheltered homeless individuals contributed disproportionately high loads of methamphetamine and heroin to the Wash, far exceeding community-level averages reported in other studies. In contrast, MDMA was consistently absent at the location with higher influence of homeless encampments, while broader WWTP effluents contributed a more diverse suite of illicit drugs and metabolites to downstream waters. Finally, QMRA modeling revealed that exposure to HAdV in surface waters impacted by untreated runoff posed non-negligible health risks, with estimated probability of illness ranging from 8–16% per event at areas with high concentrations of unsheltered individuals, compared to 2–5% at sites with fewer direct human inputs. PMMoV consistently produced higher modeled HAdV concentrations and higher illness-risk estimates than crAssphage, underscoring its potential as a more conservative and protective indicator. Collectively, these results showed that chemical markers, illicit-drug residues, and viral indicators offered complementary and powerful tools for characterizing contamination sources, quantifying human activity, and identifying public-health risks in urban watershed systems shaped by both wastewater inputs and unsheltered homeless populations.
Keywords
Chemical; crAssphage; Epidemiology; Illicit Drugs; Indicator; PMMoV
Disciplines
Civil and Environmental Engineering | Engineering | Environmental Engineering
File Format
File Size
2900 KB
Degree Grantor
University of Nevada, Las Vegas
Language
English
Repository Citation
Sarria Cortes, Mayra Alejandra, "Chemical Contaminants and Microbial Risk in the Las Vegas Valley" (2025). UNLV Theses, Dissertations, Professional Papers, and Capstones. 5466.
https://oasis.library.unlv.edu/thesesdissertations/5466
Rights
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