Browsing by Author "Cohen, Alasdair Gordon"

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    Advancing Rural Public Health: From Drinking Water Quality and Health Outcome Meta-analyses to Wastewater-based Pathogen Monitoring
    Darling, Amanda Victoria (Virginia Tech, 2024-10-07)
    A rural-urban divide in health status and healthcare infrastructure has been well-documented in the U.S., where populations residing in census regions classified as rural often exhibit more negative health outcomes, adverse health behaviors, and have reduced access to affordable and proximal health services, compared to their urban and peri-urban counterparts. However, it is important to note that such disparities vary based on specific rural regions and individual circumstances. Rural areas may face elevated risk factors for infectious diseases such as increased proximity to wildlife and livestock and disproportionately high reliance on private, non-federally regulated, primary drinking water sources. Chronic conditions prevalent in rural communities such as diabetes and hypertension are frequently linked with longer duration and higher severity of symptoms than in urban areas; this association suggests that the risk of exposure to infectious diseases and the likelihood of progression to serious illness and hospitalization may be elevated, although this is not universally the case across all rural settings. Alongside documented urban-rural health disparities, there also exist disparities in the nature and quality of data on health-related behaviors, outcomes, and service provision in rural areas compared to urban and peri-urban regions. In this dissertation, two key environmental matrices –drinking water and wastewater– were highlighted as vectors of information to better estimate levels of contaminant exposures and health outcomes in rural communities. First, baseline data on drinking water contaminant levels and associated health outcome data were highlighted as crucial for refining holistic exposure estimates as well as understanding drinking water related health burdens in rural communities where a larger proportion of households use private drinking water sources, such as well water, that are not federally regulated. Second, systematic sampling and testing of pathogen biomarkers in wastewater to non-invasively measure population-level health status, also known as wastewater based surveillance (WBS) and, depending on the context, wastewater based epidemiology (WBE) is not constrained by disadvantages of clinical testing, e.g., limited health-care access, long travel times to testing facilities, delay between symptom-onset and testing. Thus, expanded implementation of WBS in rural communities is proposed here as a strategy to address data disparities in clinical testing for infectious diseases. Collectively, this dissertation advances knowledge on estimated drinking water contaminant levels, exposures, and associated public health outcomes and corresponding research gaps in rural Appalachian U.S., and elucidates pathways toward best practices and considerations for public-health focused wastewater testing adoption in rural communities. For the latter, the question of whether WBS challenges unique to rural wastewater systems hinder application of WBS in small, rural communities was explored, as well as methods to advance best-practices for rural WBS. To summarize existing publicly available peer-reviewed literature on drinking water contaminants in rural Appalachian U.S., in Chapter 2, a systematic review and meta-analysis of microbial and chemical drinking water contaminants was performed. Key contaminants were identified as being elevated beyond regulatory, health-based, maximum contaminant levels in our meta-analyses from rural drinking water sources in Appalachia, including E coli, lead, arsenic, uranium. Overall, we found data on drinking water source quality under baseline conditions (i.e., rather than post anomalous contamination events such as chemical spills) in rural Appalachian U.S. was sparse relative to widespread media coverage on the issue. Epidemiologic-based research studies that collected both drinking water exposure data and paired health outcome data were also limited. As a result, although some instances of anomalously high levels of drinking water contaminants were identified in rural Appalachia from the published literature, we could not obtain a clear picture of baseline exposures to drinking water contaminants in most rural Appalachian communities, highlight need to address these knowledge gaps. In Chapter 3, to evaluate whether wastewater could serve as a reliable metric for estimating community circulation of viruses and antimicrobial resistance (AMR) markers, even when sourced from aging and low-resource sewer collection networks, a 12-month wastewater monitoring study was conducted in a small, rural sewer conveyance system with pronounced infrastructural challenges. Specifically, the field site under study was compromised with heavy inflow and infiltration (IandI). Detection rates and concentrations of viral, AMR, and human fecal markers were grouped by levels of IandI impact across the sewershed, and location-, date-, and sample- specific variables were assessed for their relative influence on viral, AMR, and human fecal marker signal using generalized linear models (GLMs). We found that while IandI likely adversely impacted the magnitude of wastewater biomarker signal to some extent throughout the sewershed, especially up-sewer at sites with more pronounced IandI, substantial diminishment of wastewater signal at WWTP influent was not observed in response to precipitation events. Thus, our data indicated that WWTP influent sampling alone can still be used to assess and track community circulation of pathogens in heavily IandI impacted systems, particularly for ubiquitously circulating viruses less prone to dilution induced decay. Delineations were also made for what circumstances up-sewer sampling may be necessary to better inform population shedding of pathogens, especially where IandI is prevalent. Various normalization strategies have been proposed to account for sources of variability for deriving population-level pathogen shedding from wastewater, including those introduced by IandI-driven dilution. Thus, in Chapter 4, we evaluated the temporal and spatial variability of viral and AMR marker signal in wastewater at different levels of IandI, both unnormalized and with the adoption of several normalization strategies. We found that normalization using physicochemical-based wastewater strength metrics (chemical oxygen demand, total suspended solids, phosphate, and ammonia) resulted in higher temporal and site-specific variability of SARS-CoV-2 and human fecal biomarker signal compared to unnormalized data, especially for viral and AMR marker signal measured in wastewater from sites with pronounced IandI. Viral wastewater signal normalized to physicochemical wastewater strength metrics and flow data also closely mirrored precipitation trends, suggesting such normalization approaches may more closely scale wastewater trends towards precipitation patterns rather than per capita signal in an IandI compromised system. We also found that in most cases, normalization did not significantly alter the relationship between wastewater trends and clinical infection trends. These findings suggest a degree of caution is warranted for some normalization approaches, especially where precipitation driven IandI is heightened. However, data and findings largely supported the utility of using human fecal markers such as crAssphage for normalizing wastewater signal to address site-specific differences in dilution levels, since viral signal scaled to this metric did not result in strong correlations between precipitation and wastewater trends, higher spatial and temporal variation was not observed, and strong correlations were observed between viral signal and viral infection trends. Finally, in chapter 5, we assessed the relationship between monthly Norovirus GII, Rotavirus, and SARS-CoV-2 wastewater trends with seasonal infection trends for each of the viruses to ascertain whether WBE could be used in a rural sewershed of this size with substantial IandI impacts to track and potentially predict population level infection trends. Though up-sewer, or near-source sampling, at sites with permanent IandI impacts did not exhibit a clear relationship with seasonal infection trends for Rotavirus, SARS-CoV-2, and Norovirus GII, WWTP influent signal and consensus signals aggregated from multiple up-sewer sites largely mirrored expected seasonal trends. Findings also suggested that for more ubiquitous viral targets, such as SARS-CoV-2, viral trends measured at WWTP influent in a small IandI impacted system may still provide a sufficiently useful measure of infection trends to inform the use of WBE (assuming appropriate normalization to sewershed population). These findings elucidate the potential utility and relative robustness of wastewater testing to ascertain community-level circulation of pathogens in small, rural sewersheds even those compromised by extensive IandI inputs. Overall, this dissertation examined drinking water and wastewater as critical metrics for assessing contaminant exposures and infectious disease trends in rural communities, particularly in the context of small, rural communities which tend to have more limited health infrastructure and lower-resource wastewater systems. Overall, findings underscore the need for baseline data on drinking water quality by identifying gaps in current knowledge and calling for further research to better understand drinking water contaminant exposure levels in rural areas. Wastewater as a non-invasive, population-level health metric was evaluated in the context of a small, rural sewer system overall, and by varying observed levels of IandI, as well as associated tradeoffs for normalization adoption. By evaluating these environmental surveillance metrics using both desk-based and field-based research study designs, findings from this dissertation offer valuable insights and practical recommendations for improving baseline drinking water quality monitoring and wastewater pathogen testing, all with the overarching goal of supporting more targeted public health interventions in rural settings.
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    Understanding Mechanisms of Water Lead Contamination by Nitrate Spallation Corrosion and Lead Removal by Point-of-Use (POU) Filters
    Villalona, Chantaly (Virginia Tech, 2024-06-25)
    Lead enters drinking water by a process of corrosion, dissolution or particle detachment from lead bearing plumbing materials. Preventing contamination of water from lead-tin solder corrosion and achieving effective removal of particulate lead by point-of-use (POU) filters are important public health goals. These topics are especially timely given forthcoming revisions to the Lead and Copper Rule and ongoing efforts to reduce lead levels at the tap. Recently a switch from non-corrosive groundwater to a surface water source at a utility in Illinois caused unusual drinking water contamination from the release of large lead solder chunks from plumbing to water. Point-of-use (POU) filters distributed to remove the lead at this utility and elsewhere were not always completely effective. Here, we elucidate the mechanism of lead solder release in two chapters, followed by two more chapters examining lead removal by POU filters. The lead solder contamination arose after the water utility switched sources from high sulfate and low nitrate groundwater to a surface water with lower sulfate and high nitrate during runoff events. Such problems were unexpected because the surface water with high nitrate was not considered corrosive according to current theory. A chapter entitled A Novel Mechanism of Lead-Tin Solder Spallation in the Presence of Nitrate describes how 1) nitrate is extremely corrosive to lead:tin solder galvanically connected to copper, 2) nitrate corrosion can sometimes cause detachment of solder chunks to water, and 3) nitrate corroded the metal by reduction to ammonia and other reaction products. Another Chapter reports a follow up study, that reproduced the essence of nitrate induced spallation corrosion as observed in homes, using copper pipe with beads of lead-tin solder attached. During a 4-month experiment, the non-corrosive groundwater with high sulfate caused no solder beads to detach and only about 1% of the total lead was released to water. But in the surface water with high nitrate believed to cause the lead problem, 100% of the solder beads detached after just two months, and 80% of the total lead in the solder was released to water after 4 months. In the same surface water that had lower nitrate, with or without zinc orthophosphate or polyphosphate inhibitors, only 8 to 17% of the solder beads detached. Electrochemical studies also found that equimolar concentrations of chloride did not cause the disintegration of tin solder or as much weight loss as nitrate. Moreover, sulfate concentrations as low as 0.75 mM could effectively inhibit tin corrosion caused by 10 mg/L NO3-N. Studies focused on efficacy of POU filters have indicated that soluble lead in water is reliably removed, but sometimes particulate lead can escape capture and contaminate the treated water. To better understand this issue and practical limitations of filter use, field studies were performed in occupied and unoccupied homes in Enterprise, LA and New Orleans under both normal and extreme conditions of water lead contamination. For severe lead contamination present after lead pipes were disturbed or when a very long lead service line was present, and filters were tested to 200% of their rated capacity, the treated water occasionally had more than 15 ppb lead even when a very high percentage of the lead was removed. In Enterprise and New Orleans water with more typical levels of influent lead, the treated water was always below 1 ppb lead. But in Enterprise water with high iron and manganese the filters clogged quickly, causing higher costs for filtered water and consumer dissatisfaction. The occasional problems in removing particulate lead observed in this and prior research gave impetus to a series of bench-scale experiments elucidating particulate lead removal mechanisms by conventional ion-exchange media in sodium (Na+), strong acid (H+), chloride (Cl-) or strong base (OH-) form. Suspensions of lead phosphate particles of varying sizes and age revealed marked differences in dissolution rates under acidic, circa neutral and basic pHs that are caused by treatment with H+, Na +, OH -, Cl- form resin. Fresh nanoparticle lead phosphate particles were very labile, and immediately dissolved at pH 4 to form soluble Pb+2 ions which were quickly removed by strong acid media. High pHs > 10 and phosphate removal by OH– form resin could also dissolve the particles, and then remove the anionic soluble lead formed at high pHs. Na+ and Cl- resin caused little or no dissolution at the circa neutral pHs associated with their use and had lower rates of lead removal from water as a result. Older lead phosphate particles acquired from a New York City harvested lead pipe loop rig or purposefully synthesized in the laboratory, did not dissolve as readily as fresh nanoparticles which profoundly affected their relative removal efficiency by the different media. Overall, dissolution of lead phosphate particles in the ion-exchange media can sometimes have a range of important effects that can enhance or hinder lead removal dependent on circumstance. This thesis enhances our understanding of water lead contamination mechanisms by spallation of lead-tin solder and factors affecting lead removal by some POU filters. These novel insights can be helpful in preventing and mitigating future water lead contamination events.