Date of Award
Open Access Dissertation
Environmental Health Sciences
Quantifying and characterizing engineered particles in environmental systems is key for assessing their risk but remains challenging and requires the distinction between natural and engineered particles. The Ph.D. dissertation research described in this thesis contributes to the current attempts to improve environmental nanoparticle analysis and better understand nanoparticle behavior in natural systems, with the focus being on natural streams, and the application of single particle inductively coupled plasma-time of flight-mass spectrometry (SP-ICP-TOF-MS) for distinguishing and tracing the origins of environmental nanoparticles. The objective of this dissertation is to characterize and quantify the concentrations of titanium dioxide engineered particles in urban surface water during and following rainfall events, establish a time and cost-efficient surrogate measure to monitor titanium dioxide engineered particles in urban surface water, evaluate the impact of urbanization on the concentrations of titanium dioxide engineered particles, and compare urban and rural river basins.
Four water sampling campaigns were performed to quantify engineered nanoparticle (ENP) concentrations in dynamic natural water systems (i.e., urban runoff impacted Broad, Congaree, and Saluda River and agricultural runoff-impacted Edisto River). The first three campaigns were performed at the discharge event scale in the urban Saluda, Broad, and Congaree Rivers. In contrast, the fourth sampling campaign was a long-term campaign performed between 2017 and 2019 in the Edisto River. The first sampling campaign was performed in 2018 following hurricane Florence to investigate the impact of rainfall on the concentrations of TiO2 engineered particles in the Broad River. The second sampling campaign was performed in 2019 during a range of hydrologic settings to investigate the impact of wet and dry weather on the concentrations of TiO2 engineered particles in the Broad River. The third sampling campaign was performed in 2020 to determine the impact of urbanization on the concentrations of TiO2 engineered particles in the Saluda, Broad, and Congaree Rivers. The fourth sampling campaign was performed by collecting water samples on a biweekly basis from the Edisto River to investigate the seasonal variability in TiO2 engineered particle concentrations.
For all field studies, water samples were analyzed for total metal concentrations following acid digestion. Bulk elemental ratios (e.g., Ti/Nb, Ce/La) were determined to determine whether water samples were contaminated with anthropogenic Ti and Ce. The concentrations of anthropogenic Ti and Ce were determined using mass balance calculations and shifts in elemental ratios above the natural background ratios. Selected samples were analyzed for particle number concentration and elemental composition using single particle-inductively coupled plasma-time of flight-mass spectrometer (SP-ICP-TOF-MS). Agglomerative hierarchical analysis was used to group particles into clusters of similar elemental compositions and to compare particles across samples.
In the urban Rivers (Saluda, Broad and Congaree), the elemental ratios of Ti/Nb increased with discharge and with urbanization. In contrast, the elemental ratio of Ti/Nb in the rural Edisto River varied seasonally with increases during spring and summer and decreases during the fall and winter. The elemental composition of multi-element titanium-bearing particles at the single particle level were determined by SP-ICP-MS and were similar throughout rain events in urban Rivers and seasons in the rural River, and consisted of clusters of FeTiMn, AlSiFe, and TiMnFe, which are typical of naturally occurring iron oxide, clay, and titanium oxide particles. The elemental ratio distributions of Ti/Nb, Ti/Fe, and Ti/Al, determined on a single particle basis using SP-ICP-TOF-MS, were similar between samples during the different rainfall events, indicating that naturally occurring particles had the same elemental ratios and origin. Therefore, the changes in Ti/Nb ratios in the bulk water samples were attributed to the introduction of titanium dioxide engineered particles into the rivers with urban/agricultural runoff during and following rainfall events.
Water samples were collected from the Broad River during seven discharge events in 2018 and 2019. Discharge, bulk elemental concentrations (e.g., Ti, Al, Fe, Nb and Ce), bulk elemental ratios (e.g., Ti/Al, Ti/Fe, and Ti/Nb), TiO2 engineered particle concentration, and turbidity displayed the same trend of rise and fall as the discharge/runoff following storm events. Linear relationships were established between turbidity and TiO2 engineered particle concentrations in the Broad River for different flow regimes. The established correlations between turbidity and TiO2 engineered particle concentrations are important as they can be used to translate the continuously monitored turbidity to TiO2 concentrations. The concentrations of titanium dioxide engineered particles in the Broad River varied between 20 and 140 µg TiO2 L -1 following the rainfall events in 2018. During a range of hydrologic settings in 2019, the concentrations of titanium dioxide engineered particles in the Broad River varied between 4 and 412 µg TiO2 L -1.
This study demonstrates that diffuse urban runoff results in high concentration of TiO2 particles in urban surface waters during and following rainfall events which may pose increased risks to aquatic organisms during these episodic events. The urbanization impacted concentration of anthropogenic TiO2 increased following the order 0 to 24 µg L-1 in the Lower Saluda River < 0 to 663 µg L-1 in the Broad River < 43 to 1051 µg L-1 in Congaree River at Cayce µg L-1 in the Congaree River at Columbia.
On the other hand, in a rural river basin (Edisto River, < 1% urban land cover) in South Carolina, United States, the total concentrations of Ti, Nb, Al, Fe, Ce, and La trended higher during spring/summer compared to autumn/winter, indicating agricultural prep and growing season related increases in TiO2 engineered particles. Surface water concentrations of TiO2 engineered particles varied between 0 to 129 µg L-1 in the rural Edisto River. Increases in TiO2 concentrations over the spring/summer were associated with increases in phosphorous, orthophosphate, nitrate, ammonia, anthropogenic gadolinium, water temperature, suspended sediments, organic carbon, and alkalinity, and with decreases in dissolved oxygen. The association between these contaminants together with the timing of the increases in their concentrations is consistent with diffuse wastewater source, such as reuse application overspray, biosolids fertilization, or leaking sewers or septic tanks, as the driver of instream concentrations; however, other diffuse sources cannot be ruled out.
This study provides clear evidence that significant concentrations of TiO2 engineered nanoparticles enter aquatic systems with urban/agricultural runoff, and that the concentration of TiO2 engineered nanoparticles entering surface waters via runoffs are expected to increase with the increased applications of TiO2 engineered particles in consumer products, which may pose higher risks to urban/rural stream aquatic ecosystems during the storm events. Hence, the demonstrated results of this dissertation illustrate the importance of monitoring temporal and/or seasonal variations in engineered particles concentrations in surface waters for a more representative assessment of ecosystem risk.
Nabi, M.(2022). Monitoring Titanium Dioxide Engineered Particles in Rural and Urban Surface Waters. (Doctoral dissertation). Retrieved from https://scholarcommons.sc.edu/etd/7087