Monitoring of engineered nanomaterials in environmental systems is one of the major challenges in environmental nanoscience because of difficulties in differentiating engineered versus natural nanomaterials (ENMs vs NNMs) due to the similarities in their physical and chemical properties. The overall project hypothesis is that despite their similarities, subtle differences in the properties of NNMs and ENMs can be used to differentiate ENMs from NNMs and to quantify their concentrations. To this end, we 1) developed new methods to isolate nanomaterials from environmental samples, 2) determined the properties —including sizes, shapes, elemental fingerprints, concentrations of natural tracers, and elemental ratios— of NNMs that were extracted from non-contaminated and ENMs used in commercial products, 3) used the subtle differences in the properties —size, shape, elemental composition— of natural and ENMs to estimate the total concentrations of ENMs above the NNM concentrations, 4) monitored the concentrations of ENMs in various environmental systems, 5) trained three graduate students on the use of state-of-the-art nano-analytical approaches, 6) integrated the research findings in undergraduate and graduate environmental science courses taught at the University of South Carolina, and 7) disseminated the project findings in 20 peer-reviewed journal articles and many conference presentations. Below we highlight the key specific project findings.

We determined the optimal conditions —highest recovery and aggregate disaggregation— for nanoparticle extraction from environmental matrices as the use of sodium pyrophosphate at pH 10. We identified the elements naturally presented in different types of NNMs. For instance, titanium bearing NNMs contain a range of metals, including Al, Fe, Ce, Si, La, Zr, Nb, Pb, Ba, Th, Ta, W and U. Given that Nb occurs predominantly in naturally occurring Ti-bearing minerals, we determined the elemental ratio of Ti/Nb as a function of particle size and at the single particle level and found that these ratios in NNMs extracted from soils in South Carolina are constant and are close to the average crustal elemental ratios. Thus, we used Ti/Nb in subsequent studies to determine anthropogenic concentrations of Ti in environmental samples using mass-balance calculations and shifts in Ti/Nb above the natural background level.  

We then focused on determining the concentrations of engineered particles (e.g., nanosized and pigment sized particles, 1 to 100 nm and 100 to 300 nm, respectively) in engineered and environmental systems including wastewater treatment plants, sewage spills, urban stormwater runoff, biosoils, urban and rural rivers. In all these systems, we validated the natural background Ti/Nb ratio and demonstrated increases in Ti/Nb with the introduction of engineered TiO₂ particles into these systems. We demonstrated the occurrence of high concentrations of TiO₂ engineered particles (in µg TiO₂ L^-1) in wastewater treatment plant influent (70-670), activated sludge (3570-6700), effluent (7-30), sewer overflows (5-100), and urban runoff (5-150). We also demonstrated that stormwater green infrastructures can potentially limit the spread of engineered particles in the environment.

We also monitored the concentrations of engineered particles in urban and rural rivers during and following rainfall events in South Carolina, including the Saluda, Broad, Congaree, and Edisto Rivers. The concentrations of TiO₂ engineered particles in the Broad River varied between 20 and 140 µg TiO₂ L^-1 following rainfall events. The source of TiO₂ was attributed to urban runoff. Linear relationships were established between turbidity and TiO₂ engineered particle concentrations in the Broad River for different flow regimes. Thus, urban runoff is a major source of TiO₂ engineered particles to urban rivers, which results in episodic high concentrations of TiO₂ engineered particles, which may pose environmental risks during and following rainfall events.

We then investigated the impact of urbanization on the concentrations of TiO₂ engineered particles in urban surface waters by selecting the Saluda-Broad River confluence forming the Congaree River as a study site. This sampling area is unique as the Saluda River sampling sites is located downstream of Lake Murray, a larger water reservoir, limiting the urban contribution to this site. In contrast, the Broad and Congaree sampling sites capture a significant footprint of the urban area of the City of Columbia. The concentration of 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 <58 to 5050 µg L^-1 in the Congaree River at Columbia.

We also monitored the concentrations of TiO₂ engineered particles in a rural river basin (Edisto River, < 1% urban land cover). Surface-water concentrations of TiO₂ engineered particles varied between 0 and 128.7 ± 3.9 µg TiO₂ L^-1. The source of TiO₂ in the Edisto River is attributed to diffuse wastewater sources, such as reuse application overspray, biosolids fertilization, leaking sewers, or septic tanks.

Overall the project highlights the importance of spatiotemporal monitoring of ENMs in environmental systems in order to determine their sources and understand their fate in environmental systems.

Last Modified: 08/16/2022
Modified by: Mohammed Baalousha