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The use of engineered nanoparticles has significantly increased over recent years. Several industries have benefited from the use of nanoparticles, whose small size gives them unique properties in a wide range of applications.
More is being discovered about nanoparticles each year and they continued to be leveraged in new technologies. However, this increased use of nanoparticles is not without its drawbacks. They are becoming increasingly prevalent in the environment and pose health risks to people and animals. Nanoparticles enter the food chain, exist in the air, and infiltrate water supplies. Wastewater treatment plants (WWTPs) have been identified as a major source of nanoparticles entering aquatic systems.
While the use of nanoparticles continues to rise, and, therefore, as does their presence in the environment, the levels at which they exist in the environment and their impact on human health is poorly understood.
Here, we report the findings of recent research that has explored the concentrations and removal efficiencies of certain nanoparticles in the WWTPs of various US states, as well as the impact of engineered nanoparticle contamination on natural systems.
The Impact of Nanoparticles on Human Health and the Environment
Engineered nanoparticles are often not harmful within the applications that they are designed for. However, once they enter the environment and are inhaled or ingested, they can pose toxicity to the body, with some studies linking nanoparticle exposure to lung inflammation and heart problems.
The human-made materials measure between just 1 and 100 nm. Their small size makes them highly reactive, meaning that they pose significant risks to the structure and function of our ecosystems.
With the nanoparticle industry showing exponential growth, increasing 25-fold between 2005 and 2010, their potential threat to the environment and human health has inspired a growing number of studies.
Concentrations and Removal Efficiencies of Engineered Nanoparticles in US WWTPs
Titanium dioxide (TiO2) and silver (Ag) engineered nanoparticles are two of the most used nanoparticles. Scientists have developed their use in a variety of commercial products. Their use continues to rise, increasing the likelihood of contaminating the environment.
In 2014, TiO2 engineered nanoparticles were the most frequently manufactured and used type of nanoparticle in the world. TiO2 is common in food whitening agents, sunscreen, cosmetics, and toothpaste. It is also used in plastics as a pigment or filler. Ag, on the other hand, is most commonly used to create medical equipment due to its excellent antibacterial properties.
Scientists estimate that most of the TiO2 and Ag produced for these applications will find its way into municipal WWTPs. To gain a deeper understanding of the nature of TiO2 and Ag contamination of WWTPs in the US, researchers gathered data on the concentrations, removal efficiencies, and particle size distributions of these engineered nanoparticles in five WWTPs across three US states.
The research team, from institutions in South Carolina, California, and Massachusetts, highlighted that it was vital to identify particle size distribution (PSD) in addition to particle concentration due to the fact that toxicity tends to correlate with particle size, with smaller particles posing higher levels of toxicity.
To date, most studies investigating the occurrence and removal of engineered nanoparticles from WWTPs have focused on recording particle concentrations. There is a lack of data describing particle size. For this reason, the current study is significant in uncovering valuable PSD data.
The team’s results revealed that the treatment process was successful at removing between 90 and 96% of incoming TiO2 and between 82 and 95% of incoming Ag particles. However, this removal efficiency was not consistent across different WWTPs. Although most engineered particles were successfully removed, TiO2 particles remained in relatively high concentrations.
The results also showed that between 55 and 97% of TiO2 particles and more than 99% of Ag particles found in the treated effluent sewage measured less than 100 nm. The team concluded that the release of these small engineered nanoparticles into surface waters might result in their long-distance transportation and that aquatic organisms may face a significant risk to exposure to these small particles.
The Impact of Engineered Nanoparticles on the Environment
An international team of researchers from institutions in India, South Korea, and Nigeria conducted a review of the current literature regarding the impact of engineered nanoparticles on the environment. The researchers investigated what the currently available data concluded about the life cycle of engineered nanoparticles, and how these parties affect our eco-systems, particularly, how they impact bio-accessibility in food chains.
The team found that several environmental stressors, including the composition of solid media, solution chemistry, mineral composition, pore size, fluid velocity, and the presence of natural organic matter, influence the fate of engineered nanoparticles in the environment. These stressors have been shown to impact nanoparticle mobilty, as well as how they are transported and transformed.
The team found that transformed nanoparticles were capable of harming living organisms, with evidence showing their ability to reduce cell viability, growth, and morphology. They have also been shown to damage the DNA of living creatures.
Continued research into engineered nanoparticles in WWTPs and their impact on the environment is vital to securing the safety and health of our eco-systems and human health. As we continue to increase our use of engineered nanoparticles, research into their influence on the environment must continue to ensure we can protect it from adverse effects.
References and Further Reading
Bundschuh, M., Seitz, F., Rosenfeldt, R. and Schulz, R., 2016. Effects of nanoparticles in fresh waters: risks, mechanisms and interactions. Freshwater Biology, 61(12), pp.2185-2196. https://onlinelibrary.wiley.com/doi/pdf/10.1111/fwb.12701
Goswami, L., Kim, K., Deep, A., Das, P., Bhattacharya, S., Kumar, S. and Adelodun, A., 2017. Engineered nano particles: Nature, behavior, and effect on the environment. Journal of Environmental Management, 196, pp.297-315. https://www.sciencedirect.com/science/article/pii/S0301479717300191
Nabi, M., Wang, J., Meyer, M., Croteau, M., Ismail, N. and Baalousha, M., 2021. Concentrations and size distribution of TiO2 and Ag engineered particles in five wastewater treatment plants in the United States. Science of The Total Environment, 753, p.142017. https://www.sciencedirect.com/science/article/abs/pii/S0048969720355467
Westerhoff, P., Atkinson, A., Fortner, J., Wong, M., Zimmerman, J., Gardea-Torresdey, J., Ranville, J. and Herckes, P., 2018. Low risk posed by engineered and incidental nanoparticles in drinking water. Nature Nanotechnology, 13(8), pp.661-669. https://www.nature.com/articles/s41565-018-0217-9