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According to the European Commission, a ‘nanomaterial’ is defined as any particle that exhibits one or more external dimensions in the size range 1 nanometer (nm) to 100 nm. As a result of their spatial constraint in the electronic properties, nanoparticles exhibit a high specific surface area and a potential difference in their behavior as compared to their bulk counterparts when present at this extremely small scale1.
Nano-sized particles, whether they originate from natural or manufactured materials, must therefore be investigated for their potential impact on human health and the environment. A vast amount of research has been devoted to investigating naturally occurring the structural and chemical varieties of naturally occurring nanomaterials.
Environmental Nanoparticles and Colloids
As compared to nanoparticles, colloids are similar molecules or particles that will instead exhibit a dimension that is within the range of 1 nm to 1 micrometer (µm). When present in nature, environmental colloids and nanoparticles can exist in a variety of different compositions and conformations.
As a result of biological decaying and chemical weathering processes, numerous environmental colloids can arise. These nanoparticles are principally oxides and oxyhydroxides of iron (Fe), manganese (Mn), aluminum (Al) and aluminosilicates1.
Humic Substances
Humic substances (HS), which are chemically extracted fractions of total natural organic carbon, are the most studied environmental colloid, as their trace metal binding ability1. As a dispersed material, HS can also aggregate through charge and static stabilization to form larger structures that can increase in sizes greater than that nano-range.
Volcanic Ashes
Erosion and volcanic eruption are commonly referenced origins of natural nanoparticles. The ashes that are released during volcanic eruptions can reach temperatures that exceed 1,400° C2. As these ashes reach the atmosphere and neighboring water supplies, their chemical interaction with the environment can result in the deposition of a wide range of nanoparticles that can have negative health effects.
These particles typically range in size from 100 to 200 nm in diameter and will be readily suspended in the air. As a result of this suspension within the atmosphere, the inhalation of nanoparticles that originate from volcanic ashes can lead to serious respiratory disorders following the deposition of these particles in the upper, tracheobronchial and alveolar regions of the respiratory tract.
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Desert Sources of Nanoparticles
Dust storms appear to be the most important source of nanoparticles in the atmosphere, as it has been estimated that approximately 50% of aerosols in the troposphere are minerals that originate from deserts. The chemical composition of nanoparticles that originate from deserts has been determined to exhibit high silicon (Si) concentrations, as well as some traces of Al, calcium (Ca) and Fe.
In fact, a recent study conducted in Xian, China determined that dust transport from the Gobi desert contained high a carbon and nitrogen concentration, as well as sulfate, nitrate and ammonium ions present within the wind-carried sample.
Biological Nanoparticles
A number of biological processes are associated with the production of nanoparticles. For example, bacteria such as Shewanella and Lactobacillus species are responsible for the fermentation of milk proteins but are also capable of reducing selenite to elemental selenium nanoparticles2. These biological origins of nanoparticles are important for future endeavors involved in the removal of environmental contaminants, such as heavy metals, organic and inorganic pollutants, as natural nanoparticles derived from plants, fungi, and bacteria are environmentally friendly and economical alternatives to traditional chemical methods.
Researchers have also been investigating the potential of harmless microorganisms, such as Saccharomyces cerevisiae and Staphylococcus carnosus to generate homogenous selenium nanoparticles for application in food supplements and even antimicrobial agents2. This area of nanotechnology research is particularly promising in the agriculture industry, as a method of enriching the soil with selenium for fortified food products while simultaneously providing plants with a natural defense system is a promising future against harmful pathogens that exhibit destructive tendencies against crops.
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References
- Hartland, A., Lead, J. R., Slaveykova, V. I., O’Carroll, D., & Valsami-Jones, E. (2013). The Environmental Significance of Natural Nanoparticles. Nature Education Knowledge 4(8): 7.
- Griffin, S., Masood, M. I., Nasim, M. J., Sarfraz, M., Ebokaiwe, A. P., Schafer, K., Keck, C. M., & Jacob, C. (2017). Natural Nanoparticles: A Particular Matter Inspired by Nature. Antioxidants. DOI: 10.390/antiox7010003.
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