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Nanotoxicology

Nanotoxicology is a branch of science that investigates the effects of nanoparticles (particles less than 100 nm in size) on human health. The increase in production of nanomaterials for various manufacturing, biomedical, and consumer products has attracted the attention of the scientific community worldwide to study the potential benefits of nanomaterials on our daily lives. It is estimated that the production of nanoparticles will increase from an estimated 2,300 tons produced in 2009 to 58,000 tons by 2020.

Compared to larger size particles, the extremely small size of nanoparticles affords them easy entry into the human body. Furthermore, the small volume-to-surface area ratio of these particles imparts them with the potential to induce toxic health effects. Currently, with the increase in use of nanomaterials in commercial products ranging from cosmetics to tennis balls, it is extremely important that toxicologic evaluation of these nanomaterials receive greater attention than ever before. In addition to consumer products, emerging biomedical applications of nanoparticles as drug-delivery agents or biosensors involve direct ingestion or injection of nanoparticles into the body, indicating the importance of evaluating the toxicity of these nanoparticles along with their potential benefits for usage in drug delivery.

Nanomaterials and Toxicity

The main characteristic of nanomaterials is their size, depending on which, modification of the physiochemical properties of the material takes place. This creates an opportunity for increased uptake and interaction with biological tissues, and generates an adverse effect in biological organisms that would not otherwise be possible with the same material in larger forms. Experimental evidence has indicated that their small size, large surface areas, and the ability to generate reactive oxygen species (ROS) play a role in the ability of these nanoparticles to induce damage. ROS production has been observed in a variety of nanomaterials, ranging from carbon fullerenes, carbon nanotubes, and nanoparticle metal oxides. Further, it has been found that as the particle size decreases, there is a tendency for toxicity to increase, even if the same material is relatively inert in bulkier form (e.g., carbon black, titanium dioxide). ROS and free radical production is one of the main mechanisms of nanoparticle toxicity and results in oxidative stress, inflammation, and damage of cell membranes and DNA.

Due to the small size of these particles, they readily gain access to the cell by crossing the cell membranes. Inhalation and ingestion are the main routes of entry of these particles into the body. In addition, these particles also have the ability to penetrate the skin, especially broken skin, indicating that skin conditions like acne, eczema, wounds, and sunburn could accelerate the uptake of these nanoparticles. Once in the blood stream, they are transported to various parts of the body and taken up by tissues like the brain, heart, liver, kidneys, and bone marrow. In addition to size, other properties of nanoparticles that influence toxicity include their chemical composition, shape, surface structure and charge, solubility, aggregation, and the presence of functional groups.

Air Pollution and Nanoparticle Toxicity

With the increase in air pollution, the potential effects of human exposure to airborne nanosized particles (also known as ultrafine particles (UFPs) by toxicologists) have increased dramatically. Several epidemiological studies have found that exposure to UFPs have resulted in adverse respiratory and cardiovascular effects. A strong association between UFPs as a predictor of mortality and morbidity of adults was documented in six polluted and less polluted cities of United States. Further, these particles have also been associated with increased cardiovascular mortality. An increase in blood pressure and heart rate was reported to be associated with increased exposure to UFPs.

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