Nanotoxicology is a subfield of toxicology that deals with the assessment of the toxicological properties of nanoparticles with a diameter of less than 100 nm with the intention of determining whether they may pose an environmental threat. The gradually enhanced toxicity is due to their very high surface-to-volume (S/V) ratio making them highly reactive. The cell membrane, mitochondria, and cell nucleus are the most appropriate targets for nanoparticles to induce toxicity.
Carcinogenicity, genotoxicity, and teratogenicity may occur as a result of the effects of nanoparticles. When nanoparticles are discarded, they can enter the aquatic environment as aggregates and soluble ions driven by the size and surface properties as well as by the stability of natural colloids, which can be highly toxic to aquatic organisms. The formation of smaller aggregates due to the dissolution of nanoparticles at elevated temperatures can result in higher toxicity. Silver, carbon, and titanium nanomaterials are most widely used as additives in cosmetics and pharmaceuticals exhibiting different properties and hence have different toxicity potencies. Nanoparticles could induce toxicity by releasing reactive oxygen species (ROS) causing oxidative stress and inflammation which in turn may lead to cytotoxicity, DNA damage, and other effects. This may be referred to as ecotoxicity. Most of the nano-ecotoxicological experiments are done on Daphnia Magna.
Nanoparticles are known to have adverse genotoxic effects such as chromosomal fragmentation, alterations in gene expression profiles, oxidative DNA adducts, and point mutations. Surface coating and particle size are major factors responsible for genotoxicity. Potential human exposures of nanoparticles can be through inhalation, ingestion with food, or application to the skin. Over the past few decades, nanoengineered particle source, transport, and toxicity have been a major focus of environmental health and safety research.
During inhalation, the particles enter the deep zones of the lung where they can attach to the epithelium and cause chronic effects on cells. Carbon nanotubes have a broad range of applications in biomedicine, textiles, sports equipment, and polymer chemistry. Humans can get exposed to them through inhalation and dermal contact. Carbon nanotubes if consumed at high doses can cause lung toxicity. Airborne nanoparticles having hydrophobic surfaces are more prone to accumulation in the spleen and liver. If non-biodegradable nanoparticles are taken up by macrophages, they would release free radicals resulting in cell damage and inflammation. Coated or non-coated nanoparticles are more likely to affect the liver and endothelium. Nanoparticles can induce toxicity via inhalation and gastrointestinal absorption, distribution into the blood and lymph circulation, nasal nerves, and transcytosis across cells. Nanoparticles in food can cross into the gut lymphatics and redistribute to other organs more easily than other materials or larger particles.
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