Nanotoxicology, a branch of bionanoscience (a field of research that has emerged at the interface of nanoscience and biology), deals with the study and applications of toxicity of nanomaterials (that takes a materials science-based approach to nanotechnology). Nanomaterials are basically made of inert elements such as gold; it has unique properties and larger surface area. Nanomaterials have quantum size effect compared with other corresponding particulars. At nanometer (a unit of length in the metric system, equal to one billionth of a metre) dimensions nanomaterials become greatly active. Nanotoxicological studies are projected to regulate these properties which are posing threats to the environment and to human beings at greater level.

Recent studies have shown that Diesel nanoparticles damage the cardiovascular system of mouse. Further studies have shown that nanoparticles, as they have extremely small size, can easily move into lung tissues after inhalation which cause greater pro-inflammatory damage and can lead to long-lasting breathing problems. For example, air pollution can have pro-inflammatory effects.

Nanotoxicology addresses the toxicity of nanoparticles ((or nanopowder or nanocluster or nanocrystal) is a microscopic particle with at least one dimension less than 100 nm) which are unseen when seen with the larger particles.

Nanoparticles are divided into two categories;

• Combustion-derived nanoparticles, following inhalation exposure, like diesel soot, carbon black (typical nanoparticle), welding fume and coal fly ash.
• Manufactured nanoparticles, may introduce health threat, like bucky balls, carbon nanotubes (typical nanoparticle) and naturally arising nanoparticles from atmospheric chemistry, volcanic eruption etc.

Some nanoparticles have the ability to transfer from their site of removal to upstage sites like brain and blood. This ability of nanoparticles has shown that how particle's toxicology is observed in other parts of the body instead of being observing lung tissues. Toxicologists have started studying the blood, brain, skin, liver and gut and trying to better understand the effect of nanoparticles in human body that are possible dangerous.

There are some particles that are smaller in size and have greater surface area to volume ratio, chemical reactivity and biological activity.If we increase the chemical reactivity of nanomaterials which may result in increased production of reactive oxygen species (ROS) (chemically-reactive molecules containing oxygen. Examples include oxygen ions and peroxides). These reactive oxygen species has been found in an assorted range of nanomaterials which includes carbon nanotubes, carbon fullerenes (any molecule composed entirely of carbon, in the form of a hollow sphere, ellipsoid, or tube) and nanoparticle metal oxides.

Production of reactive oxygen species may result in oxidative stress (represents an imbalance between the production and manifestation of ROS and a biological system's ability to readily detoxify the reactive intermediates or to repair the resulting damage), inflammation, and damage to membranes, proteins, and DNA.

There are complications with nanotoxicity studies and most important key factor is the size that determines the prospective toxicity of a particle. This is not the only important key factor which influences the toxicity of particles. There are some other properties of nanomaterials that affect the toxicity; these factors include shape, surface charge, aggregation, surface structure, chemical composition and solubility. Because of larger number of variables it is very difficult to simplify about health risks that are allied with exposure to nanomaterial. For this each nanomaterial must be calculated individually and all their properties must be concerned.

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