Source: Health and Environmental Alliance (Brussels, Belgium)
The toxicity of nanomaterials is often linked to their extremely small size. Smaller particles have a greater reactive surface area than larger particles, are more chemically reactive and produce greater numbers of reactive oxygen species that include free radicals.
Reactive oxygen species production has been found in a diverse range of nanomaterials including carbon fullerenes, carbon nanotubes and metal oxides. This is one of the primary mechanisms of nanoparticle toxicity; it may result in oxidative stress, inflammation, and consequent damage to proteins, membranes and
DNA.
The extremely small size of nanomaterials also means that they are much more readily taken up by the human body than larger sized particles. Nanomaterials are able to cross biological membranes and access cells, tissues and organs that larger sized particles normally cannot.
Nanomaterials can gain access to the blood stream following inhalation or ingestion. At least some nanomaterials can penetrate the skin, especially if skin is flexed.Broken skin is an ineffective particle barrier, suggesting that acne, eczema, shaving wounds or severe sunburn may enable skin uptake of nanomaterials more readily.
Once in the blood stream, nanomaterials can be transported around the body and are taken up by organs and tissues including the brain, heart, liver, kidneys, spleen, bone marrow and nervous system. Nanomaterials have proved toxic to human tissue and cell cultures, resulting in increased oxidative stress, inflammatory cytokine production and cell death. Unlike larger particles, nanomaterials may be taken up by cell mitochondria and the cell nucleus. Studies demonstrate the potential for nanomaterials to cause DNA mutation and induce major structural damage to mitochondria, even resulting in cell death.
Size is clearly a key factor in determining the potential toxicity of a particle. However it is not the only important factor. Other properties of nanomaterials that influence toxicity include: chemical composition, shape, surface structure, surface charge, aggregation and solubility, and the presence of “functional groups” of other chemicals. The large number of variables influencing toxicity means that it is difficult to generalize about health risks associated with exposure to nanomaterials – each new nanomaterial must be assessed individually and all material properties must be taken into account in safety assessment.
Preliminary scientific studies indicate that nanomaterials now used in consumer products could present serious risks to human health and the environment. The Scientific Committee on Emerging & Newly Identified Health Risks (SCENIHR) issued a preliminary opinion on “The appropriateness of the risk assessment methodology in accordance with the Technical Guidance Documents for new and existing substances for assessing the risks of nanomaterials (March 2007).
In general, the report concluded that it is “unclear” whether existing EU risk assessment methods could capture the potential environmental impacts of
nanomaterials, though it was “generally likely” to identify risks to human health.
The following conclusions (Page 51, 4.3.1.
Conclusions of human health chapter) are specifically relevant to human health, and also single out certain vulnerable groups: “… there is evidence that nanoparticles may cross the blood – brain barrier under some circumstances, that they may be associated with long term inflammation in several different types of tissue and organ and may be associated with cardiovascular effects.