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Approaches

Acute or Chronic? Direct or indirect effects?

Nanomaterials have the capacity to affect the biological and physical compartments (ground, surface and ground water, atmosphere, sediment) of the environment. Most of the studies have been performed in the aquatic environment, mainly in fresh water. Because of  the difficulty of characterizing nanomaterials in the ground or in the sediments, little data are available.

Several studies concern the acute toxicity (response to an occasional and massive aggression) rather than the chronic toxicity (response to a regular but minor aggression).

A direct effect is observed by cellular assimilation of nanoparticles: intrinsic toxicity. In the sludge's from  water treatment plant, the soils or the surface waters, nanoparticles are in interaction with others polluting's (oxides, silicates, phosphates). Due to this adsorption, indirect effects may be observed.

Nanoparticle polluting interaction

Some studies have shown that the presence of nanoparticles can be the source of modifications of the preexisting pollutant toxicity.

For example, the heavy metals such as nickel can absorb on carbon nanotubes. This adsorption facilitates the ingestion by living organisms and the toxicity increase of heavy metals [C. Wang et al., Environmental Toxicology and Chemistry 33 (2014) 2522-2528].

Despite some results, it is too early to draw general conclusions as regards the role and the mechanisms of action of nanoparticles. But, the studies agree on the fact that in a liquid environment, the presence of nanoparticles produce a more important accumulation of polluting's in the organisms. Due to nanoparticles or through their role of vector for contaminating, risks are present all along the food chain.

Internal Ni concentration (micrograms of Ni per gram dry weight) with different concentrations of hydroxylated multiwalled carbon nanotubes (OH-MWCNTs) at ph = 8 [C. Wang et al., Environmental Toxicology and Chemistry 33 (2014) 2522-2528].