How nanomaterials change in the environment
Research shows that nanomaterials undergo immediate and complex transformations once released into the environment. These can be biological, physical, or chemical transformations that are influenced by the specific characteristics of the materials and by environmental conditions.
Nanomaterials can get into the environment at any stage of their lifecycle, during the production of the raw material, when using a product containing nanomaterials or when that product is recycled or turned into waste. It can happen directly, for example when swimming while using sunscreen containing a nanomaterial or indirectly through technical systems such as a wastewater treatment plant.
To understand how different nanomaterials behave under different environmental conditions it is important to consider their chemical, physical and biological transformations.
Transformation processes are complex and happen simultaneously
How nanoparticles change in the environment depends on their unique composition defined by its size, core composition and surface treatment, called coating or capping. These parameters strongly determine their stability, dissolution or agglomeration leading to transformed materials with different behaviour.
This is further complicated by the influence of environmental conditions like temperature, presence of different salts, or other organic and inorganic particles on the transformation of nanoparticles.
And finally, the interaction with organisms has an impact on the specific transformation reactions. This interaction works in both ways – particles and organisms influencing each other e.g. detoxification reactions changing key features of the particles.
These physical, chemical and biological transformation processes happen immediately and very often simultaneously after release and influence transport, mobility, uptake potential into organisms and interaction with organisms. The interplay between these processes and the nanoparticles transport determines the fate and ultimately the ecotoxicological potential of nanoparticles.
What about biodegradation of organic nanomaterials and surface coatings?
Biodegradation is a natural process in the environment where microorganisms break down any organic material to recycle biologically essential elements.
This principle of biodegradation applies also to organic chemicals. The faster the biodegradation rate of a chemical is the better, because then the compound disappears faster from the environment and can cause less harm. It is therefore a requirement to investigate potential persistency in chemical hazard assessment with long-established standard tests (e.g. OECD test guidelines) to determine the biodegradability of a chemical.
As for any ‘conventional’ chemical it is therefore a central question if and how organic nanomaterials or coatings biodegrade when released into the environment. In light of the unique properties nanomaterials possess, researchers are looking into the suitability of established standard tests to analyse their potential to biodegrade.
While first indications show that existing test methods work in principle, more effort needs to be put in technological improvements that acknowledge nano-specific requirements rather than changing existing tests or developing new methods.