5. What are the potential environmental effects of nanomaterials?
- 5.1 What happens to nanomaterials in the environment?
- 5.2 How could nanomaterials in the environment interact with living things?
- 5.3 Environmental effects
5.1 What happens to nanomaterials in the environment?
Increased production and use of nanomaterials will lead to an increase in environmental exposure. Estimation of relevant exposures is hampered by lack of knowledge about rates of release or concentrations of nanomaterials in the environment. There is also a lack of any theory to estimate environmental concentrations from release rates. Existing theory on behaviour of chemicals and particulates in the environment is not necessarily applicable to nanomaterials. Current thinking on what happens to nanomaterials in the environment is based on general considerations rather than much in the way of direct measurement and assessment.
The behaviour of nanomaterials in the environment depends as much on where they are released as on the materials themselves. Important conditions include acidity (pH), presence or absence of charged ions, and levels of organic matter in the environment (water). As with other small particles, nanomaterials might:
- Latch on to other chemical molecules or ions
- Be transformed into other chemicals by action of organisms, or undergo mineralization or partial or complete degradation.
- Clump together, and unclump, depending on conditions
- Settle out into sediment
So far, there is little reliable information on spread of nanomaterials in the environment. Estimates of quantities of nanomaterials in surface waters, for instance, are based on predicted nanomaterial use rather than actual measurements.
Future measurements will need to take account of the possibility of “hot spots”. These are places where particles are concentrated, perhaps by agglomeration, or interaction with organic matter. Wastewater treatment plants will be likely sites for accumulation of some nanomaterials in sewage.
There is also the possibility of bioaccumulation, in which nanomaterials are concentrated in particular organs of a species which is exposed. As aggregated nanomaterials are likely to end up in sediments, bioaccumulation studies on organisms which dwell in sediments are especially important.
5.2 How could nanomaterials in the environment interact with living things?
Organisms may take up nanomaterials by breathing, eating or - in the case of plants - through their roots. Some may also transfer into organisms across epithelial surfaces such as the skin, or lining of the lungs, gills or intestines. Plants and fungi have cell walls which tend to exclude nanomaterials. Microorganisms may take up nanomaterials by simple diffusion, transport across cells membranes, or after membrane damage. Uptake in any particular case will depend on whether the material remains dispersed, is concentrated in some medium which affects a particular creature, or dissolves, either before ingestion or afterwards.
Some nanomaterials could also be concentrated by the eaters being eaten, so they pass up in a food chain. There is evidence that the semiconductor nanoparticles known as quantum dots can be transferred between aquatic microorganisms in this way in simplified model ecosystems, though there was no significant concentration as a result in this case.
5.3 Environmental effects
A number of nanomaterials tested have been found to have antibacterial or viricidal effects. This may be why they are used, as in the case of nano-silver, bus also raises the possibility of environmental effects.
Experiments on other water and land-dwelling organisms have shown a wide range of effects of different nanoparticles, but no strong evidence of implications for survival of organisms so far.
A large number of new scientific studies appeared in 2007-2008. The main focus is on micro- organisms and invertebrates, followed closely by studies on fish. Still lacking are studies on soil systems and terrestrial species in general, and on marine species. However, results to date do indicate the potential for hazardous effects, at lethal and sub lethal levels, including behaviour, reproduction, growth and development, production of reactive oxygen species, inflammatory responses and cytotoxic effects. In addition, a small number of studies have indicated the potential for transfer to embryos, accumulation and potential food chain transfer.
The exposure levels organisms may endure in their natural environments are less clear and it is not known how results in the laboratory can be extrapolated to assess hazard in the field.