Biomedical Engineering Reference
In-Depth Information
differences, and the presence of organic or inorganic material). The characteristics and properties
of a nanomaterial also play a major role. Bioavailability is decisive in determining potential toxic-
ity. This depends strongly on whether nanoparticles remain stable in an environmental medium or
are removed from the respective medium through agglomeration and deposition, or are transformed
into a form that organisms cannot take up.
The current lack of data prevents a comprehensive and accurate picture of the fate and behavior
of nanomaterials in the environment. It is difficult to compare results because different nanomateri-
als with different properties are used, and because both the methodology and the duration of the
studies also often differ considerably. As interest in nanoscale materials matures, regulators are
challenged to find ways to gather hazard information while continuing to assure the public that
nano-enabled products do not pose risks that the government is tasked with addressing.
The issues to address are numerous. There is the effect on the air. As nanoparticles enter the
atmosphere, they move from zones of higher concentration to zones of lower concentration (dif-
fusion). Air currents distribute the particles rapidly; these can migrate great distances from their
original source. Nonetheless, nanoparticles tend to aggregate into larger structures (agglomeration).
Detecting nanoparticles in the air is very difficult because simple measurements of size distribu-
tions can hardly distinguish such agglomerates from natural particulates. The speed with which
particles in the air are deposited on the ground, in the water, or onto plants (deposition) depends on
particle diameter. Nanoparticles from the air are deposited much slower than larger particles due to
their smaller diameters. In water, nanoparticles are relatively unstable because they rapidly adhere
to one another due to electrostatic attractive forces and then sink as a result of gravity. Natural water
bodies typically contain dissolved or distributed materials, including natural nanomaterials. As
expected, synthetic nanomaterials that enter a natural water body bind themselves to such natural
materials. The fate and behavior of nanomaterials in the water, however, are also influenced by fac-
tors such as pH, salinity (ionic strength), and the presence of organic material, which can lead to the
decomposition of substances or of their aggregates and thus alter particle size and shape.
With regard to soil and sediment, the data are insufficient to draw any general conclusions.
Considerably fewer studies are available for this sector than for water or air.
There are also potential environmental processes that can influence the behavior and the proper-
ties of nanomaterials. These include the aforementioned dissolution, precipitation and sedimenta-
tion, transformation, and agglomeration. As for toxicity, nanoparticles have been naturally present in
the environment since the origin of earth in the form of combustion processes such as forest fires, in
volcanic ash, in most natural waters, or as dust in the air due to weathering and erosion. Organisms
produce various substances in nanoform in their cells (e.g., proteins, DNA) or are themselves only
several nanometers large, such as viruses. During their evolution, all living organisms have adapted
to an environment that contains nanoparticles, some of which can also be toxic (e.g., volcanic ash).
This adaptation is a function of exposure, dose, and the speed with which habitats change. These
natural nanoparticles in the environment are now accompanied by those that have been released
unintentionally due to human activities such as household heating, industry, slash-and-burn clear-
ance, transport and, most recently, through the industrial application of various extremely poly-
morphic synthetic nanoparticles in unknown amounts. This additional burden on humans and the
environment has taken place over a very short period, at least from an evolutionary standpoint.
To date, no ecotoxicological studies are available that could explain in detail the mechanisms
of uptake, distribution, metabolization, and excretion of nanoparticles. The few studies on the
effects of ENPs on ecological communities failed to detect significant increases in mortality rates
or changes in their compositions. Whether ENPs pose a risk to the environment depends not only
on the toxicity of the respective material but also on exposure, that is, on the amount released
into the environment. Unfortunately, little quantitative data are available and few studies have
addressed the environmental exposure to nanomaterials. These are based on rough estimates of
production volumes and releases, as well as on model calculations, which do not allow compre-
hensive risk assessments. Knowledge about production volumes alone is insufficient to estimate
