Biomedical Engineering Reference
In-Depth Information
however, it remains to be identified how this toxic potential can be influenced
by biotic and abiotic environmental factors. Knowledge gaps for aquatic toxi-
cology have been described [12]. There is no general consensus on the “dose-
metric” or the measure of exposure, or of bioaccumulation in wild fish. Most
of the available toxicity data were obtained under controlled laboratory set-
tings using standard test species such as freshwater fish or invertebrates.
Whether these results can be extrapolated to ecological receptors under field
conditions is not known. It is essential to validate these effects using marine
and estuarine fish, and also on sediment-dwelling fish species and inver-
tebrates [147]. A similar type of interpretation can be applied for terrestrial
toxicology, where only a limited number of laboratory species are in use.
Further, some studies have involved terrestrial receptors (microbes, plant
seeds) without using soil as the exposure medium.
Standard and research-based techniques need to be developed to mea-
sure NMs in environmental samples, including animal and vegetal tissues.
While a few approaches have been proposed, it is still difficult to distinguish
between the manufactured NMs and natural NMs. Other knowledge gaps
include the effects of abiotic factors (salinity, hardness, dissolved organic
matter, pH) on the bioavailability of NMs to ecological receptors. It is antici-
pated that advances in the chemistry of the individual NM will make it pos-
sible for a better prediction of NM bioavailability. Some data are available
concerning the uptake of NMs by fish; however, information on the distribu-
tion, metabolism, and excretion of these particles is still lacking [12].
Fate and transport, as well as bioavailability of NMs in the environment and
in biota are not presently well known, and a better knowledge concerning these
aspects will increase the scientific value of future ecological risk assessments
for NMs [12,147]. Likewise, there are numerous information gaps related to
algae, plants, and fungi as environmental receptors, including the development
of mechanistic models to explain NM passage through their cell membranes
and walls, and trophic transfer of NM in their food chain [10], as well as a better
understanding of specific properties of NM related to their toxicity.
Clearly, the field of nanoecotoxicology is a young and evolving discipline.
Presently, toxicological observations are NM specific based on the available
data, and it is very difficult to make broad conclusions with great certainty.
Nevertheless, it seems that the putative effects of NPs on soil bacterial com-
munities may not be really an issue, as it seems that soil bacteria might be
protected from the toxic effect of NMs through the strong binding capac-
ity of the soil (or sediments), plus the fact that the bacterial cell wall limits
passage on NMs inside the cells [14,153]. Higher organisms might be more
susceptible than bacteria to the toxic effects of NMs, as observed in aquatic
assays using invertebrates or algal cells. Terrestrial receptors, plants, and
soil invertebrates appear relatively insensitive in most assays done for NM,
although only a very limited number of compounds have been examined.
In addition, the type of assay and duration of exposure are also impor-
tant for conclusive evidence. For example, nano-TiO
2
showed negative results
