Environmental Engineering Reference
In-Depth Information
Consumer product
manufacturing/use
Raw
material
Recycling
Human population and
ecological exposure
Product end of life
/waste
figurE 30.3
Life cycle of a consumer product containing nanomaterials.
For example, nano TiO
2
and nano ZnO have been reported as toxic to soil bacterial communities that may alter environmentally
important soil processes [5]. However, other reports found that toxicity may arise not directly from the nanosized particles act-
ing on bacteria but rather from metal ions known to be toxic for the bacteria and also from the chemical and biological dissolu-
tion of metal oxides and sulphates in the environment [6]. So one needs to establish the mechanisms underlying the real source
of toxicity before jumping to a conclusion. It is therefore highly recommended that the toxicological effect of NMs be clarified
before their commercial or practical applications or, on the other hand, to halt or modify their toxicity.
The concern on how some engineered or natural NMs may become hazardous pollutants posing a serious threat to public
and environmental health is alive and growing, as careful studies to understand and model their complex interrelations with
life systems are moving slower than the rate at which they are being introduced into new consumer products. Toxicological
studies related to NMs started two decades ago, but most of the published papers and reports are still limited to
in vitro
studies or
in vivo
analyses of laboratory animal models mainly concerning human health impact. Although the first reports
on environmental impacts of NMs are more recent [7-9], the terms “ecotoxicity” and “econanotoxicity” were not yet
used (Fig. 30.3).
According with Kahru and duborguier, nanostructured TiO
2
, ZnO, CuO, Ag, single-walled carbon nanotubes (SWCNTs),
mutiwalled carbon nanotubes (MWCNTs), and fullerenes, C
60
, are among the NMs more likely to have environmental and
health impact, due to their high volumes of production or extended use in consumer products [1]. For example, the large-scale
manufacturing of SWCNTs was estimated to reach 1500 tons per year in 2011, while the total production of nanostructured
metal oxide for cosmetic use was 1000 tons per year from 2005 to 2010 [10, 11]. The list may be extended to some other com-
mercially important materials such as nano Au, nano zero-valent iron (Fe), quantum dots (CdS, CdSe, CdTe, ZnSe), nano iron
oxides (Fe
2
O
3
, Fe
3
O
4
), nano CeO
2
, nano SiO
2
, graphene, as well as a long list of nanocomposites. All the later materials are
