Environmental Engineering Reference
In-Depth Information
Even in the absence of a complete understanding of this type of information,
governmental agencies are already considering nano-related regulations. For example,
the USEPA has already taken moves to regulate nano-silver as a pesticide (Weiss, 2006).
However, in the future, if comprehensive risk assessment methods and models are
available before NMs are mass produced, nanotechnology manufacturers may be able to
a priori design-out attributes of NMs that pose environmental or human risk. The
concepts needed to develop robust exposure assessments, based upon the identified gaps,
are discussed in this section and then specific examples are illustrated in Sections 16.5
and 16.6.
16.4.1 Detecting NMs in Environmental Samples
The ability to detect and quantify NMs in water limits NM occurrence studies
and exposure assessments during aquatic toxicity studies. “Instruments to monitor
waterborne engineered NMs” is identified as one of the grand challenges that should be
funded between 2008 and 2011 (Maynard et al., 2006). Currently, NM detection focuses
on quantifying mass concentrations in liquid (Nowack and Bucheli, 2007), although
crystallography, shape and surface area may be equally important.
Methods are being adapted from traditional analytical chemistry for detecting
organic and inorganic colloids that are ubiquitous in natural waters. These colloids
usually range from 1 nm to 1 μm in size, which does not allow them to settle with gravity
(De Momi and Lead, 2006). Analysis of water colloids should be based on effective
separation without perturbing their aggregation and disaggregation properties. Common
separation methods include filtration/ultrafiltration (Ledin et al., 1995; Doucet et al.,
2004; Liu and Lead, 2006), centrifugation/ultracentrifugation (Kim et al., 1995;
Chanudet and Filella, 2006), electrophoresis/capillary electrophoresis (Karlsson et al.,
1999; Rodriguez and Armstrong, 2004), or size exclusion chromatography (Ledin and
al., 1995; Doucet et al., 2004). Additional technologies such as field flow fractionation
(Colfen and Antonietti, 2000; Chantiwas et al., 2002; Moon et al., 2006a) and split flow
thin (SPLITT) fractionation (Contado et al., 1997; De Momi and Lead, 2006) have been
developed to fractionate colloidal particles in natural water without possible aggregation
problems associated with filtration and centrifugation (Martin et al., 2000). These
techniques will begin to provide means to quantify the mass of NMs present in different
size fractions (Vacchina et al., 1999; Liu et al., 2005), and maybe even differentiate
between colloidal and ionic forms (i.e., nanosilver in water dissolves into silver ion
(Benn and Westerhoff, 2008)). For example, capillary electrophoresis has been applied
to the separation of cadmium quantum dots (Song et al., 2006) or silver NMs (Liu et al.,
2005). Size exclusion chromatography has been applied to separate a variety of NMs
including CdSe nanocrystals (Wang et al., 2006) and nanocrystalline gold (Al-Somali et
al., 2004). The separation allowed for the distinction of various sizes of NMs, with a
resolution at nanometer level. Inductively coupled plasma mass spectroscopy (ICP-MS)
 
Search WWH ::




Custom Search