Analysis and Characterization of Manufactured Nanoparticles in Aquatic Environments - Environmental and Human Health Impacts of Nanotechnology - page 208

6.1.1 Nanoparticles in the Aquatic Environment

Nanoparticles are ubiquitous in freshwater (Wigginton et al. , 2007a ), seawater
(Wells and Goldberg, 1991), groundwater (Banfi eld and Navrotsky, 2001), soils
(Citeau et al. , 2006), sediment (Waychunas et al. , 2005; van der Zee et al. , 2003 )
and ancient ice cores (Murr et al. , 2004). In aquatic environments three main
categories of NPs may coexist; natural NPs, incidental (adventitious) NPs and
manufactured NPs.
Sources of natural NPs can be both inorganic and organic (and are usually mix-
tures of both). Examples of inorganic natural NPs are iron oxyhydroxides (Davison
and De Vitre, 1992; Perret et al. , 2000 ; Waychunas et al. , 2005 ), manganese oxides,
aluminum hydroxides and alumina silicates (Filella, 2007). Examples of organic
nanomaterials are humic substances (humic and fulvic acids) and acid polysaccha-
rides (Buffl e et al. , 1998 ; Wilkinson et al. , 1999 ).
Sources of incidentally produced NPs in aquatic systems are, for example, mining
activities, atmospheric deposition of combustion NPs, traffi c related NPs (combus-
tion, corrosion of vehicles, frictional wear of tires, road and brake system). While
there is a high background of natural NPs in most environmental waters, the inci-
dentally produced NPs are now becoming abundant in some polluted waters.
It is likely that, with rapidly developing applications of nanotechnology, manu-
factured NPs will become an increasingly important component of the aquatic
environment.
These three categories not only coexist in the aquatic environment, but most
likely also interact in complex ways which are poorly understood (Baalousha et al. ,
2008; Chen and Elimelech, 2007, 2008; Diegoli et al. , 2008). Analysis of these mix-
tures is more challenging than the analysis of each single material separately.

6.1.2 Concepts and Defi nitions Relating to Analysis and Characterization

Analysis in a physicochemical sense generally means quantifi cation of amounts,
while characterization usually stands for determination of properties. However, the
terms are overlapping since determination of a size distribution would be classifi ed
as a characterization of properties, but it actually requires quantifi cation of
the amounts (particle numbers or mass) in each size fraction. Many of the
characterization techniques that determine distributions of properties are only
semi-quantitative, or their concentration determinations are skewed in some way
(e.g. light scattering that can be used to generate size distributions that are intensity
weighted). In this chapter analysis deals with the quantitative determination of total
numbers or mass (volume), while characterization is a broader term.
It is often stated that very little is known about manufactured NPs in environ-
mental samples, and that it is not known how to measure them (RS/RAEng, 2004).
That is only partly true. Some manufactured NPs found in many new applications,
for example titanium dioxide, have actually been synthesized and at least partly
characterized in environmental waters for some time. Others, for example silica and
iron oxides, have been used as model NPs in order to better understand their natu-
rally produced analogues (Puls and Powell, 1992; Ryan et al. , 2000 ). In addition,
natural nanomaterials, often called colloids, have been extensively studied,
quantifi ed and characterized in almost all types of environmental compartments