Geoscience Reference
In-Depth Information
soil has a major impact on nanoparticle transport in soil. Results of this study
emphasize the importance of studying nanoparticle transport in natural soils, rather
than in artificial porous media, to understand the fate of nanoparticles in the soil-
subsurface environment.
TiO
2
nanoparticles are commonly used in the cosmetic industry and in pho-
tocatalytic products; they are also used in water and soil pollutant decontamina-
tion. Based on a series of column experiments, Fang et al. (
2009
) report on TiO
2
mobility as affected by soil properties (Table
12.5
) collected from 12 Chinese
provinces. From the breakthrough curves of a TiO
2
aqueous suspension
(Fig.
12.29
), the effect of soil properties on ENP retention and transport may be
seen. The TiO
2
nanoparticle content in soil suspensions after 24 h was positively
correlated to the DOC and the clay content of the soils, and negatively correlated
to ionic strength, pH, and zeta potential. The authors found that TiO
2
nanoparticles
are generally stable in soil suspensions, and that higher stability leads to higher
mobility. In a number of soils, the travel distances exceeded 30 cm, suggesting a
potential risk of ENP movement down to the groundwater region.
In contrast to the results of fullerene transport through quartz sand, the studies
of Wang et al. (
2010
) showed that transport of nC
60
in natural soils containing
organic matter and clay minerals is drastically lower than previously reported for
nonreactive minerals. In this study, a series of column experiments was performed
to assess the transport and retention of nanoscale fullerene aggregates in water-
saturated soils. Two types of soils were used—Appling and Webster—which
contain 0.75 and 3.33 % organic carbon, respectively. Complete retention of nC
60
was observed even after the applied aqueous nC
60
suspension pulse to Appling soil
increased from 5 to 65 pore volumes. It also was found that the increase in pulse
size led only to a minor increase in travel distance in the column, from 3 to 8 cm.
Addition of 20 mg/L humic acid to the influent suspension increased fullerene
travel transport in the Appling soil, but did not result in breakthrough.
12.2.5 ENP Transport in the Field
We consider two experiments related to zero valent zinc and copper oxide
nanoparticle transport in field soils, as examples of potential nanomaterial trans-
port pathways in soil-subsurface systems. Zinc oxide (ZnO) is one of the ENPs
used frequently in personal care products, pharmaceuticals, catalysis, and envi-
ronmental remediation products. Similarly, copper oxide (CuO) is used in elec-
tronics, ceramics, films, polymers, inks, metallics, lubricant oil, coatings, and
health care products. Both types of ENPs may reach the land surface via sewage
water, and waste disposals will be retained on the upper layers of the soil or
transported with depth in the soil-subsurface system. Their prevalence virtually
ensures that these ENPs may be considered chemical environmental contaminants.
The experiment of Collins et al. (
2012
) was performed on containers packed
with an agricultural soil rich in total organic matter (13,100 mg/kg) with a pH of
