Geoscience Reference
In-Depth Information
Table 12.4 Characteristics of ambient water samples used in the experiments (Modified after
Keller et al.
2010
)
pH TOC Ionic strength
lM C eq/L
Santa Barbara seawater 8.05 54 7.07 9 10
-1
Artificial seawater 7.99 55.9 6.39 9 10
-1
Bodega Bay seawater 8.08 131.8 6.79 9 10
-1
UCSB lagoon 8.9 522.6 2.15 9 10
-1
Santa Paula groundwater 7.9 842.4 9.09 9 10
-2
Santa Clara river water 8.33 163.8 1.84 9 10
-2
Estero effluent 7.68 378 3.17 9 10
-2
Mesocosm wastewater 7.07 691.8 3.18 9 10
-3
Storm runoff 7.09 1,564 9.63 9 10
-3
Mesocosm freshwater 8.38 5,283 7.18 9 10
-3
Reprinted with permission from Keller et al. (
2010
). Copyright 2010 American Chemical Society
coprecipitated within hydrosulfates (e.g., jarosite). They suggest that As release
from soils and sediments contaminated with tailings, and consequently their
transport, are controlled by either acid or reductive dissolution of the host phase.
12.2 Engineered Nanoparticles (ENPs)
Engineered nanoparticles (ENPs), or nanomaterials (recall
Sect. 3.6
), are reactive
pollutants that, after reaching the land surface, are subject to environmentally
induced transformations that may affect their redistribution in the soil-subsurface
system. The mobility of ENPs through porous media is governed by ENP com-
position and morphology, the solid-phase physicochemical status, the chemistry of
the pore water (e.g., pH, ionic strength, and the presence of natural organic mat-
ter), and by biochemically induced processes. In contrast to the transport of pri-
mary particles, ENPs tend to aggregate into clusters having a size of several
microns. As a consequence, changes in ENP stability and aggregation status are
crucial factors in defining ENP transport in the vadose zone (Hotze et al.
2010
).
12.2.1 Fate of ENPs in Aqueous Solutions
Because the pathway of ENP transport may be affected by changes in ENP aggre-
gation status during their contact with the soil-subsurface environment, we consider
it useful to present an example of the relationship between metal oxide nanoparticle
stability and aggregation. Keller et al. (
2010
) measured electrophoretic mobility,
state of aggregation, and rate of sedimentation of TiO
2
, ZnO, and CeO
2
ENPs as
affected by the chemistry of environmental aqueous matrix (mainly by natural
organic content, ionic composition, and ionic strength) as described in Table
12.4
.
