Geoscience Reference
In-Depth Information
Chapter 16
Selected Research Findings:
Transformations and Reactions
16.1 Abiotic Alteration of Contaminants
16.1.1 Transformation in Subsurface Water
Both inorganic and organic contaminants may change their specific properties in
the subsurface solution (e.g., toxicity, transport, adsorption, persistence) according
to the properties of the aqueous medium. The pH of the subsurface solution, for
example, may control basic or acid hydrolysis of contaminants, affect their dis-
solution-precipitation behavior, or influence their transformation under redox-
induced processes. Inorganic and organic chemicals present in the subsurface
solution may serve as catalysts, and at specific pH values, they can enhance
contaminant transformation. Natural and synthetic organic compounds that serve
as ligands for inorganic compounds lead to changes in contaminant dissolution in
water and, in some cases, serve as sensitizers in photochemically induced degra-
dation of organic pollutants in contaminated surface waters.
The effect of pH on transformation in the subsurface aqueous environment is
considered here for the case of two highly toxic biocides (methyl parathion and
acrolein) and for an industrial semivolatile organic pollutant (tribromoneopentyl
alcohol, or TBNPA). The examples are based on the work of Guo and Jans (
2006
),
Oh et al. (
2006
) and Ezra et al. (
2005
).
Acrolein (CH
2
=CHCHO, also known as 2-propenal) is a a,b-unsaturated
aldehyde that can be transformed reductively to saturated or unsaturated alcohols
by reduction of the C=O or C=C double bonds (Claus
1998
). In addition, a,b-
unsaturated aldehydes may undergo hydration reactions in aqueous solutions. It
was observed that, under acidic (pH \ 1) or basic (pH [ 12) conditions, acrolein
is hydrated to 3-hydroxypropanal (Jensen and Hashtroudi
1976
). In a natural
subsurface environment, where pH may range from 6.5 to 8.5, the hydration rate of
acrolein increases with the pH and its half-life decreases. Based on an experiment
to analyze effects of iron on acrolein transformation, Oh et al. (
2006
) note that,
under acidic conditions (e.g., pH = 4.4), acrolein disappears rapidly from solution
in
the
presence
of
elemental
iron
(Fig.
16.1
).
Moreover,
the
formation
of
