Geoscience Reference
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reactive with the HA. From Fig.
16.20
, we see that the time-dependent increase in
quenching of 1-naphthol fluorescence by HA occurs. This time-dependent increase
provides indirect evidence of the operating mechanisms, which may be summa-
rized as follows: direct sorption-complexation of 1-naphthol to HA is a relatively
fast reaction that is completed within 24 h, followed by sorption of oxidative
products characterized by a longer contact time.
16.1.5 Multiple-Component Contaminant Transformation
Subsurface transformations of contaminants comprising multiple components are
reflected in the composition of the residual contamination products, which may
have different physical and chemical properties than the original pollutant. Dif-
ferential partitioning dissolution and volatilization of component mixtures are the
main abiotic processes leading to alteration of the original pollutant.
One of the most ubiquitous multiple-component contaminants that reaches the
soil and deeper subsurface layers is crude oil and its refined products. In the
subsurface, these contaminants are transformed differently by various mechanisms
(Cozzarelli and Baher
2003
). Crude oil contains a multitude of chemical com-
ponents, each with different physical and chemical properties. As discussed in
(such as normal and branched alkanes and cycloalkanes without double bonds),
aromatic hydrocarbons, resins, and asphaltenes, which are high molecular weight
polycyclic compounds containing nitrogen, sulfur, and oxygen.
Bennett and Larter (
1997
) discuss the effect of partitioning dissolution in an
aqueous phase of alkylphenol. Specifically, they show that the depletion of this
crude oil component affects the chemical composition of the original pollutant.
Partitioning at equilibrium can be considered the maximum dissolution value of a
compound under optimal solvation conditions. Partitioning dissolution is obtained
by ''washing'' the crude oil with saline water at variable temperature and pressure
conditions, similar to those in the subsurface. The data reported were obtained
using a partition device able to simulate the natural environmental conditions of a
crude oil reservoir. The alkylphenol partition coefficients between crude oil and
saline subsurface water were measured as a function of variation in pressure,
temperature, and water salinity. Preliminary trials proved that the experimental
device did not allow alkylphenol losses due to volatilization.
The crude oil used by Bennett and Larter (
1997
) was a typical North Sea oil
generated from Upper Jurassic, Kimmeridge clay formation source rocks. The
alkylphenol distribution in a sample of (Miller) crude oil, determined using solid-
phase extraction (SPE), is shown in Fig.
16.21
. The crude oil is dominated by
phenol and cresol and contains appreciable quantities of dimethylphenols. The
concentrations of 2,3-, 3,4-, and 3,5-dimethylphenol also include a contribution
from
2-, 3-,
and
4-ethylphenols,
because
they coelute under the
conditions
employed (Bennett et al.,
1996
).
