Geology Reference
In-Depth Information
OH
OH
H
OH
NO
2
+ HONO
3-hydroxy-fluoranthene
fluoranthene
NO
2
H
NO
2
NO
2
OH
H
+ H
2
O
2-nitrofluoranthene
Figure 5 The gas phase OH radical-initiated reaction of fluoranthene (a 3-ring PAH) in
the presence of NOx. The reaction results in the formation of both hydroxy- and
nitro-fluoranthene, although nitro-fluoranthene can also form from the nighttime
reaction with the NO
3
radical
Reaction scheme adapted from Arey et al.
33
formation of both 3-hydroxyfluoranthene and 2-nitrofluoranthene (2-
NF). Indeed, some of the nitroarenes are strongly mutagenic and present
a risk to human health and have been reported in several recent air
sampling campaigns.
34,35
Interestingly, 2-NF is one of the major parti-
cle-associated nitro-PAHs observed in a study conducted in southern
California,
35
presumably due to its lower volatility and higher polarity
than the parent fluoranthene, resulting in its condensation/sorption to
atmospheric particles.
An important transformation process for halogenated organic com-
pounds is reductive dehalogenation, a process which largely occurs in
anoxic (oxygen free) environments, such as sediments, sewage sludges,
water-logged soils and ground-water and catalysed by the presence of
metal containing minerals, where the metal is in a low state of oxidation
e.g. zero-valent or divalent iron. The reductive potential of a halogen-
ated molecule (i.e. 'the willingness to accept electrons from the metal
donor') is based on many factors, not least the number and type of
halogen atoms around the molecule. In one common type of reaction the
breaking of the carbon-halogen bond (through the halogen atom ac-
cepting electrons) is followed by replacement with a H-atom (hydrogen-
olysis), resulting in the gradual 'de-halogenation' of the molecule. For
chlorinated solvents and chlorinated aliphatics in general, then this
