Environmental Engineering Reference
In-Depth Information
100
80
Dibenzo(a,l)pyrene
Dibenz(a,h)anthracene
Benzo(b)fluoranthene
Chrysene
Benzo(a)pyrene
1-nitropyrene
Benz(a)anthracene
Pyrene
60
40
20
0
0 2 4 6 8 0 2 4 6 8
Hours
Figure 7.4 Cometabolism of PAHs by EPA 505.
on pyrene. It is clear that of the strains studied, EPA 505 was the most
effective in terms of removing the four-, five-, and six-ring PAHs (67%
removal compared to 28% removal for next best strain, Mycobacterium strain
PYR-1) (Heitkamp et al., 1988a, 1988b) and in producing the greatest removal
of PAHs overall (91% removal). Thus, just because a strain grows well on a
particular PAH does not mean that it will have broad cometabolic capabili-
ties. The next question investigated was whether this metabolic capability
could be expected in most soils.
7.1.3.5.3 Metabolic characteristics. In preliminary mechanistic stud-
ies performed with pyrene, a nongrowth PAH for EPA 505, it appears that
at least two different partial degradation products of pyrene were produced.
Both degradation products represent the opening of an aromatic ring, and
both indicate an inability to cleave carbon moieties to use for growth. The
proposed pathway for the cometabolism of pyrene by strain EPA 505 is
shown in Figure 7.5. The pathway represents possible attacks on the pyrene
rings based on products detected by, and inferred from, gas chromatography
mass spectrometry (GC-MS) analysis.
The products suggest that pyrene was dihydroxylated at both the 2,3
position and the 9,10 position. There was no evidence to suggest two separate
dioxygenase systems and, thus, it was assumed that a single enzyme system
is able to recognize both positions. Clearly, both of the oxidized rings were
then opened, one by meta-cleavage and one by ortho-cleavage. This is con-
sistent with the mechanism by which the strain attacks fluoranthene (see
below). It is also consistent with the reported 1,2-dioxygenation of pyrene
and subsequent meta-cleavage (Heitkamp et al., 1988a, 1988b; Walter et al.,
1991) and the 4,5-dioxygenation followed by ortho-cleavage (Rehmann et
al., 1998), both seen with Mycobacterium and Rhodococcus sp. that are able to
 
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