Environmental Engineering Reference
In-Depth Information
Table 7.5
Mass Balance of Radioactivity and Fluoranthene after 48 h Incubation of
EPA 505 Cells with Different Concentrations of Triton X-100
Carbon
Dioxide
Radioactivity
FLA
Residual
(mg)
Recovery of
Radioactivity
Soluble
Radioactivity
Cell Mass
Radioactivity
a
Triton
0%
81
4
54
42
4.73
0.005%
100
4
48
48
0.25
0.03%
95
9
28
63
0.15
0.1%
95
12
26
62
<0.005
2.0%
96
26
16
58
NA
Killed cells
100
<1
99
<1
30.3
Note:
NA = not analyzed (surfactant concentration too high for GC analysis).
a
Radioactivity retained on a 0.22-μ filter.
Pritchard et al. (1995) showed that at high biomass concentrations (10
10
cells/ml), Triton X-100 was generally stimulatory to fluoranthene mineral-
ization by EPA 505 in minimal salts medium. However, at high concentra-
tions of Triton, the total mineralization of fluoranthene was decreased. An
examination of the mass balances in Table 7.5, expressed as percent of total
14
C
added, showed that the difference was in the amount of soluble product
produced.
Triton apparently caused the release of fluoranthene degradation prod-
ucts from the cell into the medium (P.H. Pritchard, personal communication).
This corresponded to the production of a bright red color, which we believe
is the recyclized hemiacetal of the initial ring-opening product of fluoran-
thene. If biomass is decreased, mineralization of fluoranthene is inhibited
initially but seems to recover after a period of days (Pritchard et al., 1995).
The extent of mineralization was less in the cases in which recovery occurred,
which was again due to the release of degradation products into the medium
that are not fully metabolized. Exposure of strain EPA 505 to Triton appar-
ently results in the lysis of many cells, and those that do survive are very
sensitive to being washed (L. Fredrickson and P.H. Pritchard, personal com-
munication). Having survived exposure to Triton, the cells become more
tolerant to the surfactant, but this acclimation was an unstable characteristic,
because cells quickly reverted to high sensitivity when cultured in the
absence of surfactant (L. Fredrickson and P.H. Pritchard, personal commu-
nication). These results are, in part, due to the limiting calcium effect. Sur-
factant effects on degradation and viability are clearly strain specific (Wil-
lumsen et al., 1998). Figure 7.7 shows the effect of Triton on four different
fluoranthene degraders. The differences in fluoranthene mineralization were
probably due to the susceptibility of the membranes to dissolution by Triton.
These results suggest that surfactants interact with the cell membrane, per-
haps allowing for greater transport of PAHs inside but at the same time
rendering the cells more sensitive to environmental situations. In the case of
