Environmental Engineering Reference
In-Depth Information
Chlorotriazines
Cl
N
N
R
x
R
Y
N
Methoxytriazines
Methylthiotriazines
SCH
3
N
OCH
3
N
N
N
R
x
R
Y
R
x
R
Y
N
N
Figure 10.2.
Backbone structures of three s-triazine herbicide serving as potential
substrates for catabolism by micro-organisms.
partially transform atrazine by carrying out hydrolytic reactions, resulting in
the cleavage of chloro, amino and alkylamino groups on the s-triazine ring
(Cook
1987
). In addition, while Erickson and Lee (
1989
) reported that some
micro-organisms dealkylated the side chains of chlorinated triazines, they
failed to dechlorinate atrazine, and reviews written in 1969 1975 reported
that atrazine was biologically transformed in the environment by hydrolysis
at carbon 2, by N-dealkylation at carbons 4 and 6 or by opening of the s-triazine
ring (Knusli et al.
1969
; Kaufman & Kearney
1970
; Esser et al.
1975
). Interestin-
gly, while micro-organisms transforming deisopropylatrazine, deethyldeisopro-
pylatrazine, ammeline, N-isopropylammelide and ammelide were previously
reported, none were shown to degrade the chlorinated s-triazine compounds
atrazine and simazine (Cook
1987
). However, despite the lack of the isolation
of a pure microbial culture with the ability to degrade atrazine, the half-life
of atrazine in soil was found to be shorter in soils with exposure history to this
compound (reviewed in Mandelbaum et al.
2008
), partial mineralisation of
atrazine in soils was shown, and microbial consortia were reported to degrade
atrazine (Behki & Khan
1986
; Mandelbaum et al.
1993
). This suggested that
micro-organisms were slowly evolving the ability to degrade and mineralise
atrazine. In hindsight, this result may not be too surprising since melamine
(the triamino substituted s-triazine), which was once considered to be xeno-
biotic and non-biodegradable (Scholl et al.
1937
), was found nearly 40 years
later to be completely biodegradable (Allan
1981
; Cook et al.
1983
), and has
been patented as a slow-release fertiliser. However, evidence for a change
in microbiologically mediated atrazine metabolism could be seen in the
