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Fig. 16.40 Atrazine catabolic pathway in Pseudomonas sp. strain ADP (Shapir et al. 2002 ).
Reprinted with permission. Copyright American Society for Microbiology
atrazine in near-surface environments may result from hydrolytic processes due to
high or low pH or from surface-catalyzed hydrolysis as a result of hydrogen
bonding between carboxyl groups in organic matter and atrazine ring nitrogen
atoms. Changes induced in atrazine metabolism by the Pseudomonas sp. strain
ADP (Mandelbaum et al. 1995 ) are given by Shapir et al. ( 2002 ) in Fig. 16.40 . The
primary microbial degradation pathway is N-dealkylation of the side chain, to
produce deethylatrazine and deisopropylatrazine (chlorohydrolase (AtzA)), fol-
lowed by a second reaction, where AtzB catalyzes the hydrolysis of hydroxyatr-
azine to yield izopropylamelide. The third metabolic step utilizes N-
isopropylammelide isopropylaminohydrolase (AtzC) to hydrolytically remove N-
isopropylamine and produce cyanuric acid. It is believed that the advent of bac-
terial atrazine catabolism requires the presence of AtzA, AtzB, and AtzC enzymes
(Seffernick and Wackett 2001 ).
The persistence (half-life) of atrazine in the subsurface is governed by chem-
ically and biologically mediated transformations. Because the solubility of atrazine
is relatively high (*30 mg/L) compared with its toxicity level in water (5 lg/L),
atrazine has become a hazard to groundwater quality. Atrazine has been detected
in groundwater more than any other crop protection chemical; two examples of
atrazine persistence-transformation in aquifer environments are discussed next.
Pang et al. ( 2005 ) examined atrazine transformation in groundwater and aquifer
materials, considering the following treatments: atrazine with natural and sterilized
groundwaters and atrazine with natural and sterilized aquifer sands and ground-
waters. The studied systems closely mimicked natural groundwater and aquifer
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