36
rats, and male hermaphroditism in amphibians; and negative effect on aquatic
organisms particularly in combination with other pesticides.
In anaerobic aquatic environment, atrazine’s overall half-life, water half-life, and
sediment half-life were given as 608, 578, and 330 days, respectively. While in terrestrial environment, half-life of atrazine may range from 13–261 days (US-EPA
2006). Atrazine dealkylation metabolites, such as deethylatrazine and deisopropylatrazine, are also regulated compounds and may pose health risks. Massive application, high mobility, and persistence are the major reasons for the frequent detection
of atrazine and its metabolites in surface and ground water at concentrations well
above the legal limits globally. European Union banned atrazine use in October
2003 but still in use in many parts of the world including the United States and
India. However, Environmental Protection Agency has set the maximum containment level for atrazine in drinking water at 3 ppb. Triazine herbicides are persisted
in the soil for 3–12 months and are slowly degraded by biological, chemical, and
physical processes. This persistence period leads to accumulation in soil and water
bodies posing a serious threat to human and environment. Therefore, utmost priority
should be given to develop effective technologies for detoxification and/or removal
of triazine pesticides and their metabolites. However, the metabolites of atrazine
including hydroxyatrazine is less acutely toxic than the parent atrazine.
2.2 Biodegradation
2.2.1 Biodegradation of S-Triazine Herbicides by Bacteria
Pseudomonas sp. strain ADP was the first isolated atrazine-mineralizing strain.
Many other bacteria are found to degrade atrazine as shown in Table 2.2. Atrazine
mineralisation by microbial consortia appears to be more common in soils than
individual species as most of the bacterial strains do not contain all the genes
required for atrazine mineralisation (Billet et al. 2019; Kolic et al. 2007; Smith et al.
2005). Bacteria use atrazine primarily as a nitrogen source. Satsuma (2010) reported
that a newly isolated Nocardioides species strain DN36 not only mineralised simetryn, atrazine, and simazine but also transformed propazine, ametryn, prometryn,
dimethametryn, atraton, simeton, and prometon.
Degradation Pathway
Triazine mineralisation is more or less similar to atrazine mineralisation and is
achieved in two stages. In the first stage, atrazine is converted to cyanuric acid
(2,4,6-trihydroxy-1,3,5-triazine) by dehalogenation and dealkylation of side chains.
Conversion of atrazine to cyanuric acid takes place via one of the three pathways as
shown in Fig. 2.2. P-1 is the hydrolytic pathway commonly found in many bacteria
K. Rajendran et al.
rats, and male hermaphroditism in amphibians; and negative effect on aquatic
organisms particularly in combination with other pesticides.
In anaerobic aquatic environment, atrazine’s overall half-life, water half-life, and
sediment half-life were given as 608, 578, and 330 days, respectively. While in terrestrial environment, half-life of atrazine may range from 13–261 days (US-EPA
2006). Atrazine dealkylation metabolites, such as deethylatrazine and deisopropylatrazine, are also regulated compounds and may pose health risks. Massive application, high mobility, and persistence are the major reasons for the frequent detection
of atrazine and its metabolites in surface and ground water at concentrations well
above the legal limits globally. European Union banned atrazine use in October
2003 but still in use in many parts of the world including the United States and
India. However, Environmental Protection Agency has set the maximum containment level for atrazine in drinking water at 3 ppb. Triazine herbicides are persisted
in the soil for 3–12 months and are slowly degraded by biological, chemical, and
physical processes. This persistence period leads to accumulation in soil and water
bodies posing a serious threat to human and environment. Therefore, utmost priority
should be given to develop effective technologies for detoxification and/or removal
of triazine pesticides and their metabolites. However, the metabolites of atrazine
including hydroxyatrazine is less acutely toxic than the parent atrazine.
2.2 Biodegradation
2.2.1 Biodegradation of S-Triazine Herbicides by Bacteria
Pseudomonas sp. strain ADP was the first isolated atrazine-mineralizing strain.
Many other bacteria are found to degrade atrazine as shown in Table 2.2. Atrazine
mineralisation by microbial consortia appears to be more common in soils than
individual species as most of the bacterial strains do not contain all the genes
required for atrazine mineralisation (Billet et al. 2019; Kolic et al. 2007; Smith et al.
2005). Bacteria use atrazine primarily as a nitrogen source. Satsuma (2010) reported
that a newly isolated Nocardioides species strain DN36 not only mineralised simetryn, atrazine, and simazine but also transformed propazine, ametryn, prometryn,
dimethametryn, atraton, simeton, and prometon.
Degradation Pathway
Triazine mineralisation is more or less similar to atrazine mineralisation and is
achieved in two stages. In the first stage, atrazine is converted to cyanuric acid
(2,4,6-trihydroxy-1,3,5-triazine) by dehalogenation and dealkylation of side chains.
Conversion of atrazine to cyanuric acid takes place via one of the three pathways as
shown in Fig. 2.2. P-1 is the hydrolytic pathway commonly found in many bacteria
K. Rajendran et al.