44
nitrogen sources, low utilization of additive substrates, and other complex environmental condition that affects the growth and metabolic activity of the atrazine
degraders. The addition of poultry manure increased atrazine removal two-fold as
compared to that of control (Gupta and Baummer 1996). Lin et al. (2018) studied
the role of earthworm in microbial degradation of atrazine. Earthworms accelerated
atrazine degradation by consuming soil humus, neutralizing soil pH, altering bacterial community structure, excreting the intestinal atrazine-degrading bacteria, and
enriching indigenous atrazine degraders. Biostimulation and bioaugmentation helps
to reduce the atrazine concentrations significantly in heavily contaminated soils.
2.3.3 Enzymatic Bioremediation
Enzymatic bioremediation will be a futuristic approach in resolving the pesticidecontaminated sites especially when the usage of genetically modified or engineered
microorganisms is restricted by government regulations. Enzymes help to overcome
the most disadvantages pertaining to the use of microbes and plants. Atrazinedegrading enzymes perform well in soil having high nitrogen content which supress
the atrazine degradation pathway system in the microbial cells. Enzymes can reach
the soil pores which are inaccessible to microbes and will be active in the presence
of microbial predators or antagonists. The enzymes are highly selective in degrading the pollutants when the microorganisms prefer the more easily available carbon
and nitrogen sources (Rajendran et al. 2018). Aspergillus laccase immobilised on
biosorbents prepared with peanut shell and wheat straw has a strong potential for
the effective removal of pesticides including atrazine and prometryn from water and
soil by biosorption coupled with degradation (Chen et al. 2019). Enzymatic bioremediation also suffers from some drawbacks. The free enzymes may be degraded
rapidly by the proteases released by the native soil microorganisms. Some enzymes
require cofactors which have to be applied along with the enzymes. Further higher
purity of the enzymes is much costlier compared to the use of microorganisms.
They require optimal environmental conditions for maximum activity. Enzymes
may reduce or lose their activity upon pesticide transformation and require repeated
applications. Enzyme immobilisation offers long-term stability and can be reused or
recovered. Enzymes can be immobilised on natural or synthetic supports through
various immobilisation mechanisms. Immobilised enzymes have been reported to
have higher stability and activity than the free enzymes.
2.3.4 Factors Affecting Atrazine Biodegradation
Environmental and soil conditions such as temperature, soil pH, structure, type,
moisture content, nutrient availability, cation exchange capacity, fertility, organic
matter, oxygen, and bioavailability of s-triazine pesticide greatly vary and affect the
K. Rajendran et al.
nitrogen sources, low utilization of additive substrates, and other complex environmental condition that affects the growth and metabolic activity of the atrazine
degraders. The addition of poultry manure increased atrazine removal two-fold as
compared to that of control (Gupta and Baummer 1996). Lin et al. (2018) studied
the role of earthworm in microbial degradation of atrazine. Earthworms accelerated
atrazine degradation by consuming soil humus, neutralizing soil pH, altering bacterial community structure, excreting the intestinal atrazine-degrading bacteria, and
enriching indigenous atrazine degraders. Biostimulation and bioaugmentation helps
to reduce the atrazine concentrations significantly in heavily contaminated soils.
2.3.3 Enzymatic Bioremediation
Enzymatic bioremediation will be a futuristic approach in resolving the pesticidecontaminated sites especially when the usage of genetically modified or engineered
microorganisms is restricted by government regulations. Enzymes help to overcome
the most disadvantages pertaining to the use of microbes and plants. Atrazinedegrading enzymes perform well in soil having high nitrogen content which supress
the atrazine degradation pathway system in the microbial cells. Enzymes can reach
the soil pores which are inaccessible to microbes and will be active in the presence
of microbial predators or antagonists. The enzymes are highly selective in degrading the pollutants when the microorganisms prefer the more easily available carbon
and nitrogen sources (Rajendran et al. 2018). Aspergillus laccase immobilised on
biosorbents prepared with peanut shell and wheat straw has a strong potential for
the effective removal of pesticides including atrazine and prometryn from water and
soil by biosorption coupled with degradation (Chen et al. 2019). Enzymatic bioremediation also suffers from some drawbacks. The free enzymes may be degraded
rapidly by the proteases released by the native soil microorganisms. Some enzymes
require cofactors which have to be applied along with the enzymes. Further higher
purity of the enzymes is much costlier compared to the use of microorganisms.
They require optimal environmental conditions for maximum activity. Enzymes
may reduce or lose their activity upon pesticide transformation and require repeated
applications. Enzyme immobilisation offers long-term stability and can be reused or
recovered. Enzymes can be immobilised on natural or synthetic supports through
various immobilisation mechanisms. Immobilised enzymes have been reported to
have higher stability and activity than the free enzymes.
2.3.4 Factors Affecting Atrazine Biodegradation
Environmental and soil conditions such as temperature, soil pH, structure, type,
moisture content, nutrient availability, cation exchange capacity, fertility, organic
matter, oxygen, and bioavailability of s-triazine pesticide greatly vary and affect the
K. Rajendran et al.