43
fungal biomass in soils enriched with lignocellulosic materials where the density of
fungal mycelia may be high. Immobilisation of microbial cells on solid porous
structures is used for bioremediation of triazine pesticides in water (Yu et al. 2019).
2.3.1 Phytoremediation
Phytoremediation has been suggested as an alternative bioremediation technique to
the microbial degradation of pesticide-contaminated sites. Phytoremediation
involves the use of vegetation for the in situ treatment of contaminated soil. Though
phytoremediation may take longer period for cleaning up the contaminated sites, it
is extremely useful for the sites with higher pesticide concentration that will inhibit
the microbial growth and activity. Phytoremediation helps in enhancing the organic
carbon in soil which helps in microbial growth. Phytoremediation occurs via four
mechanisms: (i) direct uptake and accumulation of pesticides and subsequent
metabolism in plant tissues are efficient mechanism of pesticide removal, (ii) transpiration of volatile organic hydrocarbons through the leaves, (iii) release of exudates that stimulates microbial activity and biochemical transformations in the soil,
and (iv) enhancement of mineralization at the root-soil interface by microorganisms
(Schnoor et al. 1995). Phytoremediation can be a cost-effective and eco-friendly
way of atrazine degradation. Pesticide-tolerant and nontarget plants can uptake and
transform the pesticides to lesser toxic metabolites. Kawahigashi et al. (2006) proposed phytoremediation of atrazine using transgenic rice plants expressing human
cytochrome P450 genes CYP1A1, CYP2B6, and CYP2C19. Sanchez et al. (2019)
indicated that the atrazine removal from soils was improved by the electric field
coupled to phytoremediation.
2.3.2 Biostimulation and Bioaugmentation
Biostimulation is the method of adding appropriate and limiting nutrient amendments to soils to enhance the rapid growth of indigenous bacteria, thereby increasing atrazine degradation rate (Getenga 2003; Qiu et al. 2009). Essential nutrients in
limiting quantities usually control the growth of native microbial population. The
atrazine removal varies significantly depending on the concentration of atrazine,
stimulant type, pH of medium, and inoculation time (Dehghani et al. 2019).
Biostimulation will not be effective when the bioavailability of the pesticide is low.
Bioaugmentation is proposed for rapid and cost-effective cleaning of atrazinecontaminated sites (Zhao et al. 2019). The addition of layered double hydroxide
bionanocomposites (Alekseeva et al. 2011) and carbon nanotubes (Zhang et al.
2015) has been reported to enhance the atrazine biodegradation rate. Bioaugmentation
is not that much successful in field trials due to the poor environmental adaptability
of the degraders, reduced bioavailability of atrazine, readily available carbon and
2 Biodegradation and Bioremediation of S-Triazine Herbicides
fungal biomass in soils enriched with lignocellulosic materials where the density of
fungal mycelia may be high. Immobilisation of microbial cells on solid porous
structures is used for bioremediation of triazine pesticides in water (Yu et al. 2019).
2.3.1 Phytoremediation
Phytoremediation has been suggested as an alternative bioremediation technique to
the microbial degradation of pesticide-contaminated sites. Phytoremediation
involves the use of vegetation for the in situ treatment of contaminated soil. Though
phytoremediation may take longer period for cleaning up the contaminated sites, it
is extremely useful for the sites with higher pesticide concentration that will inhibit
the microbial growth and activity. Phytoremediation helps in enhancing the organic
carbon in soil which helps in microbial growth. Phytoremediation occurs via four
mechanisms: (i) direct uptake and accumulation of pesticides and subsequent
metabolism in plant tissues are efficient mechanism of pesticide removal, (ii) transpiration of volatile organic hydrocarbons through the leaves, (iii) release of exudates that stimulates microbial activity and biochemical transformations in the soil,
and (iv) enhancement of mineralization at the root-soil interface by microorganisms
(Schnoor et al. 1995). Phytoremediation can be a cost-effective and eco-friendly
way of atrazine degradation. Pesticide-tolerant and nontarget plants can uptake and
transform the pesticides to lesser toxic metabolites. Kawahigashi et al. (2006) proposed phytoremediation of atrazine using transgenic rice plants expressing human
cytochrome P450 genes CYP1A1, CYP2B6, and CYP2C19. Sanchez et al. (2019)
indicated that the atrazine removal from soils was improved by the electric field
coupled to phytoremediation.
2.3.2 Biostimulation and Bioaugmentation
Biostimulation is the method of adding appropriate and limiting nutrient amendments to soils to enhance the rapid growth of indigenous bacteria, thereby increasing atrazine degradation rate (Getenga 2003; Qiu et al. 2009). Essential nutrients in
limiting quantities usually control the growth of native microbial population. The
atrazine removal varies significantly depending on the concentration of atrazine,
stimulant type, pH of medium, and inoculation time (Dehghani et al. 2019).
Biostimulation will not be effective when the bioavailability of the pesticide is low.
Bioaugmentation is proposed for rapid and cost-effective cleaning of atrazinecontaminated sites (Zhao et al. 2019). The addition of layered double hydroxide
bionanocomposites (Alekseeva et al. 2011) and carbon nanotubes (Zhang et al.
2015) has been reported to enhance the atrazine biodegradation rate. Bioaugmentation
is not that much successful in field trials due to the poor environmental adaptability
of the degraders, reduced bioavailability of atrazine, readily available carbon and
2 Biodegradation and Bioremediation of S-Triazine Herbicides