Most of the current contaminants or pesticides were synthesized as biologically
diverse organic substances that are not present in nature. They often showed strong
resistance to degradation by microbes. It may be explained that the time it takes for
these compounds to come into nature was so short that not a single microbe has
developed metabolic mechanisms regarding the degradation of such compounds.
Compared to the currently widely used synthetic heterologous substances, the
natural evolutionary process of microorganism was not able to meet the requirements of microbial pesticide degradation, because the speed of this process was far
from reaching what the environment and human needed. Therefore, the balance of
the entire ecosystem would be disturbed having a long-term impact (Ye et al. 2018).
2.5.3 Soil Organic Matter
Degradation of herbicides in modified soils with paddy straw, compost and NPK
chemical fertilizer under upland, oxidative-flooded (aerobic-flooded), and reductiveflooded (anaerobic-flooded) conditions was studied (Kumar et al. 2018b). The crop
residues acted as a source of organic matter and provided nutrients. Paddy straw,
compost, and NPK amendments accelerated the degradation of herbicides under
upland and oxidative-flooded conditions. But in reductive-flooded conditions, herbicide degradation was very slow. The degradation of benthiocarb resulted in the
formation of 4-chlorobenzoic acid, desethyl benthiocarb, benthiocarb-sulfoxide, and
4-chlorobenzyl methyl sulfone. Paddy straw amendments increased the amount of
benthiocarb sulfoxide. Under the upland conditions the amount of desethyl
benthiocarb was reduced by paddy straw and compost. The major degradation
product of MCPA was 4-chloro-2-methylphenol, resulting in large amounts of
paddy straw amendments in oxidative-flooded and NPK amendments under upland
conditions (Duah-Yentumi and Kuwatsuka 1980). Boivin et al. (2005) studied the
interaction of pesticides, viz. isoproturon, trifluralin, and atrazine, in relation to the
organic matter of the soil. Singh et al. (2006) studied fenomiphos and chlorpyrifos
for its biodegradation, but could not observe the potential of soil organic matter in
pesticide biodegradation. Fenlon et al. (2007) found that diazinon mineralized in two
types of the organic soils. Gupta et al. (2015) observed that the effect of the organic
substrate content on pesticide’s degradation in composting was greater than that of
the bacterial population when compost was mixed with soil contaminated by PAHs.
2.5.4 Environmental Factors
Temperature, humidity, salinity, pH, nutrition, carbon dioxide, oxygen, substrate
concentration, surfactant, etc. were found to affect pesticide depletion (Martin et al.
2009; Sartoros et al. 2015; Bhattacharya et al. 2006; Munawar 2010). Bacteria or
their enzymes require adequate temperature, pH, and substrate concentration for
2 Bioremediation of Pesticides: An Eco-Friendly Approach for Environment. . .
43
diverse organic substances that are not present in nature. They often showed strong
resistance to degradation by microbes. It may be explained that the time it takes for
these compounds to come into nature was so short that not a single microbe has
developed metabolic mechanisms regarding the degradation of such compounds.
Compared to the currently widely used synthetic heterologous substances, the
natural evolutionary process of microorganism was not able to meet the requirements of microbial pesticide degradation, because the speed of this process was far
from reaching what the environment and human needed. Therefore, the balance of
the entire ecosystem would be disturbed having a long-term impact (Ye et al. 2018).
2.5.3 Soil Organic Matter
Degradation of herbicides in modified soils with paddy straw, compost and NPK
chemical fertilizer under upland, oxidative-flooded (aerobic-flooded), and reductiveflooded (anaerobic-flooded) conditions was studied (Kumar et al. 2018b). The crop
residues acted as a source of organic matter and provided nutrients. Paddy straw,
compost, and NPK amendments accelerated the degradation of herbicides under
upland and oxidative-flooded conditions. But in reductive-flooded conditions, herbicide degradation was very slow. The degradation of benthiocarb resulted in the
formation of 4-chlorobenzoic acid, desethyl benthiocarb, benthiocarb-sulfoxide, and
4-chlorobenzyl methyl sulfone. Paddy straw amendments increased the amount of
benthiocarb sulfoxide. Under the upland conditions the amount of desethyl
benthiocarb was reduced by paddy straw and compost. The major degradation
product of MCPA was 4-chloro-2-methylphenol, resulting in large amounts of
paddy straw amendments in oxidative-flooded and NPK amendments under upland
conditions (Duah-Yentumi and Kuwatsuka 1980). Boivin et al. (2005) studied the
interaction of pesticides, viz. isoproturon, trifluralin, and atrazine, in relation to the
organic matter of the soil. Singh et al. (2006) studied fenomiphos and chlorpyrifos
for its biodegradation, but could not observe the potential of soil organic matter in
pesticide biodegradation. Fenlon et al. (2007) found that diazinon mineralized in two
types of the organic soils. Gupta et al. (2015) observed that the effect of the organic
substrate content on pesticide’s degradation in composting was greater than that of
the bacterial population when compost was mixed with soil contaminated by PAHs.
2.5.4 Environmental Factors
Temperature, humidity, salinity, pH, nutrition, carbon dioxide, oxygen, substrate
concentration, surfactant, etc. were found to affect pesticide depletion (Martin et al.
2009; Sartoros et al. 2015; Bhattacharya et al. 2006; Munawar 2010). Bacteria or
their enzymes require adequate temperature, pH, and substrate concentration for
2 Bioremediation of Pesticides: An Eco-Friendly Approach for Environment. . .
43