rhizosphere. Further, understanding of the involved degradation mechanisms and
enhancing degradation of pesticides by genetic engineering of microbes are essential
for improving soil health and ecosystem performance (Pellegrino and Bedini 2014)
by improving crop productivity in the sustainable agriculture sector.
2.2 Categorization of Pesticides
Pesticides are classified into different categories based on their activity, including
herbicides, insecticides, fungicides, nematicides, rodenticides, and molluscicides
(Rani et al. 2017). Based on the chemical composition, pesticides can be classified
as: (1) organochlorines, (2) organophosphates, (3) carbamates, and (4) substituted
urea. Organophosphates and organochlorines are highly hazardous and persistent
organic pollutants, which are even more dangerous to the environment. Organophosphorus pesticides (OPs), referring to chemical structures and functional groups,
are phosphates, phosphoramides, or phosphorothioates, usually contain P-O, P-N, or
P-S bonds, respectively (Liang et al. 2004; Shaker and Elsharkawy 2015). Twelve
organophosphorus pesticides (OPs) have been listed in the US EPA’s latest Candidate Contaminant List (CCL4) (Parker et al. 2017). OPs comprising high mammalian toxicity (Singh et al. 2004) can inhibit the activity of acetylcholine esters
(AChE) (Pino and Peñuela 2011), and prolonged exposure to OPs poses a serious
threat to human health (Wang et al. 2010a, b; Granella et al. 2013). Excessive
consumption of OPs can lead to severe environmental pollution and hazards. The
use of pesticides refers to the practical method by which pesticides are delivered to
their biological targets (e.g. pests, crops or other plants). Introduction of other
synthetic pesticides, organophosphate pesticides in the 1960s, carbamates in the
1970s, pyrethroids in the 1980s, and herbicides and fungicides introduced from the
1970s to the 1980s has been instrumental in pest control and agricultural production
(Table 2.1).
2.3 Pesticides and Their Toxic Effects
To control pests and diseases, farmers are using higher doses of pesticides compared
to the recommended. Most pesticides such as glyphosate, malathion, phorate,
monocrotophos, chlorpyrifos, simazine, pendimethalin, carbofuran, phosphamidon,
diazinon, mancozeb, methyl parathion, and carbendazim (Moneke et al. 2010;
Chennappa et al. 2016) are often applied for the cultivation of agricultural crops.
Organochlorine pesticides explored for pest management consist of dichlorodiphenyltrichloro-ethane (DDT), aldrin, dieldrin, endosulfan, endrin,
hexachlorocyclohexane (HCH), heptachlor, sodium pentachlorophenate, and toxaphene. Different genera of bacteria and fungi can degrade these pesticides. Although
endosulfan and HCH are banned in developed countries, these pesticides are still
28
A. Sehrawat et al.
enhancing degradation of pesticides by genetic engineering of microbes are essential
for improving soil health and ecosystem performance (Pellegrino and Bedini 2014)
by improving crop productivity in the sustainable agriculture sector.
2.2 Categorization of Pesticides
Pesticides are classified into different categories based on their activity, including
herbicides, insecticides, fungicides, nematicides, rodenticides, and molluscicides
(Rani et al. 2017). Based on the chemical composition, pesticides can be classified
as: (1) organochlorines, (2) organophosphates, (3) carbamates, and (4) substituted
urea. Organophosphates and organochlorines are highly hazardous and persistent
organic pollutants, which are even more dangerous to the environment. Organophosphorus pesticides (OPs), referring to chemical structures and functional groups,
are phosphates, phosphoramides, or phosphorothioates, usually contain P-O, P-N, or
P-S bonds, respectively (Liang et al. 2004; Shaker and Elsharkawy 2015). Twelve
organophosphorus pesticides (OPs) have been listed in the US EPA’s latest Candidate Contaminant List (CCL4) (Parker et al. 2017). OPs comprising high mammalian toxicity (Singh et al. 2004) can inhibit the activity of acetylcholine esters
(AChE) (Pino and Peñuela 2011), and prolonged exposure to OPs poses a serious
threat to human health (Wang et al. 2010a, b; Granella et al. 2013). Excessive
consumption of OPs can lead to severe environmental pollution and hazards. The
use of pesticides refers to the practical method by which pesticides are delivered to
their biological targets (e.g. pests, crops or other plants). Introduction of other
synthetic pesticides, organophosphate pesticides in the 1960s, carbamates in the
1970s, pyrethroids in the 1980s, and herbicides and fungicides introduced from the
1970s to the 1980s has been instrumental in pest control and agricultural production
(Table 2.1).
2.3 Pesticides and Their Toxic Effects
To control pests and diseases, farmers are using higher doses of pesticides compared
to the recommended. Most pesticides such as glyphosate, malathion, phorate,
monocrotophos, chlorpyrifos, simazine, pendimethalin, carbofuran, phosphamidon,
diazinon, mancozeb, methyl parathion, and carbendazim (Moneke et al. 2010;
Chennappa et al. 2016) are often applied for the cultivation of agricultural crops.
Organochlorine pesticides explored for pest management consist of dichlorodiphenyltrichloro-ethane (DDT), aldrin, dieldrin, endosulfan, endrin,
hexachlorocyclohexane (HCH), heptachlor, sodium pentachlorophenate, and toxaphene. Different genera of bacteria and fungi can degrade these pesticides. Although
endosulfan and HCH are banned in developed countries, these pesticides are still
28
A. Sehrawat et al.