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6 Bioremediation of Pesticides Containing Soil and Water

6.7

Factors Affecting Bioremediation

Microbial degradation of pesticides depends on various factors which can be divided

into external and internal factors. For the complete degradation of pesticide con-

taminants, physico-chemical parameters such as pH, temperature, water potential,

substrate availability, oxygen, etc., should be at optimum level as these parameters

influence the biodegradation efficiency.

6.7.1

Soil Type and Soil Moisture

Pesticide contaminants adhere to soil particles (absorption/adsorption) and

microorganisms are incapable of using them for degradation. Soil moisture is

considered one of the important factors for microbial functioning which helps

significantly during pesticide degradation, on the other hand, under dry soils

condition the degradation rate will be slow. Water will act as a solvent for pesticide

to move it around and enables pesticide biodegradation. The degradation rate

mostly rises with water levels. Moisture range between 50% and 80% was found to

be optimal for the biodegradation [36].

6.7.2

Oxygen and Nutrients

Availability of molecular oxygen is one of the further most vital factors constraining

the rate of biodegradation. For the aerobic degradation of pesticide by microorgan-

isms, oxygen supply can be limited by unfavorable soil porosity. Henceforth, mass

transmission from gaseous phase to aqueous phase will be hindered. In water, sub-

dued solubility of oxygen is the restrictive factor. Additionally, while implement-

ing bioremediation methods, development and activity of microorganisms must be

quickened. Biostimulation engages in the addition of oxygen and nutrition. Nutri-

ents are elementary building chunks for the life of microorganisms which lead to

production of enzymes and such enzymes have the capacity to degrade the pesti-

cides. Macro and micronutrients are essential for the growth of microorganism and

degradation of pesticides [37].

6.7.3

Temperature and pH

Temperature disturbs the adsorption by fluctuating the solubility and hydrolysis

of pesticides. As adsorption mechanisms are exothermic, it is expected that it will

decrease with increase in temperature along with increased solubility of pesticides.

Microbial activity will be intensified as there is an upsurge in temperature. The

highest growth and activity of microbes will happen in soils at 25–35 ^∘C. Further-

more, soil pH is also a chief factor that affects the biodegradation of pesticides. The

biodegradation of compounds will be done by certain enzymes produced by the

microbes. The enzyme secreting bacteria will have optimum pH between 6.5 and

7.5 and enzymes are also pH-dependent. Soil pH will also stimulate the pesticide

adsorption. It also influences the absorption of pesticide fragments on organic and