Role of Microorganisms in Bioremediation of Pesticides

Introduction

A pesticide can be defined as any substance or mixture of substances that are used for preventing and destroying unwanted pests. Insecticides, herbicides and fungicides are various pesticide used to control different pests (EPA, 2015). Pesticides and agrochemicals, in general, became an important component of worldwide agriculture systems during the last century, allowing for a noticeable increase in crop yields and food production (Alexandratos & Bruinsma, 2012). In modern agriculture practices, the extensive use of pesticides is very frequent to fulfil higher yield requirements. Dispersion of pesticide residues in the environment and mass killing of nonhuman biota, such as bees, birds, amphibians, fish, and small mammals, were also reported (Paoli et al., 2015; WHO, 2017). The problem of environmental contamination by pesticides goes beyond the locality where it is used. The agricultural pesticides that are exhaustively applied to the land surface travel long distances and can move downward until reaching the water table at detectable concentrations, reaching aquatic environments at significantly longer distances. Therefore, the fate of pesticides is often uncertain, they can contaminate other areas that are distant from where they were originally used. Thus, decontaminating pesticide-polluted areas is a very complex task (Gavrilescu, 2005). In addition to a high risk of contamination in ecosystem, pesticide also has chronic threats to human life, caused by long term exposure to pesticides. Pesticides can cause hormonal disruption, diminished intelligence, and reproductive abnormalities in humans (Gupta, 2004). Thus, the degradation of persistent pesticides is very essential for the environment (Hodaifa et al., 2009).

Earlier techniques or technologies which were used to remove pesticides from environment were landfills, recycling, pyrolysis etc., but these have opposing effects on the environment by formatting toxic intermediates (Debarati et al., 2005). All these methods have proved to be expensive and difficult in case of pesticides. One promising treatment method to remove or degrade toxic components from environment, is bioremediation. Bioremediation is the engineered process of toxic removal from environment. This is a promising alternative to physico-chemical methods of remediation, because it is reasonable and can selectively gain complete destruction of toxic components (Hussain et al., 2009). The use of microorganisms for the degradation and detoxification of numerous toxic pesticides, proved to be an efficient tool to decontaminate the polluted sites in the prevailing environment (Mervat et al., 2009). Pesticides in soil and water can be biodegraded and is the primary mechanism of pesticide breakdown and detoxification in many soils (Surekha et al., 2008). Thus, biological decontamination methods are preferable to conventional approaches because, in general, microorganisms degrade numerous environmental pollutants without producing toxic intermediates (Pieper & Reineke, 2000; Furukawa, 2003). Microbes which were commonly reported in pesticides bioremediation include Pseudomonas sp., Bacillus sp, Klebsiella sp, Pandoraea sp, Phanerochaete Chrysosporium, Mycobacterium sp. Agrocybe semiorbicularis, Auricularia auricula, Coriolus versicolor, Dichomitus squalens, Flammulina velupites, Hypholoma fasciculare, Pleurotus ostreatus, Stereum hirsutum, and Avatha discolour. (Colberg & Young, 1995). These microorganisms have shown their ability to degrade various pesticide groups like phenylamide, triazine, phenylurea, dicarboximide, chlorinated and organophosphorus compounds. In this chapter we are going to discuss about different toxic pesticide with their harmful effects and also mechanism of microorganism involved in biodegradation and bioremediation of Pesticide.