2013 http://informahealthcare.com/mcb ISSN: 1040-841X (print), 1549-7828 (electronic) Crit Rev Microbiol, Early Online: 1–9 ! 2013 Informa Healthcare USA, Inc. DOI: 10.3109/1040841X.2013.763222 REVIEW ARTICLE Microbial degradation of an organophosphate pesticide, malathion Baljinder Singh 1 , Jagdeep Kaur 2 , and Kashmir Singh 2 1 Punjab Pollution Control Board, Patiala, Punjab, India and 2 Department of Biotechnology, Punjab University, Chandigarh, Punjab, India Abstract Organophosphorus pesticide, malathion, is used in public health, residential, and agricultural settings worldwide to control the pest population. It is proven that exposure to malathion produce toxic effects in humans and other mammals. Due to high toxicity, studies are going on to design effective methods for removal of malathion and its associated compounds from the environment. Among various techniques available, degradation of malathion by microbes proves to be an effective and environment friendly method. Recently, research activities in this area have shown that a diverse range of microorganisms are capable of degrading malathion. Therefore, we aimed at providing an overview of research accomplishments on this subject and discussed the toxicity of malathion and its metabolites, various microorganisms involved in its biodegradation and effect of various environmental parameters on its degradation. Keywords Carboxylesterase, malaoxon, malathion, microbial degradation History Received 29 October 2012 Revised 14 December 2012 Accepted 31 December 2012 Published online 26 February 2013 Introduction Malathion [S-(1,2-dicarbethoxyethyl)-O, O-dimethyldithio- phosphate], also known as carbophos, maldison and mercap- tothion is a nonsystemic, wide-spectrum organophosphorus pesticide used in public health, residential, and agricultural settings (Singh et al., 2012a). Malathion is suited for the control of sucking and chewing insects of fruits and vegetables, mosquitoes, flies, household insects, animal parasites (ectoparasites), and head and body lice. Malathion is used in veterinary medicine (Osweiler et al., 1984) and also as an anti-infective agent (Wester & Cashman, 1989) to control insect vector-borne diseases such as malaria, dengue and yellow fever. Organochlorine pesticides are banned in many countries and therefore organophosphate pesticides (OPs) such as malathion are largely used for public health and agricultural purposes. Today, the pesticides industry in India comprises more than 125 basic producers of large and medium scale and more than 500 pesticide formulations (Singh et al., 2012a). Pesticide formulations include dusting powders having a major share (85%) in the market followed by water-soluble dispersible powder and emulsification concentrates (Abhilash & Singh, 2009). Malathion is formulated as an emulsifiable concentrate (EC), a dust, a wettable powder, a pressurized liquid, and as ready-to-use liquids used for ultra-low-volume application. Agrisect, Atrapa, Bonide, Prentox, Clean Crop malathion, Acme malathion, Black Leaf malathion spray, Eliminator, Fyfanon and Gowan malathion dust are examples of common product names of malathion. Malathion comes in two forms: a pure form of a colorless liquid and a technical-grade solution (brownish-yellow liquid), which generally have a specific gravity (1.23 at 25  C), vapour pressure at 30  C (3.38  10 6 mm Hg) solubil- ity in water (130 mg L 1 ) partition coefficient (2.7482). Technical-grade malathion (the grade that is usually used for agricultural purposes) may contain up to 11 impurities formed during its production and/or storage, some of these impurities, such as isomalathion, have been found to be significantly more toxic than malathion itself or to potentiate the toxicity of malathion (Uygun et al., 2007). Malaoxon is an oxygen analogue of malathion and it can be found either as an impurity in malathion, or generated during the oxidation of malathion in water, air or soil (Durkin, 2008; Singh et al., 2012b). Malaoxon is 60 times more acutely toxic than malathion but it breaks down quickly than malathion (http://www.bionity.com/en/encyclopedia/Malathion.html). Toxicity of malathion Malathion was recognized as the first organophosphorous insecticide with highly selective toxicity (Goda et al., 2010; Shan et al., 2009; Singh et al., 2012a). The Environment Protection Agency (EPA), has classified malathion as a toxicity class III pesticide and allowed a maximum amount of eight parts per million (ppm) of malathion to be present as a residue in specific crops used as foods (U.S. EPA., Office of Pesticide Programs 1988). In a green house study malathion applied at recommended rates was easily detected on plant surfaces after 9 weeks of spraying (Delmore & Appelhans, 1991). Malathion is absorbed by practically all routes including the gastrointestinal tract, skin, mucous membranes, and lungs (Indeerjeet et al., 1997). Malathion is an organophosphate Address for correspondence: Dr Kashmir Singh, PhD, Department of Biotechnology, Panjab University, Sector 14, Chandigarh 160014, Punjab, India. E-mail: kashmirbio@pu.ac.in Critical Reviews in Microbiology Downloaded from informahealthcare.com by 115.111.184.44 on 02/26/13 For personal use only.