Bioremediation of Malathion from Environment for Pollution Control
Use of pesticide is growing day by day and thus enhances the environmental pollution and hazards. Bioremediation of pesticides is a relatively new technology, which is going through intense study as of recent decades. The process is dealing either with the degradation of the pesticide molecule to smaller compounds, which may be toxic/non-toxic itself or the removal of the pesticide molecule by simple absorption/adsorption mechanism. Malathion is a widely used organophosphate pesticide. Often they are used in excess to their safe limit and they will leach from soil to surface and ground water thus causing health hazards. Malathion residue can be removed by any of the physical, chemical and biological methods but bioremediation was found to be more efficient tool for removal of the Malathion residue from soil and water.
February 15, 2010; Accepted: April 02, 2010;
Published: July 01, 2010
A single pesticide cannot control all the pests. The first chemical used to
combat plant pathogens fungi and to poison plant-eating insects were inorganic
materials containing copper, sulfur, arsenic and other substances. Some naturally
occurring organic insecticides e.g., Protenone were also used. These eventually
entered in soil and toxic elements some times accumulated to undesirable levels.
Synthetic organic chemicals, many of which contained phosphorus, mercury, arsenic
and chlorine bound to the organic molecules, largely replaced these early pesticides.
These organic pesticides were much more specific in their action and were instrumental
in raising crop yields. They too entered the soil. All organic compounds that
occur naturally and most of those synthesized by man are decomposed in soil
by a combination of chemical and biological action but the rate of decomposition
vary with the compound. Organic pesticides are attacked by soil bacteria of
several genera and eventually decomposed. But this is not true in case of a
large number of synthetic chemicals. In recent years people have added to the
number of slowly degradable or non-biodegradable compounds in the soil by adding
different pesticides in many parts of world. The chemical nature of herbicides
and insecticides covers an extremely broad range of organic compounds, organic
acids, nitro phenols, chlorinated organic acids and other organic substances
(William et al., 1973).
Malathion is an organophosphorus pesticide having molecular formula C10H19O6PS2
and structure shown in Fig. 1 (Tomlin, 1994).
It is an insecticide used for many insects including aphids, spider mites,
scale insects, house fly and mosquitoes as well as large number of other sucking
and chewing insects attacking fruits, vegetables, ornamentals and stored products.
It has a cholinesterase activity and it kills the insects by affecting their
||Chemical structure of malathion [S-1, 2-bis (ethoxycarbonyl)
ethyl o,o-dimethyl phosphorodithioate]
Malathion comes in two forms; a pure form of colorless liquid and a technical
grade solution (brownish-yellow liquid), which contains Malathion (greater than
90%) and impurities in a solvent. The technical grade is approximately 10 times
stronger in causing death to laboratory animals. The FDA and EPA allow a maximum
amount of 8 mg L-1 of Malathion to be present as a residue an specific
crops used as foods. Because Malathion can be dangerous to humans, EPA requires
that a certain time must pass between the time of application of the insecticide
and entry by a worker into a field where the chemical has been applied. Usually
at least 12 h must pass between application and entry, but in some cases such
as when workers are entering a field to hand harvest or hand prune the crops,
time period as long as 6 days must pass between application and entry into the
field. In this way, exposure to Malathion can be controlled and accidental exposures
can be prevented (ATSDR, 2001).
Malathion contamination may be originated from two sources.
These sources arise from daily/routine handling operation and waste disposal.
These include means of transportation, agrochemical operation. These have definite
identity with constant volume and fixed composition of the effluent discharged.
The sources are diffusion, situated far beyond the sight having waste of
unknown composition and volume. Also arises from the course of routine operating
practices, which include application of pesticides to the field and tank loading,
mixing and rinsing (Boopathy, 2000). General means of
removal of pesticides from soil and water are adsorption, photodecomposition,
leaching and volatilization. But the advantage of the Bioremediation process
is, it avoids the use of costly chemicals and lengthy steps of physical and
chemical removal process.
Bioremediation process can be either biodegradation or biosorption. When biodegradation occurs it can follow any of the following mechanisms.
||The pesticide can serve as a substrate for growth and energy
||The xenobiotic compound can undergo co-metabolism, i.e., the
microorganism can transform the pesticide but cannot derive energy for growth
||The entire pesticide molecule or an intermediate of it can
be conjugated with naturally occurring compound
||The pesticide is incorporated and accumulated within the organism
When biosorption occurs the pesticide molecule will be either absorbed in to the cell or it will remain adsorbed on the surface of the organism.
Bioremediation of Malathion
Malathion is degraded by carboxyesterase enzyme and it is detected in several
fungi like Aspergillus sp., Penicillum sp. and Rhizoctonia
sp. (Mostafa et al., 1972). Omar
(1998) and Hasan (1999) also demonstrated the same
type of fungal utilization and degradation of Malathion. Several Aspergillus
sp. showed greatest potential for utilizing Malathion as phosphorous and
carbon source. Not only the fungal cells but also the bacterial cells are also
capable of biodegradation of Malathion (Kamal et al.,
2008) found that a strain of Bacillus thuringiensis MOS-5(Bt) isolated
from agricultural waste water was able to degrade Malathion cometabolically.
The major degraded products were Mal-Monocarboxylic Acid (MMA) and Mal-Dicarboxylic
Acid (MDA). Xie et al. (2009) found a bacterium,
Acinetobacter johnsonii MA19, that could degrade Malathion with cometabolism.
The bacterium A. johnsonii MA19 was found to have the capability for
malathion biodegradation and environmental bioremediation when some suitable
conventional carbon sources are supplied Tsezos and Bell
(1991) studied the fate of Malathion following interaction with live and
dead microbial biomass of Rhizopus arrhizus. The experimental results
from equilibrium, kinetic and carbon-14 studies suggested that Malathion is
adsorbed and then chemically decomposed by the microbial biomass into water
soluble products. This chemical transformation that was effected by the microbial
biomass is not an active metabolic process as it is also exhibited by dead cells
and isolated microbial cell walls. Cells of isolated Bacillus sp. S14
was found to have the capability of removal of Malathion from dilute aqueous
solution and the capability of this removal by dead cell (Adhikari
et al., 2010) indicates that this process is not an active metabolic
process but fully controlled by the functional groups present on the microbial
Bioremediation technique for removal of Malathion is nothing but a very effective and interesting field with the advantages like it is a natural process with less cost requirement compared to other methods and this process can be applicable at the place where the problem is located. Although, this technique has some disadvantages like formation of undesirable degraded products, desorption of Malathion and disposal of it, disposal of cells containing Malathion in adsorbed/absorbed condition. These problems can be solved with further monitoring of the process and there are lots of scopes for research work in this field.
ATSDR, 2001. ATSDR public health statement, September 2001. US. Department of Health and Human Services, pp: 2-3.
Adhikari, S., P. Chattopadhyay and L. Ray, 2010. Biosorption of malathion by dry cells of a isolated Bacillus sp. S14. Chemical Speciations and Bioavailibility (Accepted on January 2010), pp: 22.
Boopathy, R., 2000. Factors limiting bioremediation technologies. Bioresour. Technol., 74: 63-67.
CrossRef | Direct Link |
Hasan, H.A.H., 1999. Fungal utilization of organophosphate pesticides and their degradation by Aspergillus flavus and A. sydowii in soil. Folia Microbiol., 44: 77-84.
Direct Link |
Kamal, M.Z., A.H. Nashwa, A. Fetyan, A.M. Ibrahim and E.N. Sherif, 2008. Biodegradation and detoxification of malathion by of Bacillus thuringiensis MOS-5. Austr. J. Basic Applied Sci., 2: 724-732.
Mostafa, I.Y., I.M.I. Fakhr, M.R.E. Bahig and Y.A. El-Zawahry, 1972. Metabolism of organophosphorus insecticides. XIII. Degradation of malathion by Rhizobium spp. Arch. Mikrobiol., 86: 221-224.
Direct Link |
Omar, S.A., 1998. Availability of phosphorus and sulfur of insecticide origin by fungi. J. Opthalmol., 9: 327-336.
Tomlin, C., 1994. The Pesticide Manual: Incorporating the Agrochemicals Handbook. 10th Edn., The Royal Society of Chemistry, United Kingdom.
Tsezos, M. and J.P. Bell, 1991. A mechanistic study on the fate of malathion following interaction with microbial biomass. Water Res., 25: 1039-1046.
William, G., R.A. McBee and K.L. Temple, 1973. Introduction to Microbiology. Jones and Bartlett Publishers Inc., USA.
Xie, S., J. Liu, L. Li and C. Qiao, 2009. Biodegradation of malathion by Acinetobacter johnsonii MA19 and optimization of cometabolism substrates. J. Environ. Sci., 21: 76-82.