Endosulfan
Endosulfan is a persistent, toxic broad-spectrum organochlorine insecticide and acaricide used on food and non-food crops. To overcome the problem of hydrophobicity of endosulfan, surfactants play a major role in soil remediation.
Pesticide played a major role during green revolution to attain food sustainability in the different part of the world. Presently most of the pesticides have banned due to persistent, bioaccumulative and long range transport nature. Endosulfan is one of the pesticides which is still frequently used in controlling different pests of the field crops such as cotton, fruits, vegetables, cereals etc. But presence of its residue in food commodities and environmental samples threaten human health and cause imbalance in natural processes. Endosulfan is of environmental concern because pesticide applied to agriculture areas can be drained to nearby water bodies and reached to non target organism. In present scenario remediation of pesticide contaminated sites/soils are the cause of serious concern throughout the world. The use of genetically engineered plants to degrade or remove pesticide has emerged as a powerful technology for in situ remediation. An understanding of mechanisms of how palnts biodegrade pollutants and how they interact with the environment is important for successful implimentation of this technology. Recent studies have demonstrated that engineered plants produce pesticide-degrading enzymes that can mineralize different groups of pesticides and their metabolites with greater efficiency. In this paper we have tried to portray the most recent advancement in biotechnological approaches for enhancing the potential pof plants for the enhanced metabolism, degradation and phytoremediation of endosulfan and its metabolites through the induction of catabolic pathways, characterization and transfer of pesticide-degrading genes.
Present scenario of pesticides
In present scenario pesticides are the cause of serious concern throughout the world. Among various chlorinated pesticides, intensive attention has been given to endosulfan because it is not only highly toxic but also widely used in large quantities in many countries as a broad-spectrum insecticide.
Although plants have the inherent ability to detixify organic pollutants but they generally lack the catabolic pathway for the complete degradation of these compounds compared to microorganisms. Disposal of pollutants accumulating plants is also a serious concern. Hence the feasibility of phytoremediation as an approach to remediate environmental contamination is still somewhat in black box. Studies shows that engineered plants with genes in plants which involved in metabolism, uptake, or transport of specific pollutants. Futhermore, the expression of suitable genes in root system enhances the rhizodegradation of highly recalcitrant compounds like PAHs, PCBs, OCPs, HCH, endosulfan etc. Genes from human, microbes, plants, and animals are being used successfully for this purpose. One of the promissing developments in transgenic technology is the insertion of multiple genes (for phase 1 metabolism (cytochrome P450s) and phase 2 metabolism (GSH, GT etc.) for the complete degradation of the persistant organic pollutants within the plant system. In addition to the use of transgenic plants overexpressed with P450 and GST genes, various transgenic plants expressing bacterial genes can be used for the enhanched degradation and remediation of herbicides, explosives, PCBs etc. Another approach to enhancing phytoremediation ability is the construction of plants that secrete chemical degrading enzymes into the rhizosphere. Recent studies revealed that accelerated ethylene production in response to stress induced by contaminants is known to inhibit root growth and is considered as major limitation in improving phytoremediation efficiency. However, this can be overcome by the selective expression of bacterial ACC determinase (which regulates ethylene level in plants) in plants together with multiple genes for the different phases of xenobiotic degration. In this paper we have tried to portray the most recent advancement in biotechnological approach for enhancing the potential of plants for the enhanched metabolism, degradation and phytoremediation of endosulfan and its metabolites through the enduction of catabolic pathways, characterization and transfer of pesticide-degrading genes.
Phytoremediation
Phytoremediation is an emerging technology that promises effective and inexpensive cleanup of contaminated hazardous waste sites.
Remediation of Endosulfan
Remediation of endosulfan in water using different aquatic plants showed that Salvinia molesta is more efficient in endosulfan removal.
Source: Scientific Research Publishing
Source: http://file.scirp.org/Html/4-6701826/5f1684f3-954e-431b-a638-fcdd7acb2366.jpg
Phytoremediation Using Selected Plant Species
Source: http://file.scirp.org/Html/4-6701826/8326f6cc-62e3-4ccd-bcbe-48e0aa0f1ac3.jpg
The effectiveness of commonly available aquatic plant species such as Hydrilla verticillata and Salvinia minima to remediate endosulfan contaminated water was investigated. Also the terrestrial plant species such as Spinach (Spinacia oleracea) and Tomato (Solanum lycopersicum) were transplanted into soil and artificially spiked with endosulfan. Water and soil samples were analyzed at different intervals to find out the total recoverable endosulfan.
Rhizoremediation of endosulfan:
- Insertion of pollutants degrading genes into the root system of suitable plant species for the enhances rhizospheric secretion.
- If endosulfan degrading gene causes enhanced oxidation of endosulfan, than secretion of endosulfan sulfate monooxygenase I and endosulfan hemi sulfase occurs due to which endosulfan sulfate and endosulfan hemisulfate and endosulfan alcohol is formed.
- When hydrolysis of endosulfan enhances due to endosulfan degrading genes, which results enhanced secretion of endosulfansulfate hydrolase enzyme and endosulfan doil is formed.
- Endosulfan doil hydrolase and endosulfan doil hydrogenase enzymes cause almost completew degradation of endosulfan to non toxic metabolite endosulfan hydroxy ether and endosulfan lactone.
The advantage of this method is that the plants do not need to take up the pollutants in order to detoxify them; instead, the secreted enzymes can degrade the pollutants in rhizospheric zone.
Degradation pathway in plants:
Endosulfan degradation pathway in plants envolved mainly three biochemical process:
- Conservation or transformation (Phase I)
- Conjugation (Phase II)
- Compartmentalization (Phase III)
Endosulfan isomers are converted into less toxic metabolites during I reaction. During this phase endosulfan isomers are converted into less hydrophobic metabolites such as endosulfan diol, endosulfan alcohol through N-, O-, and S-dealkylation, aromatic and aliphatic hydroxylation, epoxidation, peroxidation, oxidative desulfuration, sulfoxidation or reducing by cytochrome P450s. The second phase involved conjugation of a endosulfan metabolite (endosulfan ether and endosulfan lactone) to a sugar, amino acid or glutathione, which increase the water solubility and reduces toxicity compared with parent compound. Generally phase II metabolites have a little or no phytotoxicity and may be stored in cellular orgenelles. Finally, in phase III, conjugated metabolites are deposited in vacuoles or cell walls.
Factors affecting pesticide fate and transport
Source: http://agrikhalsa.bizhat.com/pests.htm
Environmental Effects
The two isomers (alpha and beta) have different degradation times in soil. Under neutral conditions, the half-life for the alpha isomer is 35 days, and it is 150 days for the beta isomer. These two isomers will persist longer under more acidic conditions. The compound is broken down in soil by fungi and bacteria. Endosulfan does not easily dissolve in water, and has a very low solubility. It has a moderate capacity to adhere or adsorb to soils. Transport of this pesticide is most likely to occur if endosulfan is adsorbed to soil particles in surface runoff. It is not likely to be very mobile or to pose a threat to groundwater. It has, however, been detected in California well water In raw river water at room temperature and exposed to light, both isomers disappeared in 4 weeks. Large amounts of endosulfan can be found in surface water near areas of application. It has also been found in surface water throughout the country at very low concentrations.
In plants, endosulfan is rapidly broken down to the corresponding sulfate. On most fruits and vegetables, 50% of the parent residue is lost within 3 to 7 days. Endosulfan and its breakdown products have been detected in vegetables (0.0005-0.013 ppm), in tobacco, in various sea foods (0.2 ppt-1.7 ppb), and in milk.
Source: www.csulb.edu
Toxicity to organisms
Endosulfan is highly to moderately toxic to birds with a reported oral LD50 values in mallards ranging from 31 to 243 mg/kg and in pheasants ranging from 80 to greater than 320 mg/kg. Endosulfan is very highly toxic to fish species and aquatic invertebrates. Endosulfan is moderately toxic to bees. Endosulfan was detected in adipose tissue and blood of animals in the Arctic and the Antarctic. It has also been detected in the blubber of minke whales and in the liver of northern fulmars.
Precautions
Exposure to endosulfan most commonly occurs by eating food contaminated with it. Endosulfan has been found in some food products such as oils, fats, and fruit and vegetable products. People can be also exposed to endosulfan by skin contact with contaminated soil or by smoking cigarettes made from tobacco that has endosulfan residues in it.
Sources
- Dept of Health and Human Services. ToxFAQs. ATSDR. Accessed 06.08.07.
- Extension Toxicology Network. Pesticide Information Profiles - Endosulfan. Etoxnet. (1996). Accessed 10.07.10.
- PAN Pesticides Database - Chemicals - Endosulfan. Pesticideinfo.org. Accessed 06.08.07.
- PAN Pesticides Database - Chemicals - Endosulfan. Pesticideinfo.org. Accessed 10.07.10.
- International Chemical Safety Card. ICSC. Endosulfan. (1998). Accessed 10.07.10.
- Agency for Toxic Substances and Disease Registry. ATDSR. Public health statement -Endosulfan (2000).
- Cerrillo I, Granada A, Lopez-Espinosa MJ, Olmos B, Jimenez M, Cano A, Olea N, and Fatima Olea-Serrano M (2005) Endosulfan and its metabolites in fertile women, placenta, cord blood, and human milk. Environ Res 98:233-239.
- Environmental Health News. Accessed 10.12.10.
- Stockholm Convention on Persistent Organic Pollutants - Chemical under review - Endosulfan. Anex E: Supporting document for the draft risk profile on endosulfan. Accessed 10.12.10.
- Environmental Protection Agency. (EPA). "Action to Terminate Endosulfan". Accessed 10.12.10
- http://www.toxipedia.org/display/toxipedia/Endosulfan
