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| Last Updated:: 14/11/2018


Lindane Insecticide
Lindane is an organochlorines insecticide and fumigant which has been used on a wide range of soil-dwelling and plant-eating (phytophagous) insects. It is commonly used on a wide variety of crops, in warehouses, in public health to control insect-borne diseases, and (with fungicides) as a seed treatment. Lindane is also presently used in lotions, creams, and shampoos for the control of lice and mites (scabies) in humans. Lindane used both as an agricultural insecticide and as a pharmaceutical treatment for lice and scabies.
Lindane health and environmental hazard has been viewed mainly through its ingestion pathway, since Lindane was used on crops, a key element of a food chain. While this prioritization is understandable, inhalation is the main risk factor to workers in case of building decontamination or demolition. It is worth mentioning that while building materials are the objects of decontamination, it is the air quality that defines inhalation hazard. From this prospective, it is important to draw correlations between the concentrations of Lindane (and/or other contaminants which may be present) on the surface and the concentrations in the vapor phase.
Technical Lindane
Technical Lindane is comprised of the gamma-isomer of hexachlorocyclohexane, HCH. Five other isomers (molecules with a unique structural arrangement, but identical chemical formulas) of HCH are commonly found in technical Lindane, but the gamma-isomer is the predominant one, comprising at least 99% of the mixture of isomers. Data presented in this profile are for the technical product unless otherwise stated; Lindane, HCH, or BHC refers to technical Lindane, i.e., Gamma-hexachlorocyclohexane. Gamma-HCH has been shown to be the insecticidal effective isomer.
Lindane may also be found in formulations with a host of fungicides and insecticides. It is available as a suspension, emulsifiable concentrate, fumigant, seed treatment, wettable and dust able powder, and ultra low volume (ULV) liquid.
Enzymatic basis of Lindane degradation in microorganisms
Enzymes are mainly involved in the degradation of pesticides, both in the target organisms, through intrinsic detoxification mechanisms and evolved metabolic resistance, and in the wider environment, via biodegradation by soil and water microorganisms. Among the various enzymatic groups, haloalkane dehalogenases play a pivotal role in the dehalogenation of HCH isomers. Genes encoding the enzymes responsible for degradation of Lindane have been cloned and studied extensively. The two key enzymes responsible for the dehalogenation was encoded as; lin A and lin B genes. The lin A-encoded HCH dehydrochlorinase Lin A (EC 4.5.1) mediates the initial two steps of dehydrochlroination of Lindane, which is further catabolised by the remaining enzymes encoded by the lin operon (including Line). However, the structure of Lin A has not yet been resolved, but it is predicted to belong a novel super family which includes scytalone dehydratase and naphthalene dioxygenase. The reaction mechanism proposed for Lin A is dependent upon a catalytic dyad (Asp25 and His73), where a proton is abstracted from HCH by His73 followed by release of a chloride ion and formation of a carbon-double bond. This reaction is then repeated with the product (pentachlorocyclohexane) to ultimately yield 2, 3, 5, 6-tetrachloro- 1,4-cyclohexadiene. Lin B is a halokalkane dehalogenase of the c/b-hydrolase fold family of enzymes and mediates the two sequential chlorohydrolase reactions converting 2,3,5,6-tetrachloro-1,4-cyclohexadiene to 3,6,-dichloro-2,5-dihydroxy-1,4-cyclohexadiene. These are the reactions immediately following those of Lin A with HCH. Lin B not only detoxifies the product of Lin A but can also act directly upon Lindane. The reaction mechanism of Lin B involves nucleophilic attack from the aspartic acid residue 108 at an electrophilic carbon of the substrate, followed by formation of a covalent alkyl-enzyme intermediate. The catalytic aspartic acid is then regenerated through nucleophilic attack at Asp 108 upon activation of a water molecule by histidine.
Source: Comparative bioremediation potential of four rhizospheric microbial species against Lindane, P.C. Abhilash et al.
Rhizoremediation of Lindane
Rhizoremediation, the degradation of contaminants by microorganisms in the rhizosphere (the soil affected by plant roots), holds great potential for the remediation of contaminated soil. In the ‘rhizosphere effect’ plants provide nutrients in the form of root exudates, oxygen and favorable redox conditions to soil microorganisms, and this in turn results in increased bacterial diversity, population density and activity compared with bulk soil. Moreover, plants may be used as bio-injectors of pollutant-degrading microorganisms into contaminated soil described an approach to select bacteria able to degrade a pollutant and colonize the rhizosphere of plants. This approach involves a two-step enrichment process in which bacteria are isolated in liquid culture from the roots of plants growing in contaminated sites, and these cultures are used to re-colonize plant roots so that biodegrading microbes can be isolated once again. Example: We can use two-step process to enrich HCH-degrading bacteria able to colonize the roots of maize plants. We established enrichments to isolate bacteria capable of degrading not only insecticidal ?-HCH, but also recalcitrant ß-HCH and growth-inhibiting d-HCH. In particular, we attempted to enrich ‘rhizodegraders’, root-colonizing bacteria able to degrade HCH isomers. The soil samples came from Ansio (Vizcaya, Spain) and Chemnitz-Schweizerthal (Germany), and varied greatly in levels of HCH contamination and the presence of the various HCH isomers. At some points the level of HCH was >mg of HCH per gram of soil.
Source: Rhizoremediation of Lindane by root-colonizing Sphingomonas, Dietmer Boltner et al.
Mode of dose transfer of Lindane
Environmental Fate
Remediation of endosulfan in water using different aquatic plants showed that Salvinia molesta is more efficient in endosulfan removal.
Source: Scientific Research Publishing
Breakdown in soil and groundwater: Lindane is highly persistent in most soils, with a field half-life of approximately 15 months. When sprayed on the surface, the half-life was typically much shorter than when incorporated into the soil. It shows a low affinity for soil binding, and may be mobile in soils with especially low organic matter content or subject to high rainfall. It may pose a risk of groundwater contamination. The pesticide has been found in a significant number of groundwater samples in New Jersey, California, Mississippi, South Carolina, and in Italy at concentrations of less than 1 ug/L (ppb). Lindane is a contaminant in water in the Great Lakes at very low concentrations as well.
Breakdown in water: Lindane is very stable in both fresh and salt water environments, and is resistant to phytodegradation. It will disappear from the water by secondary mechanisms such as adsorption on sediment, biological breakdown by micro flora and fauna, and adsorption by fish through gills, skin, and food.
Breakdown in vegetation: Plants may pick up residues from not only direct application, but through water and vapor phases. Persistence is seen when plants are rich in lipid content, and crops like cauliflower and spinach will build up less residue than crops like carrots. The metabolism in plants is not well understood, but carrots are estimated to metabolize Lindane with a half-life of just over 10 weeks (based on plant uptake) whereas it may have a half-life in lettuce of only 3 to 4 days.
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