Plant Based Packages for the Phytomonitoring and Phytoremediation of Lindane
By: Vishal Tripathi1, P.C. Abhilash1*, Nandita Singh2**
Lindane, the γ- isomer of hexachlorocyclohexane (γ-HCH) was one of the widely used organochlorine insecticide worldwide during the past five decades. Initially, technical HCH consisting of five major isomers such as α-HCH (60-70 %), β-HCH (5-12 %), γ-HCH (10-12 %), δ-HCH (6-10 %), and ε-HCH (3-4 %) was used for agricultural applications. However, later it was recognized that only γ-HCH has the insecticidal properties. As it was possible to isolate and purify the γ-HCH from the technical HCH, the utilisation of γ isomer peaked later under the trade name of Lindane for the large scale use as a pesticide, pediculicide and scabicide.
Manufacturing of lindane also generates large amount of waste isomers commonly called as HCH muck. Approximately 8 to 12 tonnes of HCH muck is generated during the production of a ton of lindane. This large amount of HCH muck is mostly dumped near the production facilities. These stockpiles of the waste are not secured and may cause detrimental impacts to the environment due to leaching and volatilisation, as lindane along with its other isomers is highly persistent in nature, possessing bioaccumulative, carcinogenic, endocrine disrupting properties and also the ability to undergo long range atmospheric transport. Thus it could also contaminate the distant sites and cause toxicity to the non-target organisms as well. The uncontrolled and injudicious use of lindane and the technical HCH for the past half-decade has polluted almost all the spheres of the environment globally. Today it has become one of the most common pesticide to be detected from diverse environmental samples . This was the reason that Lindane (industrial γ-HCH) and its two key waste isomers α-HCH, and β-HCH, were included in the Stockholm list of persistent organic pollutants (POPs) for global elimination. The parties to the Stockholm convention have taken legal action to stop the production and use of lindane altogether, however India has got exemption for its use to combat malaria. To this, we would not only have to identify and evaluate the contaminated sites but also have to develop cost effective non-environment invasive technologies for the remediation and ecological restoration of such sites.
Phytomonitoring of Lindane
The extensive application of lindane and mismanagement of its waste isomers has led to widespread pollution of the environment. Thus it is necessary to monitor and evaluate the waste deposit/dump sites for lindane contamination to develop control strategies for the management of such sites. Plants have been used to indicate the contamination level of pollutants as they can be used as a passive sampler for monitoring of contaminated sites. Plants uptake and phytoaccumulate lindane in its various tissues acting as an effective sink. It reveals the level of level of pollutants uptaken by the plants. Thus, plant species can be interesting candidates for monitoring the occurrence of lindane and its contamination level at particular sites. Apart from the level of lindane in the vegetation, plants can be used as indicator of environmental pollution as they can adsorb the pesticide to their root tissues and then further uptake and transfer it to shoot. Plant leaves can also absorb lindane by trapping its atmospheric deposition as it is a volatile compound. Two years monitoring of HCH and its waste isomers in soil and vegetation of lindane manufacturing factory revealed that Lantana camara, Erianthus munja, Calotropis procera, Withania somnifera, Solanum torvum and Achyranthes aspera were the most abundant growing plants in the contaminated site. In the same study it was found that Achyranthes aspera, Calotropis procera, Dalbergia sisso, Erianthus munja, Lantana camara, Solanum torvum, and Withania somnifera were found growing naturally in lindane contaminated soils and accumulated HCH in the leaf samples. These candidate plant species could be easily used for phytomonitoring of lindane contamination as they have the capability to withstand the phytotoxicity of lindane. In other studies we have reported that the plants such as Sesamum indicum, Vigna radiata, Spinacia oleracea, and Jatropha curcas have potential to uptake and accumulate lindane from soil . Thus along with the naturally growing species in lindane contaminated soil Sesamum indicum, Vigna radiata, Spinacia oleracea, and Jatropha curcas could also be tested for phytomonitoring of lindane as they show lindane accumulation even at level of 5 mg/kg of lindane in soil. As the above mentioned plant species also have different life cycle period they could be applied for short or prolonged continuous monitoring of lindane contaminated sites. Short duration plants such as Sesamum indicum, Vigna radiata, Spinacia oleracea, Solanum torvum could rapidly give an idea about the current status of pollutant in soil, their uptake level by plants and whether the residue level is above or below the permissible limits in the edible tissues. Similarly long duration plants such as Dalbergia sisso, Jatropha curcas, Withania somnifera and Erianthus munja could be used for long term monitoring of the restoration of contaminated sites by continuously monitoring the residue level in soil and plants and physical chemical and biological attributes of the soil fertility. The perineal plant species could also be used for monitoring the seasonal variation of lindane concentration in rhizospheric soil and uptake by the plant species and its residual concentration in soil. Thus plant species are important to study the role of plants in distribution of lindane and its isomers in soil-plant system and develop a better understanding of distribution and cycling of lindane and its isomers in terrestrial ecosystems. The phytomonitoring of lindane and its isomers will help in assessing the risk of its transfer to the trophic chain. It will also help in development plant based sustainable remediation technologies for development of phytoremediation techniques that can be applied to lindane contaminated soils.
Ecological profiling of a contaminated system is the necessary requirement for adapting any in situ restoration activities. We recently developed a cost effective, simple, adequate and consistent inventorying, monitoring ecological profiling method for the screening and characterization of a soil site contaminated with lindane and its isomers. Plant diversity, microbial biomass, total organic carbon, soil dehydrogenase activity, pesticide concentration in soil and plant samples as well as the occurrence of ecologically sensitive species such as earthworms, honey bees and butterflies were taken as parameter for a complete ecological profiling of pesticide contaminated site near lindane producing industry in Lucknow North India. All these parameters clearly indicate that soil is heavily polluted with lindane and its isomers and requires consistent inventorying and monitoring. This ecological method is simple, adequate and consistent for knowing the extent and level of contamination of HCH isomers in soil, understanding the adaptive capacity of the contaminated soil system and for the in situ restoration of contaminated soil sites by adopting suitable methodical frame works.
Phytoremediation of Lindane
Plant based remediation technologies offer a more sustainable approach for the clean-up of the contaminated soils in comparison to their physicochemical counter parts. Apart from remediation plant based technologies also offers biomass, biofuel for bioeconomy, aesthetic value, timber and fibre for the stake holders. Plants can substantially support the remediation of lindane contaminated land as they can withstand its toxicity and also can dissipate it from the soil. Plants can help in the process of remediation by variety of mechanisms like immobilization, removal, phytovolatalization via evapotransportation through leaves, phytouptake and enzymatic degradation and microbial assisted rhizoremediation. Plants roots run down to several miles per acre, increasing the root surface area thus increasing the rhizospheric domain and more effective binding of soil resulting in reduced soil erosion. Due to increased root area the associated soil comes under the rhizosecretion thus increasing the carbon sources and others sources in soil enhancing microbial activity. The increased microbial activity helps in enhanced rhizoremediation of the organic pollutants like lindane.
Legumes were found to be more tolerable to the contamination of HCH in soil. Leguminous plant are known for their symbiotic relationship with Nitrogen fixing bacteria, it might help in easier supply of the nitrogen leading to increased chlorophyll synthesis in legumes, as nitrogen is a key component of the chlorophyll molecule and not easily available to plants. Though the leguminous crops seem to have tolerance towards lindane, however use of agricultural crops cannot be suggested for remediation as lindane has bioaccumulative property and its consumption may lead to the contamination of the food chain. Alternatively use of flowers, biofuel and other non-edible crops of economic importance should be promoted for the remediation of lindane contaminated soils. Using non edible crops of economic importance can provide socio-economic benefits by diversifying the regional manufacturing into newer products that may offer employment to local labour helping to build a bioremediation based value-added industry.
1Institute of Environment & Sustainable Development, Banaras Hindu University, Varanasi 221005, India
- *E-mail: (firstname.lastname@example.org; email@example.com)
2Plant Ecology & Environmental Science Division, CSIR-National Botanical Research Institute, Lucknow 226001, India
- **E-mail: (firstname.lastname@example.org)