Seasonal variation of HCH isomers in open soil and plant-rhizospheric soil system of a contaminated environment

Abstract

Lindane, technically 1, 2, 3, 4, 5, 6-hexachlorocyclohexane (gamma- HCH), is the most commonly detected organochlorine pesticide from diverse environmental compartments. Currently, India is the largest consumer and producer of lindane in the world. The production of lindane results in the generation of large quantities of waste HCH isomers (mainly alpha-, beta- and delta-). All these isomers are toxic and have a long-range environmental transport potential. The aim of this study was to monitor the seasonal variation of HCH isomers in an open soil-plant-rhizospheric soil system of a contaminated industrial area. For this, selected plant species and their rhizospheric soil (soil samples collected at a depth range of 0-45 cm near to the root system) and open soil samples (soil samples collected (0-30 cm depth) from 1-1.5 m away from the plant root system) were collected for 2 years (two summer seasons and two winter seasons). Seven plant species along with their rhizospheric soil and open soil samples were collected seasonally from different parts of the industry. Plant samples were separated into root, leaf and stem. HCH isomers in plant and soil samples were extracted by matrix solid-phase dispersion extraction (MSPD) and Soxhlet extraction, respectively, followed by GC-ECD. The seasonal difference in occurrence of HCH isomers in plant samples with their respective soil-system was studied by multivariate statistical approaches. The mean concentration of total HCH in plant samples, open soil and rhizospheric soil samples were found in the range of 14.12 to 59.29 mg kg(-1); 38.64 to 104.18 mg kg(-1) and 8.38 to 26.05 mg kg(-1), respectively. Cluster grouping reveals that S. torvum and W. somnifera can accumulate more HCH than other studied species. There was a marked seasonal difference in the occurrence of HCH isomers in plant samples (p < 0.05) and open soil samples (p < 0.01). Comparatively higher levels of HCH isomers were detected from plant samples during summer, while higher levels of HCH isomers were detected from soil samples during the winter season. There was no significant difference in seasonal variation of HCH isomers in rhizospheric soil samples; however, total HCH in rhizospheric soil samples were 4 to 5-fold lower than the open soil samples. The total concentration of HCH isomers in roots is linearly related to their rhizospheric HCH level. HCH isomers were detected in open soil, plants and rhizospheric soil samples. Monitoring studies clearly revealed that the above-mentioned industrial area is contaminated with all major isomers of HCH. Occurrence of all these isomers in the study area point out the lack of sustainable management practices of this industry for protecting the area from hazardous waste. The analytical results confirmed that accumulation depends upon the plant species, soil and climatic conditions. Recently, alpha-, beta- and gamma-HCH have been nominated by the POPs Reviewing Committee for inclusion into the Stockholm Convention to address the HCH contamination on a global level. Therefore, there is an urgent need to stop the production of lindane and remediate contaminated soil sites. Based on the monitoring studies, the promising species like W. somnifera and S. torvum may be selected for the on-site phytoremediation of HCH-contaminated soil. The mismanagement of HCH residues from the organochlorine industry and their contemporary relevance often after decades of their deposition is one key example demonstrating the necessity to evaluate the waste deposits of the respective organochlorine productions and need for a strict waste management, and the necessity of an integrated pollution prevention and control strategy for the whole organochlorine industry including also the developing countries.