Soil from a Hexachlorocyclohexane Contaminated Field Site Inoculates Wheat in a Pot Experiment to Facilitate the Microbial Transformation of β-Hexachlorocyclohexane Examined by Compound-Specific Isotope Analysis

Abstract

β-Hexachlorocyclohexane (β-HCH) is a remnant from former HCH pesticide production. Its removal from the environment gained attention in the last few years since it is the most stable HCH isomer. However, knowledge about the transformation of β-HCH in soil− plant systems is still limited. Therefore, experiments with a contaminated field soil were conducted to investigate the transformation of β-HCH in soil−plant systems by compound specific isotope analysis (CSIA). The results showed that the δ 13 C and δ 37 Cl values of β-HCH in the soil of the planted control remained stable, revealing no transformation due to a low bioavailability. Remarkably, an increase of the δ 13 C and δ 37 Cl values in soil and plant tissues of the spiked treatments were observed, indicating the transformation of β-HCH in both the soil and the plant. This was surprising as previously it was shown that wheat is unable to transform β-HCH when growing in hydroponic culture or garden soil. Thus, results of this work indicate for the first time that a microbial community of the soil inoculated the wheat and then facilitated the transformation of β-HCH in the wheat, which may have implications for the development of phytoremediation concepts. A high abundance of HCH degraders belonging to Sphingomonas sp., Mycobacterium sp., and others was detected in the β-HCH-treated bulk and rhizosphere soil, potentially supporting the biotransformation.

Uptake and Metabolization of HCH Isomers in Trees Examined over an Annual Growth Period by Compound-Specific Isotope Analysis and Enantiomer Fractionation

“…This was shown in a previous lab pot experiment. 17 The δ 37 Cl values of β-HCH in plants were smaller compared to the muck and soil, and some plant samples were identical to the muck which is also shown for α-HCH.…”

“…16 The transformation of HCHs by plants was identified in several previous studies. 15,17 However, the impact of plants, particularly trees, on the fate of HCHs at field site scales is still unknown because growth conditions in the field are much more complex than under laboratory conditions and could change dramatically during the vegetation period.…”

“…The lambda (Λ) value was used to distinguish different transformation mechanisms in complex systems. 17 Λ is defined as the slope of the regression line of the isotope fractionation of two elements during transformation processes between the source and samples in soil and plant tissues. Therefore, δ 13 C and δ 37 Cl values of HCH in soil and plants were normalized to the HCH source.…”

“…Phytoremediation, based on the interactions of plants and their associated microorganisms, has been recognized as a powerful in situ approach for remediation of organic pollutants in soils . The transformation of HCHs by plants was identified in several previous studies. , However, the impact of plants, particularly trees, on the fate of HCHs at field site scales is still unknown because growth conditions in the field are much more complex than under laboratory conditions and could change dramatically during the vegetation period.…”

Microbial Journey: Mount Everest to Mars

“…Recently, researchers have developed novel analytical concepts for multi-element compound-specific isotope analysis (CSIA) for carbon and chlorine isotope compositions (d 13 C, d 37 Cl) of HCHs [79] in combination with enantiomer fractionation (EF) as quantitative tools to study the uptake and transformation of a-HCH and b-HCH in the complex soil-plant systems to track their source and fate in the environment. They have studied the reactive transport processes of HCHs in possible food webs from soil to plants, and animals using multi-element CSIA, and the microbial transformation of b-HCH was studied using soilwheat pot systems [80]. This study detected a large number of known HCH degrading microbes including Sphingomnas sp.…”