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

beta-Hexachlorocyclohexane (beta-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 beta-HCH in soil-plant systems is still limited. Therefore, experiments with a contaminated field soil were conducted to investigate the transformation of beta-HCH in soil-plant systems by compound specific isotope analysis (CSIA). The results showed that the delta C-13 and delta Cl-37 values of beta-HCH in the soil of the planted control remained stable, revealing no transformation due to a low bioavailability. Remarkably, an increase of the d13C and d37Cl values in soil and plant tissues of the spiked treatments were observed, indicating the transformation of beta-HCH in both the soil and the plant. This was surprising as previously it was shown that wheat is unable to transform beta-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 beta-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 beta-HCH-treated bulk and rhizosphere soil, potentially supporting the biotransformation.