I. E. SCHILLING¹, I. E. SCHILLING², T. B. HOFSTETTER¹, T. B. HOFSTETTER², H.-P. E. KOHLER¹, H.-P. E. KOHLER<sup>2

1</sup>Eawag, Swiss Federal Institute of Aquatic Science and Technology, Duebendorf, Switzerland, ²IBP, Institute of Biogeochemistry and Pollutant Dynamics, ETH Zurich, Swiss Federal Institute of Technology Zurich, Zurich, Switzerland

Hexachlorocyclohexanes (HCHs) were excessively used as pesticides all over the world during the second half of the last century in agriculture and medicine. The persistence of HCHs led to their frequent detection as diffuse pollutants and point sources. In this work, we explore the use of compound-specific isotope analysis for assessing the extent and pathway of HCH biodegradation.

Degradation experiments are done with Lin enzymes isolated from HCH degrading soil bacteria of the Sphingomonadaceae family. First experiments with the enzyme LinA2, a dehydrochlorinase that catalyzes the first and second step in the metabolism of HCH, and γ-HCH as a substrate show that at high and low turnovers, C-isotope fractionation can be detected in substrate, intermediate and product. The apparent kinetic isotope effect (AKIE) for this elimination reaction is 1.019. Further experiments will be conducted with other enzymes from the Lin family and other isomers to not only determine AKIEs for the overall reaction but also model the AKIES for the single steps in the degradation. Current work also focuses on adapting and improving the experimental setup for model systems, in order to quantify hydrogen and chloride leaving group isotope effects.