Uptake and Transformation of Hexachlorocyclohexane Isomers (HCHs) in Tree Growth Rings at a Contaminated Field Site

The potential transformation of hexachlorocyclohexaneisomers (HCHs)within tree trunks could have a significant impact on the use of phytoscreening.However, the transformation mechanisms of HCH in trunks particularlyin growth rings are not yet well understood. Therefore, a field studyon an HCH-contaminated field site was conducted to investigate thefate of HCH, particularly alpha-HCH in tree trunks using multielementcompound-specific isotope analysis (ME-CSIA) and enantiomer fractionation.The results indicate that alpha-HCH was transformed, as evidencedby higher delta C-13 and delta Cl-37 valuesdetected across different growth ring sections and in the bark comparedto those in muck and soil. Remarkably, in the middle growth ring section,delta C-13 values of HCH were only marginally higher orcomparable to those in muck, whereas delta Cl-37 valueswere higher than those of the muck, indicating a different transformationmechanism. Moreover, the delta Cl-37 values of beta-HCHalso increased in the tree trunks compared to those in soil and muck,implying a transformation of beta-HCH. Additionally, dual-elementisotope analysis revealed that there are different transformationmechanisms between the middle growth rings and other sections. Ourfindings suggest that the transformation of HCHs in trunks could biasquantitative phytoscreening approaches; however, ME-CISA offers anoption to estimate the degradation extent. Elucidation of the transformation ofHCH in bark and growthrings of trees at a field site by isotope concepts shed new lighton the application of phytoscreening and dendrochemistry.