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

摘要

The potential transformation of hexachlorocyclohexane isomers (HCHs) within tree trunks could have a significant impact on the use of phytoscreening. However, the transformation mechanisms of HCH in trunks particularly in growth rings are not yet well understood. Therefore, a field study on an HCH-contaminated field site was conducted to investigate the fate of HCH, particularly a-HCH in tree trunks using multielement compound-specific isotope analysis (ME-CSIA) and enantiomer fractionation. The results indicate that a-HCH was transformed, as evidenced by higher <5I3C and <537C1 values detected across different growth ring sections and in the bark compared to those in muck and soil. Remarkably, in the middle growth ring section, <513C values of HCH were only marginally higher or comparable to those in muck, whereas <537C1 values were higher than those of the muck, indicating a different transformation mechanism. Moreover, the <537C1 values of B-HCH also increased in the tree trunks compared to those in soil and muck, implying a transformation of B-HCH. Additionally, dual-element isotope analysis revealed that there are different transformation mechanisms between the middle growth rings and other sections. Our findings suggest that the transformation of HCHs in trunks could bias quantitative phytoscreening approaches; however, ME-CISA offers an option to estimate the degradation extent.