Interconversion between methoxylated, hydroxylated and sulfated metabolites of PCB 3 in whole poplar plants

Methoxylated polychlorinated biphenyls (MeO-PCBs) are overlooked metabolites of PCBs. In general, they are more toxic to plants than their parent congeners. However, information on the fate of MeO-PCBs and the relationship between methoxylated, hydroxylated and sulfated metabolites of PCBs in plants is scarce. In this work, poplar plants (Populus deltoides & times; nigra, DN34) were hydroponically and separately exposed to 4 ' methoxy-4-monochlorobiphenyl (4 '-MeO-PCB 3) and 4 '-PCB 3 sulfate for 10 days to investigate the uptake, translocation and metabolism of MeO-PCBs and the relationship between methoxy-PCBs, hydroxyl-PCBs and PCB sulfates within plants. Results showed that 4 '-MeO-PCB 3 and 4 '-PCB 3 sulfate were taken up by the roots of poplar plants and translocated from roots to shoots and leaves. 4 '-OH-PCB 3 and 4 '-PCB 3 sulfate were identified as the hydroxylated metabolite and sulfate metabolite of 4 '-MeO-PCB 3 in poplar, respectively. In the backward reaction, 4 '-OH-PCB 3 and 4 '-MeO-PCB 3 were found as metabolites of 4 '-PCB 3 sulfate. For exposure groups, the yields of 4 '-OH-PCB 3 produced from 4 '-MeO-PCB 3 and 4 '-PCB 3 sulfate were 1.29% and 0.13% respectively. The yield of 4 '-PCB 3 sulfate which originated from 4 '-MeO-PCB 3 in wood and root samples of exposure groups was only 0.02%. Only 0.04% of the initial mass of 4 '-PCB 3 sulfate was transformed to 4 '-MeO-PCB 3 in the exposure groups. The sulfation yield of 4 '-OH-PCB 3 was higher than hydrolysis yield of 4 '-PCB 3 sulfate, indicating that formation of PCB sulfates was predominant over the reverse reaction, the formation of hydroxyPCBs. These results provide new perspective on the transport, metabolism, and fate of MeO-PCBs, and also help to better understand sources of OH-PCBs and PCB sulfates in the environment. This study provides the first evidence of interconversion of sulfate metabolites from methoxy-PCBs and methoxy-PCBs from PCB sulfates. (c) 2021 Elsevier B.V. All rights reserved.

Automated summary

This study investigated the uptake, translocation, and metabolism of MeO-PCBs in poplar plants, as well as the relationship between methoxy-PCBs, hydroxyl-PCBs, and PCB sulfates. Results showed that hydroxylated metabolites and sulfate metabolites of MeO-PCBs were identified in the plant, indicating a complex interconversion process. The formation of PCB sulfates was found to be predominant over the reverse reaction, the formation of hydroxyPCBs, providing new insights into the fate of MeO-PCBs in plants.