Effect of sulfonated graphene on uptake, translocation, and metabolism of 2,4,4′-trichlorobiphenyl in maize seedlings

Abstract

Graphene may affect fate of organic contaminants due to its strong adsorption properties, which is very crucial for accurately assessing ecological risk of graphene and concurrent contaminants, while the current information remains largely unknown. Here, we firstly explored the adsorption characteristics of sulfonated graphene (SG) for a widespread polychlorinated biphenyl 2,4,4′-trichlorobiphenyl (PCB28) (0.5–100 μg L⁻¹). Subsequently, the influence of SG on the uptake, translocation, and metabolism of PCB28 in maize seedlings was investigated through hydroponic exposure experiment. Adsorption isotherm of PCB28 to SG fitted best with the Langmuir model and the Polanyi-Dubinin-Manes (PDM) model, with the maximum adsorption capacity (Q_max) calculated as around 530 mg kg⁻¹. The presence of SG significantly promoted the maximum accumulation amount of PCB28 in roots by 112%, whereas reduced that in stems and leaves by 32 and 39%, respectively. The translocation factor (TFs) of PCB28 from roots to stems was 26–70% lower for SG exposed seedlings than nonexposed seedlings when the exposure time was longer than 24 h, demonstrating an obvious suppression of SG in the transportation of PCB28 from roots to stems. PCB28 could be metabolized to PCB8 and PCB18 through dechlorination and rearrangement in different parts of maize seedlings. SG significantly increased the accumulation of PCB8 and PCB18 in roots, but decreased that in stems and leaves. These findings might provide new implications for the risk assessment of SG and PCBs in the environment.