Anaerobic transformation of 6PPD-Q in sediment: Dominated by quinone reduction and novel O-methylation pathways

While the transformation of the toxic tire-derived contaminant 6PPD-quinone (6PPD-Q) is well studied in aerobic environments, its fate in anaerobic sediments, a critical environmental sink, is largely unknown. This study revealed that 6PPD-Q underwent attenuation (t_1/2-10 d = 5.68 days) in anaerobic sediment, with transformation significantly suppressed in sterilized controls, indicating microbially mediated processes. By developing a novel analytical approach using suspect and nontarget screening complemented by dansyl chloride derivatization with paired mass distance filtering, we tentatively annotated 15 transformation products (TPs) and elucidated a new metabolic map for 6PPD-Q anaerobic transformations distinct from those in aerobic systems. Its fate is dominated by quinone reduction to form TP300 (39.9% of TPs) and a novel O-methylation pathway generating TP312. In-silico toxicity predictions indicated reduced acute toxicity for most TPs, particularly TP300, suggesting detoxification. However, the newly identified TP312 is a potential concern due to its high abundance, increased lipophilicity (predicted logKow = 4.27), and persistence, creating a risk of long-term exposure and bioaccumulation in the benthic food webs. Our findings provide crucial insights into the anaerobic microbial metabolism of 6PPD-Q and highlight redox conditions in governing its TPs with distinct ecological risk profiles.