4-Methylphenol produced in freshwater sediment microcosms is not a bisphenol A metabolite

[Display omitted] •Partial disappearance of bisphenol A (BPA) observed in anoxic sediment microcosms.•4-Methylphenol (4-MP) detected as putative degradation intermediate.•Experiments using 13C-labeled BPA demonstrated that 4-MP was not derived from BPA.•The formation of 4-MP to suggest BPA degradation must be carefully interpreted. 4-Methylphenol (4-MP), a putative bisphenol A (BPA) degradation intermediate, was detected at concentrations reaching 2.1mgL−1 in anoxic microcosms containing 10mgL−1 BPA and 5g of freshwater sediment material collected from four geographically distinct locations and amended with nitrate, nitrite, ferric iron, or bicarbonate as electron acceptors. 4-MP accumulation was transient, and 4-MP degradation was observed under all redox conditions tested. 4-MP was not detected in microcosms not amended with BPA. Unexpectedly, incubations with 13C-labeled BPA failed to produce 13C-labeled 4-MP suggesting that 4-MP was not derived from BPA. The detection of 4-MP in live microcosms amended with lactate, but not containing BPA corroborated that BPA was not the source of 4-MP. These findings demonstrate that the transient formation of 4-MP as a possible BPA degradation intermediate must be interpreted cautiously, as microbial activity in streambed microcosms may generate 4-MP from sediment-associated organic material.