Table 1. Anaerobic and aerobic transformation reactions may lead to persistent metabolites.

Specific examples of pharmaceutical and personal care products with corresponding transformation products are shown.

Parent compound	Transformation product	References
O-Demethylation
Naproxen Over-the-counter non-steroidal anti- inflammatory drug	6-O-Desmethylnaproxen	20, 31
Guaifenesin Expectorate	3-(2-hydroxyphenoxy) propane-1,2-diol	31
Oxybenzone UV light absorber Found in sunscreens and plastics	2,4-Dihydroxybenzophenone	31
Methylparaben Preservative in cosmetics, pharmaceuticals, and food	4-Hydroxybenzoic acid	31
N-Demethylation
Diphenhydramine Anti-histamine	N-Desmethyl diphenhydramine	18
O-Methylation
Bisphenol A (BPA) Plastic precursor	BPA monomethyl ether (left), BPA dimethyl ether (right)	45
De-ethoxylation
Octylphenol and nonylphenol polyethoxylate Nonionic surfactant	Octylphenol or nonylphenol	40