It has been shown to be susceptible to significant metabolism by microorganisms in some natural waters without use as carbon or energy source, but in most waters and in sediments it has been shown to be stable towards biodegradation. Salmonella bacteria is thought to break down the aromatic ring system to yield a variety of smaller molecules. Microsomes from pea leaves or soy beans convert BaP to quinones and to polymers through a process which resembles simple chemical oxidation rather than metabolism. In mammalian cells metabolism takes place in two steps. In phase 2 these moderately polar metabolites are conjugated with glutatione, glucuronic acid or sulfate which produce substances which are sufficiently soluble in water to be excreted.
Further oxidation destroys the aromatic nucleus.
The most common reaction of BaP oxidation is catalized by light and uses oxygen from the air. This usually produces an epoxide. The fate of this epoxide depends on its structure and the environmental conditions. If the epoxide has an uneven charge distribution it might go through rearrangement and become a phenol. The epoxide might go through conjugation when the oxide reacts with nucleophiles which would yield dihydrodiol esters or ethers.