Enzacamene, (-) [Bicyclo[2.2.1]-heptan-2-one, 1,7,7-trimethyl-3-[(4-methylphenyl)methylene]-, (1S,3E,4R)-] is one of enantiomer of Enzacamene (4-MBC) -- organic sunscreen components, that protects against UV radiation and may therefore help in the prevention of skin cancer. Enzacamene can exist as a cis-(Z)- and trans-(E)-isomer due to the exocyclic carbon-carbon (styrene) double bond. A commercial Enzacamene from a major supplier of UV filters showed the presence of only the (E)-isomer However, it is known that, upon exposure to light, (E)-4-Enzacamene is photochemically isomerized reversably to (Z)-4-Enzacamene. Both (E)- and (Z)-Enzacamene are chiral and thus consist of enantiomers (optical isomers). In a technical material and in a major brand sun lotion, Enzacamene was shown to consist entirely (>99%) of (E)-isomers and to be racemic. Wastewater showed the presence of both (E)- and (Z)-Enzacamene with a clear excess of (E)-isomers (E >Z). Untreated wastewater showed a nearly racemic composition suggesting that most if not all commercial Enzacamene is racemic. Treated wastewater indicated some excess of (R)- or (S)-stereoisomers ikely as a result of some enantioselective (bio)degradation in wastewater treatment plants. Enantiomers may show different biological behavior with respect to uptake, metabolism, and excretion and often differ in toxicity and other biological effects.