Aquatic photochemistry of paracetamol in the presence of dissolved organic chromophoric material and nitrate.

PURPOSE: This study contains some new findings connected to the photolysis of the drug paracetamol (hereinafter APAP) especially in light of estimating natural conditions, and it will offer information to better evaluate environmental problems connected with this widely used analgesic agent. Only a few studies, so far, have focussed on the photodegradation process of APAP in the natural environment, and the question about the role of the colored/chromophoric dissolved organic matter (CDOM) and nitrate (NO3-) as photoinductors is almost open.
METHODS: APAP dissolved in freshwater and pure laboratory water in the presence and absence of CDOM and NO3- ions was irradiated using weak-energy photon energies simulating natural conditions.
RESULTS: CDOM and NO3- as photoinductors produced only the slow phototransformation of APAP under weak energy radiation, and APAP seemed to be practically resistant to direct photolysis under weak radiant energies available in natural conditions. The estimated reaction efficiencies, in addition to half-lives, speak for that NO3- and CDOM do not act as quite independent photoinductors but their effect in conjunction (CDOM-NO3- -water) is stronger than the separate ones. The principal phototransformation intermediates of APAP were mono-hydroxy derivatives, depending on available photon energies formed via ortho- or meta-hydroxylation, possessing substantial power of resistance to further specific transformation reactions.
CONCLUSIONS: The estimated half-life of the phototransformation of APAP in the natural aqueous environment and in the presence of suitable photoinductors will be about 30 days or more.