Hydroxyl radical induced degradation of the B-blocker Nadolol and comparison with Propranolol

The often used 8-blockers Nadolol and Propranolol are regularly detected in wastewater and purified wastewater, for their elimination high energy irradiation treatment is recommended here. Both molecules are composed of an aromatic part and an oxypropanolamine side chain. The aromatic part in Propranolol contains a naphthalene unit, in Nadolol fused benzene and cyclohexane rings. This difference in the structure causes profound effect in their hydroxyl radical (center dot OH, main reactant in degradation of organic molecules in Advanced Oxidation Processes) reactions. In Propranolol -80-90% center dot OH attacks take place on the aromatic part and only-10-20% on the oxypropanolamine side chain chromophore. In the case of Nadolol these numbers are-70 and-30%. In both molecules the degradation occurs through the formation of hydroxycyclohexadienyl (main transient intermediate), alpha-aminoalkyl, aminium and aminyl type radicals. The first formed products of Nadolol are non-toxic or have just little toxicity, while those of Propranolol are considerably toxic. For both molecules the toxicity vanishes with the increasing amount of center dot OH injected into the solution (increasing dose). The non-biodegradable Nadolol and Propranolol solutions become biodegradable upon irradiation with c.a. 1 kGy dose at 0.1 mmol dm-3 concentration.