Degradation kinetics of pharmaceuticals and personal care products in surface waters: photolysis vs biodegradation.

Poor removal of many pharmaceuticals and personal care products (PPCPs) in sewage treatment leads to their discharge into the receiving waters, where they may cause negative effects. Their elimination from the water column depends of several processes, including photochemical and biological degradation. We have focused this research on comparing the degradation kinetics of a wide number (n=33) of frequently detected PPCPs considering different types of water, pH and solar irradiation. For those compounds that were susceptible of photodegradation, their rates (k) varied from 0.02 to 30.48h-1 at pH7, with the lowest values for antihypertensive and psychiatric drugs (t1/2 >1000h). Modification of the pH turned into faster disappearance of most of the PPCPs (e.g., k=0.072 and 0.066h-1 for atenolol and carbamazepine at pH4, respectively). On the other hand, biodegradation was enhanced by marine bacteria in many cases, for example for mefenamic acid, caffeine and triclosan (k=0.019, 0.01 and 0.04h-1 , respectively), and was faster for anionic surfactants. Comparing photodegradation and biodegradation processes, hydrochlorothiazide and diclofenac, both not biodegradable, were eliminated exclusively by irradiation (t1/2 =0.15-0.43h and t1/2 =0.14-0.17h, respectively). Salicylic acid and phenylbutazone were efficiently photo (t1/2 <3h) and biodegraded (t1/2 =116-158h), whereas some compounds such as ibuprofen, carbamazepine and atenolol had low degradation rates by any of the processes tested (t1/2 =23-2310h), making then susceptible to persist in the aquatic media.