Phototransformation of cephalosporin antibiotics in an aqueous environment results in higher toxicity.
Photodegradation may be the most important elimination process for cephalosporin antibiotics in surface water. Cefazolin (CFZ) and cephapirin (CFP) underwent mainly direct photolysis (t(1/2) = 0.7, 3.9 h), while cephalexin (CFX) and cephradine (CFD) were mainly transformed by indirect photolysis, which during the process a bicarbonate-enhanced nitrate system contributed most to the loss rate of CFX, CFD, and cefotaxime (CTX) (t(1/2) = 4.5, 5.3, and 1.3 h, respectively). Laboratory data suggested that bicarbonate enhanced the phototransformation of CFD and CFX in natural water environments. When used together, NO(3)(-), HCO(3)(-), and DOM closely simulated the photolysis behavior in the Jingmei River and were the strongest determinants in the fate of cephalosporins. TOC and byproducts were investigated and identified. Direct photolysis led to decarboxylation of CFD, CFX, and CFP. Transformation only (no mineralization) of all cephalosporins was observed through direct photolysis; byproducts were found to be even less photolabile and more toxic (via the Microtox test). CFZ exhibited the strongest acute toxicity after just a few hours, which may be largely attributed to its 5-methyl-1,3,4-thiadiazole-2-thiol moiety. Many pharmaceuticals were previously known to undergo direct sunlight photolysis and transformation in surface waters; however, the synergistic increase in toxicity caused by this cocktail (via pharmaceutical photobyproducts) cannot be ignored and warrants future research attention.
Graduate Institute of Environmental Engineering, National Taiwan University, 71, Chou-Shan Road, Taipei 106, Taiwan.
Xiao-Huan
XH
Wang
Angela Yu-Chen
AY
Lin
D048908:Aliivibrio fischeri / Q000187:drug effects*; D000900:Anti-Bacterial Agents / Q000737:chemistry* / Q000633:toxicity*; D002254:Carbonates / Q000737:chemistry; D002511:Cephalosporins / Q000737:chemistry* / Q000633:toxicity*; D002853:Chromatography, Liquid; D005618:Fresh Water / Q000737:chemistry*; D049449:Luminescence; D009566:Nitrates / Q000737:chemistry; D009930:Organic Chemicals / Q000737:chemistry; D010782:Photolysis; D021241:Spectrometry, Mass, Electrospray Ionization; D053719:Tandem Mass Spectrometry
D000900:Anti-Bacterial Agents; D002254:Carbonates; D002511:Cephalosporins; D009566:Nitrates; D009930:Organic Chemicals