The influence of drug concentration and pH on the photodegradation of ciprofloxacin was investigated

and a reversephase highperformance liquid chromatographic method was developed for detecting the changes of ciprofloxacin content in water and sediments. Photodegradation of ciprofloxacin in natural light was most rapid at a concentration of 1 mg·L

-1

 among the three concentrations tested (1

5 and 10 mg·L

-1

). After 72 h

the amounts of ciprofloxacin remaining with and without sediments were 19% and 20%

respectively. The photodegradation rate was inversely proportional to the initial drug concentration. Ciprofloxacin was most sensitive to photodegradation at pH 9 among the four pH levels tested 〖JP2〗(pH =3

5

9

11)

when the〖JP〗 drug was in zwitterionic form. The stability increased considerably when pH=3. After 48 h

the amounts of ciprofloxacin remaining in water were 22.6 % and 95.7%

respectively. When ciprofloxacin was released into microcosms

the concentration of ciprofloxacin in water decreased rapidly

but increased concomitantly in sediments. After 45 days ciprofloxacin was undetectable in water

but a substantial concentration remained in the sediments.(approximately 93.86 μg·kg

-1

).