Wednesday, November 15, 2006

Evaluation of the Fate of Ciprofloxacin and Amoxicillin in Simulated Domestic Wastewater.

Michael Musey, Tuskegee Unviersity, Tuskegee, AL 36088, Ramble Ankumah, Dept. Agric. & Environ. Sci., Milbank Hall, Tuskegee, AL 36088, and Aigiuo Liu, Tuskegee University, 302 Milbank Hall, Tuskegee, AL 36088.

Amoxicillin and ciprofloxacin are two commonly used antibiotics in the US that are excreted in more than 75% in the unmetabolized form after therapeutic use. Because most of these two antibiotics are excreted almost unmetabolized, they are expected to be present in the domestic wastewater in significant quantities. The sorption behavior of ciprofloxacin and amoxicillin were studied using a synthetic wastewater (SWW) that was adjusted to different pH levels (3.5, 5.5, 6.6, 7.5 and 8.5). Sorption kinetics of ciprofloxacin and amoxicillin were conducted at 100 μgL-1 and 250 μgL-1 concentrations respectively. Adsorption isotherms of the pharmaceuticals (ciprofloxacin and amoxicillin) at different pHs were also determined. SWW (pH, 6.6) was inoculated with Rhodococcus B30 strain to determine the contribution of microbial surfaces to sorption and the possible degradation of the pharmaceuticals by this microorganism. The average percentage sorbed of ciprofloxacin ranged from 7 to 15%, with highest sorption occurring at pH=5.5, while amoxicillin sorption ranged from 2 to 5%, with pH=3.5 at the highest end. The sorption distribution coefficient (Kd) values for ciprofloxacin ranged from 0.44 and 0.89 L g-1, with pH=5.5 exhibiting the highest Kd while that for amoxicillin ranged from 0.08 to 0.39 Lg-1 with highest at pH=3.5. There was a significant difference (p<0.05) in Kd of both ciprofloxacin and amoxicillin sorbed at the different pHs used for the study. Both ciprofloxacin and amoxicillin were not degraded within 48 h by Rhodococcus B30 strain. This result indicates that sorption may not be the major processes of removal of both compounds from WWTPs and significant amounts of these compounds would enter the environment if biodegradation of these compounds are not significant in the WWTPs.