Many of the human pharmaceuticals detected in municipal wastewater effluent, surface water, and groundwater contain functional groups that could undergo transformation reactions during chlorine disinfection. To assess the potential importance of these reactions to the environmental fate of pharmaceuticals, the rate of transformation of a group of compounds was measured over a pH range of 5-10. Several of the pharmaceuticals reacted rapidly with free chlorine (i.e., HOCl/OCl-) and would be expected to undergo transformation under the conditions typically encountered in many chlorine disinfection systems. For compounds containing aromatic ether functional groups, the rate of transformation was strongly affected bythe other substituents on the ring. The amine-containing pharmaceuticals underwent a rapid reaction with hypochlorous acid to form chlorinated amines, which could be converted back into the parent compound by reaction with thiosulfate. In the absence of thiosulfate, the chlorinated amines slowly decomposed to form species that could not be converted back into the parent compound. The reaction rates of the pharmaceuticals with combined chlorine (i.e., chloramines) were significantly slower, and transformation of the compounds would not be expected under the conditions encountered during chloramination.

Increasing attention is being given to the detection, treatment, and removal of problematic effluent-derived contaminants.

Large quantities of antibiotics are used annually in human therapy and in agriculture. As results of incomplete metabolism, ineffective treatment removal or improper disposal, antibiotics may be released into the aquatic environment via wastewater effluent and agricultural runoff. Results of recent studies indicate the presence of antibiotics in municipal wastewater effluent and surface water. Despite the detection of antibiotics, little is known about their distribution in the environment, their mobility and persistence in natural and engineered systems. Contamination of aquatic systems by antibiotics could perturb microbial ecology, increase the proliferation of antibiotic-resistant pathogens, and could pose threats to human health. The presence of antibiotics in the aquatic environment also presents challenges for the water industry particularly on the issues of water reuse and water resource planning.To assess the magnitude of the potential risks associated with antibiotics released into the aquatic environment, a literature review was conducted on the usage, occurrence and behavior of antibiotics. Concentrations of antibiotics in municipal wastewater and liquid animal waste were estimated and were classified according to chemical properties. The estimation of human health antibiotics was based upon the number of prescriptions administered while the estimation of animal health antibiotics was based upon the sub-therapeutic usage in feed for growth promoting. Reported data on the occurrence of antibiotics in the aquatic environment confirm the persistence of certain antibiotics. The fate of antibiotics is significantly affected by sorption and transformation processes. By combining information on environmental fate with the predicted concentrations, we identify that antibiotics of fluoroquinolones and sulfonamides are the most likely water contaminants, followed by macrolides. Among fluoroquinolone and sulfonamide antibiotics, ciprofloxacin and sulfamethoxazole are most likely to be present in wastewater effluent and sulfamethazine is most likely to be present in agricultural runoff. Azithromycin and tylosin are the most likely macrolides present in wastewater effluent and in agricultural runoff respectively. The antibiotics identified by this literature review may serve as "indicators" in analytical survey for antibiotic contamination as analyses of antibiotic contaminants in complicated water matrices can be time-consuming and costly. Furthermore, results of this literature review can also facilitate prioritizing future studies on the fate and transport of antibiotics in natural and engineered water systems.

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The effluent from municipal wastewater treatment plants contains trace concentrations of a variety of organic compounds. To assess the removal of these compounds in full-scale treatment systems and effluent-receiving waters, approaches are needed for quantifying removal rates and mechanisms. For processes that result in near complete removal of wastewater-derived contaminants, it is reasonable to measure concentrations entering and leaving the treatment system. However, for those compounds that are not completely removed, alternative methods are needed. This paper describes several examples of approaches that combine laboratory and field studies to assess the attenuation of wastewater-derived contaminants.