Transformation of pharmaceutical and personal care product pollutants by wastewater chlorine disinfection and aqueous photolysis

Abstract

Concern has grown over the presence of pharmaceutical and personal care products (PPCPs) as pollutants in aquatic systems because these chemicals are specifically designed to elicit biological effects. To fully assess the environmental impact of these pollutants, their transformations by engineered and environmental processes must be considered. The transformation of cimetidine, an antacid drug, and triclosan, an antimicrobial compound, by wastewater chlorine disinfection was studied, as well as the photochemical transformations and environmental occurrence of triclosan, its chlorinated derivatives, and their dioxin photoproducts.Cimetidine was found to react rapidly with free chlorine, indicating that it will likely undergo significant degradation during wastewater chlorination. Four major products were identified, two of which were estimated to have lower predicted no-effect concentrations than cimetidine. Reaction pathways and reaction mechanisms were proposed. The aquatic photochemistry of triclosan and three of its chlorinated derivatives was explored. Reaction kinetics were studied, quantum yields were measured, and photoproducts were identified. Notably, dioxin photoproducts were observed to form at yields of 0.5 to 2.5% from triclosan and its chlorinated derivatives. A method was developed to analyze for triclosan and its chlorinated derivatives throughout the wastewater treatment process. A five-fold increase in the chlorinated derivatives of triclosan was observed in wastewater effluent after the chlorine disinfection step, showing this process to be a significant source or these pre-dioxins. Two sediment cores from Lake Pepin, a wastewater-impacted depositional zone of the Mississippi River, were analyzed for triclosan and the dioxin photoproducts of triclosan and its chlorinated derivatives. These dioxins were detected at levels that trended with levels of triclosan that increased over the last 45 years since its introduction in the mid-1960s, providing strong evidence for the photochemistry of triclosan and its chlorinated derivatives as their source. The triclosan-derived dioxins comprised an increasing percentage of the total mass of all dioxins detected in Lake Pepin, reaching as high as 31% in recent years.