Transformation of 17α-Ethinylestradiol during Water Chlorination: Effects of Bromide on Kinetics, Products, and Transformation Pathways

Kinetics, products, and pathways of 17α-ethinylestradiol (EE2) transformation during chlorination of water with and without bromide (Br−) were studied to evaluate the effect of chlorination on the fate of steroid estrogens. Br− can be important for the fate of EE2 during chlorination because of a rapid conversion of Br− to bromine by chlorine and a ∼1000 times higher reactivity of bromine than chlorine toward EE2. Experimental data and model calculations for EE2 chlorination show that 4-chloro EE2 and 2,4-dichloro EE2 are the major initial transformation products in absence of Br−. With increasing concentration of Br−, the bromo-analogous of the chloro EE2s becomes significant as additional initial transformation products. Those initial transformation products of EE2 are generally quickly further transformed to products with a destroyed phenolic moiety. Transformation of EE2 during chlorination becomes considerably faster at Br− concentrations higher than 0.25 μM (20 μg L−1). However, in presence of model dissolved organic matter such as glycine or phenol, the accelerating effect of Br− diminishes due to a more rapid consumption of bromine than chlorine by these compounds. A kinetic model was developed which allows to predict EE2 transformation during chlorination of natural waters and wastewaters in presence of Br− and low concentrations of ammonia (<10 μM). It could be demonstrated in these systems that bromine produced from Br− is mainly responsible for EE2 transformation.