Aqueous chlorination kinetics of some endocrine disruptors

The aqueous chlorination kinetics of six endocrine disruptors (EDs: 4-n-nonylphenol, beta-estradiol, estrone, estriol, 17alpha-ethinylestradiol, progesterone) were studied in the 3.50-12.00 pH range, at 20 +/- 2 degreesC, in the presence of an excess of total chlorine. Under these conditions, all molecules with a phenolic group in their structure were rapidly oxidized by chlorine, whereas progesterone remained unchanged. In the first step, apparent kinetic rate constants were determined at various pH levels. Then each elementary reaction kinetic rate constant, i.e., the reaction of hypochlorous acid (HOCl) with ionized EDs and neutral EDs and an acid-catalyzed reaction of HOCl with neutral EDs, was calculated in the second step. The results showed that chlorination exhibits a second-order reaction rate. The rate constants for the acid-catalyzed reaction ranged from 3.02 x 10(4) M-1 s(-1) (for 4-n-nonylphenol) to 1.82-2.62 x 10(5) M-1 s(-1) (for hormones). The rate constants of HOCl reactions with ionized EDs were found to be equal to 7.5 x 10(4) M-1 s(-1) (for 4-n-nonylphenol) and between 3.52 and 4.15 x 10(5) M-1 s(-1) (for hormones), while the rate contants of HOCl with neutral EDs were much lower, i.e., between 1.31 M-1 s(-1) (for 4-n-nonylphenol) and 3.74-4.82 M-1 s(-1) (for hormones). At pH 7, the apparent-second-order rate constants were calculated to range from 12.6 to 131.1 M-1 s(-1). For a total chlorine concentration of 1 mg/L, the corresponding half-life times at pH 7 were about 65 min for 4-n-nonylphenol and 6-8 min for hormones.