Kinetic and mechanistic investigations of progesterone reaction with ozone
Introduction
An endocrine disruptor compound (EDC) is defined as “an exogenous agent that interferes with the production, release, transport, metabolism, binding, action or elimination of natural hormones in the body responsible for the maintenance of homeostasis and the regulation of developmental processes” (Kavlock et al., 1996).
As time goes on, the occurrence of molecules owning these properties in the aquatic environment has a growing concern (Richardson, 2003). This is largely explained by the potential effects of EDCs on health. Actually, several studies have reported abnormalities in wildlife exposed to EDCs in vitro but also in situ (Kavlock et al., 1996, Davis et al., 1999, Levi, 1999, Sedlak et al., 2000). In Human, diethylstilbestrol, a synthetic oestrogen, has been proved to cause cancer via an endocrine disruption mechanism (Herbst et al., 1971). In the same way, other examples of sporadic cases have been described in specific situations of Human beings exposed to high EDCs (Jacobson and Jacobson, 1996, Mocarelli et al., 1996, Aoki, 2001).
Moreover, Human is exposed by several ways to chemicals (absorption of contaminated water or contaminated food with molecules such as pesticides, leaching compounds from packaging materials, absorption of medicines) which lead to the increase of the complexity of the problem (Levi, 1999).
Today, EDCs are suspected to be responsible of reproduction abnormalities such as uterus and ovaries diseases, spontaneous abortions, sperm quality declines, certain cancers incidences increases (breast, prostate, testicular) (Kavlock et al., 1996).
The global aim of our work is to study the fate of EDCs during drinking water production. Among processes used for disinfection, chlorination or ozonation are the most largely used.
Because of their own nature of hormone, natural hormones figure among the EDCs list. Previous studies generally focused on steroid reproductive hormones (such as estradiol, estrone, estriol) because of their environmental abundances (Huber et al., 2003, Ternes et al., 2003). To complete the knowledge of the behaviour of natural hormones during water treatment, we performed a complete study of progesterone ozonation. The structure and characteristics of this steroid molecule are presented in Fig. 1. Little is currently known about this compound, however its environmental abundance is significant. Actually, Koplin et al. (2002) detected the presence of progesterone in 4.3% of 139 United States streams and a mean concentration of (maximum ) was measured.
A previous work concerning chlorination kinetics of steroid hormones has shown that, contrary to aromatic ring containing hormones (estradiol, estrone, estriol), progesterone did not react with chlorine at pH between 3.5 and 8.5 even in the presence of a large excess of chlorine (Deborde et al., 2004).
To complete this issue, we studied the oxidation of progesterone with ozone, which is a more oxidizing agent than chlorine.
In a first step, absolute rate constant was determined by kinetic experiments with and without OH radical scavenger. Then, the mechanism was investigated with the identification of first by-products by mass spectrometry.
Section snippets
Standards and reagents
Progesterone was supplied by acros organics and all reagents used were of analytical purity. Purified water was produced with a Millipore apparatus. Stock solutions of sodium thiosulfate (32 mM), phosphate buffer (500 mM), tert-butanol (100 mM) were prepared by dissolution in water of the commercial compound. Aqueous solution of progesterone was prepared by stirring the powder in water for two days and the undissolved compound was removed by filtration over a
Determination of stoichiometric factor
For following experiments, the stoichiometry of reaction was supposed to be one mole per mole. According to this hypothesis, the amounts of ozone necessary to oxidize between 20% and 100% of progesterone were added to the reaction bottles. The experiments were conducted in presence of tert-butanol 10 mM. The remaining progesterone concentration of each reactor was measured by HPLC analyse after all ozone had reacted.
The stoichiometry was defined as the ratio where was the
Conclusions
This work dealt with kinetic and mechanistic points of view of progesterone ozonation reaction. Kinetic experiments with tert-butanol allowed rate constant estimation of for pH ranging between 2.0 and 8.0 (temperature ).
Mechanistic studies showed that reaction stoichiometry was about one and allowed the identification of two major by-products. These compounds came from progesterone ozonide formation, hydration and either loss of hydrogen peroxide molecule or Baeyer–Villiger
Acknowledgements
We wish to thank the Eau de Paris-SAGEP for financial support and Pascale Pierre-Eugène for assistance.
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