WaterSubject

A number of chemicals exist in the environment that affect the endocrine system and produce an adverse effect on aquatic life, animals, and potentially humans. There is increasing evidence that these compounds can alter endocrine functions and may disrupt growth, development, and reproduction by interfering with the production of the endocrine system. Accordingly, because of the role of estrogenic chemicals, often referred to as environmental estrogens, in contributing to the development of hormone-dependent cancers, disorders of the reproductive tract, and other effects, they are classified as “endocrine disrupting chemicals” (EDCs). EDCs have generated a vast amount of attention among the scientific, research, and regulatory communities worldwide.

Among prominent EDCs of interest currently, this study has considered two synthetic EDCs, bisphenol A (BPA) and 17?-ethynylestradiol (EE2), and three natural EDCs, estrone (E1), 17?-estradiol (E2), and estriol (E3), which have been chosen for their environmental significance. BPA, also known as 2,2-bis-(4-hydroxy-phenyl) propane or 4,4?-isopropylidenediphenol, is an important monomer chemical used for the production of various polycarbonate and polysulfone plastics and epoxy resins. It is a known EDC due to its estrogenicity, with about 500 times the estrogenic activity of octylphenol. In addition, it has been reported to cause reproductive toxicity and to affect cellular development in rats and mice and is generally regarded as a serious contributor to water pollution.

The steroid compounds, E1, E2, E3 and EE2, are derived from the biotransformation of cholesterol, a precursor of mammalian sexual steroids. The female body naturally produces the three estrogens, E1, E2, and E3, but they are also present in males, although generally at much lower levels. The synthetic estrogen EE2 (17?-ethynyl-1,3,5(10)-estratriene-3,17?-diol) is not only a key ingredient in oral contraceptives used by western women since the 1960s, but is also a hormonal agent used in the stockbreeding industry. All four steroid compounds have been reported to be responsible for a large part of the estrogenicity burden of municipal wastewaters, and E2 and EE2 have been shown to elicit a range of physiological effects in organisms at very low concentrations. In general, the steroid compounds and BPA are considered to be incompletely removed by conventional secondary wastewater treatment processes; for example, confirmed that an activated sludge in batch experiment systems removed only 20% of the initial amount of EE2 (1 ?g l^?1) in 24–48 h, and the concentration of the remaining EE2 did not decrease further. Thus, these chemicals, which are described in, were chosen for our study because of their environmental importance and because they have a common phenolic moiety.

In view of their presence in conventionally treated effluents, and the need to mitigate their discharge into natural water bodies, the comparative performance of additional, alternative treatment technologies is of considerable interest to water utilities and regulatory authorities at the moment. Among the treatment methods being evaluated currently are oxidation by ozone) and chlorine dioxide, and adsorption by activated carbon. Another strong oxidant, potassium ferrate, is receiving considerable attention at present owing to the high redox potential of the ferrate(VI) ion from 2.2 to 0.7 V in respectively, acidic and basic solutions, and associated coagulation effect arising from the reduced Fe(III) species for metals, non-metals, and radionuclides from solution. Ferrate(VI) has powerful disinfection properties that enable it to inactivate a wide variety of microorganisms at low Ferrate(VI) dosages including many chlorine-resistant organisms. Moreover, unlike ozone, Ferrate(VI) does not react with bromide ions, thus avoiding the possible formation of the suspected carcinogenic bromate ion in the treatment of bromide-containing water by ferrate(VI).

The objective of this study was to evaluate the ferrate(VI) oxidation of the five previously mentioned EDCs, with particular emphasis on the reaction pathways of BPA. The evaluation of BPA follows an earlier preliminary investigation carried out by the authors. The reaction rate constants were determined by a kinetic model incorporating the various species equilibria for the EDC compounds and ferrate, using observations of the temporal reduction in EDC and ferrate concentrations. In addition to reporting on the rate constants, we have investigated the completeness of the BPA degradation and have identified some of the intermediate products by liquid chromatography/mass spectrometry-mass spectrometry (LC/MS–MS) and gas chromatography/mass spectrometry-mass spectrometry (GC/MS–MS).

In this paper the reaction rate constants for BPA, EE2, E1, E2, and E3 have been determined, from the tests carried out in the pH range of 8–12 at different reactant molar ratios. The rate constants were determined by a second-order kinetic model incorporating the various species equilibria for the EDC compounds and ferrate, using observations of the temporal reduction in EDC and ferrate concentrations. In general, the application of potassium ferrate can achieve a major removal of these compounds. The extent of the treatment will vary with the aqueous conditions since pH, in particular, affects the nature of the ferrate ion and the degree of EDC dissociation. In agreement with other studies, the oxidation of the EDCs was found to be greater for mono-protonated ferrate, than for non-protonated ferrate. Among the five EDCs, the ferrate oxidation of the four steroid estrogens was greater (higher reaction rates) than that of BPA.

The reaction of BPA with ferrate was studied in detail in order to identify the formation of intermediate reaction products and clarify the BPA degradation pathway. From the analyses by LC/MS–MS and GC/MS–MS, nine specific compounds were identified, including IPP, p-isopropenylphenol, 4-isopropanolphenol, and dicarboxylic acids (e.g. oxalic acid). Whilst under some conditions (e.g. ferrate:BPA molar ratio 5:1) BPA can be completely degraded in less than 5 min, the degree of organic mineralization was significantly less than 100%, indicating the presence of reaction products which persist well beyond the disappearance of the BPA.

Overall, given that the molar ratio of ferrate to EDCs in practice would be several orders of magnitude, it is concluded that ferrate oxidation could be an effective treatment method for the purification of waters containing these particular EDCs.