Abatement of bisphenol analogues through ozone, hydroxyl radical and UV radiation in water: Kinetics, transformation products and toxicity

Abstract

[eng] Bisphenol A (BPA) has been one of the most produced chemicals during the last decades. However, as a result of its endocrine-disrupting behaviour, the use of this compound was restricted by legislation in different countries. To face restrictions, BPA has been replaced by other bisphenol analogues, such as bisphenol AF (BPAF), bisphenol AP (BPAP), bisphenol B (BPB), bisphenol C (BPC), bisphenol C-Cl (BPC-Cl), bisphenol E (BPE), bisphenol F (BPF), bisphenol S (BPS) and bisphenol Z (BPZ). These substitutes are expected to exhibit similar endocrine-disrupting effects compared to BPA, as the chemical structure of all bisphenol analogues is similar. In fact, some of them exhibit even higher estrogenic activity than that of BPA. Additionally, the extended use of its substitutes is resulting in the increase of their occurrence in aquatic environments. Considering these facts, the replacement of BPA by other bisphenol analogues is environmentally concerning, evidencing the requirement to study several removal strategies. Thus, this thesis evaluated the abatement of these BPA substitutes through some of the most efficient and technologically mature treatments, such as ozonation, UV/H2O2 and UV processes. This included the evaluation of the reactivity, the identification of the main transformation products (TPs) and the assessment of the resulting toxicity. The reactivity of ozone with bisphenol A substitutes resulted high under basic pH conditions (k = 8.83 x 108 - 1.43 x 109 M-1 s-1), while it decreased significantly at strong acidic pH (k = 5.01 - 1.22 x 105 M-1 s-1). This arises from the lower electron density placed in the phenol rings of the di-protonated species, resulting in lower reactivity with ozone. Then, the reactivity of hydroxyl radical with bisphenols under neutral pH conditions was determined to be high and similar for all bisphenols ((5.89 - 14.1) x 109 M-1 s-1). On the other hand, the efficiency of the UV-photolysis treatment ( λ = 254 nm) for the removal of these bisphenols at pH 7 was generally low, as well as the determined values of the quantum yield ((4.8 - 28.7) x 10-3 mol E-1). One exception was the favoured photolysis of BPC-Cl, whose determined value of the quantum yield was 4.7 x 10-1 mol E-1, which is approximately 45 times higher than that of BPA. Regarding the elucidation of the main transformation products, hydroxylation was distinguished as the main degradation pathway of bisphenol analogues by ozone and hydroxyl radical. Generally, this resulted in the formation of catechol and ortho-quinone derivatives as primary and most relevant TPs. Excluding the case of BPC-Cl, the detected TPs from the photolysis of bisphenols were equivalent to those from the UV/H2O2 treatment. This suggests the involvement of hydroxyl radical during their photolytic removal. On the other hand, BPC-Cl presented a unique photolysis mechanism, which is based on the favoured cleavage of the C-Cl bonds under UV radiation. Among the detected TPs, phenanthrene-3,6-diol was suggested as the most relevant initial product. Considering the toxicity assessment, the acute toxicity and endocrine-disrupting activity were experimentally evaluated during the oxidation of BPA, BPAF and BPC-Cl by ozone, and throughout the UV-photolysis of BPC-Cl. This was conducted by the exposure of zebrafish eleutheroembryos to several treatment samples, with the subsequent determination of the survival and swim bladder inflation rates and the execution of transcriptomic analysis. Results demonstrated that ozone is able to reduce the acute toxicity and the endocrine-disrupting activity of these bisphenols. The acute toxicity of BPC-Cl and most of the altered biological pathways in zebrafish eleutheroembryos were also mitigated during its photolysis treatment. However, the estrogenic activity increased significantly, indicating that certain of its photolysis products may exhibit higher estrogenic activity than the parent compound.

[cat] Actualment, hi ha una creixent preocupació respecte la capacitat disruptiva endocrina de diversos bisfenols, tots ells substituts del BPA, com el BPAF, BPAP, BPB, BPC, BPC-Cl, BPE, BPF, BPS i BPZ. Aquests compostos s’estan trobant cada vegada més en aigües naturals i de rebuig. És per això que aquesta tesis s’ha centrat en l’estudi de la seva eliminació mitjançant tractaments avançats eficients i tecnològicament madurs, com són l’ozonització i els tractaments UV i UV/H2O2. L’estudi ha inclòs la seva reactivitat, la identificació dels productes de transformació i l’avaluació de la toxicitat durant els tractaments. La reactivitat de l’ozó i radical hidroxil amb els bisfenols ha resultat ser alta en la majoria dels casos, a excepció de la baixa reactivitat de l’ozó amb els bisfenols, observada en condicions àcides. D’altra banda, l’eficiència del tractament UV per a l’eliminació d’aquests contaminants ha estat generalment baixa, excepte per a la fotòlisi del BPC-Cl. Respecte la identificació dels productes de transformació, la hidroxilació dels grups fenol en la posició orto s’ha distingit com la via principal de degradació dels bisfenols amb l’ozó i el radical hidroxil. Aquesta hidroxilació també s’ha detectat durant el tractament UV de la majoria dels bisfenols, suggerint la intervenció del radical hidroxil durant l'eliminació fotolítica dels bisfenols. L’excepció ha estat la fotòlisi del BPC-Cl. Aquest compost presenta un mecanisme de fotòlisi únic, basat en el trencament afavorit dels enllaços C-Cl sota radiació UV, donant lloc a l’eliminació de clor per tots els productes de la fotòlisi. L’estudi de toxicitat, realitzat mitjançant l’exposició de larves del peix zebra a diferents mostres tractades de diversos bisfenols seleccionats, ha demostrat que l’ozó es capaç de reduir tant la toxicitat aguda com també la seva activitat com a disruptors endocrins. D’altra banda, encara que també s’ha constatat una reducció de la toxicitat aguda durant la fotòlisi del BPC-Cl, l’estrogenicitat d’aquest compost augmenta amb el tractament. Aquest resultat indica que alguns dels productes de transformació del la fotòlisi del BPC-Cl poden presentar una activitat estrogènica més alta que la del propi contaminant, el BPC-Cl.