Micropollutant sorption to membrane polymers: A review of mechanisms for estrogens

Abstract

Organic micropollutants such as estrogens occur in water in increasing quantities from predominantly anthropogenic sources. In water such micropollutants partition not only to surfaces such as membrane polymers but also to any other natural or treatment related surfaces. Such interactions are often observed as sorption in treatment processes and this phenomenon is exploited in activated carbon filtration, for example. Sorption is important for polymeric materials and this is used for the concentration of such micropollutants for analytical purposes in solid phase extraction. In membrane filtration the mechanism of micropollutant sorption is a relatively new discovery that was facilitated through new analytical techniques. This sorption plays an important role in micropollutant retention by membranes although mechanisms of interaction are to date not understood. This review is focused on sorption of estrogens on polymeric surfaces, specifically membrane polymers. Such sorption has been observed to a large extent with values of up to 1.2 ng/cm(2) measured. Sorption is dependent on the type of polymer, micropollutant characteristics, solution chemistry, membrane operating conditions as well as membrane morphology. Likely contributors to sorption are the surface roughness as well as the microporosity of such polymers. While retention-and/or reflection coefficient as well as solute to effective pore size ratio-controls the access of such micropollutants to the inner surface, pore size, porosity and thickness as well as morphology or shape of inner voids determines the available area for sorption. The interaction mechanisms are governed, most likely, by hydrophobic as well as solvation effects and interplay of molecular and supramolecular interactions such as hydrogen bonding, π-cation/anion interactions, π-π stacking, ion-dipole and dipole-dipole interactions, the extent of which is naturally dependent on micropollutant and polymer characteristics. Systematic investigations are required to identify and quantify both relative contributions and strength of such interactions and develop suitable surface characterisation tools. This is a difficult endeavour given the complexity of systems, the possibility of several interactions taking place simultaneously and the generally weaker forces involved.

Considerações sobre o preparo de amostras contendo micropoluentes estrogênicos

“…4 Adicionalmente, sugere-se que os grupos fenólicos, ricos em elétrons p, podem propiciar interações do tipo p-p com grupos fenil deficientes em elétrons dos materiais poliméricos. 5 Dentre os materiais testados, os únicos que poderiam ser utilizados para transferência das soluções de Estrona, Estradiol e Etinilestradiol do frasco de amostra para o cartucho de SPE são vidro e teflon, os quais permitiram recuperações médias entre 97 e 102% de todos os estrogênios em estudo, com desvios padrão relativos da ordem de 5%. Estes resultados são coerentes com os antecedentes relatados na literatura, 4 que sugerem o uso de teflon, em função da baixa adsorção apresentada em relação à estrona.…”

“…Recentemente foram publicados três trabalhos que discutem o efeito da natureza dos meios filtrantes na recuperação de estrogênios, [4][5][6] o que demonstra a relevância da questão. No primeiro trabalho, 4 estrona foi utilizada como estrogênio modelo, observando-se significativa adsorção de matérias filtrantes constituídos de nylon, polipropileno, politetrafluoroetileno e acetato de celulose.…”

“…Em função destes resultados, foi proposta microfibra de vidro como meio filtrante para a remoção de catalisadores em estudos de degradação por fotocatálise heterogênea. No segundo trabalho, 5 foi estudada a interação entre estrogênios e superfícies poliméricas, avaliando-se o efeito do tipo de polímero, das características do micropoluente e da morfologia das membranas, dentre outros fatores. De maneira geral, foi observado que este tipo de interação é governado por efeitos hidrofóbicos e de solvatação, principalmente envolvendo ligações de hidrogênio e interações dipolo-dipolo, dentre outras.…”

Quantification of solute–solute interactions in steroidal hormone removal by ultrafiltration membranes

“…Jin et al [5] observed the impact of different organic matter types on micropollutant adsorption behaviour. Membrane material can also have a significant influence on adsorption [11]. For example, Jermann et al [12] observed up to 80% adsorption of estradiol to polyethersulfone ultrafiltration (UF) membranes compared to only 8% adsorption to regenerated cellulose UF membranes.…”

Differential Estimation of Isomeric 2- and 4-methoxylated Estrogens in Serum by Matrix-assisted Laser Desorption Ionization-Tandem Mass Spectrometry

“…Based on the chemical structures of CHCA and the methoxylated estrogens, adducts could form through π-π interactions between the aromatic ring of the estrogens and the phenyl group of CHCA, cation-π interactions between the aromatic ring of the estrogens and the cyano group of CHCA, or through general hydrogen bonding between the two compounds. 19 Although interactions between the analyte and CHCA are not very strong, the ions [M+H+CHCA] + were selected as precursor ions to produce specific fragments of isomeric 2-and 4-methoxylated estrogens. The devised method is the first report, demonstrating that methoxyestrogens can be detected by MALDI-MS as analyte-matrix adducts using CHCA as the matrix, which resulted in good selectivity through the movement of small molecules.…”