Influence of natural organic matter on horseradish peroxidase-mediated removal of 17α-ethinylestradiol: Role of molecular weight
Graphical abstract
Introduction
Endocrine disrupting chemicals (EDCs) are attracting public concern and growing research interest due to their potent and detrimental effects on human and wildlife [[1], [2], [3], [4]]. This broad class of pollutants are generally persistent and environmentally mobile, and a variety of studies have reported their occurrence in aquatic environment [5]. 17α-ethinylestradiol (EE2), the major component of the contraceptive pill, is among the most commonly detected endocrine disruptors [6]. It is more stable than natural estrogens and contributes to a lager extent to the estrogenicity in surface water [7].
The fate of EDCs is mainly governed by two intricate counter-directional processes: biochemical degradation and humification [8]. Degradation results in the decrease of contaminant sizes, while the latter are processes where small molecules are aggregated into macromolecular structures for eventual formation of humic substances. Oxidative coupling process mediated by extracellular enzymes, like horseradish peroxidase (HRP), is a class of humification process, and has been shown to be highly efficient and specific in the removal of phenolic compounds [9]. In this sense, enzymatic reaction is also supposed to be promising alternative to address EDCs and other micropollutants that are sensitive to peroxidases, as reported previously [10].
However, either in natural or water treatment process, such potentially important reaction is strongly impacted by natural organic matter (NOM) which is ubiquitous in aquatic environment. Recently, it is becoming generally recognized that NOM is supramolecular association of relatively small heterogeneous molecules by weak dispersive forces (van der Waals, CH/π) [11], which indicates NOM may serve as a substrate of peroxidase since it is partially comprised of phenolic compounds. This assumption could lead to highly variable results with different substrates. For instance, the removal efficiency of substrates which are comparatively less sensitive to peroxidase, like polychlorinated biphenyls (PCBs), is enhanced, because more nonspecific free radicals are generated in the reaction between enzyme and NOM compared to enzyme and substrate [8,12]. Conversely, inhibitory effect of NOM was observed, perhaps by the same reason, for the reaction system with substrates which are sensitive to peroxidase, like estrogens [1]. The availability of substrates may also be modified by the noncovalent interactions with NOM, which is highlighted by noting the effect of NOM on the adsorption or biodegradation process of EDCs [13,14]. Gadad et al. directly demonstrated this effect by using steady-state fluorescence spectroscopy and further distinguished the interaction type of NOMs with varying aromaticity [15]. It’s thus hypothesized that NOM may sequester EDCs from the oxidation process mediated by peroxidase.
The molecular weight (MW) of the polydispersed organic substances in NOM ranges from less than 100 Da to over 300 kDa, and the chemical complexity of NOM has far prevented researchers from finding out the primarily responsible components for the specific effect on enzymatic reactions [16]. MW fractionated NOMs (Mf-NOMs) usually differed greatly in biochemical properties. Low MW fractions are found to contain more carboxylic groups, while aromatic groups are concentrated in high MW fractions. This indicates the effect of NOM on the biochemical reactions may further diverge as a function of MW. Unfortunately, no relevant research in terms of the effect of the Mf-NOMs on the enzymatic reactions is found. In previous researches, the influence of NOM was usually investigated by considering it as simple macromolecular polymers as polysaccharide, and the results were explained with single and ambiguous mechanism, which actually were the combined effects of various components in NOM [[17], [18], [19], [20]]. In another word, the role of NOM was not differentiated.
The objective of this study is to illustrate the different mechanisms by which pristine and Mf-NOM impact the HRP-mediated transformation of EE2 and to analyze the relative importance of these mechanisms to the reaction. Suwannee River Natural Organic Matter (SRNOM) was selected and fractionated by ultrafiltration (UF) into four fractions (<1 kDa, <10 kDa, <30 kDa, Bulk). The fractionated NOMs were then applied to explore their underlying roles on the enzymatic reactions.
Section snippets
Materials
HRP (type 2, units 250 U mg−1), 2, 2′- azino - bis (3-ethylbenzthiazoline-6-sulfonic acid) (ABTS) (98% in diammonium salt form), EE2 (purity > 99%), H2O2 (30% wt), bovine serum albumin (BSA), dextran and sodium polystyrenesulfonate (PSS) were purchased from Sigam-Aldrich Corporation (St. Louis, MO, USA). Suwannee River Natural Organic Matter (SRNOM) (2R101 N) was obtained from the International Humic Substance Society (IHSS) (St. Paul, MN, USA). A solvent-resistant stir cell with 1 kDa, 10 kDa
Characteristics of pristine and Mf-NOM
Three fractions of NOM with MW <30 kDa, <10 kDa and <1 kDa were obtained by UF. Table 1 shows the characterization of pristine and Mf-NOM. From the TOC values of each fraction, it can be seen that small (<1 kDa) and large (>30 kDa) MW components were relatively abundant. It should be noted that considering only filtrate was collected, high MW NOM fraction was actually a mixture containing low, medium and high MW components. The value of SUVA254 for pristine NOM was much larger than that for
Conclusions
This study reveals that NOM can strongly inhibit the HRP-mediated transformation of EE2, and the effects of NOMs are MW-dependent. Low Mf-NOMs restrains the enzymatic reaction by acting as competitive substrates, while the inhibition from high Mf-NOMs are primarily attributed to the sequestration of EE2 from the HRP attack. The contribution of each inhibitory process to the inhibition induced by pristine NOM is quantified and found to be related to reaction conditions, especially EE2
Acknowledgement
This work was supported by the National Natural Science Foundation of China (21577059)
References (43)
- et al.
Transformation of 17 alpha-ethinylestradiol by simultaneous photo-enzymatic process in humic water
Chemosphere
(2017) - et al.
The impact of chromophoric dissolved organic matter on the photodegradation of 17alpha-ethinylestradiol (EE2) in natural waters
Chemosphere
(2014) - et al.
Natural and synthetic hormone removal using the horseradish peroxidase enzyme: temperature and pH effects
Water Res.
(2006) - et al.
Polymerization of dissolved humic substances catalyzed by peroxidase. Effects of pH and humic composition
Org. Geochem.
(2002) - et al.
Enhanced enzymatic removal of chlorophenols in the presence of co-substrates
Water Res.
(1995) - et al.
Removal of estrone and 17beta-estradiol from water by adsorption
Water Res.
(2005) - et al.
Bioavailability of HOC depending on the colloidal state of humic substances: a case study with PCB-77 and daphnia magna
Chemosphere
(2005) - et al.
Characterization of noncovalent interactions between 6-propionyl-2-dimethylaminonaphthalene (PRODAN) and dissolved fulvic and humic acids
Water Res.
(2007) - et al.
The effect of dissolved organic matter on soybean peroxidase-mediated removal of triclosan in water
Chemosphere
(2017) - et al.
Ligninase-mediated removal of 17beta-estradiol from water in the presence of natural organic matter: efficiency and pathways
Chemosphere
(2010)
Effects of humic substance characteristics on UF performance
Water Res.
Characterization of DOM as a function of MW by fluorescence EEM and HPLC-SEC using UVA, DOC, and fluorescence detection
Water Res.
Role of NOM molecular size on iodo-trihalomethane formation during chlorination and chloramination
Water Res.
Influence of NOM and SS on the BPA removal via peroxidase catalyzed reactions: kinetics and pathways
Sep. Purif. Technol.
Steady-state oxidation model by horseradish peroxidase for the estimation of the non-inactivation zone in the enzymatic removal of pentachlorophenol
J. Biosci. Bioeng.
Anhibitory effect of humic and fulvic-acids on oxidoreductases as measured by the coupling of 2,4-dichlorophenol to humic substances
Sci. Total Envir.
Interaction between polychlorinated-biphenyls and marine humic substances - determination of association coefficients
Chemosphere
Biotransformation of soil humic acids by blue laccase of Panus tigrinus 8/18: an in vitro study
Soil. Biol. Biochem.
Laccase-catalyzed removal of the antimicrobials chlorophene and dichlorophen from water: reaction kinetics, pathway and toxicity evaluation
J. Hazard. Mater.
Ligninase-mediated removal of natural and synthetic estrogens from water I. reaction behaviors
Environ. Sci. Technol.
Hormones and endocrine-disrupting chemicals: low-dose effects and nonmonotonic dose responses
Endocr. Rev.
Cited by (17)
Revealing the characteristics of biofilms on different polypropylene plastic products: Comparison between disposable masks and takeaway boxes
2024, Journal of Hazardous MaterialsPhotoelectrocatalytic selective removal of group-targeting thiol-containing heterocyclic pollutants
2023, Journal of Hazardous MaterialsTrade-off effect of dissolved organic matter on degradation and transformation of micropollutants: A review in water decontamination
2023, Journal of Hazardous MaterialsCoupling horseradish peroxidase based bioreactor with membrane distillation: Elucidating antibiotics degradation and membrane fouling mitigation
2022, DesalinationCitation Excerpt :Literature shows that co-occurring organic matter may act as substrate for HRP, leading to generation of active radicals due to the reaction between organic matter and HRP enzyme. These active radicals can help in the degradation of some contaminants that are relatively stable towards HRP treatment [50]. Moreover, organic matter can facilitate antibiotics removal by cross coupling of reactive intermediate produced during enzyme catalytic cycle.