Journal of Environmental Management 150 (2015) 387e392
Contents lists available at ScienceDirect
Journal of Environmental Management
journal homepage: www.elsevier.com/locate/jenvman
Can zero-valent iron nanoparticles remove waterborne estrogens?
a
a, Jan Filip b, *, Kla
ra Hilscherova
a, Jirí Tu
k Simek
Barbora Jarosova
cek b, Zdene
,
c, d , e
b
a
k Bla
ha
, Radek Zboril , Lude
John P. Giesy
a
Research Centre for Toxic Compounds in the Environment (RECETOX), Masaryk University, Kamenice 5, CZ-62500 Brno, Czech Republic
Regional Centre of Advanced Technologies and Materials, Departments of Physical Chemistry and Experimental Physics, Faculty of Science, Palacký
University in Olomouc, 17. listopadu 1192/12, CZ-771 46 Olomouc, Czech Republic
c
University of Saskatchewan, Department of Veterinary Biomedical Sciences and Toxicology Centre, 44 Campus Drive, Saskatoon, SK S7N 5B3, Canada
d
Department of Biology & Chemistry and State Key Laboratory in Marine Pollution, City University of Hong Kong, Kowloon, Hong Kong, China
e
State Key Laboratory of Pollution Control and Resource Reuse, School of the Environment, Nanjing University, Nanjing, People's Republic of China
b
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 18 October 2014
Received in revised form
30 November 2014
Accepted 3 December 2014
Available online 4 January 2015
Steroidal estrogens are one of the most challenging classes of hazardous contaminants as they can cause
adverse effects to biota in extremely low concentrations. They emerge in both waste waters and surface
waters serving as a source of drinking water. Environmental Quality Standards for 17b-estradiol (E2) and
17a-ethinylestradiol (EE2), promulgated within the EU Water Framework Directive, are 0.4 and
0.035 ng L1, respectively. Because nanoscale zero-valent iron (nZVI) particles have been previously used
in numerous remediation technologies and have the advantage of possible magnetic separation, interaction of nZVI with E2 and EE2 in water was investigated to assess the potential role of nZVI in removing
steroidal estrogens. A mixture of E2 and EE2 dissolved in water was shaken with varying doses of nZVI
for 1e5 h. Concentration-dependent removal of the estrogens was observed but removal did not increase
significantly with time. Concentrations of the estrogens were determined by HPLC/MS/MS and a biodetection reporter gene assay. Sorption and nonspecific oxygen-mediated oxidation of estrogens were
identified as the most probable removal mechanisms. Two independent experiments confirmed that
significant decrease of estrogens concentration is achieved when at least 2 g L1 of nZVI is applied. The
presented study provides insights into the mechanisms of nZVI interaction with steroidal estrogens
under aerobic conditions prevailing in currently applied water treatment technologies.
© 2014 Elsevier Ltd. All rights reserved.
Keywords:
Estrogens
Zero-valent iron nanoparticles
Sorption
Chemical composition
Total estrogenic activity
1. Introduction
In recent decades, the release of estrogens and other endocrinedisrupting compounds into the environment from anthropogenic
sources has become a major environmental problem worldwide
particularly affecting rivers and irrigation networks (e.g., Sumpter
and Johnson, 2005; Leusch et al., 2010). Estrogens have been
detected in wastewater, surface water, groundwater and even
drinking water (Leusch et al., 2009). In fish, as well as other aquatic
* Corresponding author. Tel.: þ420 585634959; fax: þ420 585634958.
E-mail address: jan.filip@upol.cz (J. Filip).
http://dx.doi.org/10.1016/j.jenvman.2014.12.007
0301-4797/© 2014 Elsevier Ltd. All rights reserved.
vertebrates, small concentrations (ng L1 range) of estrogens are
known to cause adverse effects, including feminization of males,
impaired reproduction and abnormal sexual development (Sellin
et al., 2009). Disruption of sexual function of wild fish, downstream of municipal wastewater treatment plants, has been
observed worldwide and attributed to estrogenic compounds
(Jobling and Tyler, 2003). The natural hormone, 17b-estradiol (E2),
and synthetic birth control pharmaceutical 17a-ethinylestradiol
(EE2) are reported to be the most potent estrogens in complex
environmental mixtures, such as contaminated surface waters
(Caldwell et al., 2012). Recently, Environmental Quality Standards
for E2 and EE2 promulgated as a part of the EU Water Framework
Directive have been set at 0.4 and 0.035 ng L1 for E2 and EE2,
respectively.
To monitor concentrations of steroidal estrogens in natural
water and wastewater, high performance liquid chromatography
388
et al. / Journal of Environmental Management 150 (2015) 387e392
B. Jarosova
combined with tandem mass spectrometry (HPLC/MS/MS) can be
used (Petrovic et al., 2004). However, such analytical method does
not provide information on possible interactions among the various
endocrine disrupting compounds within the mixture and/or other
not-measured or unexpected estrogenic compounds. This information can be complemented by in vitro biological assays which
evaluate the total estrogenicity of complex mixtures (Leusch et al.,
2010).
Improvements and optimization of water treatment technologies and/or development of advanced treatment methods are
needed to reduce concentrations of potentially harmful estrogens
in effluents and, consequently, surface waters (e.g., Grover et al.,
2011) especially when they serve as a source of drinking water.
Widely accepted technologies for efficient removal of estrogens are
based on advanced oxidation processes, sorption, filtration, and
biodegradation (Caliman and Gavrilescu, 2009). Some of these
methods are complicated by a decrease in effectiveness of sorbents/
filters over time, which therefore need to be replaced (Snyder et al.,
2003; Caliman and Gavrilescu, 2009). Ferromagnetic nanoscale
zero-valent iron (nZVI) particles are one of the promising advanced
nanomaterials suitable for water treatment technologies to remove
various inorganic and hazardous organic substances (Li et al.,
2006). The high efficiency and versatility of metallic iron in the
degradation (through effective reduction and catalysis) and
removal of more than 70 different environmental contaminants
have been demonstrated in dozens of laboratory and large-scale
studies (i.e., pilot and full-scale remediation at polluted sites,
Elliott and Zhang, 2001). Moreover, magnetic nanoparticles also
allow their simple magnetic separation from different remediation
technologies (Yavuz et al., 2006). However, to our knowledge, no
published study has focused on the interaction of nZVI with
estrogens.
Our previous experiences include synthesis, surface modification, detailed characterization and application of nZVI (Filip et al.,
2007; Klimkova et al., 2011; Marsalek et al., 2012; Filip et al.,
2014) and also detection of small concentrations of estrogens and
evaluation of their activity (Jarosova et al., 2012). The present work
examines the interaction of nZVI with estrogens (E2 and EE2).
Based on laboratory-scale experiments, including detection of
changes in estrogen concentrations and overall estrogenic activity
coupled with characterization of the solid materials, we identified
possible mechanisms for the interaction between estrogens and
commercially available nZVI particles.
2.2. Experimental design
Mixtures of estrogens were prepared in Milli-Q water at nominal
concentrations of 60 mg L1 for E2 and 120 mg L1 for EE2. These
initial concentrations are greater than those observed in the environment, but were selected so that 98% removal of the compounds
would still be greater than the detection limit of HPLC/MS/MS. Experiments were conducted in 1 L glass bottles, each containing 0.5 L
of estrogen solution and various concentrations of nZVI-A particles
(0, 2, 4 or 6 g L1). Bottles were tightly closed, kept at 21 C and
agitated at 180 rpm. Liquid samples were collected prior to nZVI
addition and after 1, 3, and 5 h of shaking. Glass vials containing the
liquid samples were placed on a magnetic plate for 8 min to separate
out the nZVI particles. Aliquots of solution (0.5 mL) were stored at
4 C until chemical analysis, which was completed within 2 d of
sampling. Verification of the effective concentration of nZVI, testing
of low concentrations of nZVI particles, and elucidation of the
possible mechanisms of E2 and EE2 interaction with nZVI were all
carried out with nZVI-B particles (at concentrations of 0, 0.04, 0.4, 2,
and 6 g L1). In these experiments, liquid samples were collected
prior to nZVI addition and after 1 and 5 h of shaking. Mixtures
containing nZVI-B particles at concentrations of 0.04 and 6 g L1 in
Milli-Q water were also prepared to act as negative controls, i.e.,
without estrogens. Separate samples of E2 and EE2 at maximum
solubility in water (i.e., about 1 mg L1) with 6 g of nZVI-B particles
(shaken for 1 h) were also prepared in order to examine the
mechanism of nZVI interaction with estrogens in further details.
Concentrations of E2 and EE2 in all the aqueous samples were
measured with HPLC/MS/MS. Simultaneously, changes in the estrogenic potencies of samples treated with 0, 2, 4, and 6 g L1 of
nZVI-A particles were investigated using an in vitro bioassay. To
elucidate the mechanism of estrogen interaction with nZVI, X-ray
€ssbauer and X-ray photoelectron
powder diffraction, 57Fe Mo
spectroscopy, Transmission Electron Microscopy (TEM) and SQUID
magnetometry were used to analyze the nZVI particles prior to and
after interaction with estrogens (i.e., 0.04 g L1 or 6 g L1 nZVI-B
interacting with 60 mg L1 of E2 and 120 mg L1 of EE2, and
6 g L1 nZVI-B interacting with 1 mg L1 of E2 or EE2), as well as in
the negative controls (for experimental details, see Supplementary
material). Particles of nZVI were obtained by magnetic separation
from the particular reaction dispersions.
2.3. Instrumentation employed for the analysis of liquid samples
(HPLC/MS/MS)
2. Materials and methods
2.1. Materials and reaction mixtures
E2 and EE2 estrogens were purchased from SigmaeAldrich
(Czech Republic). All reaction mixtures were prepared with Milli-Q
ultra-pure deionized water (18 MU cm1, Millipore). All chemicals
were of analytical reagent grade and used without further
purification.
The nZVI particles (commercially available as NANOFER 25N
with a specific surface area as z 20 m2 g1 and being manufactured
by NANO IRON company), were synthesized by thermal reduction
of iron oxide powder (Zboril et al., 2012; Filip et al., 2014). The
as-prepared dry nZVI particles were stored in hermetically
enclosed stainless steel containers under gaseous nitrogen at room
temperature and subsequently rapidly transferred (under an inert
gas but without vigorous mechanical stirring) into deionized water
(sample labeled as nZVI-A). The same type of nZVI particles were
transferred into deionized water under vigorous mechanical
stirring immediately prior to experiments (sample labeled as nZVIB).
An Agilent 1200 series HPLC system coupled to a 6410 TripleQuad MS (Agilent Technologies, Palo Alto, CA, USA) equipped
with an electrospray interface was used for HPLC/MS/MS analysis.
Separation of E2 and EE2 was performed on a C18 column ACE 3
(250 2.1 mm I.D., 3 mm, ACE, Aberdeen, Scotland, UK). Isocratic
elution (acetonitrile/1 mM L1 of ammonium acetate at pH ¼ 7, 65/
35 v/v) was carried out at 25 C with a flow rate of 0.1 mL min1.
The mass spectrometer was operated in the multiple reaction
monitoring mode with a negative polarity and a collision energy of
46 eV. The capillary voltage and fragmentation energy were 5000
and 220 V, respectively. Transition ions of E2 from m/z of 271.2 to
145.0, EE2 from m/z of 295.2 to 145.0 and estrone (E1) from m/z of
269.3 to 145.0 were monitored with a 250 ms dwell time. Quantification of E2, EE2, and E1 was achieved using external calibration
in the range from 5 to 160 mg L1. The detection limit of HPLC/MS/
MS, defined as amount of sample which produces a signal three
times higher than the noise level, was less than 2 mg L1 of injected
sample based on a 10 mL injection volume (i.e., 20 pg per injection).
The experimental error expressed as a coefficient of variation was
determined to be 11%.
et al. / Journal of Environmental Management 150 (2015) 387e392
B. Jarosova
2.4. In vitro bioassay
MVLN (human breast carcinoma) cells stably transfected with
the firefly luciferase gene under the control of an estrogenic receptor were used to determine the overall estrogenicity of the
selected samples (Demirpence et al., 1993). DMEM-F12 medium
without phenol red (Sigma Aldrich, USA) containing 10% fetal calf
serum was used for cell maintenance. For experiments, the same
medium was used but the serum was pretreated with dextrancoated charcoal, which greatly reduces the concentrations of natural steroids in the serum. During maintenance as well as experiments, cells were incubated at 37 C and 5% of CO2. For
experiments, cells were seeded into 96-well plates at a density of
25,000 cells/well. Each plate contained dilution series of standard
estrogen (1e500 pM E2) and of the samples, blank and solvent
controls (0.5% v/v methanol). Exposures were conducted in three
replicates for 24 h at 37 C. The intensity of luminescence was
measured using a Promega Steady Glo Kit (Promega, Mannheim,
Germany). For each tested sample, at least 2 independent experiments were conducted.
Results of the MVLN bioassay were expressed as estrogenic
equivalents (EEQ) following the method previously described by
Jarosova et al. (2014). Briefly, amount of E2 causing 50% of maximum
response (EC50) was related to the amount of the sample causing the
same (50%) response. Both EC50 (standard calibration and samples)
were determined by nonlinear logarithmic regression in the Graph
Pad Prism software (GraphPad Software, San Diego, USA).
3. Results and discussion
3.1. Phase, morphological, and magnetic characterization of used
nZVI particles
Since spontaneous nZVI oxidation prior to experiments may
have led to misinterpretation of the acquired data, we employed
various analytical techniques to characterize the nZVI particles in
detail prior to (and after) interaction with estrogens (for experimental details, see Supplementary material). Detailed quantitative
phase analysis of the nZVI particles, based on a combination of
Rietveld refinement of the XRD pattern (Fig. SM-1a in Supplementary material (SM)), relative spectral areas of the room€ ssbauer spectrum (Fig. SM-2), and magnetitemperature 57Fe Mo
zation measurements confirmed that the as-prepared nZVI samples
comprised of metallic a-Fe (>85 wt%) and lower abundances of
magnetite, Fe3O4 (<10 wt%), and wüstite, FeO (<5 wt%) (Fig. SM-1).
According to TEM, the nZVI particles in the used samples had a
relatively narrow particle-size distribution (from 30 to 150 nm),
with a mean diameter of 70 nm (Fig. SM-1b). The metallic iron core
of the particles was coated by a thin surface layer (approximately
4 nm thick; Fig. SM-1c) of iron oxides, resulting from the contact of
nZVI with water.
The magnetic properties of the nZVI particles were studied by
measuring their isothermal magnetization curve at room temperature (Fig. SM-3). Contrary to bulk iron, which typically exhibits
values of the room-temperature coercivity (BC,300K) and saturation
magnetization (MS,300K) of ~1.1 mT and ~210 Am2 kg1, respectively
(O'Handley, 2000), the studied multi-domain ferromagnetic nZVI
particles displayed values of BC,300K equal to 24 mT and MS,300K
equal to 174 Am2 kg1 (Fig. SM-3). An enhancement in BC,300K and
reduction in MS,300K are frequently reported for magnetically ordered materials with at least one dimension of less than ~100 nm
(Leslie-Pelecky and Rieke, 1996). In this case, dominant finite-size
effects (since particles were on average 70 nm in diameter)
together with some surface effects are likely responsible for the
increase in BC,300K and decrease in MS,300K.
389
3.2. Determination of efficiency and kinetics of estrogen removal by
nZVI
According to the results of the HPLC/MS/MS analysis, the lowest
tested concentration of nZVI to effectively remove estrogens was
2 g L1 (Figs. 1 and 2) for both types of nZVI samples (nZVI-A and
nZVI-B). At concentrations of 0 (controls), 0.04, and 0.4 g of nZVI
L1, the change in the initial estrogen concentrations (both E2 and
EE2) was within the experimental error of 11% (Fig. 2). After 1 h of
shaking with nZVI-A particles at concentrations of 2, 4, and 6 g L1,
the removal efficiency varied from 20 to 28% for E2 and from 27 to
64% for EE2, with the removal of both studied estrogens being
clearly dependent on the dose of nZVI (Fig. 1). After interaction of
2 g L1 of well-dispersed particles (nZVI-B sample) with the estrogenic mixture for 1 h, 13% of E2 and 46% of EE2 were removed
(Fig. 2). At the greatest tested concentration (6 g L1) of nZVI-B, 40%
and 93% of E2 and EE2, respectively, were removed after 1 h
interaction (Figs. 1 and 2). The efficiency of removal of estrogen by
well-dispersed nZVI-B particles was therefore better than by nondispersed nZVI particles for comparable nZVI doses (Figs. 1 and
2), indicating that the estrogen removal efficiency depended on
the free-surface availability of the nZVI particles. The effective
concentration of nZVI required to remove substantially the studied
estrogens was comparable to that determined in previous studies,
e.g., for the removal of color, chemical oxygen demand and biological oxygen demand in wastewater from distillery industry
(Homhoul et al., 2011), azo dye and carbaryl in aqueous solutions
(Cao et al., 1999; Ghauch et al., 2001) or typical toxic chlorinated
hydrocarbons in groundwater (Elliott and Zhang, 2001; Li et al.,
2006; Filip et al., 2007; Klimkova et al., 2011).
Kinetic experiments revealed that the removal of estrogens did
not increase greatly with exposure time. Maximum estrogen
removal was mostly achieved already within the first hour of
interaction with nZVI particles (Figs. 1 and 2). It is well-known that
adsorption equilibration requires much shorter time for particles
with large surface area compared to particles with smaller surface
area. For example, Liu et al. (2005) reported that equilibrium between E2, EE2 and colloids was reached within 5 min, whereas it
Fig. 1. Removal (% of initial concentration) of 17b-estradiol (E2), 17a-ethynylestradiol
(EE2) and total estrogenic activity (EEQ) after 1 h, 3 h, and 5 h of contact time with
nZVI-A particles. Concentrations of E2 and EE2 were determined by HPLC/MS/MS, EEQ
values were determined by MVLN in vitro assay. Error bars show standard deviations of
at least 2 independent experiments. For more details, see Section 2, Materials and
methods.
390
et al. / Journal of Environmental Management 150 (2015) 387e392
B. Jarosova
estrogenic activity of the mixtures. The results of the in vitro
bioassay were fairly consistent with the chemical analyses (Fig. 1).
Decrease in overall estrogenicity was significant at all the tested
concentrations, i.e., 2e6 g L1, of nZVI and it was dependent on the
amount of nZVI particles. The decrease occurred already during the
first hour of the contact time, with no significant further decrease at
prolonged times (Fig. 1). Any metabolites potentially formed from
E2 or EE2 would have much less pronounced estrogenic activity
compared to that shown by the parental estrogens. Indeed, formation of E1 with low concentrations, following estrogen contact
with nZVI, was confirmed by HPLC/MS/MS (see Section 3.4,
Mechanisms of nZVI interaction with estrogens), however, it exhibits much lower estrogenic potential in the MVLN assay than E2
and EE2 (Gutendorf and Westendorf, 2001). Therefore, partial formation of E1 did not increase the overall estrogenicity of the
sample. This finding is in contrast with Sumpter and Johnson
(2005), who reported that E1 could eventually pose environmental risks at elevated concentrations.
3.4. Mechanisms of nZVI interaction with estrogens
Fig. 2. Decreasing concentrations of 17b-estradiol (E2) and 17a-ethynylestradiol (EE2)
and increasing concentrations of E1 after 1 h and 5 h of contact time with nZVI-B
particles as determined by HPLC/MS/MS. For more details, see Section 2, Materials
and methods.
took from 10 to 14 d in the case of river sediments composed of
much larger particles (Yu et al., 2004). Powdered activated carbon
(as ranging from approximately 500 to 1500 m2 g1) used in many
full-scale drinking water treatment plants as a sorbent of taste,
odors and organic micro-pollutants (including estrogens) is typically applied for contact times of 1e5 h (Yoon et al., 2003; Humbert
et al., 2008).
Interestingly, EE2, which is more persistent in the environment
than E2 as well as being a more potent estrogen in vivo (Young et al.,
2004), was removed more rapidly than E2 (Figs. 1 and 2). Under
environmental conditions, E2 is relatively easily biodegraded to E1
and other less estrogenic compounds, whereas EE2 biodegradation
has been reported to be poor by microorganisms in different kinds
of activated sludge (Johnson and Sumpter, 2001). For the more hydrophobic estrogen, EE2, sorption onto activated sludge or other
particulate matters like sediments has been suggested as the main
mechanism of its removal (Young et al., 2004), which could also play
a role in the EE2 removal by nZVI in the present study (as discussed
in the Section 3.4, Mechanisms of nZVI interaction with estrogens).
3.3. Confirmation of reduction of overall estrogenic activity
In addition to the monitoring of E2 and EE2 concentrations by
HPLC/MS/MS, an in vitro MVLN bioassay was used to assess overall
Along with decreased concentrations of E2 and EE2 in the liquid
samples, formation of estrone, E1, was detected by HPLC/MS/MS.
Estrone was not present in substantial amounts in control samples
or samples with <2 g L1 of nZVI. E1 concentrations increased with
increasing concentration of nZVI but not with time (Fig. 2). The
maximum concentration of E1 (13 mg L1, corresponding to
approximately 20% of the initial concentration of E2 or 10% of EE2)
was detected in the samples with 6 g L1 of nZVI, which removed
about 40% of E2 and 90% of EE2, respectively.
Estrone is a typical oxidative product of estrogen chemical
degradation. Although zero-valent iron typically acts as a highly
efficient reductant, several recent studies have shown that aqueous
corrosion of nZVI by dissolved oxygen can produce reactive nonspecific oxidant(s), such as hydroxyl radical, capable of oxidatively degrading a broad range of inorganic and organic contaminants (Mylon et al., 2010). Therefore, detection of the oxidative
product of E2 or EE2 chemical degradation (i.e., E1) in the present
study is in accord with these studies, where by-products formed
during nZVI-mediated chemical degradation (e.g., of herbicide
molinate and chlorophenols) were consistent with the action of
non-specific oxidants, such as the hydroxyl radical (Feitz et al.,
2005). Feitz et al. (2005) also suggested that the high specific surface area of nZVI may allow highly efficient generation of oxidants,
but formation of iron oxides on the nZVI surface is likely to cause a
decrease in reactivity. This might be one of the important factors,
together with the expected sorption, responsible for the relatively
fast equilibration in E2 and EE2 removal observed in our study.
Even though E2 and/or EE2 were at least partially transformed
into E1, the fact that the less hydrophobic E2 was removed less
rapidly than EE2 could suggest sorption as another possible interaction of nZVI with estrogens, being one of the well-known
mechanisms of estrogen removal from water, for example, on
powdered activated carbon (Yoon et al., 2003). Indeed, iron oxides
present on the surface of nZVI particles (Fig. SM-1b) are known as
sorbents for a wide variety of chemical compounds including estrogens (Lai et al., 2000). The sorption of estrogens (and/or products
of their chemical degradation) on nZVI particles is further consistent with both the doseeresponse dependence of fast estrogen
removal and the fact that more estrogens were removed by welldispersed nZVI particles (due to more surface sites being exposed
for possible estrogen sorption).
Also, other experimental evidence supports the abovesuggested sorption of estrogens on nZVI surfaces. The slight
decrease in magnetization (see below), together with no detectable
et al. / Journal of Environmental Management 150 (2015) 387e392
B. Jarosova
changes in phase composition of nZVI after interaction with estrogens (see Figs. SM-1a and SM-2 for the XRD pattern and 57Fe
€ssbauer spectrum, respectively) could imply the partial sorption
Mo
of estrogens (and/or products of their chemical degradation) onto
the surface of nZVI. Comparison of high-resolution Fe 2p XPS
spectra of the nZVI surface prior to and after reaction with estrogens (Fig. 3) showed no changes in the surface characteristics of
iron upon interaction of nZVI with estrogens. The presence of
iron(II,III) oxides on the surface of nZVI (both in control samples
and nZVI-B interacting with 1 mg L1 of E2 and EE2; Fig. 3) indicates that the only direct reaction occurred between nZVI and
water (Filip et al., 2014), i.e., a partial surface oxidation accompanied by formation of aqueous reactive species (Keenan and Sedlak,
2008). The slight changes in C 1s and O 1s XPS spectra (Fig. 3),
namely emergence of new spectral band at a binding energy of
391
288 eV, could also indicate partial sorption of organic compounds
containing oxygen and carbon (like estrogens and/or products of
their chemical degradation) on the surface of the nZVI particles.
Comparing the acquired magnetization data of the
nZVI þ estrogen system (nZVI-B) with those obtained for bare nZVI
particles interacting solely with deionized water, only a reduction
in the value of MS,300K was observed (~160 Am2 kg1). The value of
BC,300K (~24 mT), as well as magnetic saturation capability and
strong magnetic response of the nZVI þ estrogen system towards
external magnetic fields (Fig. SM-3), remained unchanged. The
slightly increased amount of ferrimagnetic iron oxides (i.e.,
magnetite and/or wüstite) in the oxide shell of the nZVI particles
after interaction with estrogens would change the value of MS,300K
only slightly; the decrease of MS,300K from ~174 Am2 kg1 to
~160 Am2 kg1 theoretically requires the presence of ~50 wt.% of
magnetite and/or wüstite in the nZVI sample (i.e., it is inconsistent
€ssbauer spectroscopy, and TEM obwith results of XRD, 57Fe Mo
servations, where <20 wt.% of total iron oxides was detected for all
the nZVI samples). Moreover, the unchanged coercivity value and
preserved symmetry of the hysteresis loop around its origin (see
inset in Fig. SM-3) also suggest no increase in the iron oxide/hydroxide content in the reacted nZVI sample compared to bare nZVI.
Therefore, the decrease in MS,300K of the nZVI þ estrogen system
could partly be caused by adsorbed estrogen(s) (and/or products of
their chemical degradation) on the surface of nZVI particles
behaving as weakly diamagnetic to almost nonmagnetic compounds, thus reducing the overall magnetization values of the
sample. This finding also supports the hypothesis that sorption of
estrogens (and/or products of their chemical degradation) on the
surface of nZVI particles is an important mechanism during estrogen removal. Therefore, under the experimental conditions used,
the surface interaction of nZVI with estrogens appears to involve (i)
rapid sorption, accompanied by (ii) oxidative decomposition of the
estrogens.
4. Conclusions
Fig. 3. High-resolution Fe 2p, O 1s, and C 1s core level photoelectron spectra of the
control sample (nZVI-B after interaction with pure water) and nZVI-B after interaction
with 1 mg L1 of estrogens. The vertical arrow indicates the spectral band ascribed to
CeO bond of estrogens adsorbed on the nZVI surfaces.
The results from batch experiments reported here demonstrate
that E2 and EE2 can be at least partly removed by nZVI even under
oxidative conditions which are usually present at common waste/
drinking water treatment works. The removal was dependent on
the concentration of nZVI and occurred already in the shortest
tested time of exposure (1 h) in doses equal or greater than 2 g L1.
Results of chemical and effect-based analyses of estrogens in liquid
samples are highly comparable. Based on detection of oxidative
product of E2 or EE2 together with extensive analyses of nZVI
particles before and after interaction with estrogens, the proposed
mechanisms of estrogen removal involve a combination of sorption
onto the nZVI surface and chemical oxidative degradation (documented by formation of less bioactive estrone). However, the
determined effective concentrations of nZVI were about three orders of magnitude greater than doses of, for example, activated
carbon, which is traditionally used for removal of micro-pollutants
including estrogens (Yoon et al., 2003; Humbert et al., 2008). In
addition, none of the observed mechanisms of removal can be
considered as estrogen-specific. Estrogens occur and cause adverse
effects in concentrations in about three orders of magnitude less
than those of number of other pollutants commonly co-occurring in
treated waste waters (Caldwell et al., 2012). Therefore, in real water
systems, nZVI would interact preferentially with a broad range of
other compounds, but in water-treatment technologies utilizing
nZVI (e.g., nZVI-modified filters, targeted sludge treatment, etc.), it
is likely to participate in removing of estrogens and the nZVImediated partial decrease in the concentration of estrogens can
be expected.
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et al. / Journal of Environmental Management 150 (2015) 387e392
B. Jarosova
Acknowledgments
e
ra C
pe for electron microscopy charThe authors thank to Kla
acterization of the studied samples, Luk
as Kalina for XPS measurements and Zdenka Markov
a for performing supporting
experiments and measurements. This work was supported by
grants from the EU FP7 (project AQUAREHAB and NANOREM),
Ministry of Industry and Trade of the Czech Republic (projects No.
FR-TI3/622 and FR-TI3/196), Technology Agency of the Czech Republic “Competence Centers” (project No. TE01020218), Grant
Agency of the Czech Republic (GACR 13-20357S e “The study of
distribution of steroid compounds in constituents of solid environmental matrices”), and Ministry of Education, Youth and Sports
of the Czech Republic (projects LO1305 and LO1214). Prof. Giesy
was supported by the Canada Research Chair program, a Visiting
Distinguished Professorship in the Department of Biology and
Chemistry and State Key Laboratory in Marine Pollution, City University of Hong Kong, the 2012 “High Level Foreign Experts”
(#GDW20123200120) program, funded by the State Administration
of Foreign Experts Affairs, the P.R. China to Nanjing University and
the Einstein Professor Program of the Chinese Academy of Sciences.
Appendix A. Supplementary data
Supplementary data related to this article can be found at http://
dx.doi.org/10.1016/j.jenvman.2014.12.007.
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Supporting Material
Can zero-valent iron nanoparticles remove waterborne estrogens?
Barbora Jarošováa, Jan Filipb*, Klára Hilscherováa , Jiří Tučekb, Zdeněk Šimeka, John P.
Giesyc,d,e, Radek Zbořilb, Luděk Bláhaa
a
Research Centre for Toxic Compounds in the Environment (RECETOX), Masaryk University,
Kamenice 5, CZ-62500 Brno, Czech Republic
b
Regional Centre of Advanced Technologies and Materials, Departments of Physical Chemistry
and Experimental Physics, Faculty of Science, Palacký University in Olomouc, 17. listopadu
1192/12, CZ-771 46 Olomouc, Czech Republic
c
University of Saskatchewan, Department of Veterinary Biomedical Sciences and Toxicology
Centre, 44 Campus Drive, Saskatoon, SK, Canada, S7N 5B3
d
Department of Biology & Chemistry and State Key Laboratory in Marine Pollution, City
University of Hong Kong, Kowloon, Hong Kong, SAR, China
e
State Key Laboratory of Pollution Control and Resource Reuse, School of the Environment,
Nanjing University, Nanjing, People’s Republic of China
*
corresponding author: Phone: +420 585634959, Fax: +420 585634958, E-mail address:
jan.filip@upol.cz
1
Instrumentation employed for the characterization of nZVI particles
A PANalytical X´Pert PRO diffractometer (Bragg-Brentano geometry with iron-filtered
CoKα radiation: 40 kV, 30 mA) was used to obtain X-ray powder diffraction (XRD) patterns
from key nZVI samples. Magnetically pre-concentrated slurries were inserted into a conventional
front-loading shallow cavity sample holder and repeatedly scanned over the 2θ range of 20 to
105° under ambient conditions (8 fast scans per hour, during which samples were partially
dried). Phase analysis and Rietveld refinement was performed using the HighScore Plus
software, PDF-4+ and ICSD databases.
57
Fe Mössbauer spectra were collected in transmission geometry (constant acceleration
mode) with a
57
Co (in Rh matrix) radioactive source (1.85 GBq). The values of hyperfine
parameters (i.e., isomer shift values) were calibrated against a rolled metallic iron (α-Fe) foil at
room temperature. Spectra were fitted by Lorentz functions using the software CONFIT2000.
The experimental error is ± 0.02 mm s-1 for hyperfine parameters and ± 2% for relative spectral
areas.
For detailed microscopic characterization of the surface of nZVI particles we used a JEOL
JEM-2010 TEM (LaB6 cathode, accelerating voltage of 200 kV, point-to-point resolution of
0.194 nm). The nZVI particles were ultrasonically dispersed in high-purity distilled water,
dropwise placed onto copper-mesh TEM grid covered by holey carbon film (SPI Supplies, USA)
and air-dried at ambient temperature.
Sample magnetization was measured by a superconducting quantum interference device
(SQUID, MPMS XL-7, Quantum Design). Hysteresis loops of the investigated samples were
collected at 300 K under external magnetic fields ranging from – 7 to + 7 T.
Detailed surface chemistry of key nZVI samples was determined by Kratos AxisUltra DLD
X-ray photoelectron spectrometer - XPS (monochromatic AlKα X-ray source: 1486.6 eV, 600 W
and 15 kV). Binding energies were conventionally corrected by the C 1s peak (set at 284.8 eV).
A charge-neutralization was applied during all measurements. Samples were prepared by placing
air-dried nZVI particles onto a carbon tape. High-resolution XPS spectra were accumulated with
0.1 eV step size and pass energy of 23.5 eV. Data were processed using software CasaXPS.
2
Figure SM-1. Detailed characterization of nZVI particles prior to and after interaction with 1 mg
L-1 of estrogens: (a) X-ray powder diffraction patterns of nZVI particles prior to (bottom) and
after (top) interaction with estrogens, m - magnetite Fe3O4, w - wüstite FeO; (b) particle size
distribution derived from TEM images; (c) TEM image of bare nZVI particles; (d) TEM image
of nZVI particles after interaction with 1 mg L-1 of estrogens (i.e., nZVI with adsorbed
estrogens).
3
Figure SM-2. Characterization of nZVI particles by room-temperature
57
Fe Mössbauer
spectroscopy (a) prior to and (b) after interaction with 1 mg L-1 of estrogens. See the text for
further details.
4
Figure SM-3. Room-temperature hysteresis loops of (a) bare nZVI particles, and (b) nZVI
particles after interaction with 1 mg L-1 of estrogens (Note the different ranges on y-axes).
5