## Abstract

Arsenic contamination of water sources is a global problem, affecting numerous (especially developing) countries across the world. Exposure to exorbitantly high concentrations reaching 400 parts per billion of arsenic in water sources lead to numerous health complications, including the development of respiratory, neurological, and cancerous diseases. This study focused on developing an innovative, low-cost, and gravity-driven filtration system using a novel iron oxide nanoparticle-loaded polyurethane (PU) foam by which people in developing countries may have easy access to an effective, affordable, and easily fabricated filtration system. After successfully synthesizing the new iron oxide nanoparticle-loaded PU foam, effectiveness of the foam was tested by developing a filtration system consisting of vertical polyvinyl-chloride tubing inserted with 10 and 20 cm of PU foams. Samples of arsenic-contaminated water with known concentrations of 100 and 200 ppb were run through each of the systems numerous times for one and five run cases. The system with 20 cm of PU foam and five runs successfully filtered out around 50–70% of the arsenic from the 100 and 200 ppm samples. The filtration process was quite fast (and hence practical) with each run completing in 5–10 minutes' time. Future research is expected to improve this promising start.

## INTRODUCTION

Arsenic contamination of water is a widespread problem that affects many different parts of the world. Natural weathering and anthropogenic sources, such as mining and use of coal-fired power plants, leads to the exacerbation of this issue. Ranging from the developed nations, including the United States and Canada, to developing countries such as Bangladesh, India, and China, arsenic contamination has affected numerous different populations across the world and proven to be extremely injurious to human health. Arsenic exposure has many dermal, gastrointestinal (Yang et al. 2011; Alava et al. 2015; Calatayud & Laparra Llopis 2015; Chávez-Capilla et al. 2016), neurological (Halatek et al. 2009; Yorifuji et al. 2016), and cardiovascular effects (Mehta et al. 2015; Phung et al. 2017), some of which include hemorrhagic gastroenteritis, skin, lung, and bladder cancer (Lesseur et al. 2012; Melak et al. 2014; Yeh et al. 2015; Lynch et al. 2017), and peripheral neuropathy (Brocato & Costa 2015; Duan et al. 2015; Ameer et al. 2017). The International Agency for Research on Cancer (IARC) and U.S. Environmental Protection Agency (EPA) have both classified and established inorganic arsenic as a known human carcinogen (Gehle). This carcinogenic inorganic arsenic compound is what is contaminating water sources across the world, as compared to the less harmful organic arsenic compounds that are commonly found in seafood (World Health Organization 2018).

The bodies of water that are most affected by arsenic contamination are groundwater sources. The arsenic primarily present within said sources are oxy anions with two different oxidation states: arsenite (As(III)) and arsenate (As(V)) (Ferguson & Gavis 1972; Cullen & Reimer 1989). Although the introduction of arsenic into these sources of water can occur naturally due to its presence in surrounding bedrock, especially in areas of West Bengal and China, this arsenic contamination can be exacerbated through numerous human activities. These include industrial activities of mining, smelting, coal-fired power plants, and the environmental effects of various agricultural pesticides used for wood preservation (Garelick et al. 2009).

Although many countries are affected by arsenic water contamination, including Argentina, China, Chile, Mexico, India, and USA, Bangladesh is an important example of a country affected by severe arsenic exposure. Since the early 2000s, around 35–77 million of its people have been exposed to dangerously high levels of arsenic in water sources (Anthamatten & Hazen 2012). This is due to the fact that an extremely high percentage of Bangladesh's population depends on tube wells to access groundwater sources since they avoid taking water from the pathogen-contaminated surface-water sources such as lakes and ponds. In rural areas, over 97% of the rural population depends on such groundwater sources, which has resulted in a large-scale exposure to high arsenic levels due to the lack of access to clean water. Thus, in 2009, 65 million people were surveyed for national quality of water and were found to be exposed to concentrations above the national standard of 50 parts per billion (ppb) and the World Health Organization's international standard of 10 ppb (Flanagan et al. 2012). These concentrations were found to reach extremely high and dangerous concentrations of arsenic, in some areas reaching as high as 400 ppb (Figure 1, (Wilson 2009)).

Figure 1

These are four maps of Bangladesh that show four worsening levels of arsenic contamination in various areas. As presented through the map, there are alarming concentrations that surpass the World Health Organization's international standard of 10 ppb of arsenic in water sources, with concentrations beyond 400 ppb in certain areas. (Adapted from (Wilson 2009), reprinted with permission from Dr. Richard Wilson).

Figure 1

These are four maps of Bangladesh that show four worsening levels of arsenic contamination in various areas. As presented through the map, there are alarming concentrations that surpass the World Health Organization's international standard of 10 ppb of arsenic in water sources, with concentrations beyond 400 ppb in certain areas. (Adapted from (Wilson 2009), reprinted with permission from Dr. Richard Wilson).

The removal of arsenic, essentially, involves a selective separation of As(V) and As(III). The conventional treatment methods of arsenic involve a coagulation with ferric chloride or aluminum sulfate coagulants, followed by the separation of the produced insoluble by settling, or by direct filtration through sand beds (Wickramasinghe et al. 2004; Terracciano et al. 2015; Mahdavi et al. 2017). Other treatment techniques for arsenic removal are: reverse osmosis (McNeill & Edwards 1997; Ning 2002; Teychene et al. 2013; Abejón et al. 2015; Schmidt et al. 2016); flotation and adsorption on hydrated iron oxide or activated carbon (DeMarco et al. 2003; Gu et al. 2005; Gupta et al. 2005; Wu et al. 2008; Di Natale et al. 2013; Asadullah et al. 2014; Siddiqui & Chaudhry 2017; Xiong et al. 2017; Xu et al. 2017); and absorptive media (Adsorptive arsenic removal media modelled 2007; Baig et al. 2013; Chen et al. 2015; Yazdani et al. 2016; Chatterjee & De 2017). These methods have been reported to be effective, mainly, for the removal of pentavalent arsenic As(V). Therefore; a pre-oxidation step is usually required in order to achieve efficient removal of trivalent arsenic As(III).

As mentioned above, there are numerous available options for arsenic filtration, including reverse osmosis and anionic exchange systems (Oregon Health Authority), but there is a newer type of filtration material that is showing potential to be used in filtration systems: polyurethane (PU) foam. There has been some research into the synthesis and characterization of this synthetic foam, especially for its porous-medium properties of permeability and porosity that mark its potential as a filter (Cao et al. 2005). Properties such as low costs, recyclability, and easy room-temperature fabrication has made this material very attractive as a filter. Progressively, these PU foams have been modified to incorporate various compounds for specific water-filtration applications, such as the silver nanoparticle-coated PU foams developed as an antibacterial water filter (Jain & Pradeep 2005). However, to date, limited research has been conducted for the specific application of arsenic removal using this novel synthetic foam.

Solid phase nano adsorbents are becoming the core of most recent works in removing heavy metals due to their high capacity and affinity to heavy metal ions. Nano adsorbents, such as, hydrous ferric oxide (HFO) (Zhang et al. 2008) and magnesium oxide (MgO) (Choi et al. 2014), have been deposited on the surface of porous materials. However, the preparation of these adsorbents often involves complex and costly methods. Iron oxide has proven to be a popular compound used for arsenic filtration that is even incorporated into many commercial arsenic-filtration products. The high affinity that this compound has for arsenic contaminants allows iron oxide to play an important role in arsenic filtration research (Katsoyiannis & Zouboulis 2002). Iron oxide-coated polymers and various other synthetic materials have been researched to understand their filtration capabilities, and the incorporation of iron oxide into PU foam has also been investigated (Hussein & Abu-Zahra 2017b).

Prior research has been successful in synthesizing an open-cell PU foam with iron oxide nanoparticles (IONPs) embedded within it. Through a single column study, all arsenic species within the arsenic samples of 60 ppb were removed after 22 cycles (approximately 9 days) of the operating period (Hussein 2016). In addition, modified versions of the PU foam were tested through batch and column studies and showed 87–88% lead removal efficiency (Gunashekar 2015). Therefore, the potential for these specialized PU foams to have a significant impact in the future of water filtration is evident.

## RESEARCH AIM

The purpose of this study is to synthesize a nanocomposite PU foam embedded with iron oxide nanoparticles by incorporating these adsorbent particles within the foam media. After creating such a composite, the second part of the overall purpose is developing a low-cost and gravity-driven filtration system with iron oxide nanoparticle-infused PU foam to not only test the effectiveness of the foam in filtering out arsenic present in contaminated water, but also develop an alternative option for filtration that is less expensive, more sustainable, and usable in the third-world rural areas marked with low-supply/absence of electricity. By developing such a prototype device, this study hopes to present another option of an adsorptive filtration system that can successfully extract the harmful arsenic from water.

The novelty in this work lies in developing a new gravity-driven low-cost filtration system capable of utilizing the previously synthesized PU foam nanocomposites to remove arsenic from water with comparable removal efficiency at a fraction of the time, compared to what has been reported in previous works.

## METHODOLOGY

### Synthesis of polyurethane foam with iron oxide

To synthesize the nanocomposite polyurethane foam, modifications need to be made to the current PU foam synthesis processes in order to incorporate the iron oxide nanoparticles. In the standard process, the two main components that create the PU foam are 2,4-toluene diisocyanate (TDI) and polypropylene glycol (PPG). TDI is an important aromatic isocyanate that is used within the polyurethane industry. It acts as the unique and basic monomer that PU foams are comprised. The PPG is a polyol that determines the final properties of the PU foam. It is a polymer of propylene glycol and is chemically a polyether. The presence of the hydroxyl groups within this compound makes PPG the optimum raw material used in polyurethanes as the hydroxyl groups react with the TDI monomers to produce the polyurethane monomer.

Therefore, within this study, PPG was used as the only polyol to react with the TDI to control the pre-polymer chemistry and allow for the iron oxide nanoparticles to be incorporated into the PU foam synthesis process and, ultimately, functionalize the final PU foam product. The molar ratio of TDI to PPG used in this synthesis process was 2:1 (Hussein 2016), thus requiring 18.4 g of TDI to 50 g of PPG, based on molar mass values. Before the start of the synthesis and mixing process of the chemical compounds of the PU foam, the PPG was heated and sealed in a vacuum furnace at around 70 °C for 24 hours in order for the PPG to be effectively expressed.

An experimental setup was established using a three-necked round-bottom reaction flask to correctly mix and allow for the PPG and TDI chemical molecules to thoroughly react with one another (Figure 2). The round-bottom flask was submerged halfway in a mineral oil bath in order to provide uniform heating for the reaction between the chemical constituents of TDI and PPG. This entire system was placed on a hotplate stirrer, and a magnetic stir bar was placed inside the round-bottom flask in order to mix the components during the reaction process. As shown in Figure 2, as the round-bottom flask was clamped to a stand, the middle neck was plugged in order to maintain a sealed environment during the synthesis. After the measured 18.4 g of TDI was added to the flask, the leftmost neck of the reaction flask was plugged shut with a separating funnel, which was also used to drip the 50 g of vacuum-treated and heated PPG into the reaction flask. In the rightmost neck of the reaction flask, an inlet of nitrogen gas was plugged into the opening and the closed environment was supplied with nitrogen gas from a low-flowing source in order to maintain an inert atmosphere. Thus, the reaction was allowed to go to completion in 4–5 hours with the magnetic-bar rotation rate of approximately 200–300 rpm and a hot-plate temperature of 75 °C (Figure 2).

Figure 2

The setup for making PU foam – mixing PPG and TDI under inert (nitrogen-filled) conditions at 75 °C temperature.

Figure 2

The setup for making PU foam – mixing PPG and TDI under inert (nitrogen-filled) conditions at 75 °C temperature.

After the reaction had been sustained for 4–5 hours, the round-bottom flask was disconnected from the system, and its contents were emptied into a glass container greased with silicone spray lubricant. Then the iron oxide nanoparticles (of size 15–20 nm and forming 10% of mass) in powder form and a few drops of polysiloxane surfactant were added to the PPG-TDI mixture. The polysiloxane surfactant was used within the synthesis of the polyurethane foam because it helps to lower surface tension, promote the nucleation of bubbles during mixing, and stabilize the rising foam by reducing stress concentrations in thinning cell-walls (The Dow Chemical Company). Approximately 6.5–7 mL of deionized water was then added to the entire mixture before all of the components of this novel PU foam were mixed thoroughly for 15 seconds with the use of a mechanical mixer. A homogeneous distribution and dispersion of the nanoparticles was sought by high shear mixing with the polymer mixture before foaming. The distribution of the iron oxide nanoparticles in the foam is likely to have an amplified effect at the local pore levels with more homogeneous distribution likely to enhance the arsenic removal.

After the mixing process, the glass containing the now well-incorporated components is set aside in an environment with minimal movement to allow for the natural rising and development of the foam for 24 hours as the water reacts with the remaining isocyanate groups to release CO2, thus forming the final structure of iron oxide nanoparticle-loaded polyurethane (IONP-PU) foam.

Based on the porosity analysis, the cell size distribution is bimodal or falls into two pore sizes: (0.001–0.1) μm and (0.1–10) μm, and the open/closed cell ratio is 2:1 (66% open cell and 33% closed cell). The molar ratio of TDI:PPG (2:1) provides flexible structure of PU foam which, in turn, facilitates the water flow during filtration (high content of opened cells). In a preliminary test, the pure PU foam did not show a removal capacity toward arsenic.

Now we add some more nuts-and-bolt details on the materials used in our foam preparation. The following is a list of raw materials which were used in the synthesis of PU foam nanocomposite: polypropylene glycol1200 (PPG; Sigma Aldrich Co. LLC) dehumidified in a vacuum oven at 70 °C, toluene di-isocyanate (TDI; 2,4–80%, 2,6–20%, Alfa Aesar), polysiloxane surfactant (Sigma Aldrich), nitrogen gas (Air-gas, O2free UHP), iron oxide nanoparticles (IONPs; Fe3O4, high purity 99.5%, US Research Nanomaterials Inc.) in the size range 15–20 nm, and 18.2 M Ohm-cm deionized water.

### Creating the gravity-driven low-cost filtration system

For the development of such a water-filtration system, the two key goals focused on in this specific model were the low overall cost of production and the user-friendly nature of the product. The majority of the Bangladeshi population that suffers from chronic arsenic exposure primarily lives in rural areas and has little education or understanding about the severity of the problem (Human Rights Watch 2016). Therefore, our system was devised and developed to be not only low cost and simple, but also gravity-driven, which would eliminate the need for electricity to power any components of the filtration system.

## SUMMARY AND CONCLUSIONS

Many countries suffer from the problem of arsenic in groundwater, which can lead to severe health issues if the polluted water is used without filtration. Here, we demonstrate that the nanocomposite polyurethane foam, with embedded iron oxide nanoparticles, could be used to develop a simple, low-cost, gravity-driven filtration device that has shown the promise of effectively removing (or at least reducing significantly) arsenic from polluted water. Through the testing of water samples with 100 and 200 ppb arsenic, it was shown that the 20 cm PU foam plug, compared to the 10 cm plug, was more effective at removing arsenic from the water samples. With only one run, it was able to effectively remove close to half of arsenic present within the water sample, and with just five runs in only 28 minutes, up to 70% of the arsenic was filtered. In addition, the models created performed better for higher (200 ppb) concentrations of arsenic, thus providing a viable filtration mechanism for nations affected by higher arsenic concentrations. The time taken for one run increased from around 4.7 minutes to around 8.2 minutes at the end of 20 runs. This performance was much better than reported in a previous published study where it took several days to purify similarly polluted water.

## FUTURE INVESTIGATIONS

Future work will look into optimizing and studying further the overall filtering capability of the proposed simple, inexpensive, gravity-driven filtration system. The reusability and regeneration capabilities will also be studied for the proposed designed system.

Already, if close to 70% of arsenic within water can be filtered from water with just 20 cm of iron oxide nanoparticle-loaded PU foam plug, an increased length of foam plug could potentially lead to even 100% filtration of contaminated water samples. This will be studied in the near future. We will also look into correlating the time needed for one trial with the permeability of the porous plug as well as with the effectiveness in arsenic removal. By the falling head permeability test, the permeability, a property of porous foam which determines how fast water will flow through the foam (Bear 1972), will be determined. In fact, such a determination can easily be made using the data recorded for the change in water level with time in the proposed setup. We also plan to propose a detailed mathematical model for predicting spatial changes in arsenic concentration within the PU foam plug. Using the volume averaging method, often employed for upscaling transport phenomena in porous media, we will aim to couple the adsorption of arsenic ion on pore walls with the macroscopic flow of water and transport of arsenic ions through the porous plug.

Usage of this device (or its suitable derivative) within the rural areas of developing countries will be planned to confirm the effectiveness and reliability of this filtration system in realistic operating situations. Given the fact that this model was simply a prototype, more research can be attempted into making the system easier to synthesize and fabricate for starting the regular production of this model. For example, more work can be done to make the overall insertion and removal of foam within the plastic tube easier. Research will also be done for recharging of the PU foam filter by removing the arsenic adsorbed on pore walls through some chemical treatment as well as safe disposal of adsorbed arsenic obtained from this process.

In addition, the efficiency of the device will be evaluated in the presence of other heavy metal contaminants, such as lead and mercury, and at different water pH levels. The multiple functionalization of the foam surface may be used to target various contaminants simultaneously.

If successful, this innovative low-cost technology has the potential to have a tremendously significant impact on the well-being of numerous communities in developing countries across the globe and ultimately help those people live healthier and longer lives.

## ACKNOWLEDGEMENTS

We would like to acknowledge the help of Dr. Steve Hardcastle in the use of the AAS system.

## REFERENCES

REFERENCES
Abejón
A.
,
Garea
A.
&
Irabien
A.
2015
Arsenic removal from drinking water by reverse osmosis: minimization of costs and energy consumption
.
Separation and Purification Technology
144
,
46
53
.
2007
Membrane Technology, 6
.
Alava
P.
,
Du Laing
G.
,
Tack
F.
,
De Ryck
T.
&
Van De Wiele
T.
2015
Westernized diets lower arsenic gastrointestinal bioaccessibility but increase microbial arsenic speciation changes in the colon
.
Chemosphere
119
,
757
762
.
Ameer
S. S.
,
Engström
K.
,
Bakhtiar Hossain
M.
,
Concha
G.
,
Vahter
M.
&
Broberg
K.
2017
Arsenic exposure from drinking water is associated with decreased gene expression and increased DNA methylation in peripheral blood
.
Toxicology and Applied Pharmacology
321
,
57
66
.
Anthamatten
P.
&
Hazen
H.
2012
An Introduction to the Geography of Health
.
Routledge
,
Abingdon
,
UK
.
M.
,
Jahan
I.
,
Boshir Ahmed
M.
,
P.
,
Malek
N. H.
&
Sahedur Rahman
M.
2014
Preparation of microporous activated carbon and its modification for arsenic removal from water
.
Journal of Industrial and Engineering Chemistry
20
,
887
896
.
Baig
S. A.
,
Sheng
T.
,
Hu
Y.
,
Lv
X.
&
Xu
X.
2013
.
Ecological Engineering
60
,
345
353
.
Bear
J.
1972
Dynamics of Fluids in Porous Media
.
American Elsevier Publishing Company
,
New York
,
USA
, p.
764
.
Brocato
J.
&
Costa
M.
2015
10th NTES conference: nickel and arsenic compounds alter the epigenome of peripheral blood mononuclear cells
.
Journal of Trace Elements in Medicine and Biology
31
,
209
213
.
Calatayud
M.
&
Laparra Llopis
J. M.
2015
Arsenic through the gastrointestinal tract
. In:
Handbook of Arsenic Toxicology
(
Flora
S. J. S.
, ed.).
,
Oxford
,
UK
.
Cao
X.
,
Lee
L. J.
,
Widya
T.
&
Macosko
C.
2005
Polyurethane/clay nanocomposites foams: processing, structure and properties
.
Polymer
46
,
775
783
.
Chávez-Capilla
T.
,
Beshai
M.
,
Maher
W.
,
Kelly
T.
&
Foster
S.
2016
Bioaccessibility and degradation of naturally occurring arsenic species from food in the human gastrointestinal tract
.
Food Chemistry
212
,
189
197
.
Chen
A. S. C.
,
Sorg
T. J.
&
Wang
L.
2015
Regeneration of iron-based adsorptive media used for removing arsenic from groundwater
.
Water Research
77
,
85
97
.
Choi
H.
,
Woo
N. C.
,
Jang
M.
,
Cannon
F. S.
&
Snyder
S. A.
2014
Magnesium oxide impregnated polyurethane to remove high levels of manganese cations from water
.
Separation and Purification Technology
136
,
184
189
.
Cullen
W. R.
&
Reimer
K. J.
1989
Arsenic speciation in the environment
.
Chemical Reviews
89
,
713
764
.
DeMarco
M. J.
,
SenGupta
A. K.
&
Greenleaf
J. E.
2003
Arsenic removal using a polymeric/inorganic hybrid sorbent
.
Water Research
37
,
164
176
.
Di Natale
F.
,
Erto
A.
&
Lancia
A.
2013
Desorption of arsenic from exhaust activated carbons used for water purification
.
Journal of Hazardous Materials
260
,
451
458
.
Duan
X.
,
Li
J.
,
Zhang
Y.
,
Li
W.
,
Zhao
L.
,
Nie
H.
,
Sun
G.
&
Li
B.
2015
Activation of NRF2 pathway in spleen, thymus as well as peripheral blood mononuclear cells by acute arsenic exposure in mice
.
International Immunopharmacology
28
,
1059
1067
.
Ferguson
J. F.
&
Gavis
J.
1972
A review of the arsenic cycle in natural waters
.
Water Research
6
,
1259
1274
.
Flanagan
S. V.
,
Johnston
R. B.
&
Zheng
Y.
2012
Arsenic in tube well water in Bangladesh: health and economic impacts and implications for arsenic mitigation
.
Bulletin of the World Health Organization
90
,
839
846
.
Garelick
H.
,
Jones
H.
,
Dybowska
A.
,
Valsami-Jones
E.
2009
Arsenic pollution sources
. In:
Reviews of Environmental Contamination Volume 197
(
Garelick
H.
&
Jones
H.
, eds).
Springer
,
New York
,
USA
, pp.
17
60
.
Gehle
K.
,
Arsenic Toxicity, Agency for Toxic Substances and Disease Registry
.
Agency for Toxic Substances and Disease Registry
. .
Gu
Z.
,
Fang
J.
&
Deng
B.
2005
Preparation and evaluation of GAC-based iron-containing adsorbents for arsenic removal
.
Environmental Science & Technology
39
,
3833
3843
.
Gunashekar
S.
2015
A Study on the Synthesis-Structure-Property-Performance Relationship of Bulk Functionalized Polyurethane Foams for Water Filtration Applications
.
PhD dissertation
,
University of Wisconsin-Milwaukee
.
Gupta
V. K.
,
Saini
V. K.
&
Jain
N.
2005
Adsorption of As (III) from aqueous solutions by iron oxide-coated sand
.
Journal of Colloid and Interface Science
288
,
55
60
.
Halatek
T.
,
Sinczuk-Walczak
H.
,
Rabieh
S.
&
Wasowicz
W.
2009
Association between occupational exposure to arsenic and neurological, respiratory and renal effects
.
Toxicology and Applied Pharmacology
239
,
193
199
.
Human Rights Watch
2016
Bangladesh: 20 Million Drink Arsenic-Laced Water
.
Human Rights Watch
,
New York
,
USA
.
Hussein
F. B.
2016
Synthesis and Performance Analysis of Polyurethane Foam Nanocomposite for Arsenic Removal From Drinking Water
.
Thesis
,
The University of Wisconsin-Milwaukee
.
Hussein
F. B.
&
Abu-Zahra
N. H.
2017a
Adsorption kinetics and evaluation study of iron oxide nanoparticles impregnated in polyurethane matrix for water filtration application
.
Journal of Minerals and Materials Characterization and Engineering
5
,
298
.
Hussein
F. B.
&
Abu-Zahra
N. H.
2017b
Extended performance analysis of polyurethane–iron oxide nanocomposite for efficient removal of arsenic species from water
.
Water Science and Technology: Water Supply
17
,
889
896
.
Jain
P.
&
T.
2005
Potential of silver nanoparticle-coated polyurethane foam as an antibacterial water filter
.
Biotechnology and Bioengineering
90
,
59
63
.
Katsoyiannis
I. A.
&
Zouboulis
A. I.
2002
Removal of arsenic from contaminated water sources by sorption onto iron-oxide-coated polymeric materials
.
Water Research
36
,
5141
5155
.
Lesseur
C.
,
Gilbert-Diamond
D.
,
Andrew
A. S.
,
Ekstrom
R. M.
,
Li
Z.
,
Kelsey
K. T.
,
Marsit
C. J.
&
Karagas
M. R.
2012
A case-control study of polymorphisms in xenobiotic and arsenic metabolism genes and arsenic-related bladder cancer in New Hampshire
.
Toxicology Letters
210
,
100
106
.
Lynch
H. N.
,
Zu
K.
,
Kennedy
E. M.
,
Lam
T.
,
Liu
X.
,
Pizzurro
D. M.
,
Loftus
C. T.
&
Rhomberg
L. R.
2017
Quantitative assessment of lung and bladder cancer risk and oral exposure to inorganic arsenic: meta-regression analyses of epidemiological data
.
Environment International
106
,
178
206
.
Mahdavi
M.
,
Ebrahimi
A.
,
Azarpira
H.
,
Tashauoei
H. R.
&
Mahvi
A. H.
2017
Dataset on the spent filter backwash water treatment by sedimentation, coagulation and ultra filtration
.
Data in Brief
15
,
916
921
.
McNeill
L. S.
&
Edwards
M.
1997
Arsenic removal during precipitative softening
.
Journal of Environmental Engineering
123
,
453
460
.
Mehta
A.
,
Ramachandra
C. J. A.
&
Shim
W.
2015
Arsenic and the cardiovascular system
. In:
Handbook of Arsenic Toxicology
(
Flora
S. J. S.
, ed.).
,
Oxford
,
UK
, pp.
459
492
.
Melak
D.
,
Ferreccio
C.
,
Kalman
D.
,
Parra
R.
,
Acevedo
J.
,
Pérez
L.
,
Cortés
S.
,
Smith
A. H.
,
Yuan
Y.
,
Liaw
J.
&
Steinmaus
C.
2014
Arsenic methylation and lung and bladder cancer in a case-control study in northern Chile
.
Toxicology and Applied Pharmacology
274
,
225
231
.
Ning
R. Y.
2002
Arsenic removal by reverse osmosis
.
Desalination
143
,
237
241
.
Oregon Health Authority
.
Drinking Water Program Fact Sheet: Recommendations for Arsenic Removal From Private Drinking Water Wells in Oregon
. .
Schmidt
S.-A.
,
Gukelberger
E.
,
Hermann
M.
,
Fiedler
F.
,
Großmann
B.
,
Hoinkis
J.
,
Ghosh
A.
,
Chatterjee
D.
&
Bundschuh
J.
2016
Pilot study on arsenic removal from groundwater using a small-scale reverse osmosis system – towards sustainable drinking water production
.
Journal of Hazardous Materials
318
,
671
678
.
Siddiqui
S. I.
&
Chaudhry
S. A.
2017
Iron oxide and its modified forms as an adsorbent for arsenic removal: a comprehensive recent advancement
.
Process Safety and Environmental Protection
111
,
592
626
.
Terracciano
A.
,
Ge
J.
&
Meng
X.
2015
A comprehensive study of treatment of arsenic in water combining oxidation, coagulation, and filtration
.
Journal of Environmental Sciences
36
,
178
180
.
Teychene
B.
,
Collet
G.
,
Gallard
H.
&
Croue
J.-P.
2013
A comparative study of boron and arsenic (III) rejection from brackish water by reverse osmosis membranes
.
Desalination
310
,
109
114
.
The Dow Chemical Company
.
Dow Polyurethanes – Surfactants Role in Foam Formulations
. .
Wickramasinghe
S. R.
,
Han
B.
,
Zimbron
J.
,
Shen
Z.
&
Karim
M. N.
2004
Arsenic removal by coagulation and filtration: comparison of groundwaters from the United States and Bangladesh
.
Desalination
169
,
231
244
.
Wilson
R.
2009
Chronic Arsenic Poisoning: History, Study and Remediation
.
World Health Organization
2018
.
Wu
Y.
,
Ma
X.
,
Feng
M.
&
Liu
M.
2008
Behavior of chromium and arsenic on activated carbon
.
Journal of Hazardous Materials
159
,
380
384
.
Xiong
Y.
,
Tong
Q.
,
Shan
W.
,
Xing
Z.
,
Wang
Y.
,
Wen
S.
&
Lou
Z.
2017
Arsenic transformation and adsorption by iron hydroxide/manganese dioxide doped straw activated carbon
.
Applied Surface Science
416
,
618
627
.
Xu
X.
,
Chen
C.
,
Wang
P.
,
Kretzschmar
R.
&
Zhao
F.-J.
2017
Control of arsenic mobilization in paddy soils by manganese and iron oxides
.
Environmental Pollution
231
,
37
47
.
Yang
Z.
,
Wu
X.
,
Li
T.
,
Li
M.
,
Zhong
Y.
,
Liu
Y.
,
Deng
Z.
,
Di
B.
,
Huang
C.
,
Liang
H.
&
Wang
M.
2011
Epidemiological survey and analysis on an outbreak of gastroenteritis due to water contamination
.
Biomedical and Environmental Sciences
24
,
275
283
.
Yazdani
M.
,
Tuutijärvi
T.
,
Bhatnagar
A.
&
Vahala
R.
2016
Adsorptive removal of arsenic(V) from aqueous phase by feldspars: kinetics, mechanism, and thermodynamic aspects of adsorption
.
Journal of Molecular Liquids
214
,
149
156
.
Yeh
T.-C.
,
Tai
Y.-S.
,
Pu
Y.-S.
&
Chen
C.-H.
2015
Characteristics of arsenic-related bladder cancer: a study from Nationwide Cancer Registry Database in Taiwan
.
Urological Science
26
,
103
108
.
Yorifuji
T.
,
Kato
T.
,
Ohta
H.
,
Bellinger
D. C.
,
Matsuoka
K.
&
Grandjean
P.
2016
Neurological and neuropsychological functions in adults with a history of developmental arsenic poisoning from contaminated milk powder
.
Neurotoxicology and Teratology
53
,
75
80
.
Zhang
Q.
,
Pan
B.
,
Zhang
W.
,
Pan
B.
,
Zhang
Q.
&
Ren
H.
2008
Arsenate removal from aqueous media by nanosized hydrated ferric oxide (HFO)-loaded polymeric sorbents: effect of HFO loadings
.
Industrial & Engineering Chemistry Research
47
,
3957
3962
.