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PRINTED ELECTRONICS: A LANDFILL SIMULATION STUDY TO
ASSESS ENVIRONMENTAL IMPACTS
JAMES ATKINSON
Dr. Thomas Joyce - Dept. of Chemical and Paper Engineering, Western Michigan University
Dr. Margaret Joyce - Dept. of Chemical and Paper Engineering, Western Michigan University
First Analytical Labs - Raleigh, NC
james.e.atkinson@wmich.edu, thomas.joyce@wmich.edu, margaret.joyce@wmich.edu
ABSTRACT
A landfill simulation study was conducted using EPA Method 1311 and SW 846 in combination to assess
the potential environmental impacts that could occur by the landfilling of printed electronics containing
silver flake, silver nanoparticle, and nickel conductive inks. It appears that the amounts of inks used to
print electronics might pose a threat to the environment even at low application rates. It was found that the
nickel ink used could have a potential environmental impact if printed electronics were landfilled in large
quantities. The silver flake and nanoparticle inks did not exceed the concentration threshold named in
TCLP procedure. However, due to the low ratio of ink to substrate in this experiment, it is recommended
that more research should be conducted to fully evaluate these inks.
Keywords: TCLP, Printed Electronics, Environmental toxicity, Silver, Nickel, Nanoparticles, EPA method
1311, EPA method SW 846
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Printed electronics (PE) are cost- 59
effective ways to create an electrically functional 60
device by printing with a conductive ink, 61
typically containing silver, copper, or nickel, on 62
various substrates, including paper and film. 63
Examples of PE are RFID (radio-frequency ID 64
tags), glucose sensors for diabetics, advertising 65
displays, and LED lighting. PE are expected to be 66
very useful in the near future for applications 67
that
require
low-performance,
low-cost 68
electronics. (Subramanian et al.) Currently, the 69
most common substrates being used are polymer 70
films, glass, silicon, and ceramics. Paper is also a 71
possible functional substrate, but further research 72
is needed to ensure the functionality of the 73
electronic circuit when printed on paper. Paper is 74
an attractive substrate due to its low cost, 75
recyclability, and sustainability. (Tobjörk and 76
Österbacka)(Berggren, et al.) A key consideration 77
is that the metals used in the inks are heavy 78
metals, which are known to be toxic and will be 79
scrutinized for regulation. Research suggests that 80
nanoparticle silver does have a damaging effect 81
on photosynthesis in in certain types of algae. 82
(Navarro et al.) Even if the heavy metals did not 83
reach the environment, a recycled paper mill 84
would still be faced with the ultimate disposal of 85
a sludge containing a high concentration of these 86
toxic metals. It appears that production 87
technology for PE has been the focus of most of 88
the research and very little attention has been paid 89
to the life cycle or end fate of the PE material or 90
the heavy metals contained in PE. The exact 91
disposal route will strongly affect the amount of 92
Ag nanoparticles that might be released into the 93
environment. (Fabrega et al.) A recent study also 94
suggests that there needs to be a plan for 95
recovering these metals, due to their high cost and 96
also that it is a limited availability. (Oguchi et al.) 97
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The way the inks are applied on the 99
substrate depends on whether the inks are solvent- 100
based, water-based, or UV curable. (Tobjörk and 101
Österbacka) The functionality of the PE circuit is 102
minimal on a paper substrate because of paper’s 103
high roughness and absorbency, when compared 104
with film and other substrates. Currently the 105
biggest challenge in the printed electronics 106
industry is finding suitable materials, besides film 107
and other non-sustainable materials, to use for 108
substrates. Paper is a leading candidate for 109
inclusion as a substrate, but only a few specific 110
paper grades are available and known to be 111
functional. (Tobjörk and Österbacka)(Bollström 112
1. INTRODUCTION
et al.)(Kim, et al.) There are multiple nanoparticle
inks and other materials available, but researchers
are working on formulating functional inks with
such materials (carbon nanotubes and other
organic and inorganic conductive polymers) for
successful PE. (Subramanian et al.)(Tobjörk and
Österbacka)(Berggren, et al.)(Bollström et al.)(Ko
et al.) Much research is being conducted to find a
way to better improve the use of PE with paper as
the substrate because its low cost and multiple
applications make it an attractive substrate.
(Subramanian et al.)(Tobjörk and Österbacka)
Eventually, the fate of the toxic metal containing
inks printed on paper versus film will become a
significant factor for consideration. This would
particularly be the case if there were significant
differences in the ability of film and paper to bind
or release the ink over the substrate’s life cycle.
IT is desirable in the production of PE have a
responsibility to society as a whole to protect the
environment for the future generations by
reclaiming heavy metals, i.e. gold, silver, copper,
nickel, etc. This not only prevents environmental
contamination, it promotes sustainability based on
the use of natural resources.
According to the IDtechEx 2014-2024
forecast, the utilization of PE for consumer and
military uses is expected to expand rapidly in the
next ten years. (Ghaffarzadeh and Zervos)
Research is needed to understand the effects that
disposal or recycling these printed materials
might have on the environment. Virtually no
research has been done on the potential
environmental problems that could be caused by
recycling or landfilling PE materials and the toxic
heavy metal-containing inks. Separation of PE
items from the household good waste stream is
difficult and uncertain, and therefore should a
source of concern. (Niu and Li)(Köhler, et al.)
Research is being conducted on nanoparticles and
there is significant concern about the silver
nanoparticle. For example, a study done by Dr.
Samuel N Luoma in 2008 calls for in depth study
and regulation on production and use of
nanosilver in consumer products due to its, toxic,
bioaccumulative, and persistence properties.
There is debate about the mechanism by which
the silver nanoparticle creates toxicity, but in
general it is agreed that releasing silver into the
water or waste stream has a great potential for
ecological damage. (Navarro et al.)(Tolaymat et
al.)(Xiu et al.)(Levard et al.) (Luoma)
The purpose of this research is to
understand the potential environmental concerns
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that might arise from recycling or disposal of PE
material. It is noted that most of PE material
presently uses film as the substrate. Paper as a
substrate for PE should be investigated to assess
any advantages/disadvantages it might have on
the environmental effect of disposal or recycling
of these materials. For example, film might
release the environmentally toxic conductive inks
quite easily, while paper, through different
binding mechanisms, may retain these toxic
metals with it.
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Table 1: Printed ink weights
2. EXPERIMENTAL PROCEDURES
2.1 Sample Preparation
Paper and polyethylene terephthalate
(PET) substrate samples were printed with
conductive inks using laboratory scale proofing
techniques. The silver flake and silver
nanoparticle inks were printed using the
flexographic process, while the nickel ink was
screen-printed. The printed samples were cured
using the Novacentrix (Austin, TX) Pulseforge
1200 photonic sintering unit. All of the print
samples displayed some resistance somewhere on
the sheet, and could therefore be considered
representative of PE. Substrate samples were
weighed prior to and after printing in order to
quantify the weight of ink transferred onto the
substrate. Table 1 below shows the average
amount of ink transferred to the sheet for each
substrate/ink combination. The sheet used to print
the samples was delivered as an 8.5x11 inch
sheet, but was cut in half lengthwise and joined to
form a sheet 4.25x22 inches for printing.
used in combination to create the testing
methodology. The TCLP test is designed to
determine the mobility of both organic and
inorganic materials present in liquid, solid, and
multi-phase waste. For this procedure to be
carried out, the solid waste needed to be reduced
in particle size. A crosscut office shredder was
used in order to ensure that no particle was larger
than 1 square centimeter in area. The extraction
fluid was made by first measuring 5.7 mL of
acetic acid and adding to 500 mL of reagent
water. The next step is to add 64.3 mL of sodium
hydroxide to this mixture and then dilute to
1000mL. The pH of the fluid after preparation
was 4.93 ± 0.05. This was measured on a
calibrated electronic pH meter from Fisher
Scientific. The samples were separated according
to deposited ink weights and placed into the
extraction vessels, with a volume of extraction
fluid equal to 20 times the weight of the waste
sample. The extraction vessel, made of
borosilicate glass by Wheaton Industries Inc.
(Millville, NJ), and the rotary agitator by
Associated Design and Manufacturing Company,
model no. 3740-6-BRE (Alexandria, VA) can be
seen below in Figure 1. The samples were
agitated for 18±2 hours and then filtered through
a 0.7 micron, acid-washed, glass fiber filter. The
filtered liquid is analyzed as the TCLP extract.
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Figure 1: TCLP Rotary Agitator and Extraction
Vessel
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Silver Nano - Paper
0.0351
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Silver Nano - PET
0.0109
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2.2 TCLP Testing Procedures
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EPA method 1311 is a landfill 88
simulation procedure. SW 846 is a solid waste 89
analysis procedure. These two standards were 90
The printed samples were arranged in
three sets for TCLP extraction. The paper
extraction samples used seven sheets. The PET
samples used four printed sheets to achieve the
weight indicated as minimally acceptable by SW
846, which is 30 grams of solid waste for each
sample to be tested. The ink weights are
significantly different between paper and PET,
although are representative of commercial
practice. The weights are also different between
inks as well. PE are concerned with small
features, so the low ink weights are an artifact of
creating representative PE samples to analyze for
Sample
Nickel Paper
Nickel PET
Silver Flake -Paper
Silver Flake - PET
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Average ink
weight deposited
– g/m2
0.1015
0.0473
0.0221
0.0034
3
1 toxicity. The average ink weight deposited for
2 TCLP extraction is listed in Table 2.
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4 Table 2: Ink weights deposited into extraction vessels
Sample
Nickel - Paper
Nickel -PET
Silver Nano - Paper
Silver Nano - PET
Silver flake - Paper
Silver Flake - PET
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Ink weight into
extraction -g
1.6821
0.7843
0.3656
0.0572
0.582
0.1802
2.4 AA Spectrometer analysis
The TCLP samples were collected and
stored at 4oC until analysis. Each sample was
acidified with 70% nitric acid below a pH 2. In
this case, a 2% v/v of the nitric acid was sufficient
to acidify the samples for analysis. Concurrently,
standard samples of known concentration were
made from a 1000-ppm solution purchased from
Fisher Scientific (Waltham, MA). The standard
solutions were made at 1, 5, 10, 20, 50, 100, and
500 ppm concentrations, respectively. The Varian
AA240FS Flame AA spectrometer (Mulgrave,
Victoria Australia) was used to analyze the
acidified TCLP samples. Flame Atomic
Absorption Spectrometer can be used to
determine the concentration of the silver by
plotting the Atomic Absorption (AA) values
against a calibration curve and interpolating the
values. Atomic Absorption Spectroscopy is a
spectroanalytical procedure for the quantitative
determination of chemical elements using the
absorption of optical radiation (light) by free
atoms in the gaseous state. Figure 2 below is a
diagram showing how the AA spectrometer
gathers its data.
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fluid was filtered through a 0.7 micron glass fiber
filter. The PET samples appeared to readily
release the metal into the extraction fluid, while
the paper samples did not show a ready release of
the metal into the extraction fluid. Figure 3 shows
the glass filter fiber pads used. The filter for the
PET sample is on the right and the paper sample
filter is on the left. The initial observation was
that the PET sample would definitely have a
significantly higher amount of metal in the
extraction fluid. This was based on the
observation that the PET releases the ink quite
readily. This could correlate to the release into the
environment if PE printed with nickel ink was
placed into a landfill.
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Figure 3: Nickel Ink Extraction Filters
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Figure 2: www.orgspectroscopyint.blogspot.com
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3. RESULTS AND DISCUSSION
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3.1 Nickel Ink Results
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3.1.1 Visual Observations
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The previously described substrate 90
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3.1.2 AA Spectrometer Analysis
The TCLP extracts were all collected
and analyzed. Nickel ink appears to have
surpassed the regulatory limit for hazardous
material. The TCLP extract contained a
concentration of 6.46 parts per million (ppm) on
paper, and 6.82 ppm on PET. The wastewater
regulation for nickel is 5 ppm. (“Wastewater
Discharge Regulations -- Introduction”) This
means the nickel ink used in this experiment
presents a potential hazard if placed into a
landfill. It is important to note that only about 5%
of the total weight placed into the extraction
vessel was nickel ink. Nickel inks are still largely
in the developmental stages for use in PE, so it
will be important to formulate these inks in the
future to prevent the release into the environment,
or should not be used for PE due the potential for
environmental damage.
3.2 Silver Flake Ink Results
3.2.1 Visual Observations
The silver flake ink samples were
collected, extracted and filtered. The filter papers
for the PET samples appeared to release a more
significant amount of metal into the extraction
fluid than did the paper samples. This observation
led to the belief that the PET sample’s potential
for environmental damage was more significant
4
1 than that of the paper PE samples. The filter 51 greater concentration in the TCLP extraction fluid
2 papers are shown in Figure 5 below.
52 based on these observations.
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Figure 4: Silver Flake Extraction Filters
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The AA spectrometer in the lab at WMU 57
has detection limits in the hundreds of parts per 58
billion (ppb). The absorption numbers appeared 59
inconsistent, so First Analytical Labs (Raleigh, 60
NC) was contacted and agreed to carry out the 61
analysis by Inductive Coupled Plasma Mass 62
Spectometry (ICP-MS) for verification. This 63
spectrometer has a much lower detection limit, as 64
in fractions of ppb. The silver flake samples were 65
analyzed by FAL and the concentration levels 66
were quite low. The paper sample had a 67
concentration in the extraction fluid of 0.054 68
mg/L. The PET sample had a concentration of 69
0.117 mg/L. This translates to less than 1 ppm for 70
both of the samples. The maximum concentration 71
limit for TCLP method 1311for silver is 5 72
ppm.(“The EPA TCLP: Toxicity Characteristic 73
Leaching Procedure and Characteristic Wastes 74
(D-Codes)”) Both of these samples are below the 75
limit, but it is important to note that PET sample 76
had more than double the amount of silver in the 77
extraction fluid. It is also important to note that 78
the weight of ink placed into the extraction vessel 79
was quite low. For the PET samples, the ink only 80
accounted for approximately 0.6%, and around 81
2% of the total weight for paper. This artifact is a 82
result of the thin ink films printed and the nature 83
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of PE having small features.
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3.3 Silver Nanoparticle Ink Results
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3.3.1 Visual Observations
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The nanoparticle silver ink printed PE
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samples were extracted and filtered. The filter
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papers appeared to have much more ink released
from the PET sample than from the paper sample, 93
but the paper sample filter had much more ink on 94
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it than either the nickel or silver flake ink PE
samples on paper. The nanoparticle silver seemed 96
to be more readily released from the paper due to 97
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its smaller particle size. The filter papers are
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shown below in Figure 5. It was thought that the
100
silver nanoparticle ink would probably have a
3.1.2 AA Spectrometer Analysis
Figure 5: Silver Nanoparticle Ink Filters
3.3.2 AA Spectrometer Analysis
The AA spectrometer readings obtained
did not appear consistent, so the FAL analysis
will be presented. The concentration level for the
nanoparticle ink printed on PET is 0.361 mg/L,
and the concentration for the paper PE sample is
0.144mg/L. These are both well below 1 ppm.
The maximum concentration limit for TCLP
method 1311for silver is 5 ppm.(“The EPA
TCLP:
Toxicity
Characteristic
Leaching
Procedure and Characteristic Wastes (D-Codes)”)
It is important to note again that the ink weight to
total weight ratio placed into the extraction vessel
was quite low, about 0.2% for the PET samples
and about 1% for the paper samples. However,
the concentration levels for the nanoparticle ink is
significantly higher than the flake ink, even at the
lower weight percentages. This holds true for
both PET and paper PE samples.
4. CONCLUSIONS AND
RECOMMENDATIONS
EPA method 1311 and SW 846 were
utilized to perform this landfill simulation. It
appears that paper as a substrate retains more
metal than PET. AA spectrometry and ICP-MS
analysis seems to indicate that silver flake
concentrations are at very low levels, below 1
ppm for both paper and PET substrates with the
weight proportions at approximately 2.0 wt.% for
paper and 0.6 wt.% for PET. Silver nanoparticle
ink shows a level below 1 ppm for PET, and for
paper, even at the low ink/substrate weight
proportions added to the TCLP extraction vessels
(approx. 0.2 wt.% for PET and 1.0 wt.% for
paper). The nickel ink has a much higher
concentration in the TCLP extract. At
approximately 5.0 wt.% for nickel on paper and
2.5% for nickel on PET, the concentration levels
are above 6 ppm for paper and for PET. However,
the TCLP filter pads tell a different story. The
filter pads for the PET substrate samples are
completely covered with metal, whereas the paper
substrate sample filter pads have little or no metal
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present on them after filtration. This tells us that
even though most of the metal can be filtered out,
the PET substrate still releases the metal more
readily into the environment, while the paper
substrate retains it. There should be some concern
over landfilling printed electronics, especially if
large quantities of printed electronic material are
being landfilled. Nickel inks are a cause for
concern. The concentration level for regulation of
nickel for industrial semiconductor producer
wastewater effluent is 3.98 mg/L on any one day,
with a monthly average of 2.38 mg/L as a
discharge concentration. (US EPA, Office of
Pollution Prevention and Toxics) The drinking
water standard for silver is 0.1mg/L (~ppm). (US
EPA, OW) Printed electronics with nickel
conductive inks should be highly regulated if and
when they are produced.
For silver, the concentration level for
regulation of nickel for industrial semiconductor
producer wastewater effluent is 0.43mg/L on any
one day, with a monthly average of 0.24
mg/L.(US EPA, Office of Pollution Prevention
and Toxics) This would put the nickel TCLP
extracts above the standard for wastewater
effluent, and all of the silver ink TCLP
extractions except for the flake ink on paper. The
drinking water standard MCL for nickel is
0.1mg/L (~ppm). There is a definite need for
more extensive research in this area. The PE
industry does not want to be responsible for an
environmental issue, as abatement is very costly
and can be avoided by employing measures to
prevent these materials from being dumped into a
landfill.
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5. REFERENCES
1. Berggren, M, D Nilsson, and N D Robinson.
“Organic Materials for Printed Electronics.”
Nat Mater 6.1 (2007): 3–5. Web. 10 June
2014.
2. Bollström, Roger et al. “Printability of
Functional Inks on Multilayer Curtain
Coated Paper.” Chemical Engineering and
Processing: Process Intensification 68
(2013): 13–20. Web. 4 July 2014.
3. Fabrega, Julia et al. “Silver Nanoparticles:
Behaviour and Effects in the Aquatic
Environment.” Environment international
37.2 (2011): 517–31. Web. 24 May 2014.
4. Ghaffarzadeh, Khasha, and Harry Zervos.
“Conductive Ink Markets 2014-2024:
Forecasts, Technologies, Players.” N.p., n.d.
Web. 8 July 2014.
4. Kim, Y.-H., D.-G. Moon, and J.-I. Han.
“Organic TFT Array on a Paper Substrate.”
IEEE Electron Device Letters 25.10 (2004):
702–704. Web. 26 June 2014.
5. Ko, Seung H et al. “Direct Nanoimprinting of
Metal Nanoparticles for Nanoscale
Electronics Fabrication.” Nano letters 7.7
(2007): 1869–77. Web. 9 June 2014.
6. Köhler, Andreas R., Lorenz M. Hilty, and
Conny Bakker. “Prospective Impacts of
Electronic Textiles on Recycling and
Disposal.” Journal of Industrial Ecology
15.4 (2011): 496–511. Web. 18 June 2014.
7. Levard, Clément et al. “Environmental
Transformations of Silver Nanoparticles:
Impact on Stability and Toxicity.”
Environmental science & technology 46.13
(2012): 6900–14. Web. 9 June 2014.
8. Luoma, SN. Silver nanotechnologies and the
environment: old problems or new
challenges? Project on Emerging
Nanotechnologies, The Pew Charitable
Trusts; 2008. Web. 16 Dec 2014.
9. Navarro, Enrique et al. “Toxicity of Silver
Nanoparticles to Chlamydomonas
Reinhardtii.” Environmental Science &
Technology 42.23 (2008): 8959–8964. Web.
31 May 2014.
10. Niu, Xiaojun, and Yadong Li. “Treatment of
Waste Printed Wire Boards in Electronic
49
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79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
Waste for Safe Disposal.” Journal of
hazardous materials 145.3 (2007): 410–6.
Web. 30 June 2014.
10. Oguchi, Masahiro et al. “Fate of Metals
Contained in Waste Electrical and
Electronic Equipment in a Municipal Waste
Treatment Process.” Waste management
(New York, N.Y.) 32.1 (2012): 96–103.
Web. 24 May 2014.
11. Subramanian, Vivek et al. “Printed
Electronics for Low-Cost Electronic
Systems: Technology Status and
Application Development.” ESSDERC 2008
- 38th European Solid-State Device
Research Conference (2008): 17–24. Web 9
June 2014.
12. “The EPA TCLP: Toxicity Characteristic
Leaching Procedure and Characteristic
Wastes (D-Codes).” N.p., n.d. Web. 24 Oct.
2014.
13. Tobjörk, Daniel, and Ronald Österbacka.
“Paper Electronics.” Advanced materials
(Deerfield Beach, Fla.) 23.17 (2011): 1935–
61. Web. 23 May 2014.
14. Tolaymat, Thabet M et al. “An EvidenceBased Environmental Perspective of
Manufactured Silver Nanoparticle in
Syntheses and Applications: A Systematic
Review and Critical Appraisal of PeerReviewed Scientific Papers.” The Science of
the total environment 408.5 (2010): 999–
1006. Web. 5 June 2014.
15. US EPA, Office of Pollution Prevention and
Toxics, Design for the Environment
program. “Federal Environmental
Regulations - Sect. B. Clean Water Act
Requirements | Design for the Environment
(DfE) | US EPA.” N.p., n.d. Web. 15 Nov.
2014.
16. US EPA, OW. “Drinking Water
Contaminants.” N.p., n.d. Web. 25 July
2014.
17. “Wastewater Discharge Regulations -Introduction.” N.p., n.d. Web. 17 Nov.
2014.
18. Xiu, Zong-ming et al. “Negligible ParticleSpeci Fi c Antibacterial Activity of Silver
Nanoparticles.” Nano Letters 12 (2012):
4271–4275. Web. 9 June 2014.
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