LEACHING OF TOXIC METALS FROM ELECTRONIC WASTE
Benjamin Estabillo, Ian Hernandez, Jessica Ho, Omar Kawam, Caroline Kranefuss, Charlton Lu,
Connor Marti, Elizabeth Menten, Alexa Ramlall, Lauren von Berg, Tiffany Yang
Advisor: Dr. Ryan Hinrichs
Assistant: Kelsie Kolb
ABSTRACT
Electronic waste, or E-waste, is scrapped electronic appliances, most commonly
computers, televisions, and cell phones. The disposal of electronic waste is becoming an
increasingly severe problem as heavy metals leach out into the surrounding environment in
potentially toxic concentrations. A leaching study was performed to evaluate the threat of heavy
metal contamination as a result of E-waste. Components from two laptops and a cellphone were
analyzed to determine the toxic metal concentrations in various solutions. The solutions
simulated slightly acidic landfill conditions, the acid extraction fluid used in E-waste recycling
centers, pond water, and drinking water. A microwave digestion was performed for electronic
samples to establish a baseline of the amount of each element capable of being leached out; we
determined barium, copper, arsenic, and lead to be the most significant within our samples.
Further experiments included analyzing the effect of burning components on leaching to simulate
open field burning, as well as watering plants with toxic leachate. The E-waste components were
then placed within the aqueous solutions; the resulting leachates were analyzed using inductively
coupled plasma optical emission spectrometry (ICP-OES) in order to evaluate the presence of
toxic elements, notably As, Ba, Cu, Ni, Pb, Sr, and Zn. Several deionized water leachates were
found with lead concentrations over the toxicity level of drinking water regulations established
by the Environmental Protection Agency (EPA) with the highest being 91.6 ppm. Similarly, two
out of the nine arsenic samples were found to have concentrations nearly twice the EPA
standards. Heavy metal concentrations in the other aqueous solutions were comparably elevated.
The results from this study suggest that international recycling standards are in need of revision
due to the potential health and environmental risks of polluted water, atmosphere, and soil.
INTRODUCTION
Electronic waste, commonly abbreviated as E-waste, has emerged as a serious threat to
human health and to the environment in the past couple decades. The increasing prevalence and
shrinking life span of electronics has dramatically increased global production of E-waste since
the 1990s. While developed countries are the primary producers and exporters of E-waste, it is
often developing countries that are faced with the consequences of this industry. As many
components of electronic devices contain hazardous materials, disposal and recycling is often a
difficult and expensive process. In order to avoid this financial burden, many companies ship the
waste—oftentimes illegally—to developing countries that have little to no standards for waste
management. The United States, for example, ships over 50% of its E-waste to foreign countries
that are poorly equipped to deal with the imported materials (1). This mass exportation of Ewaste from industrialized nations is hugely economically favorable: a study conducted by the
EPA concluded that outsourcing E-waste recycling to foreign countries was ten times cheaper
than domestic processing (2).
[3-1]
As a result of the crude recycling methods utilized in countries such as China and India,
E-waste has had significant repercussions for both the environment and the surrounding
populations due to contamination of natural resources. These primitive recycling facilities have
led to the leaching of heavy metals, such as lead or copper, into water—contamination which
oftentimes results in the ingestion of water containing toxic levels of heavy metals (3, 4). For
example, 82% of children living in Guiyu, China--the location of one of the largest E-waste
recycling centers, were found to have lead poisoning from polluted drinking water (5).
Such processing stations also employ dangerous techniques such as open field burning in
order to collect the precious metals, including copper and platinum, within E-waste components
(6). These rudimentary methods allow for the contamination of various media--primarily air and
water--by producing particulate matter which settles through atmospheric deposition. This
exacerbates the risk of heavy metal ingestion or inhalation by humans and causes further water
and soil contamination. While direct exposure to contamination poses a great threat, indirect
pathways, such as heavy-metal uptake in plants and animals that may later be consumed, also
pose considerable danger to the health of both the environment and human population. However,
perhaps the greatest danger to human health is the leaching of heavy metals into drinking water
from the e-waste deposited in dumpsites and the disposal of acids used in the metallurgical
process of isolating valuable metals.
This leaching process refers to the dissolution of solid metals in aqueous environments-forming aqueous metal ions. In leaching, metal ions may be mobile (aqueous) or immobile
(precipitates) depending on their chemical environments. The mobile metals ions are more likely
to undergo redox reactions, which are the chemical processes responsible for leaching. For
example, lead metal may be oxidized while dissolved oxygen is reduced in order for lead to
leach into the solution as an ion. A major factor of leachability is the acidity of the different
aqueous solutions. In the majority of cases, increased acidity leads to increased leachability (7).
Consequences. The long term impacts of the significant presence of heavy metals and
other potentially hazardous materials on human health and the environment have been actively
studied in relation to E-waste. One study conducted on the hazards presented by atmospheric
contamination has concluded that foliar uptake of atmospheric lead is the dominant pathway of
lead entering plant tissue (8). It was concluded that the health risk of adults consuming
vegetables in the surrounding area of an E-waste processing site was comparable to or higher
than those associated with the consumption of vegetables impacted by wastewater irrigation,
mining, or smelting activities. Other studies conducted in Guiyu, a prominent recycling center in
southeast China, have found high concentrations of contaminants such as Cr, Cu and Zn in the
air and dust surrounding the recycling field, and concluded the main source of the contamination
to be the recycling sites (6). Studies of the surface dust in areas near processing centers, which is
a comparable representation of the heavy metal particulate contamination in the air, have
estimated that adults living in such conditions could ingest up to 100 mg dust/day, consequently
posing serious health risks to residents, particularly to children, to whom the potential health
risks of the contaminated dust are 8 times greater than that of adults (6). This heavy
contamination has been the subject of various studies, one of which links concentrations of lead
in surface dust to lead levels in children’s blood-- a phenomenon that has been inversely
associated with children’s IQ scores and academic skills (6).
[3-2]
High levels of heavy metals in water and air not only pose a serious danger to humans,
but also the surrounding ecosystems. A study of an E-waste workshop in the Anrong village of
Taizhou analyzed the microbiome of the paddy soils nearby (9). Combined with polycyclic
aromatic hydrocarbons (PAHs), increased concentrations of heavy metals decreased the amount
of beneficial bacteria and enzyme activity. The paddy soil ecosystem is the largest man-made
wetlands on Earth used for agriculture, and pollution in these wetlands can greatly influence the
safety of crops that animals as well as humans grow and ingest. Thus, the effects of heavy metal
leaching in the soil and microbial level will compound as the leachates progress through the food
chain, a process called bioaccumulation.
Even contamination at levels that fulfill EPA standards can be potentially dangerous due
to biomagnification, a natural process that correlates increased concentrations of contaminants to
higher levels in the food chain. Moreover, studies of the effects of water contamination on
organisms have been conducted near E-waste recycling plants, specifically into how the
proximity of these processing facilities has affected locally grown foodstuffs such as rice (10).
The study found elevated levels of heavy metals in the rice samples. These concentrations were
reported to surpass the maximum allowable concentrations (MAC) of Cd, Cu, and Hg for
Chinese agricultural zones by 4.0, 2.0, and 2.2-folds respectively (the MAC values being set at
0.30, 50.00, 0.30 μg g−1, respectively.) The study concluded that while the daily intake of Hg and
As through the contaminated rice was below the tolerable daily intake level, bioaccumulation of
the heavy metals in consumers should be of concern.
E-waste poses a large problem for human and environmental health world-wide due to
the leaching of heavy metals. With the very poor recycling techniques currently in place and the
increasing amount of electronic waste produced each year, this problem will only worsen in the
future. The rising severity and prevalence of the e-waste issue prompted us to examine the issue
more in depth. The focus of this study was to simulate the leaching of heavy metals from
electronic components into various liquid matrices in order to evaluate the potential threat of
environmental contamination as a result of improper E-waste disposal. Inductively coupled
plasma optical emission spectrometry (ICP-OES) was used to determine which heavy metals
were present in components of e-waste and whether or not the amount of heavy metals that
leached from these components was greater than the EPA drinking water standard levels. If
heavy metal concentrations were found to be greater than the safety standard, this would indicate
that dangerous effects could be produced by the leaching of those heavy metals.
METHODS AND MATERIALS
Metal Concentration Baseline in E-waste. Microwave digestion is a process that
dissolves a small sample (20-40 mg) using concentrated acid with high pressure and temperature.
In this study, microwave digestion of E-waste was performed in order to determine a baseline for
the metals present in each electronic product. Electronic components were inserted into a sealed
container with concentrated nitric and hydrochloric acid. The microwave digester then heated the
samples for 45 minutes using microwave irradiation. Inductively coupled plasma optical
emission spectrometry (ICP-OES) was used to analyze the concentrations of any metals present.
[3-3]
Leaching Study. Three E-waste samples were analyzed in this study: two different
laptops, a 2006 HP Pavilion dv6000 and a Lenovo laptop, and an LG cell phone. The machines
were disassembled to separate their individual components. We selected three samples from each
device, including two motherboards, a magnet, sections of metal or glass, a CPU, RAM, and
several computer chips. Samples ranged from about 1.0 grams to 2.0 grams each. Each of these
samples were placed in a Teflon container holding 20 mL of one of three solutions: deionized
water to simulate standard water supply, 0.1 M acetic acid to simulate acidic landfill
concentrations, and 1 M hydrochloric acid to simulate the hydrometallurgical byproduct process
often used in E-waste recycling centers (Fig.1).
Figure 1. Nine samples from the Intel laptop. Solutions from
left to right are deionized water, TCLP, and hydrometallurgical
byproduct.
In addition to the basic leaching studies conducted, a leaching study in pond water was
conducted with one of the samples. Two Teflon containers were filled with water taken from a
pond located in the Zuck Arboretum, a part of Drew University’s Forest Preserve in Madison,
NJ. 20 mL of the pond water were measured out and separated into two containers. A computer
chip from the HP laptop processor was then submerged in one of the containers. After 48 hours,
the microorganisms in the pond water were removed from both containers via syringes tipped
with 0.45 μm filters.
Due to the fact that many primitive electronic waste recycling facilities often employ
other dangerous disposal techniques such as open field burning, we conducted an experiment to
determine the effect burnt electronic components had on heavy metal leaching in an aqueous
solution. In order to emulate burning, a RAM chip was placed inside a crucible and covered with
a watch glass to prevent the escape of gases. The chip was heated until a gas was released, and
then cooled and placed in deionized water for 48 hours. In order to extract the materials on the
watch glass, it was placed in a solution of concentrated nitric acid, scraped, and left to sit for 48
hours. The solution containing the burned chip was then filtered and introduced into the ICPOES for analysis.
Once all of the samples were prepared, the inductively coupled plasma optical emission
spectrometer (ICP-OES) was used to identify the concentration of certain trace metals in the Ewaste leachates. The ICP-OES transports an aqueous solution of metal ions to a nebulizer, which
pumps the solution with argon gas. The sample is then heated via high power radio frequency
until the gas is ionized to produce a plasma. Once the metal ions are introduced into the plasma,
they emit electromagnetic radiation and strike a diffraction grating. This produces certain
[3-4]
wavelengths of light according to the metal ions present in the sample. These wavelengths are
measured using charged coupled devices to obtain specific concentrations of elements. We
created standards for the ICP-OES by diluting 50 ppm stock solution of various metals (50 ppm
of Al, As, Ba, Cd, Co, Cr, Cu, Mn, Ni, Pb, Se, Mo, Sr, Zn, and 500 ppm of K) with 5% HNO3.
The 25 mL diluted solutions used to create the calibration curve were 2 ppm, 1 ppm, 750 ppb,
500 ppb, 250 ppb, 100 ppb, and 75 ppb. Analysis of the electronic samples by the ICP-OES was
used to create calibration curves (Fig. 2) and determine the concentrations of present elements.
Figure 2. Sample Calibration Curves for Arsenic, Barium, Cadmium, and Copper. These calibration
curves were used to calculate the values for concentrations of the four metals in three different parts of the
HP laptop motherboard.
Bioaccumulation Study. A separate study was conducted to mimic leachates’ path in the
environment and up the food chain. While it is crucial to understand the leaching potential of Ewaste in many different water solutions, it is also important to keep in mind that the leachates’
paths do not stop in these bodies of water. Rather, the leachates have the potential to travel up
through the food chain, in a bioaccumulation pattern that can end with human ingestion. This
process was imitated in the plant study to see what would happen if plants were to uptake water
with concentrations of heavy metals such as lead, barium, and arsenic.
Two Petunia atkinsiana plants were used, one as a control and the other as the
experimental group, for this part of the study. Both plants were watered for approximately every
other day for 1 week. Each time, the control plant received either a nitric acid solution of varying
concentrations (initially 5% concentration but reduced over time) or deionized water. The 50
ppm nitric acid solution used to water the experimental plant contained metals. Nitric acid is an
ideal solvent for metallic solutes because it thoroughly dissolves the metals and retains them in
solution (even in containers where, with a solvent of water, the metals would stick to the sides of
[3-5]
the container). The deionized water contained no heavy metals and was used simply for
hydration and general care of the plants. Using microwave digestion, the concentrations of heavy
metals in the roots, stems, and soil of each plant were measured. The microwave digester
solutions were then further analyzed for elements using the ICP-OES.
RESULTS
Microwave Digestion. The element percent composition of the motherboard and copper
chip of the phone were determined to act as baselines for the following experiments. Most of the
microwave digester were components other than the heavy metals being analyzed, such as silicon
pieces. Many toxic heavy metals such as arsenic, cadmium, and lead made up a negligible
percentage of the total mass. As shown in Figure 3, both devices were composed of primarily
copper, along with trace amounts of aluminum, nickel, and barium.
Figure 3. Percent Composition of HP RAM. The pie chart on the left represents the percent
composition of the total heavy metals found in the HP RAM piece. Since the sample was composed of
primarily copper, the pie chart on the right gives a more detailed depiction of other metals.
Leachates and Solutions. The study focused on the leachates of many elements in three
different types of solutions: deionized water, TCLP, and hydrometallurgical byproduct. Due to
their toxicity and commonality, arsenic, barium, cadmium, copper, nickel, strontium, and zinc
(Figure 2) were chosen to be analyzed further in the results. Figure 4 shows the concentration of
each element leached out of each sample using the specified solution. For deionized water, the
highest concentration detected was about 100 ppm in the Intel CPU. Many of the components
analyzed using deionized water had element concentrations below the detection level, such as
arsenic, cadmium, copper and strontium. TCLP yielded higher concentrations of the majority of
elements from the samples compared to deionized water. Only arsenic and cadmium were
undetected and the highest concentration found was lead with 310.8 ppm. Hydrometallurgical
byproduct was the most effective solution by leaching concentrations of every element and
leaching almost 400 ppm of lead.
[3-6]
When assessing the risk for human consumption of toxic substances, the EPA calculates a
reference dose (RfD). Below the RfD, no harmful effects will occur in humans, and above the
RfD, harmful effects are more likely to become present. To calculate RfD, the EPA first assumes
no observed adverse effect level (NOAEL) for a substance and conducts animal studies. Three
safety factors are then considered: the fact that animal studies do not simulate humans
completely accurately, the distribution of human responses, and the higher sensitivity of children
to toxins. Each factor results in decreasing the NOAEL by a factor of 10, with a total decrease by
a factor of 1000. Based on this idea, the concentration of an individual metal in a solution was
divided by the EPA’s reference dose. An output less than one deems the concentration of the
metal in the solution to be below the reference dose and safe, and an output greater than or equal
to one suggests that there are risk factors coinciding with the amount of the metal in the solution.
This concept was applied to determine percent toxicities for each solution in order to evaluate if
leaching in deionized water, TCLP, and hydrometallurgical byproduct.
[3-7]
Figure 4. Concentration of Selected Heavy Metals in Deionized Water (A), TCLP (B), and
Hydrometallurgical Byproduct (C). Concentrations of the most toxic metals were measured by the
ICPOES. Note that a logarithmic base ten scale was used on the vertical axis in order to compensate for
the wide range of concentrations recorded in each solution.
Pond Water. Analysis of the pond water sample from the Zuck Arboretum in Drew
University showed that the majority of its heavy metal levels were all below detection level
(BDL). The pond water leachate containing the HP CPU showed elevated levels of barium
(0.0501 ppm), nickel (0.0806 ppm), and lead (0.8806 ppm), as shown in Table I. Compared with
the deionized water leachate containing an identical CPU, the pond water leached out less
barium and significantly less lead; 0.0501 ppm barium and 0.8806 ppm lead leached out from the
pond water, while 1.030 ppm barium and 91.60 ppm lead leached out from the deionized water.
On the other hand, the pond water leached out 0.081 ppm nickel, while the concentration of
nickel in the deionized water leachate was BDL.
Table I. Concentration of Elements in Pond Water versus DI Water Solutions
Element
Pond Water (ppm)
De-ionized Water (ppm)
BDL
BDL
As
0.0501
1.030
Ba
BDL
BDL
Cd
BDL
BDL
Cu
0.0806
BDL
Ni
0.8806
91.60
Pb
BDL
BDL
Sr
BDL
BDL
Zn
As shown in Figure 5, the percent toxicity for each element was calculated by dividing its
concentration in the samples by its Maximum Contaminant Level (MCL) established by the
Environment Protection Agency (EPA). Values above 1% indicate that the element was found in
greater concentrations than the MCL, posing a possible environmental hazard. In the deionized
water solutions, two samples of arsenic (Intel CPU and Intel RAM) had values greater than one,
of 1.6% and 1.9% respectively. In addition, three samples of lead (HP Chip, HP CPU, and Intel
CPU) had values of 21%, 6100%, and 4.7% respectively -- substantially higher than 1%. In the
[3-8]
TCLP solutions, the same samples had elevated levels of arsenic and lead, except on a greater
magnitude. In the hydrometallurgical byproduct leachate, samples of most elements yielded
values greater than one, with the exception of six samples analyzing copper (phone motherboard,
HP RAM, HP Chip, Intel CPU, Intel RAM, and Intel Chip), and all the samples of strontium.
This indicates that arsenic and lead pose a dangerous threat to the environment when leaching
from E-waste, especially in acidic landfill areas, which was mimicked by TCLP. In the extreme
case of animal digestion or use of acid extraction fluid, represented by the hydrometallurgical
byproduct, the concentrations of nearly every element analyzed were high enough to have
detrimental health effects.
[3-9]
Figure 5. Percent Toxicity of Elements in Different Solutions. The percent was calculated
by dividing the concentrations we found for six elements in each solution above by the
maximum contaminant level (MCL) determined by the EPA.
Burning Study. Analysis of the burnt RAM showed that the burnt RAM leached lower
amounts of all elements except for copper. We predicted that there would be more leaching with
the burnt chip, but we found that most elements were instead found in smaller concentrations.
We believe that this is due to the large amounts of heavy metals that were released as a gas
during the combustion reaction. A thick residue was observed on the crucible, which most likely
contained high concentrations of heavy metals, leaving less metals to leach out during the
leaching process.
Table II. Concentration of Elements (mg/L) Found in the Burnt Chip Submerged in DI Water
Arsenic
Barium
Cadmium
Copper
Nickel
Lead
Zinc
0.01
BDL
BDL
0.76
0.29
BDL
BDL
Plant Absorption. While a variety of elements were tested for using the ICP-OES, only
certain ones were detected above the detection level (Table II). These four metals (Al, Cu, Mn
and Ni) had the most prevalent concentrations in the majority of plant samples. The highest
concentrations were detected from aluminum, with 0.494 mg/L in the control root. For
aluminum, all control components had higher concentrations of metals than their respective toxic
parts. However, for the other elements, the toxic sections had a far greater presence of heavy
metals than the control components. For instance, the toxic soil had a concentration of 0.028
mg/L, while the control soil only had 0.008 mg/L. Regarding manganese and nickel, the
concentrations of the toxic soil and toxic stems were substantially higher compared to the
concentrations of the controlled parts as they were below the detection level. Even so, for some
samples like copper, the control stem had a higher concentration of 0.014 mg/L than the toxic
stem with 0.010 mg/L - a result inconsistent with the majority of the data.
[3-10]
Table III. Concentration (mg/L) of Elements in Toxic and Control Plant Components
Toxic Soil
Toxic Root Toxic Stem Control
Soil
Control
Root
Control
Stem
Al
0.370
0.291
0.003
0.494
0.292
0.075
Cu
0.028
0.061
0.010
0.008
0.015
0.014
Mn
0.047
0.012
0.040
BDL
0.008
BDL
Ni
0.030
0.020
0.012
BDL
0.026
BDL
DISCUSSION
The several experiments conducted depicted the different toxic metals that leached from
E-waste into various solutions. The concentrations of the metals were compared to the EPA
drinking water reference dose standards to determine the likelihood of detrimental health effects.
The data is separated by element to link the concentrations of specific metals to the possible
ramifications. Metals such as lead had overwhelmingly high concentrations while others such as
strontium had low concentrations and posed little risk for human consumption.
Lead and Arsenic. As seen in Table III, much of the leachate that was analyzed in this
experiment was found to have higher concentrations of lead than the EPA drinking water
standard of 0.015 ppm. The hydrometallurgical byproduct (HMB) yielded the highest
concentrations of lead. However, since ingestion of electronic waste is unlikely, we will
primarily analyze the DI water solutions, which mimic drinking water. Four out of the nine
solutions of DI water had concentrations of lead higher than the safety level, the highest
concentration being 91.6 ppm in the Motherboard 3 (~6000 times the drinking water standard).
This means that if the lead from electronic waste dumping and recycling sites was able to leach
into the water supply, it could have many adverse health effects in humans after long-term
exposure, including poor muscle coordination, nerve damage, hearing and vision impairment,
reproductive problems, cancer, or even death. Lead exposure is much more harmful to children,
greatly affecting their brain development and decreasing their and IQ. Children living in
developing countries are doubly at risk on account of their bodies absorbing more lead to
compensate for malnourishment, as well as the fact that most electronic waste recycling centers
are located in these nations, increasing the risk of exposure (11).
Table IV. Concentrations (mg/L) of Lead in Various Solutions
Motherboard
(Phone)
Magnet
Glass/
Metal
HP
RAM
HP
Chip
HP
CPU
Intel
CPU
Intel
RAM
Intel Chip
DI Water
BDL
BDL
BDL
BDL
0.32
91.6
0.07
BDL
BDL
TCLP
1.95
0.14
BDL
1.25
0.32
310.8
5.09
0.07
BDL
[3-11]
HMB
5.874
7.419
BDL
5.26
0.29
435.4
4.59
0.2
0.18
Similar to lead, arsenic may pose a detrimental health risk based on the concentrations
detected in the study. As of January 2006, the EPA set the standard for arsenic concentration in
drinking water at .010 ppm (10). Arsenic was not detectable in DI water, except in the Lenovo
chips with levels reaching as high as 0.019 ppm in the RAM. Likewise, in the TCLP, arsenic was
undetected. However, in the hydrometallurgical byproduct, the concentration of arsenic was
1.225 ppm in the cell-phone magnet and as high as 0.02 ppm in all chips of the HP computer and
one chip of the Lenovo computer. This is alarming as the hydrometallurgical byproduct was used
to model the acid leaching methods used in electronic waste recycling plants. Arsenic is found
most naturally in groundwater supplies at dangerous levels for human consumption. As a result,
arsenic can contaminate irrigation systems, the food they produce, and drinking water, posing a
threat to both the environment and human beings. With elevated arsenic levels in drinking water,
humans face several health threats in the form of cancer, skin lesions, diabetes, neurotoxicity,
and cardiovascular diseases (12).
Nickel and Copper. While nickel may not pose extreme health and environmental
threats, it is necessary to note the level of leaching from the computer samples. From DI water, a
maximum of 4.91 ppm of nickel leached out from the RAM of the HP computer. As shown in
Table IV, the concentration of nickel for the CPU in the TCLP solution reached 64.7 ppm and
similarly elevated values in the other samples.
Table V. Concentrations (mg/L) of Nickel in Various Solutions
Motherboard
(Phone)
Magnet
Glass/
Metal
HP
RAM
HP
Chip
HP
CPU
Intel
CPU
Intel
RAM
Intel
Chip
DI Water
2.38
1.53
BDL
4.91
0.12
BDL
3.24
3.47
BDL
TCLP
33.49
0.06
0.05
8.78
0.033
0.389
64.73
14.72
0.04
HMB
8.711
4.207
0.933
4.89
0.0762
1.2764
6.58
1.1
1.98
Intriguingly enough, nickel leached out less in the hydrometallurgical byproduct - the
highest concentration of only 8.71 ppm - than in the TCLP, despite hydrometallurgical byproduct
having lower pH. Based on further tests, the hydrometallurgical byproduct did leach out more
nickel than TCLP, however this took a prolonged period of time of two weeks. This suggests that
it takes a significantly longer amount of time for nickel and hydrometallurgical byproduct to
react compared to the solution’s reactions with other heavy metals. Although we did obtain
relatively large concentrations of nickel, especially in TCLP, nickel is a relatively common metal
and requires great amounts of exposure to have a significant effect on human health. The most
common effect is allergic reactions by direct contact with nickel. Any significant health threats
caused by ingesting water with nickel occurs when the metal is 100,000 times more concentrated
the average presence of it (13). Exposure to nickel in water solutions is rare, and most
complications occur by breathing in nickel at metal refineries, in which the metal may pose more
hazardous threats such as bronchitis and cancer (13).
[3-12]
Copper also does not cause extreme health effects unless at extremely high
concentrations. The leaching of copper from deionized water was much lower than the EPA
drinking water standard of 1.3 ppm, with seven out of the nine E-waste components having
concentrations below the detection level. In both the TCLP and hydrometallurgical byproduct
solutions, eight of the nine components leached copper, but only two concentrations were greater
than the safety standard - the highest being 34 ppm in the hydrometallurgical byproduct solutions
of Glass/Metal solution. Adverse effects of copper range from short term gastrointestinal distress
to liver and kidney damage depending on the length and severity of exposure. For infants or
people with Wilson’s disease, the effects are exacerbated (14). However, the main danger
associated with copper is that many recycling centers in developing countries use acid baths to
extract the copper from electronic waste. The acid used then has the potential to pollute
waterways, injure the workers, and leach into drinking water. For example, in Guiyu, China, the
acid baths used to extract materials from E-waste are located right at the bank of rivers (15). The
amount of copper that leaches out from these acid extraction fluids would resemble the TCLP
and hydrometallurgical byproduct data, both of which exceed the EPA levels and represent a
stronger link to copper’s adverse health risks.
Barium, Strontium, and Zinc. The concentrations of barium, found in Table V, were
very high in the hydrometallurgical byproduct solutions with the highest concentrations falling
just under 98 ppm. However, the concentrations were fairly low in the DI water - none of them
higher than the EPA standard of 2 ppm. This indicates that the leaching of barium from
electronic waste into groundwater does not pose a large threat to human health. Moreover,
barium has not been found to have dangerous health effects except at extremely high
concentrations such as 500-1000 ppm (16).
Table VI. Concentrations (mg/L) of Barium in Various Solutions
Motherboard
(Phone)
Magnet
Glass/
Metal
HP
RAM
HP
Chip
HP
CPU
Intel
CPU
Intel
RAM
Intel
Chip
DI Water
0.34
0.21
BDL
0.65
0.08
1.03
BDL
0.1
0.1
TCLP
3.67
0.86
0.02
1.78
1.25
0.92
0.54
2.96
0.23
HMB
97.57
0.477
0.94
45.4
3.4
93.3
44.26
8.33
60.07
Moreover, the leachates analyzed in this experiment did not contain large amounts of
strontium – the highest concentration being 2.57 ppm for the CPU in the hydrometallurgical
byproduct solution. In the DI water solutions, only two samples of E-waste had concentrations
above 0 ppm, but the concentrations were still about 70 times lower than the EPA drinking water
standard of 4 ppm. The safety standard for strontium is fairly high because strontium is present
in the environment naturally and not particularly hazardous to human or environmental health.
The main danger that strontium presents is emulating calcium to effectively integrate itself into
bones, thereby weakening them. Children in developing countries are at a higher risk because
calcium deficiency is more common. This results in more strontium assimilating into their bones
and negatively affecting their growth (17).
[3-13]
Similarly, zinc is not a particularly dangerous element and the EPA drinking water limit
is only in place to preserve water taste. Zinc levels were moderately high in the DI water ranging
from concentrations of 0.013 ppm in the RAM of the HP computer to 0.76 ppm in the magnet of
the cell phone. Levels rose strikingly to 156.89 ppm in the Magnet in the TCLP and 187.39 ppm
in the hydrometallurgical byproduct data. The data suggests that zinc is used in large
concentrations in electronics and can easily leach out of E-waste in the right conditions. While
zinc is a vital metal for human health, large quantities of exposure may harm humans by causing
dehydration, abdominal pain, vomiting, and lack of muscular coordination (18). Zinc often
settles in lakes and rivers and can sometimes be consumed by fish or absorbed into their bodies.
It can also often be absorbed by soil and seep into groundwater, most dangerously near
hazardous waste sites (18).
Limitations of Real-Life Simulations. It is important to note that EPA standards were
for drinking water and not landfill water or acid wash. For instance, the leachates from the pond
water study had less concentration of lead and barium than the deionized water. Thus, the values
obtained from the TCLP and especially the hydrometallurgical byproduct, which tend to leach
out more than deionized water, may be more extreme than what actually leaches out into
drinking water. To determine the relative ability of solutions to perform heavy metal leaching,
the average amount of heavy metals leached from the nine samples was calculated for each
solution (Fig 6). Overall, deionized water was the least effective leaching solution, while
hydrometallurgical byproduct was the most effective. For instance, the levels of barium for the
deionized water, TCLP, and hydrometallurgical byproduct, were 0.28 ppm, 1.4 ppm, and 39 ppm
respectively. The trend was apparent for all elements, except nickel and zinc. In these cases,
TCLP leached a higher element concentration than hydrometallurgical byproduct did, yielding
concentrations of 14 ppm of nickel and 33 ppm of zinc, versus 3.3 ppm of nickel and 23 ppm of
zinc.
Figure 6. Average Concentration of Leachate in three different types of solution. The concentrations
calculated by the ICP-OES were averaged among the 9 different samples for the deionized water, TCLP,
and hydrometallurgical byproduct solutions.
[3-14]
The data suggests that, with the exception of nickel and barium, the lower the pH of the
solvent, the more leachability of the metal. This is consistent with data from research that
compared the leachability of heavy metals in solutions of different pH (7). While one can
attribute the transport of metal ions into the solution to the pH of the aqueous solution, it is also
necessary to recognize that the mere solubility of the ions in the solution itself plays a large role.
With certain elements, such as lead, it is favorable to have solutions with higher acid
concentrations for more leachability. However, in other cases, a solution’s water solubility plays
a larger factor than its pH on leaching. While we studied the significant leaching of metals in
highly acidic solutions, it was discovered that alkaline solutions with high pH solutions, which
we did not study, can also lead to increased leaching (7).
In addition, a piece of RAM was burnt to simulate open fires where E-waste is disposed
of in other countries, and the amount of leaching was expected to increase. However, the heavy
metal concentrations were higher for every element in the un-burnt RAM in the deionized water
than the burnt RAM in deionized water. For instance, the concentration of arsenic in the unburnt
sample was 0.0156 ppm, and it decreased to 0.0030 in the burnt sample. Additionally, the
concentration of nickel was 3.24ppm for the unburnt sample while none was detected in the
burnt sample. A possible explanation is that the metals from the RAM collected on the watch
glass and crucible, which were difficult to remove and analyze accurately.
The plant study attempted to simulate bioaccumulation by analyzing plant growth when
exposed to heavy metals. Unfortunately, the results of the plant study were inconclusive - most
of the concentrations measured by the ICP-OES were zero or negligible values - as the plant
study was limited by time and resource constraints. For example, the two plants were only
watered with toxic solutions twice over the course of one week. The nitric acid watering also
negatively impacted the plants before they had a chance to grow and, in the case of the
experimental plant, effectively take up any metals. Possibly, if the plants were given a lower
concentration in toxic dosage, or were watered more frequently, the results could have been more
significant in terms of the amount of E-waste leachate found in parts of the plant.
FUTURE STUDIES
A change in this experiment could include microwave digestion of equivalent
components to find the percentage of heavy metals that leached as compared to the total possible
concentration of heavy metals in each component. Due to a lack of samples, not every
component used in the leaching study was able to be evaluated using microwave digestion. If
every sample was run through the microwave digestion process, the total amount of metal
present in the sample could be compared with the amount of metal that was leached out through
the various solutions to calculate a percentage; extrapolating this data would allow us to estimate
how much metal would leach out from a larger collection of electronic devices. These standards
could be compared to the values obtained from the microwave digestion, which determined the
composition of metals in the sample.
In 2006, the European Union passed the directive for the “Restriction of the use of certain
Hazardous Substances in electrical or electronic products” (RoHS) (19). This legislation sets
standards for the levels of certain toxic chemicals in the manufacturing of electronic devices. As
[3-15]
of 2007, United States formulated its own national RoHS standards. In future experiments, it
would be valuable to know the total amount of each metal for every device to see whether or not
it follows RoHS standards. One could then compare the metal content of E-waste manufactured
before and after the RoHS standards were established to ascertain if the legislation was effective.
Though our bioaccumulation results were promising, further study is needed before
conclusions can be reasonably extended to have implications for the agricultural industry. Future
studies could expand upon these efforts to quantify the effects that absorption of contaminated
water could have on large agricultural crops and what health hazards this could pose to humans.
Testing smaller-scale edible plants such as cucumbers or tomatoes could also quantify the
possible effects of leachates from improperly disposed E-waste on home gardens.
It is also important to recognize the limitations of this study design in that the solutions
only imitate real-life environmental conditions of drinking water, landfill water, and acid wash
recycling. For instance, the TCLP solutions represented the worst-case scenarios of landfill
leachates, so actual concentrations of heavy metals may be less than what was projected. Future
studies may analyze the specific metals identified with high toxicity levels, such as lead and
arsenic, in water samples from the environment itself.
CONCLUSION
The results of our research indicate that E-waste disposal poses a considerable threat to
water sources as a result of heavy metal leaching. The laptop and cell phone components were
shown to leach significant amounts of heavy metals including arsenic, nickel, lead, and zinc in
the presence of deionized water alone. The samples studied in TCLP and the hydrometallurgical
byproduct had a greater degree of leaching as a result of the acidity of the solutions, which
simulated aqueous environments including landfills and the acid washes used in
hydrometallurgical separation at recycling centers. Furthermore, the high concentrations of the
most toxic metals, lead and arsenic, should be rapidly addressed as they are severe health
hazards. However, our experiments also yielded promising results in terms of other some other
toxic metals like cadmium, which were in concentrations BDL for all samples.
Even though electronic devices may be approved by EPA standards during the
manufacturing process, the amount of heavy metals that can leach out afterward can greatly
surpass the maximum contaminant level decreed safe in drinking water. Overall, our study
indicates that legislation for stricter environmental regulations regarding heavy metal disposal
methods is necessary to avoid harmful levels of E-waste contamination. Moreover, as the
world’s dependence on electronic products grows and the lifespan of these products decreases,
more electronic waste will be shipped to developing countries to be recycled; this will only
exacerbate the environmental health in countries that lack the infrastructure to properly deal with
the increasing threat of heavy metal contamination.
ACKNOWLEDGEMENTS
We would like to extend our appreciation and gratitude to Dr. Ryan Hinrichs and Kelsie Kolb for
their continuous support and assistance throughout the experiment, Dr. Adam Cassano, Dr. Steve
Surace, the New Jersey Governor’s School in the Sciences, our sponsors and Drew University.
[3-16]
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APPENDIX Table VII. Concentrations (mg/L) of Elements in Various Solutions
Motherboard (Phone)
Glass/
Metal
Magnet
HP RAM
HP Chip
HP CPU
Intel CPU
Intel RAM
Intel Chip
Aluminum
DI Water
BDL
BDL
0.59
BDL
BDL
0.14
BDL
BDL
TCLP
1.12
BDL
1.11
0.19
0.23
0.1
0.7
0.31
BDL
0.04
HMB
10.6
82.17
2.27
4.11
8.82
3.98
10.62
6.15
11.75
DI Water
BDL
BDL
BDL
BDL
BDL
BDL
0.016
0.019
0.01
TCLP
BDL
BDL
BDL
BDL
BDL
BDL
BDL
BDL
BDL
HMB
BDL
1.26
BDL
0.022
0.024
0.019
0.025
BDL
0.011
DI Water
BDL
BDL
BDL
BDL
BDL
BDL
BDL
BDL
BDL
TCLP
BDL
BDL
BDL
0.0005
BDL
BDL
BDL
BDL
BDL
HMB
BDL
0.2
BDL
BDL
BDL
BDL
BDL
BDL
BDL
DI Water
BDL
BDL
BDL
BDL
BDL
BDL
BDL
0.01
BDL
TCLP
1.46
BDL
BDL
0.0082
BDL
BDL
0.02
0.01
BDL
HMB
0.039
0.17
BDL
0.039
BDL
BDL
BDL
BDL
BDL
DI Water
BDL
BDL
BDL
BDL
BDL
BDL
BDL
BDL
BDL
TCLP
BDL
0.05
BDL
BDL
BDL
BDL
BDL
BDL
BDL
HMB
0.68
1.51
0.0018
0.13
0.12
0.42
0.11
0.03
0.21
DI Water
0.1
BDL
BDL
BDL
0.03
BDL
BDL
BDL
BDL
TCLP
0.23
BDL
0.68
0.18
0.3
0.0026
0.08
0.28
0.4
HMB
0.86
2.44
34.2
0.11
0.098
BDL
0.05
0.13
1.17
DI Water
BDL
BDL
BDL
BDL
BDL
BDL
BDL
BDL
BDL
TCLP
4.27
0.02
BDL
0.054
0
0.0036
BDL
BDL
BDL
HMB
8.51
3.556
BDL
0.062
0
0.46
0.01
0.04
0.05
Arsenic
Cadmium
Cobalt
Chromium
Copper
Manganese
[3-18]
Molybdenum
DI Water
BDL
BDL
0.85
BDL
BDL
BDL
BDL
BDL
BDL
TCLP
BDL
BDL
0.02
BDL
BDL
BDL
BDL
BDL
BDL
HMB
0.266
1.11
1.08
0.02
0.002
BDL
BDL
BDL
BDL
DI Water
BDL
BDL
BDL
BDL
BDL
BDL
BDL
0.015
BDL
TCLP
BDL
BDL
BDL
BDL
BDL
BDL
0.01
0.02
0.013
HMB
BDL
BDL
BDL
BDL
BDL
BDL
0.02
0.025
0.051
DI Water
0.07
BDL
0.05
BDL
BDL
BDL
BDL
BDL
BDL
TCLP
0.89
BDL
0.12
BDL
BDL
BDL
2.35
BDL
BDL
HMB
1.83
0.95
0.053
0.17
0.13
0.16
2.57
0.15
0.63
Selenium
Strontium
Zinc
DI Water
0.34
0.76
0
0.013
0.011
BDL
BDL
BDL
0.02
TCLP
126.72
156.89
0.14
0.62
0.26
0.016
14.62
1.19
0.16
HMB
8.75
187.39
0.22
0.39
0.97
0.7
2.81
1.26
1.34
[3-19]