Environ. Sci. Technol. 2006, 40, 2721-2726
RCRA Toxicity Characterization of Discarded Electronic Devices STEPHEN E. MUSSON, KEVIN N. VANN, YONG-CHUL JANG,† SARVESH MUTHA, AARON JORDAN, BRIAN PEARSON, AND TIMOTHY G. TOWNSEND* Department of Environmental Engineering Sciences, University of Florida, Gainesville, Florida 32611-6450
The potential for discarded electronic devices to be classified as toxicity characteristic (TC) hazardous waste under provisions of the Resource Conservation and Recovery Act (RCRA) using the toxicity characteristic leaching procedure (TCLP) was examined. The regulatory TCLP method and two modified TCLP methods (in which devices were disassembled and leached in or near entirety) were utilized. Lead was the only element found to leach at concentrations greater than its TC limit (5 mg/L). Thirteen different types of electronic devices were tested using either the standard TCLP or modified versions. Every device type leached lead above 5 mg/L in at least one test and most devices leached lead above the TC limit in a majority of cases. Smaller devices that contained larger amounts of plastic and smaller amounts of ferrous metal (e.g., cellular phones, remote controls) tended to leach lead above the TC limit at a greater frequency than devices with more ferrous metal (e.g., computer CPUs, printers).
Introduction Discarded electronic devices pose a concern because of the magnitude of the waste stream and the possible environmental impact from toxic elements and compounds in their components. Industry experts have projected that approximately 500 million computers will become obsolete between 1997 and 2007 (1) and that 100 million cell phones will be discarded annually by 2005 (2). The United States Environmental Protection Agency (U.S. EPA) reported that electronic devices comprised 14% of all miscellaneous durable goods disposed of in 2001 and 1.3% of all municipal solid waste (MSW) (3). The growing consumer demand for electronic products and the tendency for the in-service lifetime of many devices to be short (often just a few years) result in a growing waste stream often referred to as “E-Waste”. With respect to the presence of toxic elements or compounds, electronic devices and their components are known to contain small amounts of chemicals that can exert negative impacts on human health and the environment. These chemicals are usually integral to the operation of the device and are selected because of valued material properties. Lead, for example, may be found in most electronic devices, either in the cathode ray tube (CRT) or in the printed wire board (PWB, i.e., the circuit board). Reports document that approximately 6.3% (weight/weight) of a typical computer is lead, a majority of which is attributed to the CRT (4). Tin/ lead solder (63% tin and 37% lead) is the most common * Corresponding author phone: 352-392-0846; fax: 352-392-3076; e-mail:
[email protected]. † Current Address: Department of Environmental Engineering, Chungnam National University, Daejeon 305-764, South Korea. 10.1021/es051557n CCC: $33.50 Published on Web 03/14/2006
2006 American Chemical Society
TABLE 1. Electronic Device Composition by Component Weight Percentage device VCRS remote controls printers smoke detectors keyboards cell phones computer monitors computer CPUs flat panel displays laptops computer mice color TVs electronic toys
non- printed ferrous ferrous wire metal metal board plastic wires
other
45 1 41 13 27 8 3
9 0 5 2 0 0 1
21 17 7 17 11 40 12
23 82 46 67 55 45 18
2 0 1 1 7 0 4
0 0 0 0 0 7 62 (CRT)
68 25
5 9
16 10
8 24
3 4
0 28
7 5 6 11
11 0 0 0
16 11 10 6
38 52 22 72
1 32 2 2
27 0 60 (CRT) 10
solder alloy used in the PWBs of electronics (5). The U.S. EPA estimated lead to comprise 4 wt % of all discarded electronics (3). Although lead is the most widely studied element in E-Waste, other elements such as mercury, cadmium, and chromium are present and also of potential concern (5-9). The toxicity characteristic leaching procedure (TCLP) is the U.S. EPA method used to determine a solid waste’s status as a hazardous waste due to the Toxicity Characteristic (TC). Color CRTs of televisions and computer monitors usually exceed the RCRA TC limits for lead (10) and several studies have documented that PWBs frequently exceed the lead TC limit of 5 mg/L (11-13). Although these tests indicate that electronic devices have the potential to fail the TCLP, TC data encompassing entire electronic devices are scarce. Research indicates that the composition of the entire electronic device can strongly affect TCLP results (14, 15). It is not sufficient to test only the component containing the lead (or other element of interest) and then calculate the TCLP concentration of the whole device from the TCLP concentration of the single component. Prior research by the authors utilizing computer central processing units (CPUs) examined modified leaching methods which were modeled upon the TCLP but which allowed more rapid and representative testing of this waste stream (15). In the present paper, both the standardized TCLP methodology and modified TCLP methods were used to test a wide array of discarded electronic devices. In a federal register notice describing a proposed rule for managing CRTs, the EPA stated that “we are not currently aware of any nonCRT computer components or electronic products that would generally be hazardous waste” (16). The objective of the research presented in this paper was to provide data addressing this unknown. Although no single study can characterize the myriad of different electronic device models and manufacturers, the study does provide a basis for determining whether these devices have a potential to be TC hazardous wastes.
Experimental Section Sample Collection and Processing. Electronic devices were collected from a variety of sources including electronics demanufacturing facilities, individuals, and a local household hazardous waste collection center. The electronic devices were disassembled and separated into material categories. The material categories and the average composition (percent by weight) of each type of device are presented in Table 1. VOL. 40, NO. 8, 2006 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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The table shows that smaller devices such as remote controls, computer mice, and smoke detectors have a larger percentage of plastic and a smaller percentage of ferrous metal when compared with larger devices such as computer CPUs, VCRs, and computer printers. The table shows the five major categories of materials in electronic devices with a sixth nonspecific category that was primarily composed of the leaded glass of CRTs in computer monitors or televisions and the LCD panels of flat panel displays. Leaching and Analysis Methods. The leachability of the TC heavy metals (arsenic, barium, cadmium, chromium, lead, silver, selenium) from discarded electronic devices was determined. The leachability of the eighth TC heavy metal, mercury, was measured for flat panel displays and laptop computers due to the mercury-containing fluorescent light used to illuminate these devices. Three different leaching methodologies were employed, all using the same leaching fluid and the same liquid-to-solid ratio: the TCLP, a modified version of the TCLP in which size reduction was not employed, and a second modified version of the TCLP employing a large-volume extraction vessel without size reduction of the sample. The modified methods allowed the testing of whole devices or nearly whole devices. These methods were considered appropriate because (1) sampling error was minimized by allowing a more representative sample to be easily obtained, (2) characterization of devices that would have otherwise been infeasible without elaborate size reduction devices was permitted, and (3) the methods more accurately simulated the expected condition of the devices in a landfill (15). Prior research by the authors examined factors affecting the TCLP testing of CPUs and utilized the modified methods of performing the TCLP on CPUs (14, 15). The results reported in the present paper further this research by including TCLP results for a wide variety of electronic devices, including computer CPUs, keyboards, mice, remote controls, laptop computers, cell phones, electronic toys, and smoke detectors. Toxicity Characteristic Leaching Procedure. Materials from the specific material categories were randomly selected from the electronic devices and reduced in size by hand (using shears) to pass a 0.95-cm sieve (a requirement of the TCLP). A 100 g sample of each device was then created corresponding to the composition of each device determined during sample collection. For example, a VCR composed of 45% ferrous metal, 9% nonferrous metals, 21% PWB, 23% plastic, and 2% wires was size reduced to produce a 100 g sample comprising 45 g of ferrous metal, 9 g of nonferrous metals, 21 g of PWB, 23 g of plastic, and 2 g of wires. Eleven of the CPU samples were prepared utilizing industrial shear shredders to reduce disassembled units to 1.75 cm pieces that were further reduced to the required 0.95 cm size by hand (14). The 100-g samples were placed into 2.34-L TCLP highdensity polyethylene (HDPE) extraction vessels. Individual testing of the electronic device components per the TCLP procedure required the use of TCLP extraction fluid #1. Two liters of TCLP extraction fluid #1, which consists of 11.4 mL of glacial acetic acid and 128.6 mL of 1-N sodium hydroxide solution diluted to 2 L with reagent water, were added to each extraction vessel. The initial pH of the TCLP extraction fluid was 4.93 ( 0.05. The samples were rotated at 30 ( 2 rpm for 18 ( 2 h in a 12-vessel rotary extractor (Analytical Testing Corporation). After rotation, the final pH of the leachates was recorded. pH was measured using an Orion model 710A+ benchtop meter equipped with an Orion model 91-55 combination pH electrode. The TCLP leachates were filtered through glass fiber filters (0.7-µm pore size) using pressure filtration and preserved by adding concentrated nitric acid until the pH of the filtrate was below 2. The leachate samples were digested 2722
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using a hotplate acid digestion procedure (Method 3010A, ref 17). The digested samples were then analyzed for arsenic, barium, cadmium, chromium, lead, silver, selenium, iron, and zinc following Method 6010B (inductively coupled plasma-atomic emissions spectrometry) on a Thermo Terrell Ash Trace Analyzer ICP (17). Laptop computers and flat panel displays, due to the fluorescent lamps used to illuminate the screens, were also analyzed for mercury using the cold-vapor atomic absorption technique, following EPA Method 7470 (17). Modified Small-Scale TCLP. In addition to the TCLP, an alternate method was utilized to leach cell phones and remote controls. The small size of these devices permitted the testing of disassembled, whole devices in 2.34-L HDPE extraction vessels. The samples were not size-reduced as required by the regulatory TCLP; they were only disassembled. All other procedures were conducted as previously described for the TCLP. Large-Scale TCLP. The large-scale TCLP method was performed on computer CPUs, laptop computers, computer monitors, keyboards, printers, color televisions, VCRs, and flat panel displays. Large devices up to 10 kg in mass were disassembled and leached in their entirety. The volume of the large-scale extraction vessel permitted a maximum of 200 L of extraction fluid. Thus, to maintain the 20:1 liquidto-solid ratio required by the TCLP, samples were limited to a maximum weight of 10 kg. For devices weighing more than 10 kg, representative fractions of each material type for that particular device were chosen at random to obtain a 10-kg sample. For example, a CPU composed of 5 kg (40%) of ferrous metal, 1kg (8%) of nonferrous metals, 3 kg (24%) of PWB, 3 kg (24%) of plastic, and 500 g (4%) of wires would have components randomly chosen to obtain a 10 kg sample of matching percent composition (i.e., 4 kg of ferrous metal, 800 g of nonferrous metal, 2.4 kg of PWB, 2.4 kg of plastic, and 400 g of wires). These components were not size-reduced, but portions were trimmed in size to obtain weights corresponding to the measured weight percentages of each device and totaling 10 kg. For devices of a total weight significantly less than 10 kg, multiple devices of the same manufacturer and model were leached as a group to attain as closely as possible 10 kg to minimize the potential impact of a large air volume in the extraction drum on the oxidation/ reduction chemistry (14). A 55-gallon extraction vessel (high-density polyethylene (HDPE) drum) within a Morse 1-300 Series, End-over-End Drum Rotator (Morse Manufacturing, East Syracuse, NY) was used. TCLP extraction fluid #1 was prepared in the extraction vessel and mixed by rotating the extraction drum. The total amount of extraction fluid added was dependent on the mass of the solid sample (20:1 liquid-to-solid ratio). Initial measurements were taken to verify the pH of the extraction fluid was 4.93 ( 0.05 as required by the TCLP. The disassembled device was placed into the extraction fluid and rotated endover-end at a speed of 13 rpm (maximum speed of the drum rotator) for 18 ( 2 h. After rotation, a sample was obtained from a bottom sampling connection of the extraction drum and the final pH was recorded. The TCLP leachates were filtered, preserved, and analyzed using the previously described methods.
Results and Discussion Leachate Concentrations. Thirteen types of electronic devices were tested using the TCLP or the two modified leaching methods. The composition and testing results for all the devices tested are given in the Supporting Information to this paper. All of the TC regulated heavy metals were below regulatory limits with the exception of lead. The concentrations of the other regulated heavy metals were often below the analytical detection limit of the instruments used. In
TABLE 2. Summary of TCLP Lead Leaching of Electronic Devices standard TCLP
device CPUs; manual size reduction/disassembled CPUs; mechanical size reduction computer monitors laptop computers printers color televisions VCRs cellular phones key boards computer mice remote controls smoke detectors flat panel displays toys
devices exceeding 5 mg-Pb/L
devices tested
0 1
12 11
6
6
28 0 15 4 7
38 5 15 5 10
8
10
modified large-scale TCLP
modified small-scale TCLP
devices exceeding 5 mg-Pb/L
devices tested
devices exceeding 5 mg-Pb/L
devices tested
20
41
10 9 5 6 9
10 9 10 6 10 10
14
2
5 6
6
2
9
TABLE 3. Combined Average Electronic Device Leachate Concentrations Utilizing the TCLP and Modified TCLP Methods device
methods used
iron (mg/L)
zinc (mg/L)
lead (mg/L)
VCRS remote controls printers smoke detectors keyboards cell phones computer monitors computer CPUs flat panel displays laptops computer mice color TVs electronic toys
large scale modified small/ standard large scale standard large scale/standard modified small/ standard large scale large scale/standard large scale large scale/ standard standard large scale standard
153 ( 82 19.6 ( 17.5 149 ( 89 30.9 ( 23.0 102 ( 74 44.7 ( 46.7 114 ( 27 78.9 ( 67.3 193 ( 113 82.2 ( 54.7 29.1 ( 23.1 100 ( 40 74.5 ( 37.7
94.3 ( 49.3 1.78 ( 1.37 62.3 ( 22.5 48.2 ( 76.7 86.8 ( 45.2 24.2 ( 29.7 22.0 ( 8.0 115 ( 45 92.1 ( 21.4 38.2 ( 36.6 6.39 ( 7.46 24.0 ( 15.0 27.3 ( 45.6
11.3 ( 5.0 11.1 ( 8.9 4.08 ( 2.42 20.7 ( 18.5 4.56 ( 6.99 9.23 ( 12.6 48.9 ( 28.9 3.96 ( 4.79 3.64 ( 2.06 28.8 ( 17.8 19.2 ( 11.7 24.3 ( 12.2 15.5 ( 11.4
cases where these chemicals were detected, no discernible trend or pattern was observed. The number of devices that exceeded the TC threshold concentration for lead is shown by device type in Table 2. Seven of the nine electronic device types tested using the standard TCLP had at least one device exceed the TC limit for lead and a total of 62% of all devices tested using the TCLP exceeded the TC limit. When CPUs and keyboards were removed from consideration, 81% of the other electronic devices tested exceeded the TC limit for lead. The large-scale TCLP and modified small-scale TCLP methods resulted in 65% and 80% of devices exceeding the TC limit. Every device type leached lead above 5 mg/L in at least one test with 64% of all devices exceeding the lead TC limit. Table 3 presents the average leachate concentrations of the three significant metals measured in the leachate: lead, iron, and zinc. All three metals are initially present in the electronic components in the zero oxidation state, and the acetate salt (TCLP’s primary anion) of each of these metals is readily soluble. Zinc, as with iron, has a higher oxidation potential than lead. Thus, due to redox chemistry and compositional considerations, the presence of both iron and zinc should similarly inhibit the oxidation and solubility of lead in the leachate. However, the project’s methods did not permit isolation of zinc’s effects. When comparing device types, as iron content increases, zinc present as a corrosion inhibition coating on the ferrous metal components increases proportionally and therefore the impact of each metal individually cannot be discerned. In examination of component size reduction, the iron surface area increases proportionately more than either the lead or zinc surface areas, so only the impact of iron on lead can be attained, whereas the impact of zinc on lead cannot.
The average concentrations of Table 3 include all test runs for a given device, and thus include results from different device models and testing procedures (hence the large standard deviations). However, the values do provide an indication of the ability of lead to leach from the devices. Specific data for individual devices are provided in the supplemental information to this paper. Nine of the thirteen devices tested had average lead leachate concentrations above the 5 mg/L TC limit. The four devices whose average leachate concentrations were below the TC limit were all above 3 mg/L. Method Evaluation. In the large-scale TCLP and modified small-scale TCLP, the electronic devices were disassembled in lieu of size reduction. During method development it was hypothesized that this approach would tend to underestimate the amount of pollutant leached, as the purpose of the size reduction step is expose a greater surface area of the sample and allow the solution concentrations to reach equilibrium with the solid sample more quickly. However, prior research with computer CPUs discovered that lead may leach more when the materials are not reduced in size (14, 15). Keyboards highlight the affects of the large-scale TCLP versus the standard TCLP. Although the lead concentrations observed were widely variable due to differences in manufacture and composition, comparison of the average leachate concentrations, shown in Figure 1A, demonstrates the potential method differences. Leachates had an average lead concentration of 7.6 mg/L utilizing the large-scale TCLP, but only an average of 1.6 mg/L when tested using the standard TCLP. During standard TCLP testing, size reduction increases the proportion of sample surface exposed to the solution in comparison to the large-scale method (disassembly only). Lead is primarily located in small discrete locations as solder VOL. 40, NO. 8, 2006 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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FIGURE 1. Comparison of the effects upon large-scale and standard TCLP lead concentrations for high iron content (keyboards) and low iron content (laptops) electronic devices.
FIGURE 2. Average TCLP leachate lead concentration vs the percentage of ferrous metal content for 13 electronic device types. on the printed wire boards of the electronic devices. As such, the surface area of lead is increased to a lesser extent than the ferrous metal which is primarily found as part of large components. Iron, with a higher oxidation potential than lead, inhibits the oxidation and release of lead from the sample. Furthermore, the increase in exposed surface area of iron increases the magnitude of iron oxidation, resulting in a decrease of the ORP of the leaching solution. Thus, despite the increase in lead surface exposure due to size reduction, the greater increase in iron surface area results in a decrease in the mass of lead oxidized to the more soluble Pb2+ state and decreased leachate concentrations of lead. As the iron content of an electronic device decreases, this phenomenon decreases as the greater exposure of lead surface area matches the increase in iron exposure. Laptops, with a small percentage of iron (7%), had an average largescale TCLP concentration of 23.5 mg/L while the average standard TCLP concentration was elevated to 36.2 mg/L (Figure 1B). The modified small-scale TCLP demonstrated trends identical to those observed with large-scale testing. This was expected since both methods utilized disassembled devices versus size-reduced samples. Modified small-scale testing was performed on cell phones and remote controls for comparison with the standard TCLP. The ferrous metal content of these devices (8% in cell phones, 1% in remote controls) is similar to the low content of the laptops studied in the large-scale TCLP. Therefore, the effect of ferrous metal was not significant and lead leachate concentrations between the two methods did not demonstrate a significant difference (R ) 0.05, modified small-scale TCLP leachate ) 34 mg/L, standard TCLP average ) 20 mg/L.) 2724
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The effects of iron upon lead leachability are also observed in comparing differing electronic devices within a single test method. For two devices with similar printed wire board composition (the source of lead solder), the device with the greater percentage by weight of ferrous metal would be expected to have lower lead leachate concentrations due to the same mechanisms. Tests of CPUs and laptops, each composed of 16 wt % of printed wire boards support these conclusions. CPUs (68% ferrous metal) had an average lead leachate concentration of 3.96 mg/L, while laptops (7% ferrous metal) had an average lead leachate concentration of 28.8 mg/L. Figure 2 illustrates the role that the ferrous metal content of the electronic device types plays on lead leachability. A general trend of decreasing lead leachate concentration with increasing iron composition of the device can be seen. The scatter of data points at lower iron concentrations can be attributed to differing printed wire board concentrations of the electronic devices, increased lead content through other sources such as CRT glass, and differences in test methods to which each device was subjected. The large range of the results for both the small-scale and standard methods makes comparison of the methods problematic. However, direct comparison of the methods is possible by examining the results of 12 samples composed of identical cell phone models (Piper 34106/NNDPA). As shown in Figure 3, the six samples leached using the standard TCLP method had an average concentration of 18.7 ( 2.0 mg/L while the six samples leached using the modified smallscale TCLP had an average concentration of 15.6 ( 1.2 mg/L. Statistical analysis shows these values to not be significantly different as expected due to the low iron content of the devices. The size-reduced samples did have higher lead
FIGURE 3. Comparison of leachate lead concentration for identical cell phone models using the modified small-scale TCLP and standard TCLP methods concentrations in the leachate than those simply disassembled. Thus, for any of the methods used, composition of the sample and efforts to obtain a representative sample are important factors affecting leaching results.
Implications The results indicate that discarded electronic devices will in many cases leach sufficient lead under the TCLP to be characterized as RCRA hazardous wastes unless otherwise excluded. Devices with smaller amounts of ferrous metal (e.g., cellular phones) are more likely to exceed the TC threshold for lead than devices with more ferrous metal (e.g., computer CPUs). Currently in the United States household wastes are excluded from the definition of hazardous waste (California is a notable exception). Businesses, government agencies, and other nonhousehold generators are required to manage hazardous wastes following very specific regulatory requirements. Communities with household hazardous waste collection programs will need to decide whether discarded electronic devices should be accepted at their facilities. The recognition that discarded electronic devices may be hazardous waste could also impact the transport of these devices for recycling, an issue of possible international significance. The utility of the modified test results will have to be determined by the regulatory agencies. One could argue that the modified test procedures are not true TCLP results and thus are not applicable. However, the modified testing procedures meet the intent of the TCLP which is to provide a conservative estimate of the amount of pollutant that leaches from a waste. At the very least, this research contributes to the debate regarding the appropriate utilization of leach testing of solid wastes. The results further highlight the variability of TCLP results in heterogeneous materials and the effects sample preparation and material composition may have upon TCLP results. Specifically, the oxidationreduction conditions created during testing can drastically affect TCLP results of the TC heavy metals. Finally, it is noted that this research does not attempt to interpret the TCLP results with respect to environmental impacts, such as impact on leachate quality at landfills. The ability of the TCLP to simulate actual landfill environments is currently a topic of debate in the profession. For example, the authors found that CRTs and PWBs leach much less lead when exposed to typical landfill leachate compared to when exposed to TCLP solution (13). Different redox conditions that occur in landfills in comparison to the TCLP may also
influence lead mobility. The authors are conducting other research to address this issue.
Acknowledgments This research was sponsored by United States Environmental Protection Agency Regions 4 and 5. Thanks are extended to the organizations and individuals that provided electronic devices for this study. Thanks to student Sean King for his assistance with this project.
Supporting Information Available Individual results for 13 electronics devices tested for the leaching of lead, iron, and zinc utilizing the TCLP or a modified form of the leaching procedure. This material is available free of charge via the Internet at http://pubs.acs.org.
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(9) Poison PCs and Toxic TVs: California’s Biggest Environmental Crisis That You’ve Never Heard Of; Silicon Valley Toxics Coalition (SVTC), Californians Against Waste (CAW), and The Materials for the Future Foundation: San Jose, CA, 2001. Available at: http://www.svtc.org/cleancc/pubs/ppc-ttv1.pdf), accessed June, 2001. (10) Musson, S.; Jang, Y.; Townsend, T.; Chung I. Characterization of Lead Leachability from Cathode Ray Tubes Using the Toxicity Characteristic Leaching Procedure. Environ. Sci. Technol. 2000, 34, 4376-4381. (11) Hazardous Status of Waste Electrical and Electronic Assemblies or Scrap; Guidance Paper, Department of the Environment and Heritage: Commonwealth of Australia, 1999. (12) Yang, G. Environmental Threats of Discarded Picture Tubes and Printed Circuit Boards. J. Hazard. Mater. 1993, 34, 235243. (13) Jang, Y.; Townsend, T. Leaching of Lead from Computer Printed Wire Boards and Cathode Ray Tubes by Municipal Solid Waste
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(14) (15) (16) (17)
Landfill Leachates. Environ. Sci. Technol. 2003, 37 (20), 47784784. Vann, K.; Musson, S.; Townsend, T. Factors Affecting TCLP Lead Leachability from Computer CPUs. Waste Manage. 2006, 26 (3), 293-298. Vann, K.; Musson, S.; Townsend, T. Evaluation of a Modified TCLP Methodology for RCRA Toxicity Characterization of Computer CPUs. J. Hazard. Mater. 2006, 129, 101-109. U.S. Environmental Protection Agency (USEPA) Proposed Rules. Fed. Regist. 2002, 67 (113), 40508-40528. Test Methods for Evaluating Solid Waste, SW-846; Office of Solid Waste and Emergency Response, U.S. Environmental Protection Administration: Washington, DC, 2000.
Received for review August 5, 2005. Revised manuscript received February 8, 2006. Accepted February 9, 2006. ES051557N
