Potential Environmental Impacts from the Metals in Incandescent

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Potential Environmental Impacts from the Metals in Incandescent, Compact Fluorescent Lamp (CFL), and Light-Emitting Diode (LED) Bulbs Seong-Rin Lim,† Daniel Kang,‡ Oladele A. Ogunseitan,‡,§ and Julie M. Schoenung*,∥ †

Department of Environmental Engineering, College of Engineering, Kangwon National University, Chuncheon, Gangwon 200-701, South Korea ‡ School of Social Ecology and §Program in Public Health, University of California, Irvine, California, United States ∥ Department of Chemical Engineering and Materials Science, University of California, Davis, California, United States S Supporting Information *

ABSTRACT: Artificial lighting systems are transitioning from incandescent to compact fluorescent lamp (CFL) and light-emitting diode (LED) bulbs in response to the U.S. Energy Independence and Security Act and the EU Ecodesign Directive, which leads to energy savings and reduced greenhouse gas emissions. Although CFLs and LEDs are more energyefficient than incandescent bulbs, they require more metal-containing components. There is uncertainty about the potential environmental impacts of these components and whether special provisions must be made for their disposal at the end of useful life. Therefore, the objective of this study is to analyze the resource depletion and toxicity potentials from the metals in incandescent, CFL, and LED bulbs to complement the development of sustainable energy policy. We assessed the potentials by examining whether the lighting products are to be categorized as hazardous waste under existing U.S. federal and California state regulations and by applying life cycle impact-based and hazardbased assessment methods (note that “life cycle impact-based method” does not mean a general life cycle assessment (LCA) but rather the elements in LCA used to quantify toxicity potentials). We discovered that both CFL and LED bulbs are categorized as hazardous, due to excessive levels of lead (Pb) leachability (132 and 44 mg/L, respectively; regulatory limit: 5) and the high contents of copper (111 000 and 31 600 mg/kg, respectively; limit: 2500), lead (3860 mg/kg for the CFL bulb; limit: 1000), and zinc (34 500 mg/kg for the CFL bulb; limit: 5000), while the incandescent bulb is not hazardous (note that the results for CFL bulbs excluded mercury vapor not captured during sample preparation). The CFLs and LEDs have higher resource depletion and toxicity potentials than the incandescent bulb due primarily to their high aluminum, copper, gold, lead, silver, and zinc. Comparing the bulbs on an equivalent quantity basis with respect to the expected lifetimes of the bulbs, the CFLs and LEDs have 3−26 and 2−3 times higher potential impacts than the incandescent bulb, respectively. We conclude that in addition to enhancing energy efficiency, conservation and sustainability policies should focus on the development of technologies that reduce the content of hazardous and rare metals in lighting products without compromising their performance and useful lifespan.

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INTRODUCTION The U.S. Energy Independence and Security Act1 and a European ban on incandescent bulbs2 were established with a goal to increase energy efficiency for general lighting. Therefore, consumers are replacing incandescent light sources with compact fluorescent lamp (CFL) and light-emitting diode (LED) bulbs that use about 70% and 85% less energy and have 10 and 50 times longer lifetimes, respectively.3,4 Trifunovic and co-workers have shown that replacing incandescent bulbs with CFLs leads to a high potential to reduce energy consumption and power demand.5 Recently, LEDs have been replacing both incandescent and CFL bulbs because of higher energy efficiency and absence of mercury in CFLs.3,4,6 Due to the importance of lighting to society, previous studies have investigated various environmental impacts from © 2012 American Chemical Society

incandescent, CFL, and LED bulbs. For example, various efforts have focused on managing the mercury vapor released from broken CFLs.7,8 Life cycle analyses have been performed (i) to evaluate the amount of mercury reduced by replacing an incandescent with a CFL bulb,9 and (ii) to quantify and compare energy and environmental impacts in the life cycle stages of incandescent, CFL, and LED bulbs.10,11 These LCAs highlighted high impact potentials from energy consumption: for instance, compared to the incandescent bulb on an equivalent quantity basis, the CFLs and LEDs reduced primary Received: Revised: Accepted: Published: 1040

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Figure 1. Photographs and schematic diagrams of the driver components used in CFL and LED bulbs: (a) CFL bulb driver, and (b) LED bulb driver (AC: alternating current; DC: direct current; EMI: electromagnetic interface; PWM: pulse width modulator; and IC: integrated circuit). Photographs were modified from literature.16,51

through the phosphor coating on the inside of the glass tube.16 For LEDs, the DC is used to supply power to the LED semiconductor emitting the light.14,15 Incandescent bulbs do not need a driver because the lighting principle is simply to convert heat into light through the filament.6 In addition to the drivers, CFLs and LEDs need one or two printed wiring boards (PWBs).14,16,17 Moreover, LED bulbs need heat dissipation management systems (i.e., heat sinks) because the heat from the LED chip and components can cause thermal stresses on the LED chip causing it to fail.3,18,19 Since these components include various valuable and toxic metals, CFLs and LEDs as alternatives to incandescent bulbs can contribute substantially to potential adverse environmental impacts in ways similar to those created by the rapid obsolescence of consumer electronic devices.20 Thus, the objective of this study is to evaluate and analyze the resource depletion and toxicity potentials associated with the metals in incandescent, CFL, and LED bulbs, highlighting the potentials from their ancillary components. We assessed the potentials by investigating whether the bulbs are to be categorized as hazardous waste under existing U.S. federal regulation (Toxicity Characteristics Leaching Procedure; TCLP21) and California state regulation (Total Threshold Limiting Concentrations; TTLC22) and by applying life cycle

energy demand and global warming, human toxicity, and resource depletion potentials by approximately 80% during the use and manufacturing stages.10 We recently published an LED study that addressed the potential environmental impacts derived from the metals in LED “pin-type diodes” with various light intensities and colors.12 The previous studies have not, however, investigated the resource depletion and toxicity potentials from the metals in end-of-life “complete” CFL and LED “bulbs” (note that, as presented in the results of this study, the LED bulbs have significantly higher levels of aluminum, antimony, copper, and zinc than pin-type LEDs). Thus, the impact potentials from CFL and LED bulbs should be examined to inform energy policy, design for environment (DfE), and end-of-life management. Waste CFLs and LEDs have more potential from metals in their components to impact human health and ecosystems in the disposal stages than waste incandescent bulbs because CFLs and LEDs need more metal-containing components in order to function. Figure 1 shows a series of components needed for the drivers to supply power to the CFLs and LEDs. These drivers are required for generating a high-frequency AC output for CFLs13 and a DC output for LEDs.14,15 For CFLs, the AC is used to make electrons collide with mercury atoms to release ultraviolet (UV) light,16 which is changed to visible light 1041

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federal regulations in estimating the concentration of substances that would leach in landfill facilities; and (ii) the California Department of Toxic Substances Control’s TTLC method,22 which corresponds to State of California regulations and is used to determine whether waste products should be classified as hazardous waste (see Table S-1). The TTLC also provides data on the metal content, which are used to evaluate resource depletion and toxicity potentials. The TCLP test for the LED bulb was conducted in two phases because some components (such as the heat sink) cannot be ground by the cutting mill to a particle size less than 2 mm; rather for these components an abrasive saw was used and a particle size of less than 9.5 mm was achieved. In the TCLP and TTLC procedures, U.S. EPA method 6010B23 is used to analyze the concentration of barium, chromium, copper, nickel, silver, and zinc; and U.S. EPA method 6020A24 is used for aluminum, antimony, arsenic, cerium, gadolinium, gallium, gold, indium, iron, lead (Pb), mercury, phosphorus, tungsten, and yttrium. The TCLP and TTLC results were compared to the respective threshold limits to identify hazardous waste potential. Evaluation and Analysis of Resource Depletion and Toxicity Potentials. Resource depletion and toxicity potentials were evaluated based on the metal content in the three types of bulbs and the respective heavy metal weighting factors derived from established life cycle impact-based and hazard-based assessment methodologies (each methodology is described below and summarized in Table S-2). Ideally, these bulbs should be collected and recycled, allowing for the metals to be recovered for reuse, which would reduce the resource depletion and toxicity potentials calculated below. However, because the norm is to simply throw away incandescent bulbs, to perform this comparative assessment, the same behavior is assumed for the CFLs and LEDs. The formula used to calculate the resource depletion or toxicity potential associated with each metal is12

impact-based and hazard-based assessment methods (note that “life cycle impact-based method” does not mean a general life cycle assessment (LCA) but rather the elements in LCA used to quantify toxicity potentials). Similar methods were used in our previous study on 5-mm LED pin-type diodes,12 which are used as indicator lights within products such as computers, cell phones, clocks, and toys. But the pin-type diodes are very small, and do not require the ancillary driver needed for an LED bulb used directly as an energy-efficient substitute for incandescent bulbs in ambient lighting. The three bulbs are compared and analyzed to examine which bulb has the lowest potentials per bulb and which metals contribute the most to the resource depletion and toxicity potentials. Also, the bulbs are compared on an equivalent quantity basis by taking into account their different design lifetimes (i.e., product life expectancies). We emphasize that this study focuses on the impact potentials related with the end-of-life of the bulbs, whereas the previous LCA study for bulbs has emphasized environmental benefits derived from energy savings in the use stage.10 Therefore, this study can supplement the information needed to develop sustainable energy policy for artificial lighting. Such policies aim to reduce resource depletion and toxicity potentials attributable to artificial lighting, while also encouraging energy conservation during their use.

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MATERIALS AND METHODS Sample Bulbs Used for this Study. Triplicate incandescent, CFL, and LED bulbs were selected for this study (photographs are provided in Figure S-1 and specifications are provided in Table 1). The CFL and LED bulbs are advertised Table 1. Specifications of the Bulb Samples Selected To Compare the Potential Environmental Impacts of Incandescent, CFL, and LED Bulbsa

wattage (W) luminous intensity (lumens) CRI (color rendering index) color temperature (K) lifetime (hours) working voltage (V) weight (g)

incandescent bulb

CFL bulb

LED bulb

60 860 100 3000 1000 120 26

13 800 80 2700 10,000 120 58

7.3 280 80 3000−3500 50,000 85−265 172

Pi = Ci·W ·WFi

(1)

where Pi is a potential (i.e., life cycle impact-based resource depletion potential; hazard-based occupational toxicity potential; hazard-based Toxic Potential Indicator (TPI); and life cycle impact-based toxicity potentials for human- and ecotoxicity, as listed in Table S-2) from metal i; Ci is the content of metal i in the bulb (kg/kg); W is the weight of the bulb (kg); and WFi is the weighting factor for the potential for metal i. For life cycle impact-based resource depletion potential, the weighting factors are the characterization factors for abiotic resource depletion potential derived from the CML 200125 and EPS 200026 methodologies.12 In the CML method, resource depletion potential implies the ratio of the reserve base to the extraction rate of a given resource, which is compared to the ratio for antimony as a reference substance.25 Thus, this potential is measured in units of kg of antimony-equivalents (Sb-eq). In the EPS 2000 method, resource depletion potential is valuated in a monetary unit (i.e., EUR) based on the willingness-to-pay as used in environmental economics.26 In this methodology 1 EUR is equivalent to 1 Environmental Load Unit (ELU). It should be noted that these two methods do not take into account the supply risk (i.e., all of the geological, technical, environmental, social, political, and economic aspects) of resources, which would need to be examined to evaluate resource criticality.27,28 For hazard-based toxicity potential, the weighting factors are derived as the inverse of the exposure limits, i.e., Threshold

a

These CFL and LED bulbs are advertised in the market as equivalent to 60 W incandescent bulbs, implying that due to the same function, these bulbs can be compared to one another considering their different lifetimes (note that although the LED bulb has lower luminous intensity than the CFL and incandescent bulbs, the LED bulb is used to replace the CFL and incandescent bulbs, which might be due to the structure of LED bulbs such as a lens affecting light distribution3).

in the market as equivalent to 60 W incandescent bulbs. Thus, this study compares these three types of bulbs to one another, taking into account their different lifetimes. We used new bulbs for this study with the understanding that metal content does not deteriorate with use and that the nature of the metals does not change or affect their transport, exposure, and effect in the disposal stage.3,12 Determination of Hazardous Waste Potential and Metallic Content. Hazardous waste potential for the incandescent, CFL and LED bulbs was examined by using two toxicity characterization methods:12 (i) the U.S. Environmental Protection Agency’s TCLP,21 which corresponds to 1042

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Limit Value (TLV)-Time Weighted Average (TWA),29 Permissible Exposure Limit (PEL)-TWA,29 and Reference Exposure Limit (REL)-TWA,29 which represent the volume of the fresh air needed to dilute the hazard from the substance under the exposure limit. For the hazard-based Toxic Potential Indicator (TPI),30,31 the weighting factors are calculated from R-phrase (e.g., flammability, reactivity, and toxicity), Water Hazard Class, Maximum Admissible Concentration (MAK), European Union carcinogenicity, and Technical Guidance Concentration (TRC) data, by using the TPI calculator.30 For life cycle impact-based toxicity potential, the weighting factors are the characterization factors for human- and ecotoxicity potentials, respectively, derived from USEtox32 (note that in this study we used USEtox whereas in our previous study on the pin-type LEDs12 we used the Tool for the Reduction and Assessment of Chemicals and other environmental Impacts (TRACI);33 USEtox is based on a scientific consensus model, and is now considered the preferred method for toxicity potential assessment even by the developers of TRACI 34). The USEtox method takes into account environmental fate, exposure, and effect of a chemical based on a generic model, which is generally employed in life cycle impact assessment.32 This approach is in contrast to risk assessment because life cycle impact assessment is based on the precautionary principle required to improve environmental performance of products (see ref 35 for a more comprehensive discussion on the differences between life cycle impact-based and risk-based assessments). Due to the difficulties in fully addressing fate, exposure, and effect of a chemical, the USEtox characterization factors for metals exhibit relatively high uncertainty.36 The human toxicity potential is measured in Comparative Toxicity Units (CTUh), which is an indicator of the morbidity in human population per unit mass of a metal.32 The ecotoxicity potential is measured in CTUe, which is an indicator of the potentially affected fraction of species (PAF) integrated over time and volume per unit mass of a metal (PAF m3 day kg−1).32 The toxicity potential evaluations are based on the metal content in the bulbs, and do not take into account the materials used in the manufacturing processes or the transport pathways for the metals in landfill and incinerator facilities due to the lack of data on distribution ratio for metals into flue gas and ashes,37 as noted in the work by Lim and Schoenung.38 Therefore, the resource depletion and toxicity potentials represent the best and worst case scenarios, respectively. The total of a given potential for a select bulb was calculated by summing the respective potentials of all metals.12 The three bulbs were also compared on an equivalent quantity basis to take into account their different lifetimes. Because the lifetimes of the incandescent, CFL and LED bulbs are 1000, 10 000, and 50 000 h, respectively, the resource depletion and toxicity potentials for fifty incandescent, five CFL, and one LED bulb are calculated on a 50 000 h basis and normalized to the potentials for the incandescent bulbs for the comparison. This comparison does not take into account the further lifetime reduction in CFL bulbs derived from frequent on-and-off switching.

Table 2. Results of Total Threshold Limit Concentrations (TTLC) Testsa substance aluminum antimony arsenic barium cerium chromium copper gadolinium gallium gold indium iron lead mercury nickel phosphorus silver tungsten yttrium zinc

TTLC threshold N/A 500 500 10000 N/A 500 (VI); 2500 (III) 2500 N/A N/A N/A N/A N/A 1000 20 2000 N/A 500 N/A N/A 5000

incandescent bulb

CFL bulb

LED bulb

40,100 ND ND 4.1 9.4 5.8

31,700 117 2.6 17.8 9.6 1.1

947,000 123 ND 364 7.8 120

942 ND 7.9 ND ND 372 6.9 0.1 188 ND 16.2 24.4 0.6 320

111,000 0.6 6.0 ND ND 12,800 3860 18.3 120 222 12.2 1.4 2540 34,500

31,600 0.1 108 2.2 ND 12,300 16.7 0.4 151 127 159 1.2 1.7 4540

a

Values in bold indicate that the TTLC results exceed the regulatory limit. The unit of measurement is mg/kg. Note that mercury vapor in the CFL lamp can be released to the air during the grinding process. N/A: Not applicable. ND: Not detected.

solder), mercury (spiral lamp), phosphorus, yttrium (phosphor), and zinc (protective coating to steel).3,16,39−42 In contrast, the LED bulbs have higher levels of aluminum (heat sinks), antimony (LED chip), barium, chromium (stainless steel), copper (coil), gallium (LED chip), gold (LED wire), iron, lead (PWB), phosphorus, silver (reflective coating in the LED package), and zinc (protective coating).3,12,14,18,19,41−43 The incandescent bulb contains lower levels of the metals than the CFLs and LEDs, except for tungsten (filament) and nickel.6 The total weight of the metals in the three types of bulbs differs significantly (see Table 1 and Table S-3). These results argue for an aggressive recycling program to recover and reuse metals in CFL and LED bulbs, especially for metals such as copper, for which an estimated 26% of its lithospheric stock is situated in permanent usage or wastes.44 Waste management policies for CFL and LED bulbs should include a manufacturer take-back system or deposit-refund system for end-of-life bulbs.45 In addition, product labeling to reveal potentially hazardous constituents, hazardous waste classification, and recycling options can motivate consumers against disposal of spent light bulbs into domestic waste streams. The expense of operating take-back protocols can also motivate manufacturers to implement DfE programs to conserve resources and eliminate adverse liability by reducing the metallic content of their products.45,46 Hazardous Waste Potential. The CFL and LED bulbs that we investigated would be classified as hazardous waste under U.S. EPA federal and California regulations while the incandescent bulb would not. The TCLP analysis results show that the regulatory limit that was exceeded is for lead (Pb) in the CFL and LED bulbs (132 and 44 mg/L, respectively; regulatory limit: 5) (Table 3). In contrast, the TTLC results (Table 2) show that the CFL bulbs exceed California’s

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RESULTS AND DISCUSSION Metal Content of the Bulbs. The TTLC assessment results (see Table 2) indicate that, overall, the CFL and LED bulbs contain higher amounts of metals compared to the incandescent bulbs. The CFLs have higher levels of antimony, copper (primarily in the coils and PWB), iron, lead (PWB and 1043

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that the metals can be recovered, and thereby reduce the generation of additional hazardous waste. Resource Depletion Potentials. The LEDs and CFLs have higher resource depletion potentials than the incandescent bulb, when evaluated on a per-bulb basis. Figure 2 shows the

Table 3. Results of Toxicity Characteristics Leaching Procedure (TCLP) Testsa LED bulb

substance

TCLP threshold

incandescent bulb

CFL bulb

ground to less than 2 mm

aluminum antimony arsenic barium cerium chromium copper gadolinium gallium gold indium iron lead mercury nickel phosphorus silver tungsten yttrium zinc

N/A N/A 5 100 N/A 5 N/A N/A N/A N/A N/A N/A 5 0.2 N/A N/A 5 N/A N/A N/A

13.3 ND ND 0.3 47.9 ND ND 0.2 3.6 ND ND 59.1 0.1 ND 14.1 ND ND ND 7.1 0.9

39.8 ND ND 2.4 7.6 ND 4.3 0.1 0.7 ND ND 967 132 ND 7.3 ND ND ND 64.9 16.0

59.8 ND ND 3.3 19.6 ND 3.1 0.1 1.7 ND ND 1180 44.4 ND 17.0 ND ND ND 26.3 175

less than 9.5 mm 8.9 ND ND 0.1 0.003 ND 0.027 ND ND ND ND 1.6 ND ND 0.2 ND ND ND ND 4.7

Figure 2. Resource depletion potentials of the incandescent, CFL, and LED bulbs (on a per-bulb basis) derived on the basis of the CML 2001 method. Quantitative values for the potentials are provided in Table S4 in the Supporting Information.

resource depletion potentials for the twenty metals in the three types of bulbs (note that the EPS 2000 results are provided in Figure S-2 and that the CML and EPS 2000 results are consistent with each other). The LED bulbs exhibit 2 orders of magnitude higher resource depletion potentials than the incandescent and 2−5 times higher potentials than the CFLs, due to the content of silver, gold, antimony, and copper (in decreasing order). For the CFLs, the substance with considerable impact on resource depletion is copper. Silver and gold are rare and precious metals. Antimony is classified as a critical material in the EU.28 Although copper is not yet critical in the U.S.,27 the high content of copper in the CFL and LED bulbs led to the high potential (note the copper content is 1−6 orders of magnitude higher than the other metals). For the LED bulbs, the metals accounting for the largest share of the total weight (i.e., aluminum, barium, chromium, and gallium) do not significantly contribute to the total resource depletion potential. In considering the supply risk used to evaluate resource criticality,27,28 gallium is considered as a critical material, even though its world reserve is estimated to be considerable.47 This is because gallium can be obtained only as a byproduct in processing bauxite and zinc ores.27,47 It is noted that yttrium, gadolinium, and cerium do not have significant potential, even though they belong to the rare earth element group classified as critical materials.27 This is because yttrium and cerium have sufficient world reserve47,48 and because the content of gadolinium is so low. If LEDs and CFLs continuously replace incandescent bulbs at the rapid rate currently observed, considerable resource depletion impacts will occur due to the insufficient availability of silver, gold, antimony, and copper resources. Gold is used as the conductive metallic wires to connect the electrode to the LED chip due to its low electrical and thermal resistivity, which can decrease the possibility of LED damage caused by poor thermal management.3 Silver is used as a coating material to effectively reflect the light from the LED chip.3 Antimony is used as a core material in the LED chip.3 Copper is used in the coils for the LED and CFL bulb drivers and in the PWBs.14,16,41 Thus, it is clear that the ancillary component technology (not the light source itself) would especially benefit from further

a

Values in bold indicate that the TCLP results exceed the regulatory limit. The unit of measurement is mg/L. Note that the TCLP test (protocol for the particle size: less than 9.5 mm) was performed independently with the ground parts (particle size: less than 2 mm) and the unground parts (particle size: less than 9.5 mm) to take into account the size difference. Also, note that mercury vapor in the CFL lamp can be released to the air during the grinding process. N/A: Not applicable. ND: Not detected.

regulatory limits for copper (111 000 mg/kg; limit: 2500), lead (Pb) (3900 mg/kg; limit: 1000), and zinc (34 500 mg/kg; limit: 5000) and that the LED bulb exceeds the regulatory limit for copper (31 600 mg/kg; limit: 2500). We note that in the TCLP test for the CFL bulb, mercury was not detected because mercury vapor was not captured during the grinding process used to prepare the samples for the leachability tests. The TCLP and TTLC results imply that DfE strategies are needed to reduce the content of copper, lead (Pb), and zinc for CFL bulbs and of copper and lead (Pb) for LED bulbs so that waste bulbs do not exceed the threshold limits of these metals. As CFLs and LEDs are replacing incandescent bulbs for diverse lighting applications to save energy, it is urgent to develop more environmentally friendly products by reducing the metal content to below the threshold limits or by replacing the hazardous metals with safer alternatives. Therefore, DfE strategies should be investigated in detail and implemented to prevent the need to trade off the benefits from energy savings with the costs from an increase in hazardous waste. To be effective, DfE strategies will need to be developed through the cooperation of multidisciplinary scientists and engineers to optimize the trade-offs between benefits and costs derived from material substitution and technology application from a life cycle perspective. The TCLP and TTLC results, specifically the consequential labeling as hazardous waste, should motivate consumers to avoid disposing bulbs in the trash. This behavior should further motivate the need for end-of-life collection and recycling so 1044

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TLV-TWA, PEL-TWA, and REL-TWA results, it should be noted that, because the hazard toxicity data for metallic iron are not available, the toxicity characteristics for iron oxide were used here. It is important to note that for 7 of the 20 metals, at least one assessment method could not be used due to the lack of hazard data. Figure 4 shows the life cycle impact-based toxicity potentials of the incandescent, CFL, and LED bulbs (see Tables S-10 and

development to reduce the content of metals in the context of DfE, as optical fiber cables have been replacing copper cables in the information and telecommunication industry.27 Additional examples of successful DfE in real products can be found at the U.S. EPA DfE Web site.49 In addition to implementing changes to component technology, recycling technology and management policy should be further developed to ensure the recovery of the valuable metals in the LED and CFL bulbs and to recirculate these metals in our society. Toxicity Potentials. Figure 3 shows the hazard-based toxicity potentials of the incandescent, CFL, and LED bulbs,

Figure 3. Hazard-based toxicity potentials of the incandescent, CFL, and LED bulbs (on a per-bulb basis) derived on the basis of the TLVTWA (a) and TPI methods (b). Quantitative values for the potentials are provided in Tables S-6 and S-9 in the Supporting Information.

Figure 4. Life cycle impact-based toxicity potentials of the incandescent, CFL, and LED bulbs (on a per-bulb basis) determined on the basis of the USEtox method: (a) human-toxicity potential for urban air; and (b) eco-toxicity potential for freshwater. Quantitative values for the toxicity potentials are provided in Tables S-10 and S-11 in the Supporting Information.

when evaluated on a per-bulb basis (note that the PEL-TWA and REL-TWA results are provided in Figure S-3 and that the TLV-TWA, PEL-TWA, and REL-TWA results are consistent with one another). The LEDs and CFLs have higher hazardbased toxicity potentials than the incandescent bulbs. Based on the TLV-TWA, PEL-TWA, and REL-TWA results, the LEDs exhibit the highest hazard-based toxicity potentials due primarily to copper and aluminum, and the CFLs are next due primarily to copper. These results are slightly different from the TPI results. The TPI results show that the CFLs have the highest toxicity potential due primarily to zinc and copper and that the LEDs are next due to copper. The incandescent bulb exhibits the lowest toxicity potential, which is derived primarily from aluminum, copper, and nickel. It is noted that the hazardbased toxicity potential from mercury is lower than that for copper, lead (Pb), zinc, aluminum, and nickel because our measurement of mercury content may have been lower than the level present in the lamps due to the loss of mercury vapor during the grinding procedure; thus, toxicity potentials from mercury may be underestimated. Inhalation is a potent route of exposure for toxic metals such as mercury, and it is expected to contribute to the hazards associated with the manufacture, disposal, and recycling of mercury-containing lamps.50 For the

S-11 for complete results including emissions to urban and rural air; fresh and sea water; and natural and agricultural soil, and note that the human- and eco-toxicity potential results for all the media are consistent, respectively). The CFLs have the highest human- and eco-toxicity potentials, and the LEDs are next. The CFLs exhibit at least 2.5 and 1.3 times higher humanand eco-toxicity potentials than the LEDs, respectively, and the CFLs and LEDs exhibit at least 2 orders of magnitude higher potentials than the incandescent bulb. In examining the relative contribution of each metal to the total toxicity potentials of the respective bulbs, zinc and copper are the highest contributors to the human- and eco-toxicity potentials, respectively (89−98% of the total for zinc and 74−89% for copper), regardless of the type of bulb and media (such as air, water, and soil), except for the eco-toxicity potential for seawater (the highest contributor to this potential is zinc (82−91% of the total)). The humantoxicity potential from zinc and the eco-toxicity potential from copper are at least an order of magnitude higher than those from the next highest contributors (i.e., lead (Pb) and zinc for human- and eco-toxicity potentials, respectively). It should be noted that the life cycle-based results did not take into account the contributions of aluminum, cerium, gallium, gold, indium, iron, phosphorus, tungsten, and yttrium because the character1045

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DfE needs to be implemented to reduce the content of aluminum, copper, gold, lead (Pb), silver, and zinc or to replace these metals with safer materials. Another approach is to develop CFL and LED bulbs with longer lifetimes, which can reduce the use of fresh materials for new bulbs and decrease the amount of waste bulbs. At present, LEDs are more promising as alternatives to incandescent bulbs compared to CFLs, because LED bulb technology is relatively new and can be expected to evolve, if properly guided, to be competitive in terms of resource and toxicity potential. In contrast, CFLs are less feasible as sustainable alternatives because of the considerably high resource depletion and toxicity potentials and more established development history. Revolutionary solutions that go beyond these three technologies, such as organic LEDs, are also encouraged and should be assessed for toxicity and resource depletion potentials early in the research and development stage. We conclude that energy policy (beyond enhancing energy efficiency) should target the development of technologies that can reduce the content of hazardous and limited-availability metals without compromising the performance and life expectancy of mass-produced artificial lighting products.

ization factors for these metals are not included in the USEtox database (the uncertainty created by these data gaps cannot be evaluated without characterization factors for these metals). Among these metals, it is noted, however, that, based on the characterization factors from TRACI,33 for the incandescent and LED bulbs, aluminum exhibits high human noncancer potential for air, accounting for 97% of the total (note that TRACI characterization factors for the other substances except phosphorus are not available). Thus, the LED bulb also has significant toxicity potential due to the high content of aluminum. Lifetime Effects. When the product life expectancies of the incandescent, CFL, and LED bulbs are taken into account to evaluate the environmental impacts derived from the equivalent quantity of the respective bulbs (i.e., fifty incandescent bulbs, five CFLs, and one LED) based on a constant use time (i.e., 50 000 h), the CFLs and LEDs have higher resource and toxicity potentials than the incandescent bulb, as shown in Table 4. The Table 4. Comparison of Environmental Impacts from the Incandescent, CFL, and LED Bulbs Taking into Account Design Lifetimes (1000, 10 000, 50 000 h, Respectively)a environmental impact assessment category and method resource depletion potential hazard-based toxicity potential

life cycle impact (USEtox)based toxicity potential

humantoxicity potential

ecotoxicity potential

CML 2001 EPS 2000 TLV-TWA PEL-TWA REL-TWA TPI urban air rural air freshwater sea water natural soil agricultural soil urban air rural air freshwater sea water natural soil agricultural soil

incandescent bulb

CFL bulb

LED bulb

1 1 1 1 1 1 1 1 1 1 1 1

3 5 4 13 8 16 22 22 25 22 26 22

3 2 3 3 2 2 2 2 2 2 2 2

1 1 1 1 1 1

22 22 22 23 22 22

3 3 3 2 3 3

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ASSOCIATED CONTENT

S Supporting Information *

Additional details on the materials, methods, and quantitative results. This material is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*Phone: +1-530-752-5840; fax: +1-530-752-9554; e-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This paper is based upon work supported by the National Science Foundation under grant CMS-0524903 and was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (MEST) (2011-0008373). This study was also supported by 2011 Research Grant from Kangwon National University.

a

Values for the CFL and LED bulbs were normalized to those for the incandescent bulb.

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CFLs and LEDs have 3−26 times and 2−3 times higher potentials than the incandescent bulb, respectively. The lower potentials of the LEDs are mainly due to the longer useful lifespan. An LCA study, however, has shown that, relative to incandescent bulbs, CFLs and LEDs represent approximately an 80% reduction in primary energy demand and in global warming, human toxicity, and resource depletion potentials during the use and manufacturing stages.10 The juxtaposition of these results highlights the need for DfE in the new bulbs so that both energy efficiency and minimal toxicity can be achieved. Specifically, present CFL and LED bulb technology should be further developed to reduce overall resource depletion and toxicity potentials, and a comprehensive assessment of the resulting trade-offs between benefits and costs is essential to justify the material substitutions from a life cycle perspective.

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