Environ. Sci. Technol. 2005, 39, 7741-7748
Confronting Workplace Exposure to Chemicals with LCA: Examples of Trichloroethylene and Perchloroethylene in Metal Degreasing and Dry Cleaning S T E F A N I E H E L L W E G , * ,† EVANGELIA DEMOU,† MARTIN SCHERINGER,† THOMAS E. MCKONE,‡ AND KONRAD HUNGERBU ¨ HLER† Swiss Federal Institute of Technology, Safety and Environmental Technology Group, ETH Ho¨nggerberg, CH-8093 Zu ¨ rich, Switzerland, and Lawrence Berkeley National Laboratory, University of California, One Cyclotron Road, 90R3058, Berkeley CA, 94720
Life-Cycle Assessment (LCA) aims to assess all environmental impacts “from cradle to grave”. Nevertheless, existing methods for Life-Cycle Impact Assessment (LCIA) generally do not consider impacts from chemical exposure at the workplace. This is a severe drawback, because neglecting occupational health effects may result in product or process optimizations at the expense of workers’ health. We adapt an existing LCIA method to consider occupational health effects from the use of perchloroethylene (PCE) and trichloroethylene (TCE) in dry cleaning and metal degreasing. The results show that, in applications such as metal degreasing and dry cleaning, long-term (steadystate) concentrations at the workplace are up to 6 orders of magnitude higher than ambient air levels. Legal threshold values may be exceeded, depending on machine technology, size, and surrounding working conditions. The impact from workplace exposure to the total humantoxicity potential of the complete life cycle of PCE and TCE (including use, production, and disposal) is accordingly high. We therefore conclude that occupational health effects need to be considered in LCA to prevent overlooking key environmental-health impacts in LCA.
Introduction Numerous chemicals are used in the production of almost all goods. Environmental assessment tools such as Life-Cycle Assessment (LCA) aim at understanding the environmental impacts associated with the use of chemicals. LCA is particularly useful because it includes all impacts of a product’s life cycle from “cradle to grave”, i.e., from resource extraction to product use and disposal. While the cradleto-grave approach is commonly employed with respect to the impacts of chemical emissions to ambient and residential environments, less attention has been paid to effects of exposure to chemicals in the workplace. * Corresponding author phone: +41-1-6334337; fax: +41-16321189; e-mail:
[email protected]. † Swiss Federal Institute of Technology. ‡ Lawrence Berkeley National Laboratory. 10.1021/es047944z CCC: $30.25 Published on Web 08/30/2005
2005 American Chemical Society
Occupational health hazards arise from inhaling chemical agents in the form of vapors, gases, dusts, fumes, and mists, by dermal contact (1), or by inadvertent ingestion from handto-mouth contact. Chemicals at the workplace may have acute narcotic effects or cause reproductive harm or cancer. After intake, chemicals may enter the bloodstream and reach internal organs or a developing fetus. Current Life-Cycle Impact Assessment (LCIA) methods generally neglect occupational health effects. The Nordic countries are an exception; here initial efforts have been made to address occupational exposures (2). The most prominent example is the Danish Environmental Design of Industrial Products (EDIP) method (3), which defines an “exposure threshold” as 1/10 or 1/100 (depending on the effect) of the legal limit. Workers’ exposure to airborne toxic agents above this threshold and also dermal contact are accounted for by the EDIP method. Although this method is a step in the right direction, it neglects specific emissions and does not allow comparisons with other health effects from environmental exposure. More recent methods (2, 4) use statistics of occupational accidents and illnesses to estimate impacts to the working environment per industry sector. This “top-down” approach is easy to apply but is rather uncertain, because a large number of occupational diseases remain unreported. Another factor contributing to the uncertainty is the long latency periods from exposure to disease for many chemicals. Diseases will not be properly accounted for if they appear in later stages of a worker’s life, often years after employment stopped. The lack of adequate methods to assess occupational health effects in LCA is a potentially severe drawback, because important impacts may be neglected and product or process optimizations may be done at the expense of workers’ health. Hofstetter and Norris (4) used U.S. input/output tables and statistics about occupational accidents and illnesses to estimate the overall relevance of occupational health effects in LCA. They estimate that these effects may contribute 10% of the overall environmental damages, which they consider a small fraction. In our opinion, 10% is a considerable fraction of the total impact, which may be even larger for certain industrial sectors. For instance, von Grote et al. (5) have shown in a risk assessment study that occupational exposure to solvents in dry-cleaning and in the metal-degreasing industry can be significant. The goals of this paper are (a) to present a method that includes human-health effects from workplace exposure to chemicals in LCA, (b) to illustrate the application of this method in three case studies on the use of trichloroethylene and perchloroethylene in metal degreasing and perchloroethylene in dry cleaning, and (c) to examine the importance of such occupational health effects in comparison to the total human-toxicity potential in each case study.
Methods Inclusion of Workplace Exposure to Chemicals in LCA. Our method for considering workplace exposure to chemicals in LCA focuses on the inhalation pathway. It is based on the USES (Uniform System for the Evaluation of Substances)LCA method (6, 7) for the impact assessment of toxic releases to the environment. In the original version, the multimedia model USES-LCA (6, 7) includes two different scales: continental and global (Figure 1). To assess workplace exposure, we embed another scale for the working environment (Figure 1). This scale for workplace exposure links with the outer environment via air exchange. Thus, our method for evaluVOL. 39, NO. 19, 2005 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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FIGURE 1. Embedding a scale for indoor workplace exposure in USES-LCA (parts of graph taken from refs 7 and 10). ating workplace exposure is consistent with the USES-LCA method for the assessment of emissions to the environment (6, 7). This has the advantage that impacts to human health at the workplace and in the environment can be assessed on the same methodological basis. To better represent the different exposure concentrations in large industrial settings, von Grote et al. (5) used a model with two homogeneously mixed boxes (Figure 1). The inner box represents the surrounding environment of the machine that emits chemicals (near-field), while the outer box represents the larger workplace environment (far-field). Air and pollutant are exchanged between these two boxes. In addition, the outer box exchanges air with the ambient environment. We assumed that concentrations of chemicals in the ambient air are negligible. For industrial chemicals such as TCE and PCE this assumption is reasonable. For instance, typical background concentrations, in urban areas, are between 0.23 and 9 µg/m3 for PCE (8) and between 0.8 and 18.5 µg/m3 for TCE (9). Therefore, only pollutant transport from the workplace to the environment is considered, but not vice versa. To be consistent with USES-LCA (6, 7), we perform steadystate modeling. Concentrations in the two boxes are calculated as
dCA E˙ A VB ) - CA ‚ k A + CB ‚ ‚k dt VA VA B VA dCB ) CA ‚ kA - CB ‚ (kB + kL) dt VB
(1)
E˙ A + CB VA ‚ kA
CB )
E˙ A VB ‚ kL
(2)
E˙ A was calculated for various machine types and sizes (5, 10), as well as for a fictitious, USES-LCA-specific, continuous emission to calculate characterization factors. Characterization factors are used to weigh emissions so that they can be compared within a single impact category (human-toxicity 7742
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RCRhuman,wp,a,x )
PDIinh,wp,a,x HLVinh,x
(3)
weighted RCR human,wp,a,x )
PDIA,inh,wp,a,x ‚ npop,A + PDIB,inh,wp,a,x ‚ npop,B ) HLVinh,x CA ‚npop,A + CB ‚ npop,B (4) HLC
where Cx is the concentration in box x (g/m3), E˙ A is the emissions to air in box A (g/h), Vx is the volume of box x, and kA,B,L (1/h) are the air exchange rates between the various boxes with the relationship kB ) kA ‚ VA/VB (Figure 1). Equation 1 does not take into account indoor degradation and adsorption. Indoor degradation is small for chemicals such as TCE and PCE, as half-lives in air are several days and months, for TCE and PCE (6, 7), respectively. At steady state, eq 1 resolves to
CA )
potential in the current work). In USES-LCA (6, 7) these characterization factors were calculated with the fictitious emission flow of E˙ A ) 1000 tonnes/day. This emission flow is by no means realistic with respect to most chemicals, neither for the workplace nor for the environment. However, traditional LCA merely aims at a relative weighting of chemicals, without trying to quantify actual impacts (11) (as opposed to risk assessment). Therefore, the magnitude of flow is not important, as long as linear models are applied. To be compatible with the USES-LCA method, we calculate risk-characterization ratios (RCR) and characterization factors using the same emission flow. Later on, these factors are multiplied by emission amounts, to quantify the “humantoxicity potential” (6, 7). The characterization factors for impacts to human health are based on weighted risk quotients (eqs 3 and 4).
ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 39, NO. 19, 2005
weighted where RCR human,wp,a,x is the risk-characterization ratio of substance x to humans at the workplace (wp) after emissions to air (a), PDI is the predicted daily intake (kg/kg(bw)/d), HLV is the human-limit value (kg/kg(bw)/d), HLC is the limit concentration in air corresponding to HLV (kg/m3), and npop is the number of exposed workers in the near-field (npop,A) and far-field (npop,B). The HLV is equivalent to the more common notation “acceptable daily intake”. We use the term HLV because this is the notation used in USES-LCA. HLV is equal to HLC‚IR/bw, where IR is the inhalation rate of humans (m3/d) and bw is the body weight (kg). The legal threshold values listed in Table 1 are used directly as human-limit concentrations; in addition, the environmental human-limit concentration corrected for exposure time is used. From Table 1 it is apparent that the differences between the legal limits and the environmental HLCs (original and adjusted) are large. One reason for this is that the legal and advisory limits refer to workers, who are generally of good health, and a 40-hour working week. By contrast, the HLCs for environmental exposure also consider more susceptible parts of the population (e.g., children and elderly people). For this purpose, an uncertainty factor for intraspecies variability is included in the HLC. Additional uncertainty factors include ones for interspecies differences, for extrapolation from short term to chronic exposure, for relying on the LOAEL
TABLE 1. Human-Limit Concentrations (HLCs) and Occupational Limits Used in This Study for the Workplace and the Environment environment (mg/m3)
TCE PCE
workplace (mg/m3)
environmental HLC (6, 7)
adjusted environmental HLVa
MAKb
PELc
TLV-TWAd
0.0054 0.27
0.023 1.1
270 340
540 680
130 170
weighted ) HTPwp,RCR
rather than the NOAEL, and for the use of an insufficient database (12). Such use of uncertainty factors has been criticized (13), as these factors have not been developed for the purpose of comparing chemicals but for avoiding risks. Whereas new LCIA methods avoid the use of uncertainty factors, we still apply them in this paper to be consistent with USES-LCA. While the environmental HLC is based entirely on health concerns, occupational limit values may be influenced by parameters such as the feasibility of achieving the required levels (14-16) and cost-benefit issues (14, 1719), which are not relevant for comparative risk assessment or LCA. Therefore, and in order to be consistent with the USES-LCA method for the assessment of ambient air emissions (6, 7), we argue that the environmental HLC (adapted for exposure duration) is more suitable than regulatory limits (Table 1) for making solely health-based comparisons within LCA. In USES-LCA (6, 7), population number is used as the weighting factor at different spatial scales. Similarly, we use the number of exposed workers as the weighting factor at the workplace scale (eq 4). As a result, human-health effects from workplace and environmental exposure can be compared within LCA studies. In USES-LCA (6, 7), the characterization factor for a weighted substance x is calculated as the ratio of RCR human,x for weighted substance x and RCR human,ref for a reference substance (1,4weighted dichlorobenzene emitted to ambient air). RCR human,ref is a constant and has no meaning beyond that of a normalizing factor. By forming this ratio, emissions contributing to the same impact category are merely normalized to a specific unit, i.e., “1,4-dichlorobenzene-equivalents” in the case of human-health effects in USES-LCA (6, 7). In this work, we quantify the human-toxicity potential on the basis of both weighted the weighted risk-characterization ratios RCR human,x and the overall characterization factors. In contrast to the characterization factors, which add effects from exposure at the workplace and in the ambient environment (eq 5), the weighted analysis on the basis of RCR human,x shows the relevance of potential effects at the workplace and effects from subsequent emissions to ambient air separately. weighted weighted (RCR human,wp,a + RCR human,env,a )x weighted (RCR human,env,a )1,4dichlorobenzene
∑RCR
weighted human,wp,a,x
‚ EA,x
x
a Corrected for exposure duration by applying a factor of 168 h/40 h (40 h work time per week). b German regulatory limit, Maximale Arbeitsplatzkonzentration (MAK, 20). c U.S. Occupational Safety and Health Administration (OSHA) Permissible Exposure Limit (PEL) (21). d Advisory threshold-limit-value time-weighted average (TLV-TWA) set by the American Conference of Governmental and Industrial Hygienists (ACGIH) and proposed by the Japanese Society for Occupational Health (JSOH) (22, 23).
CFhuman,wp,a,x )
characterization ratios and with the characterization factors to quantify the cumulative human-toxicity potential (HTPwp) that accounts for workplace exposure (eq 6). HTPwp can be directly compared to the HTP of emissions to the ambient environment, calculated with the characterization factors weighted and RCR human,env,x for emissions to ambient air, from refs. 6 and 7.
(5)
where CF is the characterization factor for emissions of substance x to workplace air with respect to the impact category human health. Finally, emission amounts per functional unit (EA,x, see following section) are multiplied by the weighted risk-
HTPwp,CF )
∑CF
human,wp,air,x
‚ EA,x
(6)
x
where EA,x is an emission of substance x into box A (Figure 1) (kg per functional unit, see eq 7 below). Case Study. We illustrate our approach with case studies on the use of TCE and PCE in textile cleaning and metal degreasing. Both are solvents used in large quantities leading to widespread human exposure. Solvent degreasing is performed in a wide range of industrial applications, such as metal-degreasing facilities and the automobile repair and electronics industries (24). Acute and chronic inhalation exposure studies have shown neurological, liver, and kidney effects for PCE. Studies for TCE report effects on the central nervous system, liver, kidney, and immune system (25). Both chemicals have also been associated with some types of cancer in mice. The EPA has classified PCE as intermediate between a possible and probable carcinogen (Group B/C). TCE, as of 2002, has been reclassified by the HSE as a category 2 carcinogen (26). The simultaneous study of the two solvents in different industrial sectors allows the examination of the influence of industrial parameters on occupational exposure. To reduce emissions and meet stricter health and environmental regulations, machine technology has been improved substantially over the past decades in these two applications. There are now five types of machines. In metal degreasing (4), these range from open top, cold-cleaners, with a series of solvent and vapor baths (Types I and II), to closed systems with refrigerated recirculation systems (Types IV and V). In the dry-cleaning industry, first generation “transfer machines” have a separate washer and dryer. In some countries, such as Germany, transfer machines are no longer used (4), but in many countries they are still in use, e.g. in the United States (13, 14) (for a technology overview of various countries see Table S6). The next four generations are all “dry-to-dry” machines, which eliminate the need for manual transfer of solvent-covered clothing. The U.S. National Institute of Occupational Safety and Health reports that only the two last machine generations are able to contain their peak emissions below the OSHA maximum peak level of 2040 mg/m3 (13). For a more detailed technology description, see the Supporting Information. Because inhalation is the most important exposure pathway in the case studies, we focus on emissions to air (5). Workplace emissions to air are a function of the properties of the chemical (e.g., vapor pressure), type of industrial application and machine, and ambient conditions such as temperature, and venting. For the case of chemical emissions from textile cleaning and metal degreasing, von Grote et al. (5) distinguish among (1) diffuse emissions that are emitted constantly over time, such as emissions from open baths or from leakage, (2) emissions from residual chemicals on the materials treated, (3) repetitive emissions from chamber air that are released during the loading and unloading of machines, and (4) emissions from maintenance operations. In this paper, we assume normal working conditions. Therefore, we consider only the first three types of emissions. We first quantify the different emissions separately using VOL. 39, NO. 19, 2005 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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TABLE 2. TCE and PCE Emissions in g per m2 Metal Surface Area and per kg Garment (EA,x in eq 6) for Metal Degreasing and Dry Cleaning, Respectively (Data Taken or Calculated from Ref. 5) Emissions from Metal Degreasing Type I Type II Type III
Type IV
Type V
0.36 2.6 10 10d
0.061 0.18 1.5 0.18
0.016 0.031 0.16 0.031
0.49 6. 5 14 13d
0.12 0.20 1.1 0.20
0.051 0.068 0.20 0.068
fourth generation
fifth generation
2.3 3.3 6.5
0.35 0.69 1.7
TCE Emissions workplace emissions EA,TCEa minb average maxb outdoor emissionsc
1.7 8.1 29 32d
1.4 7.2 22 32d PCE Emissions
workplace emissions EA,PCEa min average max outdoor emissionsc
3.5 20 43 48d
3.4 20 40 48d
PCE Emissions from Dry Cleaning first second third generation generation generation workplace emissions EA,PCEa min average max outdoor emissionsc min average max
10e 18e 25e
5.8 8.7 15
4.1 6.4 12
13e 95e
50
15 20 25
16 17 18
0.35 0.69 1.7
a The values for the three components of E b Minimum/maximum emissions among technologies with and A,x (eq 7) are shown in Table S2. without vapor degreasing and among sphere and plate metal shapes. c Outdoor emissions include both direct emissions and indoor emissions that eventually reach the environment through ventilation. d Ref 29. e Total emissions to air, including indoor and outdoor emissions, are between 13 and 95 g/kg (30). Workplace emissions from loading and unloading (Erep in eq 7) account for less than 13 g/kg (30). On this basis, we estimated total workplace emissions to be between 10 and 25 g/kg.
mainly the data of von Grote et al. (5, 10). In a second step, we combine emissions (eq 7).
EA,x ) Ediff,x + Erc,x + Erep,x E˙ A,x ) E˙ diff,x + E˙ rc,x + E˙ rep,x
(7)
where EA,x is the total emissions of substance x to the workplace (box A) under normal working conditions (in g/h and g/functional unit for E˙ A,x and EA,x, respectively), Ediff,x denotes diffuse emissions from the machine during the cleaning/degreasing process, Erc,x are the emissions from evaporation of residual chemicals on the material treated, and Erep,x are periodic emissions from loading and unloading machines. For each of the different machine types and sizes (5, 10), we calculate total emissions E˙ A,x (g/h) under steady-state conditions, to quantify long-term exposure, and to see whether legal limit values are surpassed. Even though it is acknowledged that legal limits are not necessarily toxicological thresholds (14-16), this type of analysis is standard procedure in risk assessment (5, 10). For PCE and TCE, the lowest observed adverse effect levels (LOAEL) have been reported as 102 mg/m3 and 269 mg/m3, respectively (25). These values are lower than the occupational limit values of Table 1. The next step of our assessment is to normalize emission flows to the functional unit, as is typically done in LCA. The functional unit is defined as the production, use, and disposal of PCE and TCE for the degreasing of 1 m2 of metal surface in the metal-degreasing case studies and for the cleaning of 1 kg of garments in the textile-cleaning case study. The amounts of solvents used and disposed as well as the direct emission flows to the environment (vented emissions) were taken from the literature (see Tables 2 and S7 for references). Furthermore, to consider the whole life cycle of TCE and 7744
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PCE, information on the amounts released and the resources used during the production and disposal phase was gathered. Production inventory data of TCE and PCE were taken from Althaus et al. (27). We used the models of Capello et al. (28) and Seyler et al. (29) to calculate emissions and amounts of ancillaries used during waste solvent distillation and incineration. Model parameters describing the workplace (eqs 1 and 2) for the case studies are shown in Table S4 (5, 10). The HLCs (eq 4) used in this study are presented in Table 1. For weighted and the charoutdoor emissions, we use the RCR human,env acterization factors from USES-LCA.
Results Workplace Emissions of TCE and PCE in Metal Degreasing and Dry Cleaning. Table 2 shows indoor and outdoor emissions of TCE and PCE per m2 of metal surface and kg of garments, for metal degreasing and dry cleaning, respectively. Table S3, in the Supporting Information, provides total emission flows to workplace air for various machine generations and sizes (in g/h). Ranges are given for each emission. Variability arises from factors such as machine technology and size (see machine technology description and Table S1 in the Supporting Information), garment type and metal part shape (spheres and plates), and ambient working conditions (ventilation rate, room size, etc.) (5, 10). Polluted solvent is distilled and reused, which reduces fresh solvent demand. With respect to the nonrecovered fraction of solvent (5-6% according to ref. 31), we assume that these solvents are incinerated. Tables S7-S9 in the Supporting Information provide data on the total consumption of TCE and PCE as well as inventory data on solvent incineration and distillation. We obtained background data for utilities and ancillaries (Table S9) from the inventory database Ecoinvent (32).
FIGURE 2. Near-field concentration, CA (g/m3) (left bars) and far-field concentration, CB (g/m3) (right bars), versus machine type/generation for PCE (left) and TCE (right) in metal degreasing (top) and in dry cleaning (bottom). The uncertainty bars display the range between minimum and maximum concentrations. The horizontal lines represent different occupational limit values for the working environment (Table 1). Workplace Concentrations of PCE and TCE. Figure 2 depicts the steady-state concentrations in the working environment (far-field and near-field) for TCE and PCE. According to the model results, machine types I-III in the metal-degreasing industry may expose workers, in both near and far fields and for both chemicals, to concentrations beyond the occupational advisory limits or even legal limits. Also, type IV machines may expose workers to elevated concentrations but only in the near-field and under the assumption of worst-case emission factors. The technologically advanced type V machine is the only one able to maintain levels below any of the limit values at all times. The same situation is observed in the dry-cleaning industry where all machine generations in use, except the fifth-generation machines, emit enough chemical to the workplace to cause a potential health risk to humans operating the machines. Workplace exposures are up to 6 orders of magnitude larger than corresponding ambient-air exposures to the nonworking population. Assessing the extent of workers’ exposure can lead to different results when the OSHA 8-h-TWA PEL or the Japanese and U.S. advisory threshold limit value (TLV) are used (Table 1 and Figure 2). For example, in metal degreasing, nearfield, for Type III machines, the average concentration of TCE surpasses the MAK value, leading to a risk quotient (eq 3) of 1.68, whereas if the PEL were used this working concentration would be deemed relatively safe, with a risk quotient of 0.84. These results illustrate the variation in the evaluation of potential health impact for the same exposure under different legal exposure standards. The difference derives in part from the fact that standards are often not based on consistent levels of health protection alone, but also on factors such as feasibility and monitoring strategies (14-16). weighted Characterization Factors. We calculated RCR human,wp,a and characterization factors for workplace exposure to TCE
weighted TABLE 3. RCR human,a (eq 4) for the Fictive Emission Flow of 1000 t/d in Metal Degreasing and Dry Cleaning and for Direct Emissions to the Environmenta
workplace (emissions to indoor air at the workplace, without considering later transfer to outdoor air) metal metal degreasing degreasing dry type I and II type III-V cleaning TCE PCE
TCE PCE
MAK based 3.9‚105 1.3‚106 3.0‚105 1.0‚106
min max min max
5.2‚105 1.8‚106 4.0‚105 1.4‚106
min max min max
adjusted environmental HLC based 6.2‚109 4.7‚109 2.2‚1010 1.6‚1010 1.3‚108 1.0‚108 7.3‚107 4.6‚108 3.4‚108 2.2‚108
environment (emissions to ambient air) (6, 7) 6.3‚107
2.2‚105 6.5‚105
1.0‚107
6.3‚107 1.0‚107
a Values from Table 1 used as HLCs (eqs 3 and 4). RCR weighted human,wp,a based on the PEL and TLV (Table 1) not shown (they would be a factor weighted 2 smaller or larger than the MAK-based RCR human,wp,a, respectively).
and PCE in metal degreasing and dry cleaning using eqs 4 and 5. Tables 3 and S11 (Supporting Information) show the weighted and the characterization factors for workplace RCR human,a (eqs 4 and 5) and outdoor emissions (6, 7). weighted The weighted risk-characterization ratios RCR human,wp,a for indoor emissions (eq 4) are smaller than the corresponding weighted RCR human,env,a for outdoor emissions, if the legal or advisory limits are used as HLCs. There are two explanations for this result. First, the strong population weight of the environmental scale in comparison to the workplace scale (compare VOL. 39, NO. 19, 2005 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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FIGURE 3. Human-toxicity potential on the basis of RCRweighted (HTPwp,RCRweighted in eq 6) from the use of PCE (left) and TCE (right) in the degreasing of 1 m2 metal surface (top) as well as from the use of PCE in the dry cleaning of 1 kg of garments (bottom). The bars for workplace emissions only include impact to workers, while the effect of subsequent outdoor emissions are included in the bars “total outdoor emissions”. The uncertainty ranges show the range of minimum and maximum emissions (see Tables 2, 3, and S7). values in Table S10) and, second, that the limits for occupational health are 3 and 5 orders of magnitude higher than HLC values used for environmental exposure of PCE and TCE, respectively (Table 1). When the environmental human-limit concentration (Table 1, column 4) is used for workplace exposure (corrected for a 40-hour working week), the situation changes dramatically. With this HLC, the risk ratios for workplace exposure to TCE are 2-3 orders of magnitude higher than for direct emissions to the environment, and up to 1 order of magnitude higher for PCE. The characterization factors for TCE and PCE emissions in these case studies take into consideration that the amount of chemical emitted in the workplace will eventually be released to the environment. The characterization factors for workplace (eq 5) and the characterization factors for direct environmental emissions (6, 7) are on the same order of magnitude, except for workplace factors based on the environmental HLCs, which are 1-3 orders of magnitude higher than for emissions to the environment. LCA Results. To calculate the human-toxicity potential for the workplace, the weighted risk-characterization ratios and characterization factors of Tables 3 and S11 are multiplied by the emissions in Table 2. For emissions to the environment, the default factors from USES-LCA are used. The results are shown in Figure 3 (HTPwp,RCRweighted, eq 6) and in Figure S2 (HTPwp,CF, eq 6). The overall impact (i.e., the sum of all bars) from the use of TCE and PCE in metal degreasing and dry cleaning decreases with modernization of machine technology. Solvent emissions (sum of indoor and outdoor emissions) contribute significantly to the overall human-toxicity potential (contributing from 11% to more than 99% of the total impact, Figure 3 and Table S13). The two bars on the left side of each group in Figure 3 show the impact from workplace 7746
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emissions, using different values for the HLC. When environmental HLCs, corrected for 40-h-week exposure duration, are used, workplace emissions contribute a large share to the total impact for older machine generations/types (between 59% and 97%, Figure 3 and Table S13), and a considerable share for newer machine generations (more than 30%, except for the use of PCE in metal degreasing). By contrast, if the regulatory or advisory values are used as HLC, the impact of workplace emissions is rather small.
Discussion Case-Study Results. The results of the case studies show that emissions from the use of PCE and TCE (indoor and outdoor) are very important in the complete life cycle assessment of impacts of these solvents when the same HLC is used (adjusted for exposure duration) for workers and the general population. This result is in contrast to previous LCAs on chemicals that have concluded that energy impacts contribute the major part of cumulative impact (27, 33, 34). The importance of solvent emissions in our case studies suggests that too little attention has been paid so far to the use phase of chemicals (indoor and outdoor emissions), as opposed to chemical production and disposal. Furthermore, we demonstrate that LCA can be a powerful tool in assessing the health effects arising from chemical exposure in the workplace. We show that when we apply environmental HLCweighted based weighted risk-characterization ratios (RCR human,wp,a ) and characterization factors as measures of relative harm, the occupational exposure becomes relevant in the life cycle of the chemical (Figures 3 and S2). In our case studies, the potential human-health effects from occupational exposure as well as those from environmental exposure decrease with increasing modernization of the technologies considered.
In other cases, occupational health effects may be at tradeoff with environmental impacts (35). We conclude that LCA needs to consider occupational health effects to ensure that burden shifting from the environment to workers’ health is avoided. Relevance of Workplace Exposure Concentrations in the Case Study. Our investigation of the emissions of TCE and PCE in the metal-degreasing and dry-cleaning sectors confirm the result of von Grote et al. (5) that elevated concentrations of those chemicals exist in the workplace (Table S5). This is especially true in the case of early, less-advanced machine types and generations. Workers’ health may be compromised particularly in cases where these elevated concentrations surpass legal limit values. The actual values of legal limits are in many cases revised multiple times as new research provides further insight into possible health hazards and as public awareness and concern increase. This is evident in Table 1 and Figure 2 where the concentration in the workplace is compared with limit values of different countries (United States, Germany, and Japan). OSHA decided in 1989 that a new PEL of 170 mg/m3 was required for perchloroethylene (21) but after a court decision the legal limit was reinstated to the current value of 680 mg/m3 (36). However, the investigation is currently ongoing and further changes may be made. In Germany the legal limit values are 270 and 340 mg/m3, for TCE and PCE, respectively, while the ACGIH and JSOH advise the use of a TLV-TWA of 135 mg TCE/m3and 170 mg PCE/m3. This range of occupational limit values, observed for the same substances, demonstrates how ongoing research and differing perspectives can influence the perceived severity of exposure. By separating the work environment into two boxes representing near- and far-field exposures, we see a pronounced effect on exposures to machine operators in the near-field. Breathing zone concentrations may even be larger than the near-field concentrations assessed in this paper. For instance, Wilson et al. (37) found an average difference of a factor of 3 between breathing zone and average concentrations measured at a distance of about 3 m from the emission source, with respect to solvent application in automotive repair shops. Other tasks that further enhance operator exposure to solvents, especially in the breathing zone, are duties such as filter replacements, solvent transfer to the machine, and maintenance operations. If the occupational legal limits are surpassed, as displayed in Figure 2, workers may be exposed to levels of chemicals that are comparable to the NOAEL or LOAEL. LOAELs for TCE and PCE have been reported to be 102 mg/m3 and 269 mg/m3, respectively (25). Exposure to these levels could lead to acute health effects that may be downplayed if we assume that a linear relationship assumed for lower doses applies at higher doses. The problem of linearity also becomes an weighted important issue when RCR human,wp,a in volumes A and B in the workplace are compared. If a linear dose-response relationship is assumed, as is usually done in LCA, it is expected that the same effect should result from the same weighted RCR human,wp,a . Hence, since volumes A and B exhibit comweighted parable RCR human,wp,a values (Table S11) due to the difference in number of workers in the two compartments (Table S4), the potential effect in population A and population B is assumed to be the same. However this method dismisses the severity of a health effect and does not take into account the fact that a person in volume A may be exposed to concentrations that legally are not acceptable. Unfortunately, LCA in its current state is not able to assess actual but only relative health impacts. Therefore, to find out whether thresholds are surpassed requires a more detailed risk assessment as a complement to an LCA (e.g., see ref 5, Table S3, and Figure 2) or changes to the linear approach inherent in the LCA method.
Methods: Considering Workplace Exposure to Chemicals in LCA. It is important to note that in this study the main exposure path is inhalation and the outcomes shown only apply to this route of intake. Exposure may be even greater if other uptake routes, such as dermal contact or ingestion, are considered. In a study of intake fractions for various chemicals, Bennett et al. (38) suggest that the dermal pathway may be potentially significant for chemicals that have a log Kow between 2 and 4.7. The log Kow values of TCE (2.49) and PCE (3.49) are within this range (39). Dermal contact in dry-cleaning facilities can be greatly reduced with the use of nonpermeable gloves. However, poor work practices persist (40). Therefore, exposure through dermal contact may be relevant and should be examined in future work. The choice of the human-limit concentrations has sigweighted nificant influence on the RCR human,wp,a (Table 3). When adjusted for occupational exposure duration, environmental HLCs translate into acceptable concentrations that are 2 and 4 orders of magnitude smaller than the regulatory limits for PCE and TCE (Table 1). One reason for this large discrepancy is that occupational limits are based on factors other than health protection alonessuch as measurement feasibility (14-16) and health/benefit considerations. Another reason derives from different goals and choices in selecting the uncertainty factors for the environmental HLC and occupational limits. In LCA, uncertainty factors should be used consistently for the assessment of environmental and workplace exposure. Therefore, we argue that the use of the environmental HLC, adjusted for exposure duration, is more appropriate than the use of occupational limits, if the USESLCA method is used. We recognize that this approach has the drawback that it ignores the postulated “healthy worker” effect (41), i.e., the assumption that workers are less susceptible to chemical exposure than the general population. But this effect has only been rarely demonstrated and has only been explicitly articulated by the ICRP (41), who suggest this occupational/nonoccupational susceptibility ratio is on the order of 20. We conclude that studies about the sensitivity of the human population and subgroups thereof (such as workers) as well as about human variability within these groups should be taken into consideration in future work.
Acknowledgments We gratefully acknowledge funding from the Swiss National Science Foundation. T. McKone was supported in part by the U.S. EPA through Interagency Agreement DW-988-3819001-0 with the Lawrence Berkeley National Laboratory operated for the U.S. Department of Energy (DOE) under Contract Grant DE-AC03-76SF00098.
Supporting Information Available Description of machine technologies, data on emission flows, modeling parameters, pollutant concentrations, technology overview in various countries, background inventory data, number of workers, characterization factors, and LCA results. This material is available free of charge via the Internet at http://pubs.acs.org.
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Received for review December 27, 2004. Revised manuscript received July 11, 2005. Accepted July 14, 2005. ES047944Z
