Including exposure variability in the life cycle impact assessment of indoor chemical emissions: The case of metal degreasing
Introduction
In Life Cycle Assessment (LCA), the environmental impact of a product or service is determined for its complete life cycle. The use of resources and the emission of pollutants are quantified in an inventory (Rebitzer et al., 2004). Subsequently, in a Life Cycle Impact Assessment (LCIA) the potential environmental impacts are determined for all impact categories of relevance, e.g. depletion of resources, global warming, or human toxicity (Finnveden et al., 2009, Pennington et al., 2004). Health impacts due to chemical exposure can be quantified with the use of characterization factors (CFs) (Hauschild et al., 2008, Rosenbaum et al., 2008, Rosenbaum et al., 2011). These are based on the fraction of the chemical emission that is taken in by the people exposed, i.e. the intake fraction (iF), and the chemical's toxicity.
Human toxicity in LCIA is primarily focused on the potential impacts of chemicals that are emitted into the ambient environment. However, the life cycle of goods or services also involves indoor exposure in occupational settings or at home (Zhu et al., 2001). Despite developments in occupational hygiene over the past 50 years, the concentrations to which a part of the working population is exposed in occupational settings exceed by far the concentrations to which the general population will ever be exposed — often by a factor of 100 (Nieuwenhuijsen et al., 2006). The human health impacts from indoor exposure throughout a chemical's lifecycle can be important (Hellweg et al., 2005, Kohler et al., 2008, Ostertag and Husing, 2008), and may even exceed the human health impacts from production or disposal (Hellweg et al., 2005). As a consequence, excluding health impacts from indoor chemical exposure can lead to optimization of products or processes at the expense of the workers' and/or the consumers' health (Hellweg et al., 2005, Hellweg et al., 2009, Hofstetter and Norris, 2003, Meijer et al., 2005a, Meijer et al., 2005b, Nazaroff, 2008, Vernez et al., 2006, Wilson et al., 2007). Therefore, indoor exposure should be routinely addressed within LCA.
Hellweg et al. (2009) provided a generic, time-independent framework to integrate indoor exposure to air pollutants within LCIA. The intake fraction, however, depends on a combination of operational conditions, and protective measures. Operational conditions that influence the level of exposure are e.g. the volume of the room and the duration of the exposure. Protective measures that can be applied to reduce a person's exposure, and thereby the possible adverse health impacts, are e.g. local exhaust ventilation and respiratory protective equipment. The operational conditions and protective measures needed for the safe manufacturing and use of chemicals throughout their life cycle are described in exposure scenarios (ES) (EC, 2006). Chemical suppliers have to provide their downstream users with extended safety data sheets (ext-SDS), including exposure scenarios, as part of the European Community Regulation on chemicals and their safe use (REACH: EC 1907/2006). At present, however, a method to determine CFs while accounting for the large variability in exposure settings in the LCIA of indoor chemical emissions is lacking.
The goal of the present paper was to develop and apply an LCIA method for indoor exposure to chemicals, accounting for differences in operational conditions and protective measures. A case study on metal degreasing was carried out to show the application of this method in practice. The case study focuses on the industrial solvent dichloromethane (DCM), also known as methylene chloride (CAS 75-09-2).
DCM is a suspected human carcinogen (IARC, 1999). Short-term exposure to DCM is associated with functional impairment of the central nervous system (WHO, 2000). The permissible exposure limit (PEL) for an 8-hour workday with occupational exposure is 25 ppm (i.e. 88.25 mg·m− 3) (OSHA, 1998a, OSHA, 1998b). The chemical is used, e.g., as an aerosol spray propellant in automotive products; as a solvent in the manufacture of drugs; in electronics manufacturing; and as a metal cleaning solvent (Agency for Toxic Substances and Disease Registry (ATSDR), 2000, National Toxicology Program (NTP), 1989). Demou et al. (2011) made an occupational chemical priority list of chemicals for which more detailed and industrial-sector specific quantitative exposure, risk and life-cycle assessments should be completed. Based on its chemical properties, quantity used, toxicity, exposure duration and number of people exposed, DCM was the top ranked solvent.
Section snippets
Methods
This section provides the modeling framework proposed in this study, including details about the metrics used to assess indoor exposure and human toxicity, and default values for the parameters influencing the intake fraction of chemicals. Subsequently, the goal and scope, inventory analysis, and impact assessment for human toxicity for the case of metal degreasing are described.
Results and discussion
The exposure scenario-specific method proposed in this article was applied in a case study on metal degreasing with DCM. In this section we report and discuss the results of the case study as well as the limitations of our framework.
Conclusion
We proposed a method to include human toxicity from indoor chemical exposure in LCA, accounting for variability in exposure settings. As a case study, human toxicity related to the degreasing of 1 m2 of metal surface was quantified for different exposure scenarios involving industrial workers, professional users, and home consumers. It appeared that for all exposure scenarios, human toxicity per functional unit was mainly caused by indoor exposure to metal degreaser (> 60%). Our findings stress
Acknowledgments
We thank Marisa Vieira for her suggestions to perform the life cycle assessment. This research was partly funded by the European Commission under the Industry-Academia Partnerships and Pathways; IAPP 2011: TOX-TRAIN — The implementation of a toxicity assessment tool for practical evaluation of life-cycle impacts of technologies, grant agreement number 285286.
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