Alternatives for significant uses of perchloroethylene in Massachusetts
In July 2005, the Commonwealth of Massachusetts requested that the Toxics Use Reduction Institute perform an alternatives assessment for five chemicals. For each chemical, the Institute was charged with identifying significant uses in manufacturing, consumer products, and other applications; reviewing health and environmental effects; and evaluating possible alternatives. The results of this study will serve as a guide for those seeking safer substitutes to the chemicals studied.
Presented here is an executive summary of the findings for high priority uses of perchloroethylene in Massachusetts. The full report, the Five Chemicals Alternatives Assessment Study available from the link below, presents extensive factual information on each alternative
Perchloroethylene (PCE) is a synthetic chlorinated hydrocarbon. It is used primarily as a solvent in dry cleaning and industrial degreasing and as a chemical intermediate.
Short-term exposure to PCE can cause symptoms such as skin, eye, and respiratory irritation, headache, and nausea; very high exposure can be fatal. Long-term exposure to PCE may cause liver, kidney or central nervous system damage. PCE may also affect the developing fetus. The International Agency for Research on Cancer (IARC) lists PCE as a probable human carcinogen (Group 2A).
PCE most often enters the environment through fugitive emissions from dry cleaning and metal degreasing industries and by spills or accidental releases to air, soil or water. Exposure results from environmental contamination, presence in consumer products or occupational sources. PCE has been found in breast milk, one indication of its ubiquitous presence in the environment.
The Institute assessed alternatives to PCE in three categories of use: dry cleaning, vapor degreasing, and aerosol automotive cleaning.
The Institute analyzed five categories of PCE alternatives for dry cleaning: hydrocarbons (HC), volatile methyl siloxanes (VMS), substituted aliphatic glycol ethers (SGE), wet cleaning, and liquid carbon dioxide (CO2). Like PCE, the first three of these categories are based on organic solvents. For each category except CO2, the Institute selected an individual chemical or process as a representative of the broader category.
- Health. All the alternatives are superior to PCE from the perspective of carcinogenicity. VMS and CO2 are superior from the perspective of irritation, while SGE and wet cleaning are roughly equivalent to PCE on this metric. HC, wet cleaning, and CO2 are superior from the perspective of exposure limits. Recent research has raised concerns about adverse effects of decamethylcyclopentasiloxane (D5), the dry cleaning solvent used in the VMS system, in laboratory animals.
- Other hazards. Unlike PCE, HC and VMS are combustible.
- Environment. The alternatives are less persistent than PCE in water, soil, sediment, and air, with some exceptions: the hydrocarbon alternative is more persistent than PCE in soil. The CO2 used in the process is captured from industrial processes and thus the garment cleaning adds no net CO2 to the atmosphere.
- Technical criteria. The first four alternatives are commercially available in Massachusetts. No commercial CO2 facilities were identified in Massachusetts, although there are facilities in other states. Thus, all of the alternatives are known to have commercial viability at this time. Technical criteria of interest for this application include time for washing; load capacity; the range of soils that can be removed effectively; the types of clothing that can be washed using a given system; and the efficiency of spot cleaning before washing.
- All the alternatives require more time for cleaning than PCE, except CO2, which requires less time. This time differential is decreasing as operators gain more experience with the alternatives. The alternatives are variable on the metric of load capacity: VMS is superior on this metric and wet cleaning is superior in some cases, while carbon dioxide is similar to PCE and HC and SGE are inferior.
- The hydrocarbon and VMS alternatives are able to clean fewer types of soil compared with PCE. The SGE and carbon dioxide systems are similar to PCE on this metric. Wet cleaning can be either equivalent or inferior to PCE on this metric.
- HG and SGE are superior to PCE in the range of types of clothing that they can clean. VMS is similar to PCE on this metric, and wet cleaning and carbon dioxide are more limited in the range of clothing types they can clean.
- Carbon dioxide is superior on the spotting metric; hydrocarbon, VMS and wet cleaning are inferior; and SGE can be either similar or inferior to PCE on this metric.
- Cost. Cleaning system costs include equipment, solvent, labor, energy, and regulatory costs. The Institute gathered comparative cost information on these parameters from a number of Massachusetts cleaners. Hydrocarbon systems have higher equipment and labor costs, counterbalanced by lower solvent and regulatory costs. VMS systems have higher equipment cost; figures were unavailable for several other parameters. SGE systems have higher equipment and solvent costs, counterbalanced by lower regulatory costs. Wet cleaning has higher labor costs, counterbalanced by lower equipment, solvent, and regulatory costs. Carbon dioxide has higher equipment costs and lower regulatory costs.
The Institute carried out alternatives assessments on one product based on n-propyl bromide (nPB), a product based on a volatile methyl siloxane (VMS), and two hydrochlorofluorocarbons (HCFCs). All of these are solvent-based vapor degreasing substitutes for PCE. The Institute did not conduct an alternatives assessment on aqueous cleaning systems as part of this project because the Institute's Surface Solutions Laboratory has already produced extensive resources in this area. As documented in other work by the Institute, approaches other than use of a drop-in solvent replacement are often superior from a health, environmental, technical and cost perspective.
- Health. All of the alternatives have potentially significant environmental and occupational health and safety impacts. The HCFC products have significant adverse environmental impacts, including persistence and global warming potential, but should be somewhat less toxic than PCE. There are significant concerns about the toxicity of nPB; it is a neurotoxin, and its carcinogenicity is now under study. Exposure to high levels of VMSs can cause dizziness, disorientation, and shortness of breath.
- Other hazards. All of the alternatives have higher vapor pressures than PCE, which will lead to greater evaporation and the potential for more vapors to escape from the degreaser; this will increase the potential for worker exposure, and may cause greater fugitive emissions than with PCE. A significant safety hazard is presented by the VMS product, which is highly flammable with a very low flash point. Its use as a vapor degreaser would present a significant fire and explosion hazard, and special handling would be required to use it safely, including the requirement for a closed system, spark-proof equipment, and worker training.
- Environment. nPB and VMS are superior to PCE on measures of persistence in water, soil, sediment, and air. The two HFCs are inferior on these measures. nPB is superior from the perspective of bioaccumulation, while the others are inferior on this measure. The two HFCs also have global warming potential.
- Technical criteria. Over all, the vapor degreasing alternatives have technical features comparable to those of PCE. The alternatives all have higher vapor pressures than PCE, which will contribute to product loss through evaporation. On the other hand, the alternatives all have lower surface tensions than PCE, which should enhance their ability to clean complex parts. Soil removal testing performed at the Institute’s Surface Solutions Laboratory found that all four alternatives were as effective as PCE in removing oil-based soils.
- Cost. All the alternatives currently cost more to purchase than PCE, creating an initial barrier for companies interested in switching to an alternative vapor degreaser. Operating costs such as energy use, waste solvent handling costs, and solvent lifetime may help to offset this higher purchase price. For example, many of the alternatives can be used at lower operating temperatures than PCE to achieve the same level of cleaning performance. On the other hand, all of the alternative solvents are more volatile than PCE, which might increase costs due to greater evaporative losses.
When addressing a specific cleaning need it is important to consider all options, including process and product modifications. Therefore, other options to consider include alternative cleaning processes such as an aqueous or a semi-aqueous system, working within the supply chain to change the contaminant on the part that requires cleaning, or investigating a material change to prevent contamination and thereby making cleaning unnecessary. All of these options would be preferable to using PCE or any of the drop-in alternatives discussed here. The Institute has demonstrated the viability of this approach in projects to assist industry in replacing chlorinated solvents with safer alternatives.
Aerosol automotive cleaning
The Institute carried out alternatives assessments on four brake cleaning alternatives, seven external engine cleaning alternatives, three internal engine cleaning alternatives, and four tire cleaning alternatives.
- Health. With regard to human toxicity, products containing n-hexane, 2-butoxyethanol, DGME, toluene, and glycol ethers are of equal or more concern compared with products containing PCE. Aqueous-based products will have lower human health concerns than any of the solvent-based products.
- Other hazards. Most of the solvent-based cleaners are highly flammable, and great care must be taken in their use, especially around hot engines. PCE is nonflammable, as are the aqueous-based cleaners, so these alternatives are preferable with regard to fire potential.
- Environment. Many of the alternative cleaners have the potential for significant environmental impact upon release. The medium of most concern is air, since these products are used as aerosol sprays. Most of the alternative products have ingredients with atmospheric half-lives exceeding two days and thus, like PCE, are considered persistent.
- Technical criteria. It is difficult to assess the technical performance of the alternatives objectively, since test data are not available. Stakeholders indicated that the alternative solvent-based cleaners are likely to perform as well as PCE-based cleaners, while aqueous-based cleaners may require more mechanical agitation to achieve equivalent results.
- Cost. Cost information is also difficult to assess. Some alternative products were more expensive per ounce than the corresponding PCE product, and some were less expensive per ounce. The actual cost per use may be quite different, however, since more or less of the different products may be required to obtain equivalent levels of cleaning.
- For a full report on this and other chemicals see the TURI Five Chemical Alternatives Assessment Study
- Chemical Economics Handbook, SRI Consulting (SRIC)
- Massachusetts Department of Environmental Protection, Toxics Use Reduction
- Toxics Use Reduction Institute homepage