Perchloroethylene (PERC) is the most common solvent used for dry cleaning in the United States. PERC is a reproductive toxicant, neurotoxicant, potential human carcinogen, and a persistent environmental pollutant. The Environmental Protection Agency is evaluating PERC under the Frank R. Lautenberg Chemical Safety for the 21st Century Act, which amended the Toxic Substances Control Act (amended TSCA), and has mandated that PERC dry cleaning machines be removed from residential buildings. Some local and state programs are also requiring or facilitating transitions to alternative cleaning technologies. However, the potential for these alternatives to harm human health and the environment is not well-understood. This review describes the issues surrounding the use of PERC and alternative solvents for dry cleaning while highlighting the lessons learned from a local government program that transitioned PERC dry cleaners to the safest current alternative: professional wet cleaning. Implications for future public health research and policy are discussed: (1) we must move away from PERC, (2) any transition must account for the economic instability and cultural aspects of the people who work in the industry, (3) legacy contamination must be addressed even after safer alternatives are adopted, and (4) evaluations of PERC alternatives are needed to determine their implications for the long-term health and sustainability of the people who work in the industry.
Dry Cleaning and the Use of Perchloroethylene
Dry cleaning uses non-aqueous solvents to clean fabrics. The first dry cleaning operations in the United States (US) date back to the 1800s when people washed fabrics in open tubs with solvents such as gasoline, kerosene, benzene, turpentine, and petroleum and then hung to dry. In the 1900s, the US started using specialized machines for the dry cleaning process. However, the use of highly flammable petroleum solvents caused many fires and explosions, highlighting the need to find a safer alternative. The dry cleaning industry first introduced Stoddard solvent (less flammable than gasoline) followed by several nonflammable halogenated solvents, such as carbon tetrachloride, trichloroethylene (TCE), trichlorotrifluoroethane, and perchloroethylene (PERC). Beginning in the 1940s, PERC—also known as tetrachloroethylene or PCE—became the most frequently used dry cleaning solvent and continues to be the primary solvent used to dry clean fabrics both in the US and the European Union (EU).
To comply with environmental regulations, dry cleaning machines have evolved through several “generations” to minimize PERC release. The 1st generation machines were “transfer machines,” where cleaned fabrics were manually transferred from the washer to a dryer. Since then, various pollution prevention controls have been implemented through the subsequent generations, culminating in the latest 5th generation machines, which are closed-loop and equipped with refrigerated condensers, carbon absorbers, inductive fans, and sensor-actuated lockout devices. As the newer generations of machines were introduced, the amount of PERC used was reduced from 300 to 500 g-PERC/kilogram of fabrics (1st generation) to <10 g-PERC/kilogram cleaned garment (5th generation). In many EU countries, dry cleaning machines older than 15 years are typically prohibited—only 5th generation machines are allowed. However, 4th generation machines may be used if best practices (e.g., good housekeeping, optimal machine operation, and recycling) are implemented and they meet EU emission requirements. The US EPA’s National Emission Standards for Hazardous Air Pollutants (NESHAPS) regulations stipulate that 2nd generation machines must be upgraded to 4th generation, and 3rd generation machines must be retrofitted or upgraded to 4th generation machines; only 4th generation and later machines can be sold, leased, or installed.
As of 2017 in the US, there are ~20,600 dry cleaning shops and the industry employs nearly 160,000 workers, with ~80% identifying as a racial or ethnic minority. The majority of owners are of Korean ancestry. Nationwide, 60–65% of dry cleaners use PERC as their primary solvent and most of the remainder use a high-flashpoint hydrocarbon. Other solvents currently used in the US include butylal, siloxane, liquid carbon dioxide, glycol ethers, and water (professional wet cleaning). In Europe, 60–90% of dry cleaning shops use PERC, depending on the country.
Health and Environmental Impacts of Perchloroethylene
PERC is a respiratory and skin irritant, neurotoxicant, liver and kidney toxicant, and reproductive and developmental toxicant . PERC is also considered a “potential occupational carcinogen”, “likely to be carcinogenic to humans by all routes of exposure”, and “probably carcinogenic to humans”. Neurotoxicity is the most sensitive non-cancer adverse health effect associated with PERC, with negative outcomes occurring even at low-dose exposures. Specifically, chronic (i.e., years) or sub-chronic (i.e., months) PERC exposure in humans has been associated with deficits in color vision and neuropsychological function in both occupational and community exposure studies.
A comprehensive review of 109 occupational studies with personal exposure measures estimated a mean exposure to PERC of 59 parts per million (ppm) among dry cleaning workers, with <10 ppm for spotters, pressers, and counter clerks and >100 ppm for machine operators. Another study in 2014 in The Netherlands surveyed ambient PERC concentrations for 193 dry cleaning shops before and after implementing a certification program that customers can use to select shops that are more safe and environmental friendly. Before the program, about 77% of shops reported 15-min time-weighted average (TWA) airborne concentrations ≥35 ppm. After the program, all shops showed a 15-min TWA of <35 ppm. These reductions were encouraging and below the European Union 15-min TWA limit of 40 ppm. However, decrements in visual reproduction, pattern memory, and pattern recognition were found among 65 workers when exposed to an average TWA concentration of <50 ppm for at least 3 years. Decrements on cognitive tests of attention and visual perception were seen in 100 workers with average full-shift TWA exposures of 12 ppm. Decrements were also found with cognitive tests of attention, specifically impaired reaction time, and vigilance among 60 workers typically exposed to TWA of 15 ppm. Reduced performance on vocal reaction time to visual stimuli was seen among 35 workers with TWA as low as 8 ppm. Residents who lived near a dry cleaning shop for an average of 10.6 years (mean indoor air concentration of 0.7 ppm) were found to have reduced cognitive performance on a test of reaction time, vigilance, and visual memory.
Numerous communities have been impacted through exposure to PERC. A cluster of communities on Cape Cod, Massachusetts has been extensively studied following years of PERC exposure. In this region, some water pipes were replaced with vinyl-lined asbestos-cement pipes. The vinyl lining was applied with a slurry of vinyl resin and PERC. Although it was believed that the PERC would evaporate before installation, subsequent water quality testing revealed that the people living in these communities were being exposed to PERC in their drinking water, ranging from 1.5 to 7,750 μg/L. Residents experienced adverse reproductive health outcomes, including delayed time-to-pregnancy, increased risk of placental abruptions, and an increased risk of congenital malformations. Exposure during the prenatal and early childhood period also yielded adverse impacts in adulthood, including reduced performance on neuropsychological tests, increased risk of bipolar disorder, Post Traumatic Stress Disorder, illicit drug use, vision problems, and certain types of cancer. However, no literature was found that describes the regional impact of community PERC exposures through other routes, such as inhalation.
PERC is a persistent pollutant that can contaminate air, soil, groundwater, drinking water, and is potentially toxic to wildlife . The recent draft US EPA risk evaluation on PERC found environmental risks to aquatic organisms . PERC poses a hazard to environmental aquatic receptors, including aquatic invertebrates, fish, and aquatic plants. The most sensitive species for acute toxicity were two daphnid species, Ceriodaphnia dubia and Daphnia magna; the acute toxicity value was as low as 2.5 milligrams per liter (mg/L). PERC presents an acute hazard to fish based on the mortality of rainbow trout (the most sensitive species) with acute toxicity values as low as 3.6 mg/L for mortality (i.e., the LC50—the concentration required to kill 50% of the population) . For chronic exposures, PERC is a hazard to aquatic invertebrates, with a chronic toxicity value of 0.5 mg/L, and a chronic toxicity value of 0.8 mg/L for fish . PERC is also a hazard for green microalgae with toxicity values as low as 0.02 mg/L .
