New York investigators measured perc, the dry-cleaning solvent, in apartments above two shops and in a day care next door to a third. Nearly every sample was over the state guideline of the day, the day care read high with no detectable odor, and the solvent was still there a month after the machines stopped.
If you live or work above or beside a dry cleaner, in Portland, Vancouver or anywhere else, your nose can’t tell you whether its solvent is in your air. Indoor air quality testing, a lab air sample for the solvent, can. In the New York study below, perc showed up in apartments directly above the shops, on the far side of the building and as high as the sixth floor, and in a day care where no perc odor could be detected.
778 micrograms per cubic meter:
average perc in the air of 6 families’ apartments above two dry cleaners. The authors put typical indoor air at 5 to 6.
The study
Judith Schreiber, Kenneth Hudnell and colleagues from the New York State Department of Health, the state attorney general’s office and the U.S. EPA measured tetrachloroethylene, known as perc, in the homes of 6 families, 17 people, living in two New York City apartment buildings with an operating dry cleaner on the ground floor. They picked the two buildings after preliminary readings in 16 apartments in eight such buildings. They also measured a day care center that shared a one-story building with a dry cleaner, separated by an interior wall. They sampled room air day and overnight, had residents wear personal samplers, and measured perc in breath, blood and urine. The paper appeared in Environmental Health Perspectives in 2002.
What they found
The apartments. Indoor air averaged 778 micrograms of perc per cubic meter (median 350), and the families had lived there an average of 5.8 years. The daytime median was 620. Nearly all of the samples were over New York’s guideline at the time, 100. The authors put background indoor perc at 5 to 6.
Night did not clear it. The shops did not operate at night, yet overnight samples averaged 358. Residents’ breath and blood tracked the room air.
It stayed after the machines stopped. Both shops were ordered to stop dry cleaning on site. One month later, apartment air had dropped substantially but still read 10 to 800, up to eight times the guideline.
The day care. Air in its three rooms read 1,800 to 2,400, mean 2,150. A parent had raised the concern, and the samples came back high “in the absence of a detectable perc odor.” Outside the building, under the soffits, two samples read 180 and 200. Six weeks after the dry cleaner stopped and removed its machines, the day care read 8 to 55.
Below the cited odor threshold.
One source the authors cite puts perc’s odor threshold at 8,160 to 12,240 micrograms per cubic meter, above every apartment reading in the study.
Why it works this way
Perc “readily evaporates into air,” in the words of the New York State Department of Health. The authors found the shops’ emissions “spread throughout the buildings in which they were contained.” The smell is a poor guide for two reasons. The cited odor threshold sits above the levels measured here, and the health department notes that “most people stop noticing the odor of PERC in air after a short time,” so “odor is not a reliable warning signal of PERC exposure.” Some apartment residents did report noticing an odor now and then, which, if it was perc, the authors say would likely mean higher concentrations.
For the overnight readings, the authors suggest that materials in the apartments may have absorbed perc during the day and released it at night, alongside continued emissions from the shops’ machines and freshly cleaned fabrics. That is their hypothesis. They did not measure it.
The limits, stated plainly
The paper’s headline health result was lower visual contrast sensitivity, the ability to see faint gray patterns, in the 17 residents and the 9 day care workers than in matched controls. Ordinary sharpness of vision did not differ. Color discrimination did not differ significantly. Read that result cautiously. The groups were small. The vision testers knew who was exposed. The apartment residents’ controls lived in a different city. No dose-response relationship appeared. The authors themselves wrote that “methodologic limitations preclude a definitive attribution of causation.”
In 2004, Jan Storm and Kimberly Mazor of the New York State Department of Health re-examined the apartment data in an exploratory analysis. With the four child pairs set aside, adults alone showed no significant effect of perc on contrast sensitivity (p = 0.16, 13 adults). Two of the four exposed children had a developmental delay or attention deficit diagnosis, conditions that also lower the score. The original authors published a reply disputing the reanalysis. The department’s later study, summarized in its 2013 fact sheet, found the effect in children “very small”, with mean scores “still within a normal range”, and no association in adults.
What survives the caveats is the exposure finding: perc from a ground-floor dry cleaner moved through whole buildings, it lingered after the machines stopped, and smell was not a reliable guide. The day care read high with no detectable odor.
What happens when you fix it
In the two apartments measured after their building’s shop stopped, perc fell by a mean of 81%. Residents’ blood levels in that building dropped to background within a month, while the other building’s air and blood stayed elevated. The day care went from a mean of 2,150 to 8 to 55 six weeks after the machines were removed.
Nationally, EPA issued a final rule in December 2024 that sets a 10-year phaseout for perc in dry cleaning and prohibits it in newly acquired dry-cleaning machines after 6 months. Compliance dates for machines already owned vary by machine type, with older types phased out sooner. In July 2025 EPA opened the rule to public comment as the first step in reconsidering it (EPA page last updated July 27, 2026). Some existing machines can legally keep running for years.
What gets lost in the body-testing pitch
Breath and blood tests can show perc above background levels. The New York State Department of Health is direct about what they cannot do: they “cannot conclusively determine when and for how long a person was exposed, what the source of that exposure was, or whether or not the person will develop adverse health effects.” In this study, urine was a less sensitive and less reliable marker than breath or blood. A body test tells you something got in. An air test in the room tells you where it is coming from and whether a fix worked.
What the data supports
Ask whether the cleaner in your building uses perc. Under EPA’s phaseout, some existing machines can keep running for years.
Test the air in the rooms you use most, day and overnight. The study sampled living rooms, bedrooms and kitchens, and overnight levels stayed well above background.
Read results against a current benchmark. New York’s guideline is now 30 micrograms per cubic meter, lowered from 100 in 2013. The state recommends immediate action to reduce exposure at 300 or above. In homes with no nearby source, fewer than 1 in 10 background readings top 10.
Re-test after a shop stops or switches solvents. A month after the machines stopped, readings here were still up to eight times the old guideline.
Bottom line
If you share a building with a dry cleaner, a sniff test can’t clear your air. Perc reached apartments floors away and a day care where no odor was detected, and it stayed after the machines stopped. The vision findings are uncertain; the exposure findings are solid. See how our room-by-room testing works, or book indoor air quality testing in Portland or in Vancouver, WA.
First step: ask the cleaner, or your building manager, whether it still uses perc.
Indoor air quality testing in Portland and Vancouver, room by room.
illumenair does indoor air quality testing and mold testing in Portland and Vancouver. We test and report. We do not do remediation.
971-363-5626 · info@illumenair.com · www.illumenair.com
Sources: Schreiber JS, Hudnell HK, Geller AM, House DE, Aldous KM, Force MS, Langguth K, Prohonic EJ, Parker JC. Apartment residents’ and day care workers’ exposures to tetrachloroethylene and deficits in visual contrast sensitivity. Environmental Health Perspectives 2002;110(7):655-664, doi:10.1289/ehp.02110655 (PMC1240911; read November 4, 2026). Storm JE, Mazor KA. Update of residential tetrachloroethylene exposure and decreases in visual contrast sensitivity. Environmental Health Perspectives 2004;112(15):A862-A864 (PMC1247642; read November 4, 2026). New York State Department of Health. Tetrachloroethene (PERC) in Indoor and Outdoor Air, September 2013 fact sheet; read November 4, 2026. U.S. EPA. Risk Management for Perchloroethylene (PCE). Last updated July 27, 2026; read November 4, 2026.