Ironing out doubt about dry cleaning safety

A New York Times report ("Cleaning Up the Dry Cleaners" by Barnaby J. Feder, Feb. l5, 2000) raises questions about the health effects of the most widely used dry-cleaning chemical, perchloroethylene, commonly referred to as "perc." The article pointed out that there were substantial business efforts underway to develop safer alternatives to perc -- namely a biodegradable soap that dissolves in carbon dioxide.

Feder writes that perc, currently used by the vast majority of the nation's 33,000 dry cleaners, has been "linked to cancer, nervous system ailments and other health hazards." But what does the scientific literature actually say about perc's safety?

Ironically, when perc was introduced in the l930s, it was seen as a safe alternative to other dry-cleaning processes. Before perc, most dry-cleaning solvents were petroleum derivatives such as kerosene. The use of such highly flammable substances posed a significant threat to early dry cleaners and fires were frequent. In fact, the first regulations to affect the dry-cleaning industry in the United States were local ordinances to reduce fire hazards.

In the late 1970s a laboratory test by the National Cancer Institute indicated that perc could induce liver cancer in mice, but not in rats. A 1985 study on rats and mice conducted by the National Toxicology Program also concluded that there was "clear evidence" that perc was a rodent carcinogen.

While such laboratory tests on animals can provide some indication of whether a compound is a potential carcinogen in humans, these tests are never conclusive for predicting human cancer risk. For example, we know that many naturally occurring chemicals, such as hydrazines in mushrooms and safrole in black pepper, are animal carcinogens. However, we have no reason to suspect that eating mushrooms or using pepper increases human cancer risk.

If low-to-moderate perc exposure presents a cancer threat to humans, one would expect to see increased cancer rates among dry-cleaning workers who are exposed to significant levels of perc. Some studies have found a slight increase in cancer mortality rates for dry-cleaning workers. But other studies suggest this increase could be the result of other environmental and behavioral factors. For instance, increased smoking rates among such workers could explain the difference.

The bottom line is that if dry-cleaning workers are indeed at risk because of perc, scientific studies have yet to bear that out.

So, one might ask why the New York Times article did not clarify that it was referring to rodent studies, not human studies, when examining a perc-cancer link.

This is not to say that perc is harmless. As with most chemical substances, perc's harmful effects depend on the amount of exposure.

Exposure to high levels of perc for prolonged periods of time can cause headaches, dizziness, nausea, and eye and skin irritation. Even higher exposures intensify these reactions, and in extreme cases, can result in unconsciousness or even death. Perc is also moderately toxic when ingested.

However, high-level perc exposure and perc ingestion are exceedingly rare. The level inside most dry-cleaning establishments is far below the level from which acute effects can be observed. Indeed, the Occupational Safety and Health Administration has regulations in place that protect dry-cleaning workers.

Perhaps there are economic and other health reasons that may be stimulating research for new dry-cleaning agents. Perhaps there are technologies to come that will remove stains and clean clothes more efficiently than perc. But any new dry-cleaning research or business endeavors working from the premise that regulated and appropriately used perc is unsafe is not based in scientific reality.