National Clothesline

A researcher who has examined all available epidemiological literature pertaining to the carcinogenic effects of perc has concluded that the evidence does not support a conclusion that perc causes cancer in humans.

Kenneth Mundt, president of Applied Epidemiology, Inc., of Amherst, MA, analyzed information from 44 studies on the incidence of cancer in drycleaning and other workers exposed to perc. His study, which was sponsored by the Halogenated Solvents Industry Alliance, was published in the journal International Archives of Occupational and Environmental Health.

Mundt concluded that “the current epidemiological evidence does not support a conclusion that occupational exposure to perc is a risk factor for cancer of any site.” Mundt noted, however, that scientific information is inadequate for evaluation of a few cancer sites.

Mundt said that his inability to find any difference in cancer incidence between workers exposed only to perc and those with mixed exposure “argues against a perc-specific association.”

The review includes information on 17 cancer sites.

“We found no evidence of an association between breast, prostate, skin or brain cancer and exposure to perc,” Mundt reported.

“A relationship between perc and cancer of the following sites was considered unlikely: oral cavity, liver, pancreas, cervix lung,” he said.

Scientific evidence was inadequate for laryngeal, kidney, esophageal and bladder cancers. The review was limited by incomplete information on exposure to perc and other cleaning solvents and potentially confounding variables like cigarette smoking, alcohol consumption and diet, Mundt noted.

Perc’s carcinogenicity has been a subject of much study, discussion and debate over the past 25 years. Currently, it is classified as a “possible” carcinogen by the EPA, but the agency has tried in the past to move it up to the more serious “probably” category. However, the last time EPA tried to reclassify perc, its independent Science Advisory Board disagreed and said that there was not enough evidence to label perc a “probable.”

Although perc has remained in the “possible” category — the lowest of three in EPA’s ranking system — the solvent’s use in drycleaning has been increasingly regulated over the past decade. Some states, most notably California, regard perc as a carcinogen and have put numerous rules and fees in place that restrict its use. Nonetheless, perc remains the solvent of choice for the vast majority of cleaners in the United States.

The Mundt review was sponsored by HSIA and was partly based on earlier work conducted for the German workers’ compensation insurance commission. Mundt chaired a technical conference in Germany in 2001 on ”Tetrachloroethene and Cancer? A critical review and synthesis of epidemiological literature.”

There he presented results similar to those in his recent paper; nine cancer sites were studied in that earlier work.

In a discussion following the presentation, Wilfried Coenen, director of the Prevention Department of the German Union of Industrial Professional Associations, summarized Mundt’s results: “Perchloroethylene has not been proved innocent, yet the evidence for a guilty verdict is inconclusive.”

HSIA, which represents manufacturers, importers and users of perc, is also sponsoring a study of drycleaning workers in the Nordic countries that is scheduled to be published this year. HSIA expects that study to include an unprecedented amount of information on exposures and potential confounding factors.

Since it was undertaken more than two years ago, the study has identified drycleaning workers from the 1970 censuses in Denmark, Norway, Sweden and Finland, a total of about 7,000 individuals.

The 1970 census data has provided 30 years of medical follow-up and reduced the potential for exposure to other cleaning solvents used prior to that time, HSIA said.

The study is looking at the incidence of seven cancer types, including cancer of the bladder, cervix, esophagus, kidney, liver and pancreas, as well as non-Hodgkin’s lymphoma.

Incidence of the various cancers among the drycleaning workers will be compared to an age- and gender-matched population of laundry workers.

One benefit of using data from the Nordic countries is that much information is available from surveys conducted by government, industry and other sources.

This, HSIA expects, will produce better data on worker exposures than previous investigations. In Denmark, for example, researchers were able to find historical information on the identity of owners of all drycleaning shops and the characteristics of the machines in use at each of the shops.

Also of benefit is that fact that the use of perc was more pervasive in those nations 30 years ago than in the United States. For example, the U.S. industry was about evenly split between perc and petroleum in 1970, while 85 percent of the industry used perc in Finland, 75 percent in Denmark, and 71 percent in Sweden.