The flavorings, used in a wide variety of foods, emerged as a threat in 2000 when the National Institute of Occupational Safety and Health (NIOSH) linked them to incidents of bronchiolitis obliterans at a southwest Missouri popcorn plant. Wider investigations found the disease had sickened about 200 workers and killed at least three, according to NIOSH documents on the investigation.
At first the concerns and subsequent court cases involved the flavoring industry. The Baltimore Sun this week reported that NIOSH scientists are now saying that workers at food industries that use the flavorings might also be at risk.
Kathleen Kreiss, NIOSH's chief of the field studies branch of the division of respiratory disease studies, told the Baltimore Sun that she is seeing cases in other plants.
"Now we've got cases of bronchiolitis obliterans among workers in other plants that use flavorings and in plants that make the flavorings," she told the newspaper.
She added: "We need to get into some of these plants becausue we don't have confidence that the flavoring industry has taken steps to actually prevent this disease, and we need to determine how widespread the exposure may be."
The Flavor and Extract Manufacturers Association (FEMA) disputed the claim it was not taking action to reduce the risk to workers.
"The Baltimore Sun is wrong about the flavor industry's track record on respiratory safety," the association said in a statement issued on 25 April. "Contrary to the allegation in the article that FEMA has been slow to respond to workplace safety issues concerning diacetyl, FEMA responded quickly and thoroughly."
FEMA said it "invited" government scientists from NIOSH to brief the industry within a month of the situation at the Missouri popcorn plant. FEMA has also helping its members and food manufacturers upgrade specific respiratory safety measures in relation to the issue, the association stated.
Specifically the association has retained leading experts in flavors, toxicology, respiratory illness and occupational safety to advise the industry on maintaining safe workplaces on an on going basis. It has also conducted workshops on respiratory safety in the workplace for members and their customers.
It has also compiled information on industry's best workplace practices for its members and customers. FEMA represents about 100 firms that invent and manufacture flavors for use in a wide variety of foods, drugs and cosmetics.
Bronchiolitis obliterans leads to inflammation and obstruction of the lungs through rapid thickening or scarring of the small airways. The disease is irreversible, progressive and can cause death.
In a release NIOSH noted that most chemicals used in flavorings have not been tested for respiratory toxicity via the inhalation route, and occupational exposure limits have been established for only a relatively small number of these chemicals.
Ruth Kava, a scientists with the American Council on Science and Health, yesterday noted the same lack of exposure limits in the industry.
Flavorings are composed of various natural and manmade substances. They may consist of a single substance, but more often they are complex mixtures of several substances. FEMA evaluates flavoring ingredients to determine whether they are "generally recognized as safe" (GRAS) under the conditions of intended use through food consumption, she said in a statement.
The safety of chemicals is usually established for humans consuming small amounts in food, not for food industry workers inhaling them. Production workers employed by flavoring manufacturers, or those who use flavorings in the production process, often handle a large number of chemicals, many of which can be highly irritating to breathe in high concentrations.
"Though considered safe to eat, ingredients may be harmful to breathe in the forms and concentrations to which food and chemical industry workers may be exposed," Kava stated, while assuring the public there's no reason to avoid butter-flavored popcorn or other foods because they contain traces of diacetyl.
ACSH is a consumer education group directed and advised by over 300 scientists and physicians.
"The chemical is only a problem when present in the air at very high levels," she said.
About 150 former popcorn plant workers have filed suits against companies supplying or making the butter flavorings involved. The industry has paid out about $100 million in jury awards and settlements. About 30 suits are still pending according to an Associated Press report.
Butter flavoring oils in the US market - tipped to hit $4.4 billion (€3.4bn) by 2007 - are used in biscuit and confectionery manufacturing as well as margarines and soft spreads.
In January last year NIOSH, a body that falls under the US Department of Health and Human Services, recommended that employers take measures to limit employees "occupational respiratory exposures to food flavorings and flavoring ingredients in workplaces where flavorings are made or used."