Nine employees of a microwave popcorn plant in Missouri had strikingly similar respiratory symptoms. They all had moderate to severe airway obstruction with bronchial wall thickening and air trapping. All employees had developed a dry persistent cough, shortness of breath on exertion and wheezing after an average of 1.5 years of employment, according to the National Institute for Occupational Safety and Health (NIOSH) in the United States, which investigated the matter in 2000.
After extensive testing and many incorrect diagnoses, these workers were all diagnosed with obliterative bronchiolitis, the inflammation, narrowing or obliteration of small airways (bronchioles) in the lung. The disease is uncommon, severe and irreversible. The majority of cases have limited or no response to medications. Five of the employees were on lung transplant waiting lists.
The NIOSH investigation concluded that there was “a risk for occupational lung disease in workers with inhalation exposure to butter flavouring chemicals.” Further research also confirmed exposure to diacetyl — the buttery-flavoured chemical in question — leads to decrease in pulmonary function.
After a spate of headlines on “popcorn lung,” many popcorn brands, such as Orville Redenbacher, announced they would no longer be using diacetyl in their manufacturing processes.
Many companies decided to use 2,3-pentanedione as a replacement for diacetyl, but researchers are sounding the alarm bells on this chemical, too.
“2,3-Pentanedione it is a chemical that is similar to diacetyl… and we know from studies done in the lab with animals it is just as hazardous to the lungs as diacetyl,” says Rachel Bailey, medical officer in NIOSH’s respiratory health division.
As a result, in October, NIOSH came out with recommended exposure limits for diacetyl and 2,3-pentanedione. NIOSH is recommending an exposure limit of 5 parts per billion (ppb) for diacetyl as a time-weighted average (TWA) for up to eight hours per day during a 40-hour workweek. It is also recommending a short-term exposure limit for diacetyl of 25 ppb for a 15-minute time period.
Additionally, NIOSH is recommending keeping exposure to 2,3-pentanedione below 9.3 ppb as an eight-hour TWA during a 40-hour workweek. NIOSH is also recommending a short-term exposure limit of 31 ppb during a 15-minute period.
While the American Conference of Governmental Industrial Hygienists (ACGIH) already has an exposure limit for diacetyl — which has been adopted in British Columbia and Ontario — this is the first time a limit has been recommended for 2,3-pentanedione.
Both diacetyl and 2,3-pentanedione are not confined to just popcorn manufacturing. They are both widely used as added flavourings in food processing and manufacturing across the United States and Canada, and can be found in bakery products, such as cake mixes, flours and margarine; dairy products, such as cheese and yogurt; snack foods, such as cookies, chocolates, chips and crackers; beverages, such as soft drinks and alcoholic beverages; as well as candies, ice cream, puddings, chewing gum and frozen food.
Both of these chemicals are mainly used as butter flavouring but they are also used in the formulation of a number of other flavours, such as caramel, hazelnut, vanilla and nearly any kind of fruit flavour (including strawberry, cranberry, grape and apple).
Diacetyl and 2,3-pentanedione also occur naturally during coffee production and in the fermentation process of beer and Chardonnay. They also naturally occur in a variety of foods, such as butter, bread, milk products and chicken.
According to NIOSH’s Criteria for a Recommended Standard: Occupational Exposure to Diacetyl and 2,3-Pentanedione, obliterative bronchiolitis was confirmed in diacetyl-exposed employees in at least eight flavouring manufacturing plants, five microwave popcorn plants, a diacetyl production plant, a cookie manufacturing plant and a coffee production plant.
Workers who are at risk are those who work in the processing and manufacturing of these food products as well as those who work in chemical manufacturing — actually making the diacetyl and 2,3-pentanedione — as well as those who work in flavour manufacturing — using diacetyl and 2,3-pentanedione to make flavours that are then sold to food manufacturers.
And it’s not just the operators and front-line workers who face exposure: quality assurance personnel, laboratory workers and supervisors may also be exposed. Maintenance workers are especially at risk because they are the closest to the equipment.
According to the Flavor and Extract Manufacturers Association in the United States, the use of diacetyl in U.S. food manufacturing is decreasing. In 2005, 228,00 pounds of diacetyl were used, compared to 85,000 in 2010. This is likely related to the increase in 2,3-pentanedione as a substitute, which had a reported poundage of 4,590 in 2005, compared to 38,000 in 2010.
While Health Canada and the Flavour Manufacturers Association of Canada did confirm usage of both diacetyl and 2,3-pentanedione in Canadian food processing and manufacturing, neither had data on how much of these chemicals are actually used in this country.
Companies using these artificial flavouring agents run the gamut from small mom-and-pop shops to very large, multinational corporations, says Bailey.
One particularly alarming characteristic of obliterative bronchiolitis is the rapid onset and decline in lung function.
“It’s a concern for workers because you might damage yourself before you are even aware of it,” says Brian Agnew, senior occupational hygiene and safety consultant at Pinchin in Waterloo, Ont.
“(Whereas) some other things would be slowly developing and you might see decrease in lung function over a period of years or even decades.”
At one microwave popcorn plant, employees who had at least one day of experience mixing butter flavourings into heated soybean oil had statistically significant higher prevalences of respiratory symptoms, compared to those who had never worked as mixers, according to NIOSH research.
At a company that manufactured flavourings for the baking industry, two production employees developed respiratory symptoms and severe fixed airways obstruction within seven months of starting work at the plant.
Aside from the restricted breathing symptoms, other symptoms of obliterative bronchiolitis may include fatigue, headache, fever, weight loss, night sweats, skin rashes and nausea.
If a worker is exhibiting any of these symptoms, she needs to be removed from the exposure to be evaluated and to determine the cause of decreased lung function, says Bailey.
“You want to get them away from the exposure as soon as possible so their lung function doesn’t decrease any more. The more your lung function deceases, the more disabling the disease is,” she says.
Workers should be encouraged to report any respiratory symptoms to their employer, she adds.
One of the issues with obliterative bronchiolitis is it may be misdiagnosed as other illnesses. None of the nine Missouri popcorn plant workers were initially diagnosed by their physicians as having obliterative bronchiolitis. Initial diagnoses included pneumonia, asthma, emphysema, bronchitis, chronic obstructive pulmonary disease (COPD), hay fever and sinusitis. Asthma is one of the most common misdiagnosis, largely because the symptoms are similar and it’s the most obvious choice.
“Unless the physician knows the background of the worker and knows about the possible association between diacetyl and obliterative bronchiolitis, he or she may miss this and just simply think it’s asthma,” says Ian Wheeler, principal consultant at Certified Industrial Hygiene Consulting in Calgary. “Physicians have lots of things to think about and know about but their knowledge of industrial processes and chemicals is sometimes not as good as it might be, so they may not be able to put that association together.”
One clear way to distinguish between asthma and obliterative bronchiolitis is that with asthma, the coughing, wheezing and shortness of breath are exacerbated at work. For example, symptoms will improve on the weekends but get worse come Monday morning. This is not the case with obliterative bronchiolitis. The symptoms remain the same whether the worker is at work, home or on vacation, says Bailey.
Steps for employers
If an employer is using diacetyl or 2,3-pentanedione in any aspect, it first needs to conduct air monitoring to see if there is a problem, says Agnew.
Additionally, all employees who work in areas where these chemicals are used should be in a medical monitoring program, says Bailey. A physician conducts breathing tests, such as spirometry, and looks for any abnormalities in lung function. These tests are repeated over time to identify lung function declines. And because of the rapid onset and progression of diacetyl-related lung disease, evaluations need to be done more regularly than employers may think. For example, monitoring that is suitable for slowly developing diseases, such as silicosis and coal employees’ pneumoconiosis, would not be sufficient.
Medical surveillance not only helps identify particular workers who are having issues and determine if symptoms are work related, it also helps to identify particular areas of a facility where symptoms may be prevalent, says Bailey.
When it comes to controlling worker exposure, eliminating the hazardous substance or substituting it with something else are ideal solutions. However, substitutes may need to be controlled as well, especially for those substitutes where toxicity information is limited.
If the amount of the substance being used can be reduced, that is also a step in the right direction.
“With every chemical exposure, the risk of it causing disease is a function of the amount of the chemical, the dose. It’s the dose that makes the poison,” says Wheeler. “There are safe exposures for most things.”
In the Missouri popcorn plant, NIOSH found evidence of a “dose-response relationship,” meaning higher diacetyl exposure resulted in more employees being affected or the diagnosed employees had a worse lung disease.
Local exhaust ventilation is an effective way to protect workers from flavouring chemicals.
“This is the best way to control worker exposures,” says Agnew. “The point is you want to remove the chemicals before they reach the workers’ breathing zone.”
For example, chemicals that are released from a coffee roaster are sucked up by a duct and fan system before a worker opens the roaster, he explains.
Various exhausts and hoods can be used to reduce employee exposure when blending, mixing and handling flavouring compounds in liquid and powder form. Employers should look at what engineering controls they can design for bag and drum emptying and filling, charging tanks and benchtop weighing and handling, says NIOSH.
It’s important to have effective preventive maintenance programs in place for these pieces of equipment, Agnew says.
“If you install a big duct and fan today and you know you are exhausting so much air from this piece of equipment, you want to make sure six months from now that’s not blocked and that it’s working right,” he says.
Another engineering control is to isolate rooms where flavourings are handled from the rest of the plant. At the Missouri popcorn plant, five of the affected employees were working in the room where butter flavourings, salt and colourings were combined with heated soybean oil. The other four employees were working in the adjacent room in the packaging area where the oil and flavouring mixture was combined with kernel popcorn in microwavable bags.
Flavouring mixing rooms and areas where flavourings are handled should be maintained under negative air pressure.
After the plant put engineering controls in place — specifically ventilation and isolating the flavour — it had one to three orders of magnitude reduction in diacetyl air concentrations, says NIOSH. Employees who started at the company after the interventions were put in place had fewer symptoms and higher lung functioning than their veteran colleagues.
Administrative controls for protecting workers from flavouring chemicals are also an important step, and include things like training and safe work procedures.
“The workers need to know the hazards they are dealing with… And know, for example, they have to wait five minutes for the air to be cleared out of the grinder or roaster before opening it up,” says Agnew.
Workers should know how to properly read safety data sheets and label elements and be well-versed in emergency handling procedures.
Job rotation, where workers are rotated between different areas in the plant, can also be effective in reducing worker exposure, says Wheeler. Employers should structure work tasks to minimize the amount of time employees spend near hazardous chemicals.
Due to the volatile nature of diacetyl and 2,3-pentanedione, proper handling procedures must be followed to limit worker exposure. For example, workers should avoid open pouring, measuring and transferring of the chemicals; add the chemicals into the tank last; keep tanks of the compounds sealed at all times; and use the compounds at the lowest possible temperature within the manufacturer’s recommended range.
Good housekeeping is also important. Areas should be cleaned regularly and spills cleaned up quickly. A high-efficiency particulate air (HEPA)-filtered vacuum should be used.
Warning labels and signs describing the health risks associated with flavouring compounds should be posted at entrances to work areas as well as inside.
Workers should also be wearing proper personal protective equipment (PPE), which may include protective face shields and eyewear, gloves, chemical resistant arm sleeves and respiratory protection. But the problem with PPE is that it is the last barrier between the worker and exposure, says Wheeler.
“If he’s not wearing his respirator properly and there’s a leak, a seal problem, so it does not fit properly to the face, that person could be exposed,” he says. “It’s important to fit test the respirators to make sure they seal properly.”
All workers need to be trained on the proper use of respirators, including putting them on and removing them. The respirator chosen should match the worker’s exposure. There should also be a schedule for cleaning, disinfecting, inspecting and repairing the respirators.
While research has determined that 2,3-pentanedione is a problematic substitute for diacetyl, there may be other substitutes that cause significant health risks for workers as well. Some substitutes that have come into question include 2,3-hexanedione, 2,3-heptanedione and 3,4-hexanedione. But there are likely many more that may cause issues. In a 2012 document, the Flavor and Extract Manufactures Association identified 27 “high priority” flavouring substances that could pose a respiratory hazard for workers. It also identified 62 “low priority” substances.
“The word is getting out about diacetyl in particular and there are companies that have eliminated or reduced it’s content, so we will probably see reduced use of this chemical in flavourings,” says Wheeler. “But they will be substituted by something else and the health effects of those we don’t know yet.”
Amanda Silliker is the editor of Canadian Occupational Safety magazine.
This article originally appeared in the February/March 2017 issue of COS.