Cigarettes and Coffee: Do Newly-Discovered Sources of Diacetyl Spell the End of Popcorn Lung Litigation or the Beginning of a New Phase?

• Author: Talarico, George R.

DIACETYL seemed destined to be the next big thing in toxic tort litigation. With a scary sounding scientific name, an incurable signature disease, and deep-pocketed defendants, it appeared to be the perfect foil. However, after some initial successes over a decade ago, the litigation has failed to deliver as the plaintiffs' tort bar had hoped. Recently, though, there have been several developments, including further testing that indicates diacetyl exposure in excess of proposed OSHA standards is not limited to those working in popcorn flavoring plants. It remains to be seen if these new findings will either: (i) increase the focus and viability of diacetyl litigation; or (ii) further weaken the shaky science behind injurious diacetyl exposure by introducing some logic to the analysis (to wit, how can diacetyl be dangerous at low levels when people are exposed at high levels on a daily basis?).

1. Cigarettes and Coffee: Everyday Diacetyl Exposure

   Otis Redding glamorized the guilty pleasure of smoking cigarettes while drinking coffee in his song "Cigarettes and Coffee." "I'm sittin' here talkin' with my baby over cigarettes and coffee...." (2) He also foretold two activities that can cause exposure to large doses of diacetyl. Traditional cigarette smoke contains over 3,000 organic compounds, including a large amount of diacetyl. (1) One study suggests that the mean diacetyl concentrations in cigarette smoke ranges from 250 to 361 parts per million ("ppm"). (4)

   With a touch of clairvoyance, Redding may have mentioned smokeless e-cigarettes too. Even those that now partake in that hipper version of smoking are exposed to large concentrations of diacetyl. Diacetyl has been detected in many types of flavored e-cigarettes. (5) One study found that the concentration of diacetyl in e-cigarette smoke ranged from below the detection limit to as high as 239 ppm. (6)

   Coffee is also an apparent source of significant diacetyl exposure. Recent studies have found that coffee workers are also subject to diacetyl exposure. (7) For example, long-term concentrations for coffee shop baristas ranged from 0.013-0.016 ppm, with long-term concentrations for the customers ranged from 0.010-0.014 ppm, while the mean estimated time weighted average ("TWA") exposures for the baristas ranged from 0.007-0.013 ppm. (8) Another study measured the concentration of naturally occurring diacetyl in the headspace of an open cup of unfavored coffee to be 7 ppm. (9)

   Notwithstanding these exposures, there is no credible study linking either cigarette smoke or coffee to an increase in popcorn lung.

2. Background

   1. What is Diacetyl?

      Diacetyl (2,3-butanedione) is a very volatile naturally occurring organic compound. It is a natural byproduct of beer and wine making. It has a characteristic buttery flavor and has been produced industrially as a food-flavoring additive. Most notably, it has been used as a flavoring agent in microwave popcorn.

   2. What is Popcorn Lung?

      "Popcorn Lung" is a term used to describe bronchiolitis obliterans, which is an irreversible obstructive lung disease characterized by an inflammatory blockage of the bronchioles-the tiniest and narrowest airways in the lungs. Bronchioles are found in the respiratory system where air is fed to the alveoli (air sacs) and ultimately the blood stream. Bronchiolitis obliterans can be caused by trauma to the bronchioles after organ transplant, as well as by exposure to irritant gases like chlorine, ammonia, nitrogen dioxide, sulfur dioxide, and phosgene (collectively "irritant gases"). (10) It is thought that exposure to irritant gases at high concentrations causes injury to the epithelial lining of the bronchioles. (11)

      Toxicokinetics affecting concentrations at the bronchiolar epithelium substantially drive the risk of bronchiolitis obliterans from irritant gases. Highly soluble irritant gases like ammonia generally follow a threshold-dependent cytotoxic mechanism of action, so that at sufficiently high doses, exposure results in severe inflammation of the upper respiratory tract and the bronchiolar epithelium con-currently This is followed by acute respiratory distress, pulmonary edema, and post inflammatory concentric fibrosis that become clinically obvious within a few months of exposure. In contrast, irritant gases with lower solubility like phosgene also follow a threshold-dependent mechanism of cytotoxic action, but can exhibit more insidious and isolated bronchiolar tissue damage with a latency similar to fibrosis.

      To date, animal and human studies on diacetyl, a highly soluble gas, have not identified a coherent pattern of pathology and latency similar to that which would be expected based on studies of other known causes of bronchiolitis obliterans disease.

3. Regulatory Status

   1. FDA

      The FDA has long classified diacetyl as GRAS ("generally recognized as safe"). It is not considered a food additive and therefore does not require approval for use by the FDA. (12) Note that the FDA considers diacetyl as GRAS only for consumption of small quantities and not for inhalation. However, on May 5, 2016, the FDA announced that it is assuming regulatory authority over e-cigarettes. (13) It remains to be seen if this authority will impact the diacetyl component of e-cigarettes.

   2. OSHA

      OSHA has not provided any specific standard regulating occupational diacetyl exposure, (14) and"[m]any current MSDSs [material safety data sheets] do not reflect any new information regarding health effects and respiratory hazards associated with diacetyl." (15) OSHA has published guidance for diacetyl and food flavorings containing diacetyl, recommending that employers update their MSDSs and labels to provide information regarding the possible health hazards from prolonged exposure to diacetyl. (16) OSHAs guidance is unmistakably aimed at clearer identification of health risks beyond...