Letter to County Staff, Planning Commission and Board of Supervisors on the toxicities of Cannabis emissions in simple terms.

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From: NeighborhoodCoalition <sonomaneighborhoodcoalition@gmail.com>
Date: Thu, Aug 14, 2025 at 8:49 AM
Subject: FOR THE LAY READER - AN ADDENDUM ON BETA MRYCENE
To: <Tim.Freeman@sonomacounty.gov>,<Webster.Marquez@sonomacounty.gov>,<larry.reed@sonomacounty.gov>,<Tom.Bahning@sonomacounty.gov>,<PlanningAgency@sonomacounty.gov>,<cannabis@sonomacounty.gov>,<Shaun.McCaffery@sonomacounty.gov>,<lynda.hopkins@sonomacounty.gov>,<david.rabbitt@sonomacounty.gov>,<chris.coursey@sonomacounty.gov>,<rebecca.hermosillo@sonomacounty.gov>,<james.gore@sonomacounty.gov>

Toxicities of Cannabis Emissions, Including Carcinogenicity of Beta-Myrcene

Addendum to the 2024 Myrcene Report for the Lay Reader

Neighborhood Coalition

August 13,2025

This Addendum is provided to help non-scientists better understand the toxicity and long-term carcinogenic risks detailed in the Myrcene Report.  This Addendum will not focus on the many immediate toxicities experienced from cannabis emissions as they are well documented with references to scientific publications in the Myrcene Report. 

The Neighborhood Coalition (“NC”) published a report on October 18, 2024 (“MyrceneReport”), addressing toxicities from breathing cannabis emissions (odors) encompassing      

1) immediate toxicities including nausea, headache, respiratory irritation, eye irritation and aggravation of asthma
2) mid-term toxicities including new onset asthma, with two deaths reported in workers
3) long-term toxicities due to carcinogenicity of Beta-Myrcene (“Myrcene”, and other carcinogens).

The Neighborhood Coalition contacted three esteemed scientists with expertise encompassing epidemiology and public health, pediatric medicine, pulmonary medicine, and pharmaceutical development including toxicology and pulmonary delivery.  These three scientists each agreed to review the issues and the Myrcene Report.  They all concurred that the emissions from cannabis cultivation, which include high levels of the terpene Myrcene, are harmful to the health of those forced to breathe this contaminated air, and that amounts inhaled from outdoor cannabis cultivation are in projected carcinogeniclevels.  None of these scientists were paid consultants.  The reports and CV’s of George Rutherford, MD, (Berkeley and UCSF, pediatric medicine, prior State Epidemiologist and California Public Health Officer), Alan Cohen, MD (pediatric pulmonology, extensive experience in medicinal pharmaceutical development) and Srinivasan Venkateshwaran, PhD (pharmaceutical scientist, extensive experience in drug development including toxicology and inhalation technology) are available upon request.

Myrcene was confirmed to be a carcinogen by the National Toxicology Laboratory (“NTL”) in 2010 and was listed on Proposition 65 by the state of California as a known carcinogen in 2015.  The NTL noted that this was one of the rare instances when they did not identify a lower non-carcinogenic dose. Toxicities to the kidney and liver were also observed earlier than the cancers.

The levels of Myrcene in the air from cannabis emissions can be quantitated with scientific measurements, and accordingly the amount of Myrcene inhaled by neighbors who must breathe this contaminated air can also be quantitated. These amounts of Myrcene inhaled by neighbors, compared to what was shown to cause cancer in animals, are in toxic and carcinogenic levels¹.

 As Myrcene occurs naturally in some foods and beverages, it is instructive to compare the levels of Myrcene in foods to those in cannabis emission. Myrcene levels inhaled from cannabis emissions are orders-of-magnitude higher than found in foods.  For comparison, one would need to consume 300 pounds of carrots daily, or drink 1400 beers each day, to get the same amount of Myrcene that a neighbor gets every day from breathing air containing 100 PPB Myrcene².

It is important to understand that a carcinogenic dose is reached from repeated doses of Myrcene.  The higher the amount of Myrcene in the repeated dose, the more likely it is to cause toxicities and ultimately cancer.  Although Myrcene does not accumulate in the body, it is constantly present in the body when neighbors breathe air contaminated with Myrcene 24/7, as cannabis plants continuously emit Myrcene into the air.  Cancers can take years, decades, to appear long after the carcinogenic substance is no longer present. Other liver and kidney toxicities can appear much sooner as shown in the animal studies.  Cancer is caused when carcinogens interact with cellular DNA,causing mutations in the DNA.  Multiple DNA mutations accumulate over time which can result in cancer years later.  For example, smoking tobacco can cause lung cancer many years after one ceases smoking; melanoma and other skin cancers occur decades after excess exposure to sun, which often occurred in one’s childhood.

The Myrcene Report made the analogy to a measure used by the FDA and pharmaceutical industry in evaluating safety for new drugs.  Therapeutic Index (“TI”) compares the “toxic” dose of a drug to the “efficacious” dose.  The higher the TI, the greater safety margin.   For example, if a drug only shows toxicity at a dose of 200, but shows efficacy at a dose of 2, then the TIi s 200 divided by 2 = 100.  A TI as low as 10 causes concern.  A TI of 1 means that the lowest efficacious dose equals the toxic dose, and a TI of less than one means much greater toxicity.  In the case of Myrcene, this is not a drug with therapeutic benefit to neighbors, only toxicity.  We can instead refer to this ratio as Safety Ratio.  As shown in the Myrcene Report (page 10), even at 10 PPB, a small child would experience toxicities after 30 months exposure. To achieve a projected non-toxic exposure level, 1PPB Myrcene is proposed as the cutoff.³

Multiple Carcinogens

The above calculations are based on carcinogenicity levels for Myrcene acting alone.  Yet we know that cannabis emissions also contain Limonene, another known carcinogen confirmed by the National Toxicology Laboratory, and it is well documented that Myrcene reacts with air to form formaldehyde, another potent carcinogen also listed on Prop 65 (see Myrcene Report for references).  Although there have been no carcinogenicity studies done on the mixture of these 3 known carcinogens, it is likely that carcinogenic results from the mixture of 3 carcinogens would occur at lower levels of Myrcene than when acting alone.  Cancer results from repeated insults to and mutations in cellular DNA.  Three carcinogens together will cause more mutations than a single carcinogen.

Inhalationas Direct Route to Brain

The NTL Myrcenetoxicity studies were done with oral dosing.  Yet neighbors are exposed to Myrcene by inhalation, which not only gives much greater absorption by the body but also provides a direct route to the brain (Dr. Venkatashwaren report). Theoral toxicity studies would not detect additional brain toxicities from the inhalation route.  This is a big unknown of other potential long-term toxicities from Myrcene inhaled by neighbors from outdoor cannabis cultivation.

PolicyProposal

In light of the toxicities of cannabis emissions including

·        the immediate negative health effects on neighbors

·        the longer-term carcinogenicity from Myrcene

·        the unknown toxicities on developing fetuses

·        the unknown toxicities on the brain from inhalation of large amounts ofMyrcene

·        the added toxicities from the by-products formaldehyde and ozone

in conjunction with the confirmed long-distance that Myrcene travels (over 2500 ft, referencesupon request), we recommend that Sonoma County either ban outdoor cannabis cultivation or require setbacks of at least 2500 feet from outdoor cultivation to all parcels, in conjunction with quantitative monitoring to ensure no terpenes including Myrcene leave the cultivation parcel. 

The NC urges decision makers discuss with the County Health Department.

  Nancy and Brantly Richardson, Communication Directors

 NeighborhoodCoalition <sonomaneighborhoodcoalition@gmail.com 

 Footnotes

¹The Myrcene Report (page 8) details how doses in animal are converted to the human equivalent dose, which accounts for factors including differences metabolism, longer time that a drug remains in the human body, and body surface area to body weight; these factors are used by the pharmaceutical industry and FDA when testing safety of drugs in people. For example, a dose in a mouse is divided by 12.3 to convert to the human-equivalent dose.  Initial testing of a drug in humans starts at well below the lowest dose that caused toxicity in animals.

²PPB Is Parts Per Billion, which is the number of molecules of Myrcene compared to the number of molecules of air in a specific volume of air.  PPB Myrcene is converted to grams Myrcene using standard scientific formulas involving the molecular weight of Myrcene, Avagadro’s number (the number of molecules in a mole, which is the molecular weight ingrams) and the number of air molecules in a liter of air, detailed on page 6 of Myrcene Report.

³Based on the rodent toxicity studies, 0.4 g Myrcene/dayin adults and 0.1 g Myrcene/day in a small child caused toxicities after 70 days of dosing and cancer long term.  However, since no non-toxic dose was identified in the animal studies, the toxic dose may actually occur at lower Myrcene levels.  As shown in Table 1 of the Myrcene Report, even 10 PPB projects toxicity for a small child with 30 months exposure. To achieve a projected long-term “non-toxic” level of Myrcene, a cutoff of 1 PPB Myrcene is warranted. This same figure of 1 PPB Myrcene was also calculated using the Occupational Exposure Limits (OEL) number provided in the County’s Draft Environmental Impact Report for a 154 pound adult, after applying the proper reduction factors to account for small children (1/10 reduction factor), 24 hrdaily exposure instead of 8 hr (1/3 reduction factor), 3-fold higher uptake by inhalation than oral (1/3 reduction factor), and 1/10 reduction to account for that the OEL was based on a known carcinogenic level (thus total reduction of 900 fold).

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