Elemental Composition of Commercially Available Cannabis Rolling Papers
- Derek Wright*
- Michelle M. Jarvi,
- Benjamin Southwell
- Carmen Kincaid
- Judy Westrick
- S. Sameera Perera
- David Edwards
- Robert B. Cody
Abstract
With the recent legalization of cannabis in multiple jurisdictions and widespread use as a medical treatment, there has been an increased focus on product safety and the potential impacts of contaminants on human health. One factor that has received little attention is the possible exposure to potentially hazardous levels of toxic elements from rolling (smoking) papers. The elemental composition of rolling papers is largely unregulated, with a minority of jurisdictions regulating papers only when they are part of a final cannabis product. This study reports the concentrations of 26 elements in commercially available rolling papers and estimates potential maximum exposures relative to USP232 and ICH Q3D dosages in pharmaceutical compounds. Exposure estimates indicate that the concentrations of several elements in some products, particularly Cu, Cr, and V, may present a potential hazard to frequent users. Several elements, including Ag, Ca, Ba, Cu, Ti, Cr, Sb, and possibly others, are likely present in elevated quantities in some papers due to product design and manufacturing processes. Our results further suggest that Cu-based pigments are used by a number of manufacturers and that regular use of these products might result in exposures as high as 4.5–11 times the maximum exposure limits. Further research to quantify the contribution of rolling papers to elemental exposure under realistic smoking conditions is warranted.
Introduction
ARTICLE SECTIONS
Reported cannabis use in the United States (U.S.) has been on the rise, with 49% of American adults saying they have tried cannabis in some form, up from 34% in 2012. (1) Among cannabis users, 12% say they consume mostly through “smoking”, which has held steady at 11–13% in recent years but has increased from 7% in 2013 when they were first surveyed. (1) In the United States, cannabis carries two federally defined definitions. Cannabis containing less than 0.3% tetrahydrocannabinol (THC) is classified as industrial hemp, while cannabis containing more than 0.3% THC is classified as marijuana. Currently, the majority of regulatory standards apply to marijuana. As hemp is biologically the same plant as marijuana (but with <0.3% THC), both will be designated as cannabis hereafter. While marijuana use remains federally illegal in the U.S., as of 2023, all but 12 U.S. states have medical and/or recreational cannabis use legalization laws. As of mid-2021, about 2.3% of the U.S. population were registered medical cannabis patients. (2) Medical use patients are those that have a qualifying health issue and have been prescribed cannabis to treat the symptoms of their condition. (3) Qualifying health issues vary among jurisdictions but typically include terminal illness, HIV/AIDS, autism, cancer, Crohn’s disease, glaucoma, seizure disorders, persistent nausea, and other debilitating diseases and symptoms. (3)
The disparity between the state and federal legality of cannabis in the United States has led to individual states determining the regulatory limits for tested products available in legal dispensaries. To date, there have been few studies to determine a universal standard for limits of action in cannabis products, but many states have borrowed from guidelines established by the U.S. Pharmacopeial Convention (USP). (4) The USP is a nonprofit organization that creates quality assurance standards for medicines, dietary supplements, and food, which serve as useful guidelines for acceptable exposure limits and often as a basis for legal exposure limits. (5) Thus, compliance analysis is important to protect the health and safety of consumers, especially users who may have a weakened immune system. (4,6)
Cannabis intended for commercial sale generally undergoes full compliance testing, the parameters of which vary between the products. Analytical testing includes pesticide residues, residual solvents, heavy metals, and microbes and may include foreign matter, terpenes, and mycotoxins. The regulatory limits for all tested categories vary from state to state and sometimes between medical- and recreational-grade cannabis products within a state. For example, in the state of Michigan, the action limits are the same for medical and recreational grade cannabis in all categories except for total yeast and mold count on bud, shake/trim, and kief, where the action limit is 10,000 CFU g–1 (colony forming units) for medical-use cannabis and 100,000 CFU g–1 for recreational-use cannabis. (7) In comparison, action limits are 100 CFU g–1 in California and 10,000 CFU g–1 in Colorado. (8)
Like microbial action limits, heavy metal action limits vary greatly from state to state as well as which heavy metals are included in testing. For example, the states of California, Arizona, and Colorado have tested for four heavy metals: arsenic, cadmium, mercury, and lead. Washington DC. tested for those four as well as chromium, silver, and barium. The states of Michigan and New York add nickel and copper testing to those previously mentioned, but Michigan tests for copper only in inhaled concentrates, not in flowers, regardless of its end use. The regulatory limits for lead, for example, range from 0.5 μg g–1 in the states of California and New York to <10 μg g–1 in Colorado.
Heavy metal exposure through inhalation poses a long-term health risk of accumulation in the body. (8,9) Heavy metals are toxic and carcinogenic and can cause a variety of diseases. (9) For example, chronic exposure to cadmium can result in kidney, bone, and lung disease, (10) and McGraw et al. (11) found significantly higher levels of cadmium in urine and blood from marijuana smokers and cigarette smokers compared to all nonsmokers. Elevated levels of copper, lead, and zinc in the body can lead to neurodegenerative diseases. (12) Consuming cannabis through combustion (smoking) poses the greatest risk to human health as studies have shown cannabis smoke to contain all of the mentioned heavy metals as well as selenium. (13,14)
There is a common perception that if a batch of cannabis flower has passed heavy metal analysis, subsequent products made from that flower would also pass, but this may not be the case for prerolls. Prerolls are ready-to-smoke joints that consist of cannabis flower, rolling paper, and a filter (a piece of folded paper to prevent Cannabis flower from entering the mouth during smoking). (15) Prerolls are a popular and relatively inexpensive way to buy and consume cannabis from dispensaries. Prerolls most commonly come with one gram (g) of cannabis flower but can range from 0.5 to 3 g. (15) In 2020, a cannabis testing lab in the state of California determined that finished prerolls made from cannabis flower that had previously passed heavy metal and pesticide testing were failing above the action limits. (16) Further investigation found that heavy metals in the rolling papers caused the failures. Out of 101 papers, cones, and wraps tested, 91 had detectable levels of at least one heavy metal (cadmium, lead, arsenic, or mercury), and 8 had detections over California action limits. (16) While this report was circulated widely in the cannabis industry, we are not aware of any studies published in the peer-reviewed literature.
Similar research on heavy metals in tobacco cigarettes led to the discovery that tipping papers, the part of the cigarette that touches a smoker’s lips, and filters contribute trace heavy metals (17) and that different types of rolling papers (slow, medium, or fast-burning, bleached, flavored, and wood cellulose vs other plant cellulose) contain different, and not insignificant, amounts of toxic elements. (18) Several studies also revealed that the heavy metal content in cigarette rolling paper varies significantly (Table 1).
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