Fungal and mycotoxin contaminants in cannabis and hemp flowers: implications for consumer health and directions for further research

Abstract

Medicinal and recreational uses of Cannabis sativa, commonly known as cannabis or hemp, has increased following its legalization in certain regions of the world. Cannabis and hemp plants interact with a community of microbes (i.e., the phytobiome), which can influence various aspects of the host plant. The fungal composition of the C. sativa phytobiome (i.e., mycobiome) currently consists of over 100 species of fungi, which includes phytopathogens, epiphytes, and endophytes, This mycobiome has often been understudied in research aimed at evaluating the safety of cannabis products for humans. Medical research has historically focused instead on substance use and medicinal uses of the plant. Because several components of the mycobiome are reported to produce toxic secondary metabolites (i.e., mycotoxins) that can potentially affect the health of humans and animals and initiate opportunistic infections in immunocompromised patients, there is a need to determine the potential health risks that these contaminants could pose for consumers. This review discusses the mycobiome of cannabis and hemp flowers with a focus on plant-infecting and toxigenic fungi that are most commonly found and are of potential concern (e.g., Aspergillus, Penicillium, Fusarium, and Mucor spp.). We review current regulations for molds and mycotoxins worldwide and review assessment methods including culture-based assays, liquid chromatography, immuno-based technologies, and emerging technologies for these contaminants. We also discuss approaches to reduce fungal contaminants on cannabis and hemp and identify future research needs for contaminant detection, data dissemination, and management approaches. These approaches are designed to yield safer products for all consumers.

Integrated Management of Pathogens and Microbes in Cannabis sativa L. (Cannabis) under Greenhouse Conditions

“…On the inflorescence tissues, the most commonly encountered fungal genera include Penicillium, Alternaria, Cladosporium , and Fusarium ( Figure 15 ). These microbes can be detected by conducting bud swab tests as described in recent studies [ 19 , 20 , 50 ]. This buildup of yeasts and molds can lead to the final dried product failing to meet quality standards by exceeding colony-forming unit thresholds and potentially through the production of mycotoxins [ 20 , 50 ].…”

“…These microbes can be detected by conducting bud swab tests as described in recent studies [ 19 , 20 , 50 ]. This buildup of yeasts and molds can lead to the final dried product failing to meet quality standards by exceeding colony-forming unit thresholds and potentially through the production of mycotoxins [ 20 , 50 ]. Various factors influence the levels of yeast and mold contamination, which are discussed in the following sections.…”

“…Following the harvest of cannabis inflorescences, they undergo a phase of drying to reduce the moisture content to levels that would minimize the development of microbes [ 19 , 20 , 52 ], following which they are trimmed and prepared for packaging and stored prior to shipment. During each of the post-harvest processing stages, there is the potential for microbial contamination to be increased, primarily consisting of total yeasts and molds (TYM), total aerobic microbial count (TAMC), and bile-tolerant Gram-negative count (BTGN).…”

“…Detailed studies are lacking regarding at which specific stages the levels of microbes may build-up to cause the final product to potentially fail to meet regulatory standards. However, pre-harvest, it has been shown that cannabis genotype and growing conditions can significantly influence TYM build-up; in addition, post-harvest drying methods and handling practices can affect TYM levels [ 19 , 20 , 52 ]. A number of commonly encountered fungi have been identified on dried cannabis products pre- and post-harvest ( Figure 15 ), and they contribute to TYM levels [ 19 ].…”

“…Irradiation of cannabis products with gamma and electron beam irradiation has been shown to be an effective option for producers; they can be used to sterilize commercial batches of inflorescences without major changes in quality, but they are costly [ 69 , 70 , 71 ]. Irradiation is typically used in cases where microbial levels have exceeded regulatory limits or where zero tolerance is recommended, i.e., for medical patients with immunocompromised immune systems that rely on cannabis [ 20 ]. Other approaches have been described that require more in-depth studies to demonstrate their commercial utility [ 72 , 73 ].…”