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Contaminants of Concern in Cannabis: Microbes, Heavy Metals and Pesticides


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Microbiological contaminants pose a potential threat to cannabis consumers. Bacteria and fungi may cause opportunistic infections in immunocompromized individuals. Even dead organisms may trigger allergies and asthma. Toxins from microbial overloads, such as Shigla toxin and aflatoxins, may pose a problem—unlikely, but possible. The Cannabis plant hosts a robust microbiome; the identification of these organisms is underway. Cannabis bioaccumulates heavy metals in its tissues, so avidly that hemp crops have been used for bioremediation. Heavy metals cause myriad human diseases, so their presence in crops destined for human consumption must be minimized. Pesticide residues in cannabis pose a unique situation among crop plants—the Environmental Protection Agency (EPA) will not propose pesticides guidelines, because Cannabis is illegal on the federal level. The use of illegal pesticides is a rising crisis, and a breakdown in ethics. Testing for pesticide residues and maximal limits are proposed.
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Chapter 22
Contaminants of Concern in Cannabis:
Microbes, Heavy Metals and Pesticides
John M. McPartland and Kevin J. McKernan
Abstract Microbiological contaminants pose a potential threat to cannabis con-
sumers. Bacteria and fungi may cause opportunistic infections in immunocom-
promized individuals. Even dead organisms may trigger allergies and asthma.
Toxins from microbial overloads, such as Shigla toxin and aatoxins, may pose a
problemunlikely, but possible. The Cannabis plant hosts a robust microbiome;
the identication of these organisms is underway. Cannabis bioaccumulates heavy
metals in its tissues, so avidly that hemp crops have been used for bioremediation.
Heavy metals cause myriad human diseases, so their presence in crops destined for
human consumption must be minimized. Pesticide residues in cannabis pose a
unique situation among crop plantsthe Environmental Protection Agency
(EPA) will not propose pesticides guidelines, because Cannabis is illegal on the
federal level. The use of illegal pesticides is a rising crisis, and a breakdown in
ethics. Testing for pesticide residues and maximal limits are proposed.
22.1 Introduction
Cannabis (the plant) and cannabis (the plant product) may be contaminated by
microbes, heavy metals, or pesticide residues. The rst two contaminants, microbes
and heavy metals, present a Janus-face or ip-side of the coinin relation to
Cannabis. Some bacteria and fungi are part of the plants microbiome. They pro-
vide benets to Cannabis. See the book chapter by Parijat Kusari and Oliver Kayser
for more about the Cannabis microbiome. On the ip-side of the coin,other
bacteria and fungi cause disease, and these must be controlled.
J.M. McPartland (&)
GW Pharmaceuticals place, 1 Cavendish Place, London W1G 0QF, UK
K.J. McKernan
Courtagen Life Sciences, 12 Gill Street Suite 3700, Woburn, MA 01801, USA
©Springer International Publishing AG 2017
S. Chandra et al. (eds.), Cannabis sativa L. - Botany and Biotechnology,
DOI 10.1007/978-3-319-54564-6_22
Heavy metals are harmful to humans, and these contaminants must be mini-
malized in cannabis destined for human consumption. Cannabis pulls heavy metals
from soil with great efciency. Therein lies a second Janus face: the plant has great
potential as a tool for bioremediation. Bioremedial plants extract pollutants from
soil and accumulate the pollutants in their tissues, for harvesting and removal.
Pesticide residues have no ip-side of the coin,they are just bad. Growth in
the cannabis industry, from outdoor hippie gardens to indoor commercial ware-
houses, has multiplied pesticide usage. Pesticide regulation in the USA is primarily
a responsibility of the Environmental Protection Agency (EPA). The EPA will not
register pesticides for use on Cannabis or set tolerance levels because the crop is
illegal on the federal level (Stone 2014). For that same reason, no cannabis can be
labeled as Organicby the USA Department of Agriculture.
This chapter focuses on microbes, heavy metals, and pesticide residues in can-
nabis inorescences and seed oil. Other contaminants exist, such as butane residues
in cannabis extracts. For these, the reader is directed elsewhere (Upton et al. 2013;
Farrer 2015). Adulterantsdeliberately added contaminantsare a separate issue,
particularly hashish diluents and psychoactive adulterants (Bell 1857; Dragendorff
and Marquis 1878; Indian Hemp Drugs Commission 1894; Perry 1977; Wilson
et al. 1989; McPartland and Pruitt 1997; McPartland 2002; Caligiani et al. 2006;
McPartland et al. 2008; Busse et al. 2008; Venhuis and de Kaste 2008; Scheel et al.
22.2 Microbial Contaminants
Cannabis is often characterized as a disease-freecrop. In fact, a plethora of plant
pathogens attack the plant. At least 88 fungal species cause diseases in Cannabis
(McPartland 1992), as do eight pathovarieties of plant pathogenic bacteria
(McPartland et al. 2000). Some phytopathogens are unique to Cannabis
(McPartland 1984), and some organisms are ubiquitous. The most threatening
diseases of owering tops are caused by three ubiquitous fungiBotrytis cinerea
(the cause of gray mold), Trichothecium roseum (white mildew or pink rot), and
Alternaria alternata (brown blight).
Phytopathogens cannot infect humans, except perhaps immunocompromized
individuals. Opportunistic infections by A. alternata have been reported in patients
receiving chemotherapy, recent organ transplant patients, and people with AIDS.
Airborne conidia (spores) of B. cinerea and A. alternata cause mold allergies and
asthma, particularly in greenhouse workers (Jurgensen and Madsen 2009).
From a consumer perspective, a separate population of bacteria and fungi is of
greater concern than phytopathogens: post-harvest storage microbes (McPartland
1994a). Storage organisms are saprophytes, rather than pathogens. They can only
invade dead plants after harvest. Fungi are the primary cause of storage contami-
nation. They thrive under low oxygen levels, limited moisture, and intense com-
petition for substrate.
458 J.M. McPartland and K.J. McKernan
The spectrum of post-harvest storage fungi has changed in the past 40 years.
Most black-market cannabis available in the 1980s came from Latin America. It
was sweat curedby drying herb in a pile, covered by cloth. Heat arising from
fermentation quickly cured the product, but allowed storage organisms to gain a
foothold. Then the cannabis was compressed into bricks for smuggling, and stored
under ambient humidity and warm temperatures. Under these conditions, fungi
from four genera commonly contaminated the product: Aspergillus, Penicillium,
Rhizopus, and Mucor (Fig. 22.1).
Kagen et al. (1983) isolated three worrisome Aspergillus species from marijuana:
A. niger, A. fumigatus, and A. avus. Schwartz (1985) scraped an aspergilloma
(fungus ball) caused by A. niger from the sinuses of a marijuana smoker suffering
severe headaches. Llamas et al. (1978) implicated A. fumigatus-contaminated
marijuana in a case of bronchopulmonary aspergillosis. Aspergillosis is an invasive
disease, unlike an aspergilloma. It usually stays localized (e.g., a pneumomycosis)
but sometimes becomes systemically disseminated. Chusid et al. (1975) reported A.
fumigatus causing near-fatal pneumonitis in a 17-year old. They noted that the
patient buried his marijuana in the ground for aging.Penicillium, Rhizopus, and
Mucor have also been cultured from moldy cannabis (Kagen et al. 1983; Kurup
et al. 1983; Bush Doctor 1993).
Mycotoxins produced by fungi are hepatotoxic, nephrotoxic, and carcinogenic.
Ochratoxins, citrinin, and patulin are produced by Aspergillus and Penicillium
species. Paxilline is produced by Penicillium paxilli. Trichothecenes gained noto-
riety for their reputed use in biological warfare (yellow rain). Trichothecenes are
Fig. 22.1 Common storage fungi in the 1980s. From left to right:Rhizopus stolonifer, Mucor
hiemalis, Penicillum chrysogenum, P. italicum, Aspergillus avus, A. fumigatus, and A. niger.Top
row sporophores cross-sectioned to reveal internal structures (400x). Bottom row natural habitat
(25x). From McPartland (1989), reprinted with permission
22 Contaminants of Concern in Cannabis 459
produced by Fusarium oxysporum, a biological control fungus deployed against
illegal Cannabis cultivation (McPartland and West 1999). Aatoxins are the most
common mycotoxins.
Aspergillus species (A. avus, A. parasiticus) produce aatoxins in warm and
humid conditionsoptimally 33 °C (91.4 °F), and 0.99 water activity. Aatoxins
are acutely poisonous as well as carcinogenic. Llewellyn and ORear (1977)
identied aatoxins in cannabis, but under articial conditions. They added 15 ml
water to 5 g pulverized owering tops, autoclaved the material, and inoculated it
with A. avus or A. parasiticus. After 14 days at 25 °C (77 °F), the fungi sporu-
lated and produced moderateamounts of aatoxins. Importantly, no studies have
reported aatoxins in cannabis under normal storage conditions (McPartland and
Pruitt 1997).
Kurup et al. (1983) isolated three thermophilic actinomycetes from questionably
sourced material, Thermoactinomyces candidus, T. vulgaris, and Micropolyspora
faeni. These endospore-forming microbes cause farmers lung,which is a
hypersensitivity reaction rather than an infection.
Turning to bacteria, Ungerleider et al. (1982) cultured several members of the
Enterobacteriaceae from NIDA-sourced cannabisspecies of Klebsiella,
Enterobacter, and Enterococcus (group D Streptococcus). It should be noted that
NIDA marijuana at that time was sweat cured by placing harvested material on
concrete oors (B. Thomas, pers. commun. 1999)an unacceptable method today.
A disease outbreak caused by another member of the Enterobacteriaceae
Salmonella muenchenwas associated with cannabis (Taylor et al. 1982). The
investigators concluded that the plant material, sourced from Mexico, was con-
taminated or adulterated by untreated manureanother unacceptable method today.
Some of these organisms, particularly Rhizopus, Mucor, and thermophilic acti-
nomycetes, reduce cannabis to a deteriorated state that is no longer acceptable by
todays consumers. The product is dark brown, crumbly, smells musty or moldy,
and produces a brown or sooty smoke (McPartland et al. 2000). Although methods
of sweat curing are still promoted on websites, todays product is carefully air dried,
often vacuum-sealed (sometimes under nitrogen), and stored in cold, dry condi-
tions. This process maintains potency and also prevents the growth of storage
Here in the 21st century, Aspergillus- and Penicillium-contaminated cannabis
still poses a problem (Rechlemer et al. 2015; Cescon et al. 2008; Szyper-Kravitz
et al. 2001; Verweij et al. 2000). Martyny et al. (2013) sampled grow operations in
Colorado for airborne fungal spores. Aspergillus and Penicillium spp. predominated
indoors, and Cladosporium spp. predominated outdoors. Cladosporium may be an
emerging problem; this fungus also infests hemp mills (McPartland 2003). About
1% of cannabis supplies received by Harborside Medical Cannabis Dispensary in
Oakland, California were returned to vendors because of unacceptable levels of
Aspergillus contamination (DeAngelo 2010).
460 J.M. McPartland and K.J. McKernan
22.3 Microbial Testing
The Ofce of Medicinal Cannabis in the Netherlands initiated microbial testing
(Hazekamp 2006,2016). Bedrocan BV, the primary supplier of medical cannabis in
the Netherlands, tests harvested plants as well as nal packaged products. They use
two petri plate-based screening tests recommended by the European Pharmaopoeia
one for total aerobic microbial count (TAMC), the other for total yeast and mold
count (TYMC). Degree of contamination is quantied by counting the number of
colony-forming units arising from one gram of plated cannabis (CFU/g). They placed
upper limits of <100 CFU/g for TAMC, and <10 CFU/g for TYMCwhich is close
to sterility. Certain specic pathogens must be completely absentStaphylococcus
aureus,Pseudomonas aeruginosa, and bile-tolerant Gram-negative bacteria such as
Escherichia coli. Furthermore, the absence of fungal mycotoxins must be conrmed
by additional quality control testing (Hazekamp 2016).
Health Canada (2008) mandated similar tests, with different upper limits:
<100 CFU/g for TAMC, and <100 CFU/g for TYMC, as well as specic tests for
Coliform bacteria (<3 MPN/g), and E. coli (absent). Their upper limit for aatoxins
B1, B2, G1, G2, and ochatoxin A is <20 µm/kg cannabis.
In the USA, medical cannabis was rst legalized by California in 1996.
Microbial testing was not mandated until 2011, when New Jersey instituted sample
testing for pests, mold, mildew, heavy metals and pesticides, and the certication of
organicmedical cannabis (NJMMP 2011).
The American Herbal Pharmacopoeia (AHP) issued specic protocols for
microbial testing (Upton et al. 2013). The AHPs protocols were based on tests for
commodity food products issued by the EPA and the Food and Drug
Administration, as well as assays for cannabis used in Holland (Hazekamp 2006).
The tests consist of a series of petri plate- or lm-based assays for bacterial, yeast,
and mold.
For orally consumed cannabis, the AHP recommended four tests: (1) total yeast
and mold count, (2) total coliforms, (3) Escherichia coli, (4) Salmonella spp. In
addition, they recommended immunochemical methods to screen for aatoxins. For
products to be inhaled, more stringent tests were recommended: (1) total yeast and
mold count, (2) total aerobic count, (3) bile-tolerant gram-negative bacteria,
(4) E. coli and Salmonella spp., and aatoxin assays. The AHP proposed specic
limits in CFU/g counts, but emphasized that these values did not represent pass-fail
criteria. Rather they were recommended levels when plants are cultivated and
harvested under normal circumstances.
The states of Colorado and Washington issued specic testing protocols,
reviewed by Holmes et al. (2015). Colorados list of fungi required for testing was
based on publications from the 1980s, including some species that may not be
relevant to current, domestically-produced cannabis. Washingtons protocols were
adopted from the AHP. Holmes et al. (2015) criticized the use of screening tests,
noting they are based on guidelines for food product facilities (and not necessarily
the testing of end products). Some of the tests are quite outdated (e.g., bile-tolerant
22 Contaminants of Concern in Cannabis 461
gram negative bacteria). Furthermore, anonymous CFU/g counts do not identify
relevant pathogens, or the threat of fecal contamination. Instead Holmes recom-
mended testing herbal cannabis for specic pathogens: Escherichia coli, Salmonella
spp., and four species of Aspergillus:A. avus, A. fumigatus, A. niger, and A.
In 2015 Colorado changed its testing regimen: (1) total yeast and mold count
(limit <10
CFU/g), (2) Salmonella (limit <1 CFU/g), (3) Shiga-toxin producing
E. coli (STEC, limit <1 CFU/g). Colorado recommended testing for three species of
Aspergillus:A. avus, A. fumigatus, and A. niger, although this was never
Aspergillus is a large genus with 250 species, and separating three specic
species from the others is not easy. Traditionally, identication required culturing
on Aspergillus-selective plating media, and morphological measurements by a
specialist (Samson et al. 2004). Due to the challenges associated with
species-specic detection, Colorado changed their testing requirements again in
2016, to a 10,000 CFU/g total yeast and mold test, but left in place single CFU/g
testing for E.coli and Salmonella spp.
Microbial tests that require CFU/g detection are prone to sampling bias, since the
cannabis sample (usually 250 mg to 1 g) is usually wetted with 34 ml of Tryptic
Soy Broth (TSB), a general purpose culture medium. This large volume cannot be
placed into a given petri dish, PCR reaction, or culture based detection device. Thus
a subsample of the large volume is taken after a dened growth time (termed
enrichment) to accommodate for the subsampling.
Because of these difculties, and to accelerate testing turn-around time, some
laboratories now use quantitative polymerase chain reaction (qPCR) assays. This
method detects DNA sequences in cannabis samples. Primers for 18S rDNA ITS
(Internal Transcribed Spacer) are particularly useful for identifying specic
Aspergillus species.
The drawback to qPCR is the methods indifference to living or non-living
DNA. To accommodate this, an enrichment step is performed, where the cannabis
samples are incubated overnight in TSB broth prior to qPCR detection. Overnight
growth in TSB ensures only live organisms are measured, but raises questions over
preferential culture conditions for broader total yeast and mold tests. To address this
conundrum, some labs perform a qPCR on total yeast and molds, and positive
results are conrmed with an additional test extracted 24 h later to ensure the signal
from the pre-incubation test was from live organisms.
McKernan et al. (2015) compared results between qPCR and three petri plate- or
lm-based detection systems: 3 M Petrilm, Simplate-Biocontrol Systems,
and BioLumix. They tested 17 dispensary-obtained cannabis samples. Six sam-
ples tested positive with the qPCR assay, ve samples tested positive with the
Biocontrol Systemsassay (>10,000 CFU/g), four samples test positive with the
3 M Petrilmassay (>10,000 CFU/g), and only one sample tested positive with
the BioLumixassay, which is a simple pass-fail test.
McKernan and colleagues then subjected ITS amplicons to DNA sequencing, to
identify specic fungi. All three Aspergillus species on the bad list turned up:
462 J.M. McPartland and K.J. McKernan
A. avus (one sample), A. fumigatus (one sample), and A. niger (three samples).
Twelve other Aspergillus/Emericella species were detected: A. candidus, A.
ostianus, A. sepultus, A. sydowii, A. tamari, A. terreus, A. versicolor, E. rugulosa,
E. nidulans, E. lifera, E. repens, E. bicolor. Two of these produce toxins, A.
versicolor and A. terreus.
ITS amplicons identied 17 Penicillium species. The most common fungus was
P. paxilli, surpassing all Aspergillus species. This species has not previously been
reported in association with Cannabis or cannabis. P. paxilli produces paxilline
toxin, so McKernan and colleagues conrmed its presence with PaxPss1 and
PaxPss2 DNA primers. Paxilline has been shown to decrease the antiseizure ben-
ets of cannabidiol in a mouse epilepsy model (Shirazi-Zand et al. 2013).
Although Holmes et al. (2015) questioned the need to test cannabis for E. coli,
Listeria spp., and Pseudomonas aeruginosa, McKernan (unpublished study 2016)
has identied several Pseudomonas species in cannabis with DNA testing. The
most dangerous pathogen, P. aeruginosa, was not seen. The array of organisms that
need to be screened is not yet formalized.
Screening herbal cannabis for moisture content (MC) is another approach. Bush
Doctor (1993) and McPartland et al. (2000) recommended drying herbal cannabis
to 1012% MC. Fungi and bacteria cannot grow below 15% MC. Herb dried below
10% MC becomes brittle and disintegrates easily. Hazekamp (2006) recommended
510% MC. The AHP monograph recommended not more than 15% MC (Upton
et al. 2013). Holmes et al. (2015) used water activity (a
) as a metric; a
the partial vapor pressure of water in a substance. The a
of pure distilled water
equals 1.0. Bacteria usually require a minimum of 0.9 to grow, and fungi require a
minimum of 0.7. Holmes and colleagues recommended a maximum a
of 0.65 for
herbal cannabis, approximately 13% MC.
22.4 Microbial Harm Reduction
Prevention is the best strategy to avoid microbial contamination. Growers must
harvest disease-free Cannabis. This books chapter by David Potter discusses GW
Pharmaceuticals methods of growing healthy Cannabisby controlling humidity,
using biological controls and natural predators, and without resorting to pesticides.
The use of pesticides is addressed below.
To kill microbial contaminants in medical cannabis, Ungerleider et al. (1982)
used radioactive
Co gamma rays, a dose of 15,00020,000 grays. Dutch and
Canadian medical cannabis is treated with 10,000 grays (Hazekamp 2006; Health
Canada 2008). Microbial counts in Dutch cannabis are tested before and after
irradiation, because badquality cannabis should not be rescued by irradiation
(Hazekamp 2016). In comparison, packaged meat and poultry may be irradiated
with up to 70,000 grays. Gamma radiation remains controversialit may destroy
terpenoids, and it does not destroy mycotoxins (Lucas 2008).
22 Contaminants of Concern in Cannabis 463
Hazekamp (2016) evaluated the effects of 10,000 grays in four cultivars of THC-
or CBD-dominant Cannabis. Quantication with ultra performance liquid chro-
matography (UPLC) and gas chromatography-ame ionization detector (GC-FID)
showed that levels of total THC and/or CBD were not altered by irradiation
treatment in any of the cultivars tested, compared to controls. Irradiation decreased
four monoterpenoidsa-guaiene (10%), cis-ocimene (723%), b-myrcene (8
18%), terpinolene (1638%), and seven sesquiterpenoidsguaiol (6%), nerolidol
(7%), trans-b-farnesene (710%), b-caryophyllene (610%), c-selinene (1317%),
eudesma-3,7(11)-diene (14%), and c-emelene (819%). Hazekamp compared these
reductions to similar decreases arising from short term storage in a paper bag (Ross
and Elsohly 1996).
Hazekamp (2006) compared the inoculum load of irradiated medical-grade
herbal cannabis (MC) to that of untreated recreational coffeehouse cannabis (CC).
An Enterobacteriaceae assay revealed <10 CFU/g in MC samples (n = 2), and a
mean of 1.4 !10
CFU/g in CC samples (n = 11). An assay for molds and aerobic
bacteria revealed <100 CFU/g in MC samples, and a mean of 5.4 !10
CFU/g in
CC samples. Because screening tests do not identify species, one CC sample was
sent out for further testing, which identied E. coli and Aspergillus, Penicillium,
and Cladosporum spp.
Ruchlemer et al. (2015) tested three other ways to sterilize cannabis: gas plasma,
autoclaving, and ethylene oxide. These methods decreased THC content 12.6, 22.6,
and 26.6%, respectively. Levitz and Diamond (1991) killed condia (spores) of A.
fumigatus, A. avus, and A. niger in marijuana by baking herb at 150 °F (300 °C)
for 15 min. Water pipes do not prevent the transmission of fungal spores from
contaminated cannabis (Moody et al. 1982), not even water pipes with lters
(Sullivan et al. 2013). Fungi and bacteria are capable of passing through vaporizers
(Ruchlemer et al. 2015). Some toxins produced by fungi and bacteria, such as Shiga
toxin, are resistant to heat treatment (pasteurization).
22.5 Janis FaceEndophytes
A microbiome is the ecological community of commensal, symbiotic, and generally
non-pathogenic microorganisms that inhabit plants, animals, and us. The plant
microbiome is a key determinant of plant health and productivity, and has gained
attention recently (Turner et al. 2013). Over a century ago, however, botanists rst
recognized mutualistic associations between plants and fungi, termed mycorrhizae.
Emil Arzberger, a USDA scientist, discovered fungi living in the roots of healthy
Cannabis plants back in 1925. He died shortly thereafter, without reporting his
results; they were rediscovered in USDA archives (McPartland et al. 2000). The
endorhizal (root-inhabiting) microorganisms that colonize Cannabis improve plant
nutrition and disease resistance (McPartland and Cubeta 1997; Citterio et al. 2005;
Winston et al. 2014).
464 J.M. McPartland and K.J. McKernan
Researchers have turned their attention to phylloplane organisms, which live in
nooks and crannies above the leaf epidermis (epiphytes) or in spaces below the
epidermis (endophytes). Phylloplane organisms protect their plant hosts by repel-
ling pathogenic organisms. The yeast-like fungus Aureobasidium pullulans is a
ubiquitous epiphyte, and it has been isolated from Cannabis (Ondrej 1991). It oozes
chitinases and other enzymes that attack other fungi, including the dreaded gray
mold fungus, Botrytis cinerea.
Gautam et al. (2013) identied a number of Cannabis endophytic fungi. They
eliminated epiphytes from their study by surface-sterilizing plant material with
sodium hypochlorite (bleach) for 40s. They rinsed material with sterile distilled
water, and plated it on agar with antibacterial antibiotics. Fungi were identied by
their morphological and cultural characteristics. Gautam and colleagues identied
three Aspergillus species (A. niger, A. avus, A. nidulans), two Penicillium species
(P. citrinum, P. chrysogenum), and Rhizopus stolonifer. They also identied ve
other species known to be foliar pathogens of Cannabis: Curvularia lunata,
Alternaria alternata, Cladosporium sp., Colletotricum sp., Phoma sp. One plants
protective phylloplane fungus is another plants latent pathogen(McPartland et al.
Kusari et al. (2013) tested plants obtained from Bedrocan BV. Samples were
surface sterilized with ethanol and bleach, and cultured on agar with antibiotics.
Kusari and colleagues used molecular methods for species identication: DNA
extraction and PCR amplication using primers for ITS1, 5.8S, and ITS2 regions of
ribosomal DNA. Amplicons were sequenced, and the sequences were BLASTed for
matches in the EMBL nucleotide database. The predominant endophyte was
Penicillium copticola. Other species included P. meleagrinum, P. sumatrense,
Eupenicillium rubidurum, Chaetomium globosum, Paecilomyces lilacinus, and
Aspergillus versicolor. None of these fungi have previously been associated with
Cannabis except for C. globosum (McPartland et al. 2000). Kusari and colleagues
demonstrated that these endophytes antagonized in vitro growth of two common
Cannabis pathogens, Botrytis cinerea and Trichothecium roseum.
The aforementioned study by McKernan et al. (2015) highlighted the predom-
inance of Penicillium species in a majority of samples tested. They proposed that a
number of these were endophytes. They likely isolated epiphytes as well as
endophytes, because they dispensed with surface sterilization and plating, and went
straight to molecular identication. Five organisms they isolated were phy-
topathogens previously reported causing Cannabis diseases: Diplodia
spp. (McPartland 1994b), Pestalotiopsis spp. (McPartland and Cubeta 1997),
Botryosphaeria dothidea (McPartland 1994c), Fusarium oxysporum (McPartland
and Hillig 2004a), and Pseudomonas syringae (McPartland and Hillig 2004b).
These studies reveal a surprisingly depauperate Cannabis foliar microbiome.
A recent study of Genlisea species, using similar methods, identied 92 genera of
organisms (Cao et al. 2015). See Delmotte et al. (2009) for rich microbiomes in
other plant species. Many of the 97 species of fungi that Gzebenyuk (1984) isolated
from hemp stems in Russia may be phylloplane organisms.
22 Contaminants of Concern in Cannabis 465
Phylloplane research should be extended to a comparison of indoor crops and
outdoor crops. Outdoor crops may show a seasonal community succession.
Comparing the microbiome in Cannabis from different climates and continents
would be informative. Winston et al. (2014) demonstrated Cannabis
cultivar-specic differences in endorhizae (root-inhabiting bacteria). Their study
was limited to drug-type hybrids; this work should be extended to ber-type cul-
tivars and wild-type plants.
22.6 Heavy Metals and Radionucleotides
Contamination by heavy metals is a health concern because these elements accu-
mulate in the body. They are toxic, carcinogenic, and cause a variety of diseases.
Particularly dangerous elements include cadmium, mercury, lead, arsenic, and
nickel. Radionucleotides present in the environment may also contaminate plants,
and contribute to the risk of lung cancer.
Siegel et al. (1988) measured 440 ng mercury per gram of cannabis in Hawaii,
where the volcanic soil contains naturally high levels of mercury. Siegel notes that
mercury is absorbed 10 times more efciently by the lungs than by the gut. He
calculated that smoking 100 g of volcanic cannabis per week could lead to mercury
Volcanic soil also contains signicant levels of cadmium. Grant et al. (2004)
attribute this to elevated levels of cadmium in Jamaican-grown tobacco and can-
nabis. However, anthropogenic emissions, from fossil fuel combustion and
mining/smelting activities, are the primary source of cadmium.
Tainted fertilizer is another source of heavy metal contamination. Safari Singani
and Ahmadi (2012) showed that C. sativa readily takes up lead and cadmium from
soils amended with contaminated cow and poultry manures. Even reportedly
cleanfertilizer seems to increase the uptake of cadmium by C. sativa (Ahmad
et al. 2015). Phosphate ions are the main carriers of heavy metal contamination, and
hydroponic fertilizers are particularly vulnerable to contamination (Karadjov 2014).
Phosphate fertilizers targeted at Cannabis growers (bud blooms) have particular
problems with arsenic, in some cases 1050 ppm (N. Palmer, pers. commun. 2016).
Rockwool, a.k.a. mineral wool ber, used as hydroponic growth medium, may also
be contaminated.
In a study on hemp seeds, Mihoc et al. (2012) report a problem with cadmium
contamination; they measured levels of 1.34.0 mg/kg. Eboh and Thomas (2005)
showed that concentrations of arsenic, cadmium, chromium, iron, nickel, lead and
mercury were greater in leaf material than in seeds. Moir et al. (2008) measured
heavy metals in marijuana smoke, including mercury, cadmium, lead, chromium,
nichel, arsenic, and selenium. Deep inhalation, typical of marijuana smokers,
doubled the exposure to heavy metals.
Health Canada (2008) mandated upper limits for arsenic (0.14 µm/kg body
weight per day), cadmium (<0.09 µm/kg), lead (<0.29 µm/kg), and mercury
466 J.M. McPartland and K.J. McKernan
(<0.29 µm/kg). The AHP proposed maximal limits for orally consumed cannabis
products: mercury 2.0 µm/day, arsenic 10.0 µm/day, and cadmium 4.1 µm/day
(Upton et al. 2013).
22.7 Janis FaceBioremediation
Cannabis is so efcient at absorbing and storing heavy metals that it has gained
attention as a bioremediation crop.Bioremediation uses plants or microorganisms
to remove pollutants. Plants such as Thlaspi caerulescens (= T. alpestre) extract
toxins from soil and accumulate the toxins in their tissues. The plants are harvested
and the toxins removed. Cannabis is an excellent candidate for bioremediation (Shi
and Cai 2009), although the amount of metal taken up by Cannabis pales in
comparison to T. caerulescens (Giovanardi et al. 2002;Löser et al. 2002; Citterio
et al. 2003; Meers et al. 2005).
Jurkowska et al. (1990) measured high levels of lithium in hemp (1.04 mg/kg),
higher than the other crop plant tested, including barley, maize, mustard, oats,
radish, rape, sorrel, spinach, sunower, and wheat. Cannabis has been sown on
toxic waste sites contaminated with cadmium and copper in Silesia. The metals are
recovered by leaching the harvested seed with hydrochloric acid (Kozlowski 1995).
Other studies have shown that hemp accumulates heavy metals in its roots
(Giovanardi et al. 2002; Citterio et al. 2003; Shi and Cai 2009), and in leaf material
(Giovanardi et al. 2002; Arru et al. 2004). Plants with mycorrhizal fungi growing in
their roots show greater translocation of heavy metals from roots to shoots (Citterio
et al. 2005). Perhaps mycorrhizal-inoculated plants are healthier, and therefore can
better tolerate heavy metal stress.
Ciurli et al. (2002) showed potential for bioremediation using Fibranova
ber-type plants, which tolerated growth in zinc-contaminated soil. They also
showed that experiments of this type need to be done in soil, and not in a
hydroponic-based screening test. The plants tolerated zinc salts much better in soil
than in hydroponic culture.
Cannabis bioaccumulates sodium chloride, which kills itdespite the fact that
chloride is an essential nutrient, and sodium is benecial in trace amounts. Salty
breezes near the sea are sufcient to stunt hemp crops. Italian accessions are being
tested for tolerance to salt water, 2.5% NaCl (G. Grassi, pers. commun. 2016).
Cannabis can extract toxic polycyclic aromatic hydrocarbons from soil, such as
benzo[a]pyrene and chrysene (Campbell et al. 2002). Cannabis also extracts
radioactive caesium-137 and strontium-90 from contaminated soil (Vandenhove
and Van Hees 2005; Hoseini et al. 2012). Hemp crops were planted near the
Chernobyl site for the purpose of removing radionucleotides (Anonymous 2000).
Löser et al. (2002) were not impressed with the ability of C. sativa to uptake
heavy metal-polluted river sediment. Although the plants took up zinc, cadmium,
22 Contaminants of Concern in Cannabis 467
and nickel, about 95% of the plants died within a week. Apparently different
cultivars vary in their ability and tolerance in taking up cadmium from contami-
nated soils (Shi et al. 2012).
22.8 Pesticide Residues
Pesticide residues pose a uniquely unpredictable risk to consumers, because can-
nabis is usually smoked and inhaled, unlike most agricultural products. Up to
69.5% of pesticide residues remain in smoked cannabis (Sullivan et al. 2013). The
use of illegal pesticides is a rising crisis, and a breakdown in ethics. Voelker and
Holmes (2015) estimated that pesticide residues are found on close to half of the
cannabis sold in Oregon dispensaries.
Sloppy and unscrupulous Cannabis growers utilize over the counterpesticides
available in garden supply stores. Some of these are only approved for landscape
plants, not food plants. Hydroponic shops repackage pesticides for ornamental
plants, such as bifenazate and abamectin, for sale to Cannabis cultivators (McLean
2010). A dubious corporation marketed Guardian, a 100% naturalmiticide,
which contained undisclosed abamectinresulting in the recall of cannabis in
several states (Associated Press 2016).
McPartland et al. (2000) published a list of pesticides used by growers, derived
from anecdotal reports and the literature. This veritable witches brew included
abamectin, acephate, benomyl, carbaryl, carboxin, chlorpyrifos, chlorothalonil,
chlorpyrifos, diazinon, dichlorvos, dicofol, dimethoate, fenbutatin oxide, iprodione,
malathion, maneb, parathion, vinclozolin, and a slew of synthetic pyrethroids. The
Centre for Disease Control in British Columbia studied former marijuana grow
operations in residential homes. Their list of pesticide residues found in former
grows included chlorpyrifos, diazinon, and 11 synthetic pyrethroids (NCCEH
Medical cannabis products in southern California have been contaminated with
diazinon, paclobutrazol, and synthetic pyrethroids (Sullivan et al. 2013). The AHP
published a list of pesticides that are most likely to be used on Cannabis, including
12 insecticides/miticides (abamectin, acequinocyl, bifenazate, etoxazole, fenoxy-
carb, imidacloprid, spinosad, spiromesifen, spiromesin, and several synthetic
pyrethroids), four fungicides (imazalil, myclobutanil, trioxystrobin, paclobu-
traxol), and three plant growth regulators (daminozide, paclobutraxol, chlormequat
Testing of medical cannabis products in central California identied 12 pesti-
cides and growth regulators, in up to 49.3% cannabis samples (Wurzer 2016).
Myclobutanil led the list (40%), followed by bifenazate (20%), spiromesifen (15%),
imidacloprid (4.6%), and spinodad (1.3%), as well as abamectin, acequinocyl,
bifenazate, daminozide, fenoxycarb, pyrethrum, and spirotetramat.
A survey of 389 cannabis samples obtained from Oregon dispensatories found
residues of 24 pesticides and growth regulators: abamectin, azadirachtin, bifenazate,
468 J.M. McPartland and K.J. McKernan
bifenthrin, carbaryl, chlorfenapyr, chlordane, chlorpyrifos, coumaphos, cyperme-
thrin, diazinon, dichlorvos, ethoprophos, imidacloprid, malathion, metalaxyl,
mevinphos, myclobutanil, paclobutrazol, permethrin, piperonyl butoxide, propoxur,
and 4-4-DDE (Voelker and Holmes 2015). Two percent of the samples contained
>100,000 ppm pesticides. Piperonyl butoxide was the most commonly seen con-
taminant, with up to 407,000 ppm in one sample. This is a synthetic compound
linked with human disease.
Russo (2016) purchased 26 cannabis samples (24 concentrates, 2 cannabis
inorescences) from legal stores in Washington State, and passed the samples via a
witnessed chain to a state certied legal licensed laboratory. Pesticides residues
were detected in 22 samples (84.6%), including 24 distinct agents of every class:
insecticides (organophosphates, organochlorides, carbamates, neonicotinoids),
miticides, fungicides, an insecticidal synergist, and growth regulators. One sample
was contaminated with nine agents, include the fungicide boscalid (112,033 ppb)
and the extremely toxic insecticide carbaryl (25,483 ppb). Samples obtained from
indoor grows had a higher risk of contamination than samples obtained from out-
door grows.
Fertilizers may also contaminate Cannabis. Spraying plants with liquid fertil-
izers may result in the formation of N-nitrosamines, which are potent carcinogens
(Farnsworth and Cordell 1976). Ramírez (1990) reported four policemen con-
tracting pulmonary histoplasmosis while pulling up marijuana plants. The plants
were likely fertilized with bird guano contaminated with the fungus Histoplasma
capsulatum. The use of human dung has been associated with outbreaks of hepatitis
viral infections (Cates and Warren 1975; Alexander 1987).
The EPA claims its failure to act in the interests of the American public is simply
because it has yet to receive any applications for pesticide use on marijuana and,
therefore, we have not evaluated the safety of any pesticide on marijuana(EPA
2016). In the absence of federal regulations, individual stakeholders and states have
formulated guidelines.
In the spirit of harm reduction, the Maine legislature allowed the application of
25(b) pesticides on Cannabis (State of Maine 2013). These are minimal-risk pes-
ticides exempted by the EPAmostly botanicals (e.g., rosemary oil, thyme oil,
garlic oil, corn gluten meal, eugenol), and other substances such as 2-phenylethyl
propionate and potassium sorbate (EPA 2015). The Colorado Department of
Agriculture and the Washington Department of Agriculture released larger lists of
allowable pesticides (CDA 2016, WSDA 2016). Most of these pesticides are per-
mitted in The National List of materials designated by the Organic Foods
Production Act of 1990. They include botanical poisons (e.g., neem oil, garlic oil,
azadirachtin, pyrethrins), minerals (e.g., potassium salts, copper, sulfur), and bio-
logical control organisms (e.g., Bacillus thuringiensis, Streptomyces griseoviridis).
Both states allowed piperonyl butoxide. All these materials are described at
book-length elsewhere (McPartland et al. 2000).
Assaying for pesticide residues is more difcult than microbial testing. Each
pesticide must be tested individually, and the secretive use of pesticides leaves
regulators in the dark (Stone 2014). The Oregon Health Authority posted a list of 59
22 Contaminants of Concern in Cannabis 469
pesticides required for testing before cannabis can be release for sale (Farrer 2015).
Voelker and Holmes (2015) suggested testing for 123 pesticides, with tolerance
limits of 100 ppb. Feldman (2015) documented pesticide regulations in other states.
Detecting pesticides requires expensive analytical methods, such as GS-MS and
HPLC (Upton et al. 2013). Adequate pesticide testing costs around $400; labora-
tories charging only $100 are substandard (T. Flaster, pers. commun., 2016). To
wit, few independent laboratories have been accredited for pesticide testing in
cannabiszero in Colorado (N. Palmer, pers. commun., 2016).
There have been several high-prole cases of cannabis removed from sale due to
pesticides. In 2011 California issued a cease-and-desist order against the sale of
cannabis contaminated with daminoside and paclobutrazol (Upton et al. 2013). In
2012, a whistleblower at Maines largest medical cannabis dispensary revealed that
nine types of insecticides and fungicides were being applied to Cannabis; the
dispensary was ned $18,000 (Shepard 2013). Colorado regulators quarantined
thousands of plants grown by a dispensary chain that used myclobutanil, a turfgrass
fungicide; consumers led a lawsuit against the corporation (Wyatt 2015). This was
only one of nine marijuana recalls in Denver that year (Baca and Migoya 2015).
Mikuriya et al. (2005) reported the rst case of hospitalization due to concealed
pesticide use. The case report involved a bud trimmer working with cannabis con-
taminated with avermectin (abamectin), which a grower used against spider mites.
Acknowledgements Gianpaolo Grassi and Noel Palmer are thanked for helpful discussions
regarding this manuscript.
Ahmad A, Hadi F, Ali N (2015) Effective phytoextraction of cadmium (Cd) with increasing
concentration of total phenolics and free proline in Cannabis sativa (L.) plant under various
treatments of fertilizers, plant growth regulators and sodium salt. Int J Phytorem 17(16):5665
Alexander T (1987) Hepatitis outbreak linked to imported pot. Sinsemilla Tips 7:22
Anonymous (2000) Phytoremediation: using plants to clean soil. McGraw Hill Botany. Available
Arru L, Rognoni S, Baroncini M, Bonatti PM, Perata P (2004) Copper localization in Cannabis
sativa L. grown in a copper-rich solution. Euphytica 140:3338
Associated Press (2016) Oregon, other states stop sales of pot pesticide due to labeling problem.
USA Today, February 9, 2016
Baca R, Migoya D (2015) Denver issues ninth pot product recall in 10 weeks. The Denver Post,
November 18, 2015
Bell J (1857) On the haschisch or cannabis indica. Boston Med Surg J 56(209216):229236
Bush Doctor (1993) Stash alert: how to preserve pot potency. High Times 213:7579
Busse FP, Fiedler GP, Leichtle A, Hentschel H, Stumvoll M (2008) Lead poisoning due to
adulterated marijuana in Leipzig. Deutsches Ärzteblatt International 105:757762
Caligiani A, Palla G, Bernardelli B (2006) GC-MS analysis of hashish samples: a case of
adulteration with colophony. J Forensic Sci 51:10961100
Cao HX, Schmutzer T, Scholz U, Pecinka A, Schubert I, Vu GT (2015) Metatranscriptome
analysis reveals host-microbiome interactions in traps of carnivorous Genlisea species. Front
Microbiol 6:526
470 J.M. McPartland and K.J. McKernan
Cates WC, Warren JW (1975) Hepatitis B in Nuremberg, Germany. Epidemiology of a
drug-associated epidemic among US Army soldiers. JAMA 234:930934
Cescon DW, Page AV, Richardson S, Moore MJ, Boerner S, Gold WL (2008) Invasive pulmonary
aspergillosis associated with marijuana use in a man with colorectal cancer. J Clin Oncol 26
Campbell S, Paquin D, Awaya JD, Li QX (2002) Remediation of benzo[a]pyrene and
chrysene-contaminated soil with industrial hemp (Cannabis sativa). Int J Phytorem 4:157158
CDA (2016) Pesticide use in Cannabis production information. Colorado Department of
Agriculture. Available at:
Citterio S, Santagostino A, Fumagalli P, Prato N, Ranalli P, Sgorbati G (2003) Heavy metal
tolerance and accumulation of Cd, Cr and Ni by Cannabis sativa L. Plant Soil 256:243252
Citterio S, Prato N, Fumagalli P, Aina R, Massa N, Santagostino A, Sgorbati G, Berta G (2005)
The arbuscular mycorrhizal fungus Glomus mosseae induces growth and metal accumulation
changes in Cannabis sativa L. Chemosphere 59:2129
Ciurli A, Alpi A, Perata P (2002) Impiego della canapa nella todepurazione da metalli pesanti.
Agroindustria 1(1):6460
Colorado, state of (2015) Retail marijuana code. Available at:
Chusid MJ, Gelfand JA, Nutter C, Fauci AS (1975) Pulmonary aspergillosis, inhalation of
contaminated marijuana smoke, chronic granulomatous disease. Ann Intern Med 82:682683
DeAngelo S (2010) First look: analytical window into Californias medical cannabis supply. In:
Conference proceedings, medical Cannabis therapeutics Conference, Warwick, RI
Delmotte N, Knief C, Chaffron S, Innerebner G, Roschitzki B, Schlapbach R, von Mering C,
Vorholt JA (2009) Community proteogenomics reveals insights into the physiology of
phyllosphere bacteria. PNAS 106:1642816433
Dragendorff G, Marquis P (1878) Note on the active principle of cannabis indica. Year-book
Pharm 1878:248
Eboh LO, Thomas BE (2005) Analysis of heavy metal content in Cannabis leaf and seed
cultivated in southern part of Nigeria. Pak J Nutr 4:349351
EPA (2015) Active ingredients eligible for minimum risk pesticide products. United States
Environmental Protection Agency. Available at:
EPA (2016) Pesticide use on marijuana. United States Environmental Protection Agency.
Available at:
Farnsworth NR, Cordell GA (1976) New potential hazard regarding use of marijuanatreatment
of plants with liquid fertilizers. J Psychedelic Drugs 8:151155
Farrer DG (2015) Technical report: Oregon health authoritys process to determine which types of
contaminants to test for in cannabis products. Oregon Health Authority. Available at: https://
Feldman J (2015) Pesticide use in marijuana production: safety issues and sustainable options.
Pesticides You 34(4):1423
Gautam AK, Kant M, Thakur Y (2013) Isolation of endophytic fungi from Cannabis sativa and
study their antifungal potential. Arch Phytopathol Plant Prot 46:627635
Giovanardi R, Marchiol L, Mazzocco GT, Zuliani F (2002) Possibilitàdi impiego della canapa
nella toestrazione di metalli pesanti in terreni contaminati: primi risultati. Agroindustria 1
Grant CN, Lalor GC, Vutchkov MK (2004) Trace elements in Jamaican tobacco. West Indian
Med J 53(2):6670
Gzebenyuk NV (1984) The occurrence of fungi on hemp stems. Mikologiya i Fitopathologiya 18
Hazekamp A (2006) An evaluation of the quality of medicinal grade cannabis in the Netherlands.
Cannabinoids 1(1):19
22 Contaminants of Concern in Cannabis 471
Hazekamp A (2016) Evaluating the effects of gamma-irradiation for decontamination of medicinal
cannabis. Frontiers Pharmacology 7:108
Health Canada (2008) Product information sheet on dried marihuana (cannabis).
Holmes M, Vyas JM, Steinbach W, McPartland J (2015) Microbiological safety testing of cannabis.
Available at:
Hoseini PS, Poursafa P, Moattar F, Amin MM, Rezaei AH (2012) Ability of phytoremediation for
absorption of strontium and cesium from soils using Cannabis sativa. Int J Environ Health Eng
Indian Hemp Drugs Commission (1894) Report of the Indian Hemp Drugs Commission, 189394.
Government Central Printing Ofce, Simla
Jurgensen CW, Madsen A (2009) Exposure to the airborne mould Botrytis and its health effects.
Ann Agric Environ Med 16:183186
Jurkowska H, Rogóz A, Wojciechowicz T (1990) The content of lithium in some species of plants
following differentiated doses of nitrogen. Pol J Soil Sci 23:195199
Kagen SL, Kurup VP, Sohnle PG, Fink JN (1983) Marijuana smoking and fungal sensitization.
J Allergy Clin Immunol 71:3893893
Karadjov J (2014) Eliminating heavy-metal toxicity in medical marijuana. Available at: www.
Kozlowski R (1995) Interview with Professor R. Kozlowski, director of the Institute of Natural
Fibres. J Int Hemp Assoc 2(2):8687
Kurup VP, Resnick A, Kagen SL, Cohen SH, Fink JN (1983) Allergenic fungi and actinomycetes
in smoking materials and their health implications. Mycopathologia 82:6164
Kusari P, Kusari S, Spiteller M, Kayser O (2013) Endophytic fungi harbored in Cannabis sativa
L.: diversity and potential as biocontrol agents against host plant-specic phytopathogens.
Fungal Biodiversity 60:137151
Levitz SM, Diamond RD (1991) Aspergillosis and marijuana. Ann Intern Med 115:578579
Llamas R, Hart DR, Schneider NS (1978) Allergic bronchopulmonary aspergillosis associated
with smoking moldy marihuana. Chest 73:871872
Llewellyn GC, ORear CO (1977) Examination of fungal growth and aatoxin production on
marijuana. Mycopathologia 62:109112
Löser C, Zehnsdorf A, Fussy M, Stärk HJ (2002) Conditioning of heavy metal-polluted river
sediment by Cannabis sativa L. Int J Phytorem 4:2745
Lucas PG (2008) Regulating compassion: an overview of Canadas federal medical cannabis
policy and practice. Harm Reduction J 5:5
Martyny JW, Serrano KA, Schaeffer JW, Van Dyke MV (2013) Potential exposures associated
with indoor marijuana growing operations. J Occup Environ Hyg 10:622639
McKernan K, Spangler J, Zhang L, Tadogotla V, Helbert Y, Foss T, Smith D (2015) Cannabis
microbiome sequencing reveals several mycotoxic fungi native to dispensary grade cannabis
owers. BioRxiv Preprint, available at:
Mclean K (2010) Pot and pesticides: a bustling illegal trade. The Bay Citizen, May 26, 2010
McPartland JM (1984) Pathogenicity of Phomopsis ganjae on Cannabis sativa and the fungistatic
effect of cannabinoids produced by the host. Mycopathologia 87:149153
McPartland JM (1989) Storage molds associated with post-harvest Cannabis decay. Cover
Illustration. Mycol Soc Am Newsl 40(1):1
McPartland JM (1992) The Cannabis pathogen project: report of the second ve-year plan. Mycol
Soc Am Newsl 43(1):43
McPartland JM (1994a) Microbiological contaminants of marijuana. J Int Hemp Assoc 1:4144
McPartland JM (1994b) Cannabis pathogens X: Phoma, Ascochyta and Didymella species.
Mycologia 86:870878
472 J.M. McPartland and K.J. McKernan
McPartland JM (1994c) Cannabis pathogens IX: anamorphs of Botryosphaeria species.
Mycotaxon 53:417424
McPartland JM (2002) Contaminants and adulterants in herbal Cannabis. In: Grotenhermen F,
Russo E (eds) Cannabis and Cannabinoidspharmacology, toxicology and therapeutic
potential. Haworth, New York, pp 337343
McPartland JM (2003) Byssinosis in hemp mill workers. J Int Hemp Assoc 8(1):3344
McPartland JM, Cubeta MA (1997) New species, combinations, host associations and location
records of fungi associated with hemp (Cannabis sativa). Mycol Res 101:853857
McPartland JM, Hillig KW (2004a) Fusarium wilt. J Int Hemp Assoc 9(2):6777
McPartland JM, Hillig KW (2004b) Striatura ulcerosa. J Int Hemp Assoc 9(1):8996
McPartland JM, Pruitt P (1997) Medical marijuana and its use by the immunocompromised. Altern
Ther Health Med 3(3):3945
McPartland JM, West D (1999) Killing Cannabis with mycoherbicides. J Int Hemp Assoc 6(1):1,
McPartland JM, Clarke RC, Watson DP (2000) Hemp diseases and pestsmanagement and
biological control. CABI Publishing, Wallingford, UK
McPartland JM, Blanchon D, Musty RE (2008) Cannabimimetic effects modulated by cholinergic
compounds. Addict Biol 13:411415
Meers E, Ruttens A, Hopgood M, Lesage E, Tack FM (2005) Potential of Brassic rapa, Cannabis
sativa, Helianthus annuus and Zea mays for phytoextraction of heavy metals from calcareous
dredged sediment derived soils. Chemosphere 61:561572
Mihoc M, Pop G, Alexa E, Radulov I (2012) Nutritive quality of Romanian hemp varieties
(Cannabis sativa L.) with special focus on oil and metal content of seeds. Chem Cent J 6:122
Mikuriya TH, North W, Lucido F, Jaffee R, Weirick J (2005) Cerebrospinal delayed allergic
reaction to pesticide residue. In: Conference proceedings, international association for
Cannabis as medicine. p 14
Moir D, Rickert WS, Levasseur G, Larose Y, Maertens R, White P, Desjardins S (2008) A
comparison of nainstream and sidestream marijuana and tobacco cigarette smoke produced
under two machine smoking conditions. Chem Res Toxicol 21(2):494502
Moody M, Wharton RC, Schnaper N, Schimpff SC (1982) Do water pipes prevent transmission of
fungi from contaminated marijuana? N Engl J Med 306:14921493
NCCEH (2009) Recommendations for safe re-occupancy of marijuana grow operations. National
Collaborating Centre for Environmental Health. Available at:
NJMMP (2011) Medicinal marijuana program rules. New Jersey Medicinal Marijuana Program.
Available at:
Ondrej M (1991) Vyskyt hub na stonínch konopi. Len a Konopí21:5157
Perry DC (1977) Street drug analysis and drug use trends 1969-1975. Part II. PharmChem
Newsletter 6(4):13
Ramírez J (1990) Acute pulmonary histoplasmosis: new recognized hazard of marijuana plant
hunters. Am J Med 88(5, Suppl.): 60 N-62 N
Ross SA, ElSohly MA (1996) The volatile oil composition of fresh and air-dried buds of Cannabis
sativa. J Nat Prod 59:4951
Ruchlemer R, Amit-Kohn M, Raveh D, HanušL (2015) Inhaled medicinal cannabis and the
immunocompromised patient. Support Care Cancer 23(3):819822
Russo E (2016) Pesticide contamination of cannabis in the legal market. In: Proceedings of the
26th Annual Symposium on the Cannabinoids. International Cannabinoid Research Society,
Research Triangle Park, NC, p 66
Safari Singani AA, Ahmadi P (2012) Manure application and Cannabis cultivation inuence on
speciation of lead and cadmium by selective sequential extraction. Soil Sed Contam 21:305321
Samson RA, Hoekstra ES, Frisvad JC (eds) (2004) Introduction to food- and airborne fungi.
Centraalbureau voor Schimmelcultures, Utrecht
Scheel AH, Kraus D, Haars H, Schmitz I, Junker K (2012) Talcum induced pneumoconiosis
following inhalation of adulterated marijuana. Diagnostic Pathology 7:26
22 Contaminants of Concern in Cannabis 473
Schwartz IS (1985) Marijuana and fungal infection. Am J Clin Pathol 84:256
Shepard M (2013) Maine marijuana company ned $18 K for pesticides. Portland Press Herald,
September 6, 2013
Shi G, Cai Q (2009) Cadmium tolerance and accumulation in eight potential energy crops.
Biotechnol Adv 27:555561
Shi G, Liu C, Cui M, Ma Y, Cai Q (2012) Cadmium tolerance and bioaccumulation of 18 hemp
accessions. Appl Biochem Biotechnol 168(1):163173
Shirazi-Zand Z, Ahmad-Molaei L, Motamedi F, Naderi N (2013) The role of potassium BK
channels in anticonvulsant effect of cannabidiol in pentylenetetrazole and maximal
electroshock models of seizure in mice. Epilepsy Behav 28(1):17
Siegel BZ, Garnier L, Siegel SM (1988) Mercury in marijuana. Bioscience 38:619623
State of Maine (2013) An Act to maintain access to safe medical marijuana. Available at: www.
Stone D (2014) Cannabis, pesticides and conicting laws: The dilemma for legalized States and
implications for public health. Regul Toxicol Pharmacol 69:284288
Sullivan N, Elzinga S, Raber JC (2013) Determination of pesticide residues in cannabis smoke.
J Toxicol Online Article ID 378168
Szyper-Kravitz M, Lang R, Manor Y, Lahav M (2001) Early invasive pulmonary aspergillosis in a
leukemia patient linked to aspergillus contaminated marijuana smoking. Leukemia &
Lymphoma 42:14331437
Taylor DN, Wachsmuth IK, Shangkuan YH, Schmidt EV, Barrett TJ, Schrader JS, Scherach CS,
McGee HB, Feldman RA, Brenner DJ (1982) Salmonellosis associated with marijuana: a
multistate outbreak traced by plasmid ngerprinting. N Engl J Med 306:12491253
Turner TR, James EK, Poole PS (2013) The plant microbiome. Genome Biol 14:209
Ungerleider JT, Andrysiak T, Tashkin DP, Gale RP (1982) Contamination of marijuana cigarettes
with pathogenic bacteria. Cancer Treat Rep 66(3):589590
Upton R, Craker L, ElSohly M, Romm A, Russo E, Sexton M eds (2013) Cannabis inorescence,
Cannabis spp. Standards of identity, analysis, and quality control. American Herbal
Pharmacopoeia, Scotts Valley, CA
Vandenhove H, Van Hees M (2005) Fibre crops as alternative land use for radioactively
contaminated arable land. J Environ Radioact 81:131141
Venhuis BJ, de Kaste D (2008) Sildenal analogs used for adulterating marihuana. Forensic Sci Int
Verweij PE, Kerremans JJ, Voss A, Meis JF (2000) Fungal contamination of tobacco and
marijuana. JAMA 284:2875
Voelker R, Holmes M (2015) Pesticide use on Cannabis. Cannabis Safety Institute. Available at:
Wilson D, Steinegger P, Parkin DP (1989) Effects of cannabis smoked together with a substance
sold as Mandrax. S Afr Med J 76(11):636
Winston ME, Hampton-Marcell J, Zarraonaindia I, Owens SM, Moreau CS, Gilbert JA,
Hartsel JA, Kennedy SJ, Gibbons SM (2014) Understanding cultivar-specicity and soil
determinants of the cannabis microbiome. PLoS ONE 9(6):e99641
WSDA (2016) Pesticide and fertilizer use on marijuana. Washington State Department of
Agriculture. Available at:
Wurzer J (2016) Safety testing of medicinal cannabis. In: Proceedings of the 2006 Cannmed
Conference. Medical Genomics, Woburn, MA
Wyatt K (2015) Marijuana subject to product liability claim in Colorado. US News & World
Report, October 5, 2015
474 J.M. McPartland and K.J. McKernan
... Today there is an emerging interest in Cannabis, concerns have arisen about the possible contaminations of hemp with pesticides, heavy metals, microbial pathogens, and carcinogenic compounds during the cultivation, manufacturing, and packaging processes (89)(90)(91)(92)(93)(94)(95)(96)(97). This is of particular concern for those turning to Cannabis for medicinal purposes, especially those with compromised immune systems (89)(90)(91)(92)(93)(94)(95)(96)(97). ...
... Today there is an emerging interest in Cannabis, concerns have arisen about the possible contaminations of hemp with pesticides, heavy metals, microbial pathogens, and carcinogenic compounds during the cultivation, manufacturing, and packaging processes (89)(90)(91)(92)(93)(94)(95)(96)(97). This is of particular concern for those turning to Cannabis for medicinal purposes, especially those with compromised immune systems (89)(90)(91)(92)(93)(94)(95)(96)(97). It has been reported that Cannabis derived products are often contaminated by microbes, heavy metals, pesticides, carcinogens, and debris, which must be addressed to ensure the safety of consumers (89)(90)(91)(92)(93)(94)(95)(96)(97). ...
... This is of particular concern for those turning to Cannabis for medicinal purposes, especially those with compromised immune systems (89)(90)(91)(92)(93)(94)(95)(96)(97). It has been reported that Cannabis derived products are often contaminated by microbes, heavy metals, pesticides, carcinogens, and debris, which must be addressed to ensure the safety of consumers (89)(90)(91)(92)(93)(94)(95)(96)(97). The large economic potential and illicit aspect of Cannabis has given rise to numerous potentially hazardous natural contaminants or artificial adulterants being reported in crude cannabis and cannabis preparations (89)(90)(91)(92)(93)(94)(95)(96)(97). ...
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This review paper highlights about Medical Cannabis sativa (Marijuana or drug type) containing psychoactive molecule, Δ9-Tetrahydrocannabinol (Δ9-THC) as a part of educational awareness programme in India. Cannabis sativa and Cannabis indica were originally a native of India growing as a wild notorious noxious weed in the Indian Himalayan region. Marijuana (Charas, Ganja and Bhang in India) is a mind-altering (psychoactive) drug, produced by the Cannabis sativa plant. Marijuana (Charas, Ganja or Bhang drink in India) is an illicit drug containing very high levels (25-35%
... It has been reported that Cannabis derived products are often contaminated by microbes, heavy metals, pesticides, carcinogens, and debris, which must be addressed to ensure the safety of consumers (11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25). These contaminants are imminent threats that directly impact public health and wellness, particularly to the immunocompromised and pediatric patients who take Cannabis products as a treatment for numerous human disorders including cancer patients and those suffering from epileptic seizures (10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25). ...
... It has been reported that Cannabis derived products are often contaminated by microbes, heavy metals, pesticides, carcinogens, and debris, which must be addressed to ensure the safety of consumers (11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25). These contaminants are imminent threats that directly impact public health and wellness, particularly to the immunocompromised and pediatric patients who take Cannabis products as a treatment for numerous human disorders including cancer patients and those suffering from epileptic seizures (10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25). Therefore, there is an urgent Wake up Call to remind hemp ...
... The major issue is inaccuracy in labeling phytocannabinoid content . Mislabeling of phytocannabinoid profiles in Cannabidiol (CBD) products is one of the major concerns producers, manufacturers, medical professionals, and legislators to recognize this risk and establish regulatory measures to educate the public and reduce the adverse effects caused by the contaminants in Cannabis, particularly in Cannabidiol (CBD)-based products (10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25). to consumers has been reviewed and updated by Montoya et al., 2020 andDryburgh et al., 2018 (16, 17, 25, 26, 27, 37). ...
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This review paper highlights the recent concerns about the possible contaminations of Cannabis products with pesticides, fungicides, insecticides, heavy metals, microbial pathogens, and carcinogenic compounds during the cultivation, manufacturing, and packaging processes which must be addressed to ensure the safety of consumers. These contaminants are usually introduced during Cannabis cultivation and storage of Cannabis products. Growth enhancers and pest control chemicals are the most common risks to both the producer and the consumer. These contaminants are imminent threats that directly impact public health and wellness, particularly to the immunocompromised and pediatric patients who take Cannabis products as a treatment for numerous human disorders including cancer patients and those suffering from epileptic seizures. For the safety and welfare of all Cannabis users, both medicinal and recreational, there is a necessity for a standardized set of guidelines for cultivation and testing of Cannabis products. This will help to improve the quality based Cannabis products in the market and safe zone for the consumers.
... Mercury is another hazardous heavy metal that has been found in approximately 440 ng/g of dry mass of cannabis cultivated in volcanic regions in Hawaii [41]. Cannabis products increase the chance of heavy metal toxicity, as mercury can be absorbed 10 times more readily by the lungs when compared to the gut [42]. ...
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Purpose of Review There is increasing interest in the use of cannabis and cannabinoid therapies (CCT) by the general population and among people with headache disorders, which results in a need for healthcare professionals to be well versed with the efficacy and safety data. In this manuscript, we review cannabis and cannabinoid terminology, the endocannabinoid system and its role in the central nervous system (CNS), the data on efficacy, safety, tolerability, and potential pitfalls associated with use in people with migraine and headache disorders. We also propose possible mechanisms of action in headache disorders and debunk commonly held myths about its use. Recent Findings Preliminary studies show that CCT have evidence for the management of migraine. While this evidence exists, further randomized, controlled studies are needed to better support its clinical use. CCT can be considered an integrative treatment added to mainstream medicine for people with migraine who are refractory to treatment and/or exhibit disability and/or interest in trying these therapies. Further studies are warranted to specify appropriate formulation, dosage, and indication(s). Summary Although not included in guidelines or the AHS 2021 Consensus Statement on migraine therapies, with the legalization of CCT for medical or unrestricted use across the USA, recent systematic reviews highlighting the preliminary evidence for its use in migraine, it is vital for clinicians to be well versed in the efficacy, safety, and clinical considerations for their use. This review provides information which can help people with migraine and clinicians who care for them make mutual, well-informed decisions on the use of cannabis and cannabinoid therapies for migraine based on the existing data.
... By creating a microclimate that is beneficial for pollinators, Cannabis contributes to the conservation of biodiversity, which is essential to the health of the planet (Flicker et al., 2020). Another potential application of Cannabis is a bioremediation crop that can absorb and store heavy metals from the soil, making it effective in cleaning contaminated soil (McPartland and McKernan, 2017). Tainted soil fertilizer is a common source of arsenic, cadmium, lead, and mercury. ...
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Cannabis sativa , also known as “hemp” or “weed,” is a versatile plant with various uses in medicine, agriculture, food, and cosmetics. This review attempts to evaluate the available literature on the ecology, chemical composition, phytochemistry, pharmacology, traditional uses, industrial uses, and toxicology of Cannabis sativa . So far, 566 chemical compounds have been isolated from Cannabis , including 125 cannabinoids and 198 non-cannabinoids. The psychoactive and physiologically active part of the plant is a cannabinoid, mostly found in the flowers, but also present in smaller amounts in the leaves, stems, and seeds. Of all phytochemicals, terpenes form the largest composition in the plant. Pharmacological evidence reveals that the plants contain cannabinoids which exhibit potential as antioxidants, antibacterial agents, anticancer agents, and anti-inflammatory agents. Furthermore, the compounds in the plants have reported applications in the food and cosmetic industries. Significantly, Cannabis cultivation has a minimal negative impact on the environment in terms of cultivation. Most of the studies focused on the chemical make-up, phytochemistry, and pharmacological effects, but not much is known about the toxic effects. Overall, the Cannabis plant has enormous potential for biological and industrial uses, as well as traditional and other medicinal uses. However, further research is necessary to fully understand and explore the uses and beneficial properties of Cannabis sativa .
... A comprehensive safety analysis encompasses all aspects of cultivation, production, and final medical / medicinal products. To ensure product safety and consistency, cultivators rely on various testing methods, including potency testing to measure the concentration of cannabinoids like THC and CBD [15], [16], pesticide testing to detect harmful residues resulting from the cultivation process [17], microbial testing to evaluate cannabis samples for harmful bacteria / mould, residual solvent testing to ensure safe levels of concentrates, and heavy metal testing to detect contaminants absorbed from the growing environment [18]. However, little research has been conducted on the safety considerations around exposure to inhalable organic particles and other bioaerosols produced during the commercial cultivation and manufacture of cannabis-based products, highlighting the need for further review in this space [19]. ...
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The limited availability of peer-reviewed scientific evidence in the cannabis industry has led many companies to rely on techniques derived from non-peer-reviewed sources for their practices. This study begins by examining the literature on the cultivation of C. sativa , investigating optimal conditions and their effects on growth, and characterising the requirements for greenhouse monitoring and control. A systematic review of current technological approaches is then conducted. The review demonstrates that technology-based control of greenhouse environments has the potential to surpass manual or traditional rule-based management techniques by reducing costs and increasing yields. However, the adoption of these technologies is impeded by the lack of publicly available labelled data on growth, pest and disease, environmental, and yield data of multiple indoor cultivation cycles. Currently, much of the research in this field is conducted privately by companies in the cannabis industry. This study recognises substantial gaps in research surrounding C. sativa cultivation and emphasises the opportunity for new research to address the absence of available C. sativa datasets and peer-reviewed scientific studies outside of private endeavours.
... Although direct use of pesticides on hemp products is regulated, occasionally the plants are indirectly exposed to banned pesticides. Cannabis is a hyperaccumulator; therefore, trace contamination of biomass is an issue when grown next to other crops (McPartland and McKernan 2017;Wu et al. 2021). For example, hemp grown in proximity to other commodity crops can be contaminated by pesticides from those adjacent fields (López-Ruiz et al. 2022). ...
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Background Cannabis sativa L. also known as industrial hemp, is primarily cultivated as source material for cannabinoids cannabidiol (CBD) and ∆9-tetrahydrocannabinol (∆9-THC). Pesticide contamination during plant growth is a common issue in the cannabis industry which can render plant biomass and products made from contaminated material unusable. Remediation strategies to ensure safety compliance are vital to the industry, and special consideration should be given to methods that are non-destructive to concomitant cannabinoids. Preparative liquid chromatography (PLC) is an attractive strategy for remediating pesticide contaminants while also facilitating targeted isolation cannabinoids in cannabis biomass. Methods The present study evaluated the benchtop-scale suitability of pesticide remediation by liquid chromatographic eluent fractionation, by comparing retention times of 11 pesticides relative to 26 cannabinoids. The ten pesticides evaluated for retention times are clothianidin, imidacloprid, piperonyl butoxide, pyrethrins (I/II mixture), diuron, permethrin, boscalid, carbaryl, spinosyn A, and myclobutanil. Analytes were separated prior to quantification on an Agilent Infinity II 1260 high performance liquid chromatography with diode array detection (HPLC-DAD). The detection wavelengths used were 208, 220, 230, and 240 nm. Primary studies were performed using an Agilent InfinityLab Poroshell 120 EC-C18 3.0 × 50 mm column with 2.7 μm particle diameter, using a binary gradient. Preliminary studies on Phenomenex Luna 10 μm C18 PREP stationary phase were performed using a 150 × 4.6 mm column. Results The retention times of standards and cannabis matrices were evaluated. The matrices used were raw cannabis flower, ethanol crude extract, CO 2 crude extract, distillate, distillation mother liquors, and distillation bottoms. The pesticides clothianidin, imidacloprid, carbaryl, diuron, spinosyn A, and myclobutanil eluted in the first 3.6 min, and all cannabinoids (except for 7-OH-CBD) eluted in the final 12.6 min of the 19-minute gradient for all matrices evaluated. The elution times of 7-OH-CBD and boscalid were 3.44 and 3.55 min, respectively. Discussion 7-OH-CBD is a metabolite of CBD and was not observed in the cannabis matrices evaluated. Thus, the present method is suitable for separating 7/11 pesticides and 25/26 cannabinoids tested in the six cannabis matrices tested. 7-OH-CBD, pyrethrins I and II (RT A : 6.8 min, RT B : 10.5 min), permethrin (RT A : 11.9 min, RT B : 12.2 min), and piperonyl butoxide (RT A : 8.3 min, RT B : 11.7 min), will require additional fractionation or purification steps. Conclusions The benchtop method was demonstrated have congruent elution profiles using preparative-scale stationary phase. The resolution of pesticides from cannabinoids in this method indicates that eluent fractionation is a highly attractive industrial solution for pesticide remediation of contaminated cannabis materials and targeted isolation of cannabinoids.
... It has been reported that if hemp moisture is higher than 15%, fungal contamination is likely to form. [15] This can cause off-odor, spoilage, and significant illness to the consumers. In addition, during the slow ambient drying process, pathogenic microorganisms may continue to grow on the biomass, which may produce other toxins that post additional safety risk along the supply chain to the end products. ...
Postharvest blanching and drying of industrial hemp (Cannabis sativa L.) by infrared (IR) and hot air (HA) heating was studied. Experiments were conducted at different IR heating times (1 and 2 min) and HA temperatures (65 and 85 C) and compared with conventional indoor drying. Drying time was decreased from 3366 min (conventional) to as low as 222 min (85 C HA). IR and HA processing reduced the total aerobic bacteria, and total yeast/mold levels by up to 0.81 and 1.85 log CFU/g, respectively from their initial levels of 4.63 and 4.75 log CFU/g, meanwhile reduced the activities of polyphenol oxidase and peroxidase by up to 91.7% and 66.7%, respectively. More than 96.1% total cannabidiol was preserved by thermal processing. Total terpene retention ranged from 18.3% to 71.1% under tested conditions with distinct terpene profiles. The results provide important information on the microbial safety and a timely solution to improve the postharvest processes of hemp. ARTICLE HISTORY
... Pesticides applied directly to plants or dispersed from nearby fields may exhibit neurotoxicity, as can metals absorbed into plant tissues from soils and fertilizers. [5][6][7][8] Bacterial and fungal pathogens that can grow on flowers before and after harvest may pose a risk of serious infection to immunocompromised users. 9 Residues of solvents used to concentrate or extract desired compounds may have other ill effects. ...
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Background: Over the past decade, there has been increased utilization of medical cannabis (MC) in the United States. Few studies have described sociodemographic and clinical factors associated with MC use after certification and more specifically, factors associated with use of MC products with different cannabinoid profiles. Methods: We conducted a longitudinal cohort study of adults (N=225) with chronic or severe pain on opioids who were newly certified for MC in New York State and enrolled in the study between November 2018 and January 2022. We collected data over participants' first 3 months in the study, from web-based assessment of MC use every 2 weeks (unit of analysis). We used generalized estimating equation models to examine associations of sociodemographic and clinical factors with (1) MC use (vs. no MC use) and (2) use of MC products with different cannabinoid profiles. Results: On average, 29% of the participants used predominantly high delta-9-tetrahydrocannabinol (THC) MC products within the first 3 months of follow-up, 30% used other MC products, and 41% did not use MC products. Non-Hispanic White race, pain at multiple sites, and past 30-day sedative use were associated with a higher likelihood of MC use (vs. no MC use). Current tobacco use, unregulated cannabis use, and enrollment in the study during the COVID-19 pandemic were associated with a lower likelihood of MC use (vs. no MC use). Among participants reporting MC use, female gender and older age were associated with a lower likelihood of using predominantly high-THC MC products (vs. other MC products). Conclusion: White individuals were more likely to use MC after certification, which may be owing to access and cost issues. The findings that sedative use was associated with greater MC use, but tobacco and unregulated cannabis were associated with less MC use, may imply synergism and substitution that warrant further research. From the policy perspective, additional measures are needed to ensure equitable availability of and access to MC. Health practitioners should check patients' history and current use of sedative, tobacco, and unregulated cannabis before providing an MC recommendation and counsel patients on safe cannabis use. (NCT03268551).
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The Center for Disease Control estimates 128,000 people in the U.S. are hospitalized annually due to food borne illnesses. This has created a demand for food safety testing targeting the detection of pathogenic mold and bacteria on agricultural products. This risk extends to medical Cannabis and is of particular concern with inhaled, vaporized and even concentrated Cannabis products. As a result, third party microbial testing has become a regulatory requirement in the medical and recreational Cannabis markets, yet knowledge of the Cannabis microbiome is limited. Here we describe the first next generation sequencing survey of the microbial communities found in dispensary based Cannabis flowers and demonstrate the limitations in the culture based regulations that are being superimposed from the food industry.
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In several countries with a National medicinal cannabis program, pharmaceutical regulations specify that herbal cannabis products must adhere to strict safety standards regarding microbial contamination. Treatment by gamma irradiation currently seems the only method available to meet these requirements. We evaluated the effects of irradiation treatment of four different cannabis varieties covering different chemical compositions. Samples were compared before and after standard gamma-irradiation treatment by performing quantitative HPLC analysis of major cannabinoids, as well as qualitative GC analysis of full cannabinoid and terpene profiles. In addition, water content and microscopic appearance of the cannabis flowers was evaluated. This study found that treatment did not cause changes in the content of THC and CBD, generally considered as the most important therapeutically active components of medicinal cannabis. Likewise, the water content and the microscopic structure of the dried cannabis flowers were not altered by standard irradiation protocol in the cannabis varieties studied. The effect of gamma-irradiation was limited to a reduction of some terpenes present in the cannabis, but keeping the terpene profile qualitatively the same. Based on the results presented in this report, gamma irradiation of herbal cannabis remains the recommended method of decontamination, at least until other more generally accepted methods have been developed and validated.
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In the carnivorous plant genus Genlisea a unique lobster pot trapping mechanism supplements nutrition in nutrient-poor habitats. A wide spectrum of microbes frequently occurs in Genlisea’s leaf-derived traps without clear relevance for Genlisea carnivory. We sequenced the metatranscriptomes of subterrestrial traps versus the aerial chlorophyll-containing leaves of G. nigrocaulis and of G. hispidula. Ribosomal RNA assignment revealed soil-borne microbial diversity in Genlisea traps, with 92 genera of 19 phyla present in more than one sample. Microbes from 16 of these phyla including proteobacteria, green algae, amoebozoa, fungi, ciliates and metazoans, contributed additionally short-lived mRNA to the metatranscriptome. Furthermore, transcripts of 438 members of hydrolases (e.g. proteases, phosphatases, lipases), mainly resembling those of metazoans, ciliates and green algae, were found. Compared to aerial leaves, Genlisea traps displayed a transcriptional up-regulation of endogenous NADH oxidases generating reactive oxygen species as well as of acid phosphatases for prey digestion. A leaf-versus-trap transcriptome comparison reflects that carnivory provides inorganic P- and different forms of N-compounds (ammonium, nitrate, amino acid, oligopeptides) and implies the need to protect trap cells against oxidative stress. The analysis elucidates a complex food web inside the Genlisea traps, and suggests ecological relationships between this plant genus and its entrapped microbiome.
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Aims: This study is aimed at assessing the effectiveness of Cannabis sativa in the absorption of cesium and strontium elements from the soil. Materials and Methods: This study was conducted in 2011, in Tehran, Iran. We employed the phytoremediation technology to refine the contamination of soil with radioactive material such as cesium and strontium. Cannabis sativa was selected because of its capability for potential radioactive absorption. It was planted in various soils with different concentrations of cesium and strontium (20 ppm, 40 ppm, 60 ppm, and 80 ppm), and after sufficient growth for about six months, it was separated into root, stem, and leaves for measuring the absorption of these elements in the main parts of the plant. The samples were measured by using the Inductively Coupled Plasma (ICP) method. Results: Strontium absorption and the main parts of the plant showed a significant relationship. The percentage of strontium absorption was 45% in the root, 40% in the stem, and the minimum absorption was found in the leaves (15%), but the corresponding figure was not significant for the cesium element. A strontium concentration of 60 ppm was possibly the maximum absorption concentration by Cannabis. Conclusion: Our findings suggest that strontium can be absorbed by Cannabis sativa, with the highest absorption by the roots, stems, and leaves. However, cesium does not reach the plant because of its single capacity and inactive complex formation.
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Eight species of Phoma and Ascochyta are described and contrasted. Diplodina cannabicola, Diplodina parietaria f. cannabina, Erysiphe communis var. urticirum, Phyllosticta cannabis, and Ascochyta cannabis become synonyms of Phoma cannabis, comb. nov. (≡ Depazea cannabis). Other Phoma species on Cannabis include P. exigua (= P. herbarum f. cannabis, Plenodomus cannabis), P. herbarum, P. glomerata, and P. piskorzii. Ascochyta arcuata, sp. nov. is described as the anamorph of Didymella arcuata. Ascochyta prasadii and Ascochyta cannabina are also described. Didymella arcuata is contrasted with D. cannabis. The pathogen complex is compared to one involving a related host, stinging nettles, Urtica dioica. Host range and geographic distribution of the eight fungi are discussed.
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Medicinal cannabis is an invaluable adjunct therapy for pain relief, nausea, anorexia, and mood modification in cancer patients and is available as cookies or cakes, as sublingual drops, as a vaporized mist, or for smoking. However, as with every herb, various microorganisms are carried on its leaves and flowers which when inhaled could expose the user, in particular immunocompromised patients, to the risk of opportunistic lung infections, primarily from inhaled molds. The objective of this study was to identify the safest way of using medicinal cannabis in immunosuppressed patients by finding the optimal method of sterilization with minimal loss of activity of cannabis. We describe the results of culturing the cannabis herb, three methods of sterilization, and the measured loss of a main cannabinoid compound activity. Systematic sterilization of medicinal cannabis can eliminate the risk of fatal opportunistic infections associated with cannabis among patients at risk.