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Cannabis Contaminants To Watch Out For

As with any product, cleanliness and purity are of the utmost importance for cannabis. Growers should be vigilant about ensuring their bud doesn’t become contaminated. Among the most common cannabis contaminants are microbes such as fungi and moulds and heavy metals, and other chemicals found in pesticides and fertilizers. Preventing these impurities from finding their way into your weed is essential if you want to produce safe, high-quality bud.

Microbial Cannabis Contaminants

Like all plants, cannabis has many microbial enemies, including pests and pathogens like powdery mildew and botrytis. The plant’s immune system is designed to keep these invaders at bay. However, the danger of contamination increases significantly during the post-harvest period when the plant is no longer alive.

Improper harvesting, drying, and storage can open the door to several common cannabis contaminants. While most of the microbes that might infect a slightly soggy crop are unlikely to harm most people, they may be damaging to immunocompromised individuals.

Species like aspergillus and penicillin, for example, are known to produce carcinogenic compounds known as aflatoxins. While these contaminants are generally absent from decent cannabis, poorly-produced batches can end up tainted with these moulds. There is even a medical case report of a lung cancer patient who died after developing pulmonary aspergillosis due to smoking some dodgy weed. While this sort of thing is infrequent, it highlights the need to take care when handling cannabis to prevent contaminants from taking hold[i].

Chemical Cannabis Contaminants

Heavy metals are among the most common cannabis contaminants and are usually absorbed from the soil by the plant’s roots. These potentially hazardous minerals often get into the ground when chemical fertilizers are used. That’s why it’s a good idea to avoid treating plants with anything that contains heavy metals like lead, mercury, or cadmium.

Fortunately, there are no reports of cadmium-contaminated cannabis causing health problems in users. And just as well. This particular heavy metal is associated with a range of illnesses, including periodontal disease, pancreatic cancer, and diabetes.

The most notable case of heavy metal contamination occurred in Leipzig, Germany.

A dealer deliberately added lead to a finished batch to increase its weight and boost its street price. This resulted in 95 lead poisoning cases. It serves as another reminder of the importance of buying cannabis from a trusted source and avoiding contaminants when growing at home.[ii]

More generally, industrial pesticides and fertilizers contain a cocktail of harmful chemicals that should be kept well away from weed. Worryingly researchers recently analysed 20 samples of street cannabis in Vancouver and found evidence of 24 different pesticides and high levels of bacteria, fungi, lead, and arsenic.

Is Street Weed Spiked?

A recent documentary produced by Vice has shed light on a serious problem within the street cannabis industry in Germany. According to a dealer named ‘Banks,’ much of the cannabis sold illegally in the country is laced with synthetic cannabinoids.

In particular, Banks says that 90 percent of the weed sold under the name Haze in Germany is sprayed with these chemicals, resulting in higher potency. The only way to end the use of these dangerous contaminants is to legalise cannabis, he says.

On the back of these revelations, certain politicians in Germany have called for the legalisation of cannabis, claiming that much of the illegally sold weed is laced with heroin. In reality, though, there is no evidence to suggest that this is the case, and there are no recorded examples of cannabis ever being adulterated with opioids.

Other Cannabis Contaminants

We’ve covered the main cannabis contaminants, although another impurity also deserves a mention. Thankfully, this particular offender is rarely present in bud but can end up in weed smuggled across borders the old-fashioned way, if you catch my drift.

To spell it out, we’re talking about poo. Naturally, this isn’t something you’d expect to find in your stash, although Spanish researchers recently analysed 90 samples of hash that had been seized by police in Madrid and detected human poop in three-quarters of these nuggets[iii].

The source of this contaminant is not hard to imagine and hailed from the digestive tracts of those who had smuggled the gear into Europe from Morocco. Fortunately, though, legally sourced or home-grown weed doesn’t tend to spend any time up people’s bottoms, so this particular cannabis contaminant needn’t be of any concern.

[i] Montoya Z, Conroy M, Vanden Heuvel BD, Pauli CS, Park SH. Cannabis contaminants limit pharmacological use of cannabidiol. Frontiers in Pharmacology. 2020 Sep 11;11:1439. –

[ii] Busse FP, Fiedler GM, Leichtle A, Hentschel H, Stumvoll M. Lead poisoning due to adulterated marijuana in Leipzig. Dtsch Arztebl Int 2008; 105: 757– 762. –

[iii] Pérez-Moreno M, Pérez-Lloret P, González-Soriano J, Santos-Álvarez I. Cannabis resin in the region of Madrid: Adulteration and contamination. Forensic science international. 2019 May 1;298:34-8. –

Cultivation information, and media is given for those of our clients who live in countries where cannabis cultivation is decriminalised or legal, or to those that operate within a licensed model. We encourage all readers to be aware of their local laws and to ensure they do not break them.

This post is also available in: French

Ben Taub