Pesticides in cannabis

Cannabis growing has grown significantly in many countries thanks to the legalisation of cannabis and the regulation of the sale of CBD flower, or hemp buds. However, the arrival of cannabis buds on the market poses new challenges in terms of the safety and quality of products intended for consumption.

In particular, the use of pesticides in cannabis growing raises concerns about the possible transfer of chemicals from pesticides into the smoke, extracts and edibles made from the plant that are intended for consumption, whether oral or inhaled. This article aims to inform you about pesticides in cannabis and how you can choose safer products.

What are pesticides and why are they used in cannabis growing?

With the legalisation of cannabis, weed and cannabidiol (CBD), demand has risen considerably, which has led many growers to turn to techniques that increase crop yields, such as the use of growth stimulants and pesticides (1).

Cannabis (Cannabis sativa) is an extraordinary plant that, like any living organism, is susceptible to diseases, infections and pests. To control these factors and ensure optimal yield, within its own plant micro-world, the cannabis plant produces various compounds, such as cannabinoids and terpenes, which act as the plant's chemical defence against certain infections and pests. However, the plant's natural defences are sometimes not enough, and growers may have to resort to pesticides, which raises questions about the safety of the people who consume that cannabis.

In countries where cannabis is legal, there is some regulation of pesticide use in its growing; however, there is still no standardised protocol for their use. Traces are allowed in the finished buds if the pesticide is considered safe or moderately hazardous by the World Health Organization (WHO).

It is important to note that the WHO's assessments are based on toxicity studies of these compounds when they are taken orally, while their safety when inhaled has not yet been studied in depth (2). This is crucial, as inhalation is one of the most common ways cannabis is consumed worldwide. Some countries do have guidelines for monitoring pesticides in cannabis, and they are mostly based on those that already exist for tobacco.

Types of pesticides used in cannabis growing

There are different types of pesticides used in cannabis growing, each with its own characteristics and applications:

• Insecticides and acaricides: These control insect pests that can damage plants.
• Fungicides: These combat fungal infections such as powdery mildew and botrytis (grey mould).
• Herbicides: Although less common, these kill unwanted weeds that compete with cannabis for nutrients and light.

What are the most common pesticides in cannabis?

• Insecticides: Pyrethroids, avermectins, sulphur-based products, neem oil (from the neem tree) and spinosad (a naturally occurring insecticide produced by the fermentation of a bacterium).
• Fungicides: Sulphur, copper-based compounds and potassium bicarbonate.
• Herbicides: Glyphosate and paraquat.

Differences between PGR and natural cannabis

Where are pesticides found in cannabis?

The pesticides used in cannabis growing are retained in the trichomes, the specialised structures found on the leaves and, above all, on the flowers or buds of cannabis, which contain the resin rich in cannabinoids and terpenes.

Cannabinoids and terpenes are hydrophobic compounds, as are pesticides. Trichome density and pesticide retention are therefore correlated, which may mean that the more trichomes there are, the higher the concentration of pesticides (3).

Impact of pesticides on the health of cannabis consumers

The WHO has studied the amounts of pesticides that pose a risk when taken orally, but intake by inhalation has been little studied. Pesticides can pass into the smoke through a process called pyrolysis, in which the chemical breakdown of organic materials through the application of heat can turn some pesticides into a chemical more toxic than the original compound, which will end up being absorbed by the consumer's lungs (4).

Some studies have quantified pesticide residues in cannabis smoke using different smoking devices (4). These studies highlight the urgent need to establish regulatory guidelines based on rigorous scientific research that can give cannabis consumers confidence.

Is it possible to have cannabis without pesticides?

Yes, it is possible to grow cannabis without pesticides by using alternative strategies. These include biological and mechanical controls, introducing natural predators and using physical barriers. In addition, selective breeding of pest-resistant plants and the use of products such as neem oil, insecticidal soaps and fertiliser, which are commonly used in organic growing, can also be effective.

One of the leading figures in this field is Jorge Cervantes, author of Marijuana Horticulture: The Indoor/Outdoor Medical Grower's Bible, who has devoted more than 40 years of his life to growing cannabis and researching organic and biological techniques for growing quality cannabis.

Organic cannabis growing

Is there a safe way to grow cannabis for smoking?

Yes, through Integrated Pest Management (IPM) and organic growing.

Integrated Pest Management (IPM)

This is a holistic, environmentally friendly approach that combines biological, cultural, physical and chemical control methods. It involves making decisions based on prevention and monitoring, using pesticides only as a last resort. IPM strategies for growing cannabis include crop rotation, introducing beneficial insects (for example, ladybirds and predatory mites) and using organic pesticides.

Preference for organic pesticides

Organic cannabis growing does without synthetic pesticides and adopts natural methods of pest control, such as the use of organic insecticides. This is because synthetic pesticides (meaning compounds made of molecules that do not occur in nature and are only synthesised in laboratories) generally have a more stable and persistent chemical structure, which makes it easier for them to build up in the environment and in living organisms. In addition, the toxicity of some of these synthetic pesticides can seriously interfere with essential biological processes, increasing the risks to human and environmental health.

The organic pesticides used in cannabis growing include neem oil, extracted from the neem tree, which has broad-spectrum insecticidal properties, and spinosad, a natural insecticide derived from the bacterium Saccharopolyspora spinosa, which is effective against a range of insect pests. In addition, this type of growing encourages keeping the soil healthy to make plants more resilient.

In many countries, an organic growing certificate is required to market cannabis products as organic. This certification generally requires compliance with strict guidelines, ensuring that the final products are free from synthetic pesticide residues.

Is neem oil really the answer?

Neem oil works as an effective pesticide thanks to its main active ingredient, azadirachtin. Although it is considered a relatively safe solution, its safety profile when inhaled has not been studied thoroughly. So far, documented cases of neem toxicity are rare and occurred when it was taken orally (5). Although we cannot assume that inhaling neem is completely safe, it could be a safer option than synthetic pesticides.

Conclusion

The use of pesticides in cannabis growing is a complex issue that underlines the importance of assessing the potential health risks. More and more cannabis consumers are choosing to grow at home to make sure they aren't smoking buds with pesticide residues; however, at present, both natural and synthetic pesticides, when used sensibly, appear to be safe in the short term. The only way to find out whether pesticides have been used on cannabis is a pesticide test, although it is expensive and offers no guarantee either. EU Regulation 396/2005 on food and agricultural products sets maximum residue levels (MRLs) for these products. However, even if the pesticides used in a product can be quantified, the safe levels of these compounds when inhaled are unknown. Furthermore, the toxicity of these molecules in combination (one pesticide can increase the toxicity of another) has not been studied. This is the “cocktail effect” described by several researchers, such as Nicolás Olea, a challenge that also arises with the levels of pesticides authorised in food.

It is crucial to keep researching the long-term effects of pesticide traces in cannabis, and for the use of these compounds to be regulated, so that consuming cannabis products does not put consumers' health at risk.