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Strong Link Observed Between Common Cannabis Growth Practices and Use of Chemical Additives

By Alexander Beadle

Published: Nov 19, 2018   
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With the expansion of recreational and medicinal cannabis markets worldwide, there is also increased recognition of the importance of safe cannabis growing practices, with growing operations expanding in size and scale to meet demand.

One of the emerging concerns for the cannabis market in terms of safety has been the reported use of Plant Growth Regulators (PGRs) as part of cannabis growth operations. These PGRs are hormone-like chemicals that are used to restrict the size of the plant while stimulating the production of the cannabis flowers. The toxicological effects of these chemicals in humans, particularly following combustion as would be the case in smoked cannabis flower, are currently unknown. However, the use of PGRs is already restricted in the food and drink industry following concern over potential adverse health effects.

Following the discovery of the PGRs paclobutrazol and daminozide in popular flowering additives being marketed towards hydroponic cannabis growers, debate over the safety of these chemical additives has been reignited in the cannabis industry. In many countries there are no legal requirements for labeling or testing these growth products, and so it can be incredibly difficult to verify whether a particular growth agent contains a potentially toxic PGR. As a result, the use of any growth chemicals that have not been explicitly tested and approved by an accredited third-party testing lab must be treated with the expectation that it could contain potentially harmful PGRs as an ingredient.

Cannabis growth practices in the UK, Australia, and Denmark

In 2012, the Global Cannabis Cultivation Research Consortium (GCCRC) conducted the International Cannabis Cultivation Questionnaire (ICCQ) which surveyed small-scale cannabis cultivators across 11 countries. This survey provided a wealth of data about patterns and trends in cannabis cultivation practices across geographic and legislative boundaries.

A recent paper published in the international drug policy journal Drug and Alcohol Dependence, further scrutinizes a subset of responses to the ICCQ in order to examine the extent of chemical use by small-scale cannabis growers, and any trends associated with chemical use and particular growth practices.

The exact subset in question includes the responses of cannabis growers from the United Kingdom, Australia and Denmark who reported having grown cannabis within the last five years. As well as answering the core questions listed in the ICCQ, respondents from these countries also asked additional questions about their use of fertilizers, supplements, and insecticides. Where appropriate the growers were also asked to list the names of the products they typically used.

By asking for the name of the products, it was hoped that it would be fairly easy to identify products that contained potentially harmful PGRs. During the data analysis stage it became clear to researchers that this would be much harder than it first appeared, on account of incomplete or misleading labeling on the products in question. Similar problems were also encountered when trying to verify whether certain additives were indeed “organic” as believed by the growers, as many additives could not be found on national online organic certification systems.

As a result, the paper became restricted to examining the general use of chemicals in cannabis cultivation, with the understanding that due to the lack of government regulation in these countries, many of the chemicals being used by growers may contain some potentially harmful ingredients such as PGRs.

Predictive factors of chemical use

A logistic regression analysis of the demographics and growing practices across the three countries revealed that there is a slightly increased likelihood of chemical use among those who grew to sell, were male, kept a small growing area (less than 3 square meters), and who communicated with other growers online. However, by far the most reliable predictor of chemical use was the growth method employed.

Respondents who grew their cannabis plants in soil under artificial light were found to be 2.86 times more likely to use chemical fertilizers and additives than those who grew outdoors in soil under natural sunlight. Growers who reported using hydroponic growing methods, or other non-soil methods, under artificial light were a staggering 11.89 times more likely to use chemicals than the outdoor growers.

By nation, growers in the UK were the most likely to use chemical fertilizers and additives, with 61% of respondents reporting doing so. By comparison, the percentage of growers using chemicals in Australia was 45.3%, and 34.6% in Denmark. These percentages support the link to growth methods, with the UK being overwhelmingly more likely to grow cannabis indoors using hydroponic methods, or soil with artificial light. The warmer climates and lower population density of Australia and Denmark mean that growers there have a higher tendency to grow their cannabis crops outdoors, lowering the overall predicted chemical usage.

The power of online resources

While investigating the observed link between chemical use and communication with other growers online, researchers encountered discussion of another growth practice in hydroponic farming, known as “flushing”: this is where the usual nutrient solution that hydroponically grown cannabis plants are suspended in is replaced with just water in the last two weeks before harvesting. The belief is that this will cause the plants to consume any traces of nutrients and flush out any other chemicals, such as PGRs, used in the growth process, thus creating a “smoother product”.

Following communication with Steven Carruthers, editor of Practical Hydroponics and Greenhouses, the researchers were informed that while flushing may be able to correct small nutrient imbalances in the plants, there is no evidence that flushing can remove systemic chemicals such as PGRs. Still, the belief in flushing’s effectiveness has persisted online.

Further research into chemical usage

Based on the links established in this paper, the researchers have a number of recommendations as to what future research could be helpful in the field.

With the prevalence of chemical use being strongly linked to common growth practices, it is necessary to know what percentage of this chemical usage may actually present a risk to health. A future study which aims to obtain and test samples of the most commonly reported chemical products could provide valuable insight into the safety of current small-scale cannabis growth operations. Additionally, scientific research into the practice of flushing using analytical techniques would be helpful in terms of categorically establishing its effectiveness.

The role of the internet in spreading information about growth methods and chemical usage is also worth further attention. It’s clear that there needs to be improved access to reliable and accurate information surrounding safe chemical usage and growth practices. In countries such as the above, where government regulation is unlikely due to the legal status of cannabis, disseminating information online could be a much more effective way to reach small-scale cannabis producers.

Alexander Beadle

Science Writer

Alexander Beadle has been working as a freelance science writer since 2017 and has covered the cannabis industry for Analytical Cannabis since 2018. He has also written for our sister publication, Technology Networks, and the cannabis industry consultant firm Prohibition Partners, among others. Alexander holds a Master's in Materials Chemistry from the University of St. Andrews, where he won a Chemistry Purdie scholarship, and conducted research into zeolite crystal growth mechanisms and the action of single-molecule transistors.


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