A research group in Brazil has recently developed a technique to determine the growth stage of cannabis at time of harvest. The authors frame their findings as potentially useful in the context of forensic analysis, but their approach also forecasts interesting scientific and agricultural applications. The article describing their findings was published last month in the journal Spectrochimica Acta Part A.
Brazil, where cannabis has an illegal status, has witnessed a change in how the plant is trafficked. Due to a significant effort by the Federal Police to eradicate large-scale outdoor cultivations as well as common avenues of trade, more and more producers have turned to indoor setups and adopted the mail as a route of delivery. This has led to an exponential increase in the frequency of cannabis products being seized this way.
While a simple chemical analysis is enough to identify cannabis for legal prospects, the ability to determine the growth stage of the plant could be useful for police investigation (e.g., to establish a connection between the product and its cultivation site and transport route). This information is difficult to obtain due to many other factors that influence the chemical composition of cannabis, such as differences between strains, gender, light exposure, weather, and altitude of cultivation.
In a previous study, this group had achieved a breakthrough that enabled them to circumvent these issues. They determined the ratio of cannabinoids to volatile compounds in cannabis plants harvested at different stages, creating a preliminary developmental profile based on this factor. Propelled by these findings, the authors aimed at creating a model that could predict the age of cannabis at time of harvest, based on a wider sample of plants.
As Brazilian law forbids the purchase of cannabis for scientific research (or any other application), the authors were constrained to use seeds that had been seized by the police. They planted 29 seeds of different brands, types and varieties in a greenhouse under controlled conditions. The grown plants were then harvested at 5.5 weeks, 7.5 weeks, or 10 weeks, after which the leaves, stems and flowers were dried and grinded, and sent for analysis.
The chemical analysis was done via Near-Infrared Spectroscopy, a tool that is widely used in agriculture to determine the quality and composition of the products harvested. Its popularity derives from it being accurate, reliable, rapid, non-destructive, and inexpensive. The obtained data (encompassing 87 samples with 6000 variables) was then processed by several statistical algorithms in order to create a model that was capable of classifying the age of the plants.
The authors judged their method practical and reliable enough to be used in judicial investigations related to cannabis trafficking. Other than that, their method might be helpful in controlling the quality and composition of harvested products, as it is commonly used in other agricultural sectors. Finally, it could be adopted by researchers to affordably study the chemical development of the cannabis plant. As an example of such application, this group was able to previously determine that the only cannabinoid whose concentration increases with age is THC.