Now legalized, hemp cultivation puts extra burden on TBI’s crime labs

J. H. Osborne • Nov 4, 2019 at 9:34 AM

KNOXVILLE — The Tennessee Bureau of Investigation has three crime labs, one each in Memphis, Nashville and Knoxville. The Times News recently visited the lab in Knoxville. One hot topic: how the legalization of hemp growing (you have to have a state license) has added to the lab’s workload. Now rather than simply prove plant samples submitted from local law enforcement agencies are cannabis sativa, the bureau’s agents must also determine whether the samples are hemp or marijuana. That’s an extra test. A third test might also be ordered by a local prosecutor to further define the strength of the chemical in the plant that makes it illegal.

The basics

• Cannabis sativa has been cultivated for both its psychoactive properties (marijuana) and as a source of fiber (hemp). Both cultivars, marijuana and hemp, are the same plant. Tennessee has legalized the cultivation of hemp and defined hemp as Cannabis sativa containing less than 0.3% THC. Marijuana, Cannabis sativa containing greater than 0.3% THC, is still illegal in Tennessee.

• TBI and other crime labs have historically performed plant material testing by microscopically looking for unique botanical characteristics and performing a color test for compounds exclusive to Cannabis sativa. This historic testing is relatively quick and inexpensive.

• At the national level, Tennessee is on the leading edge of developing crime laboratory methodology to cope with this challenge and is one of few states currently performing THC quantitation on plant material in a state crime lab.

TBI’s Testing Process

The Tennessee Bureau of Investigation uses a three-step protocol for submissions of plant material.

Presumptive Testing

In addition to traditional microscopic analysis and a color test, TBI performs a second color test to estimate the THC-to-CBD ratio. Marijuana has a high ratio of THC to CBD (typically 9:1 or greater) and will turn the second color test blue. Hemp has a lower ratio of THC to CBD and will turn the second color test red.

• Samples testing positive for the microscopic and both color tests are reported as cannabis. Visual and chemical color testing presumptively indicate the exhibit is marijuana.

• Samples testing positive for the microscopic but negative for the new color test are reported as cannabis. Visual and chemical color testing presumptively indicate the exhibit is hemp.

Laboratory Statistics

From 2005 to 2018, the statewide TBI Crime Laboratory Forensic Chemistry Unit identified plant material as marijuana an average of 9,951 times each year. This number has been relatively consistent over the years. Additionally, that unit separately identified THC 497 times in 2018. THC is typically identified in samples that are not plant material, such as foodstuffs, vape cartridges, oils, etc. THC identification has increased dramatically from 2005 to 2018.

Frequently asked questions

• What is CBD? CBD, or cannabidiol, is a chemical compound from the cannabis plant. Unlike tetrahydrocannabinol (THC), it's not psychoactive.

• What is THC? THC, or tetrahydrocannabinol, is the principal psychoactive chemical of the cannabis plant.