US hemp production: contamination concerns

Don Shelly

Hemp has a long history of production and commoditisation in the U.S., which after a period of decline has seen a resurgence today. According to the Federal Register 7 CFR Part 990 "Establishment of a Domestic Hemp Production Program":

“Hemp is a commodity that can be used for numerous industrial and horticultural purposes including fabric, paper, construction materials, food products, cosmetics, production of cannabinoids (such as Cannabidiol or CBD), and other products. While hemp was produced previously in the U.S. for hundreds of years, its usage diminished in favor of alternatives. Hemp fiber, for instance, which had been used to make rope and clothing, was replaced by less expensive jute and abaca imported from Asia. Ropes made from these materials were lighter and more buoyant, and more resistant to salt water than hemp rope, which required tarring. Improvements in technology further contributed to the decline in hemp usage. The cotton gin, for example, eased the harvesting of cotton, which replaced hemp in the manufacture of textiles. 

“Hemp production in the U.S. has seen a resurgence in the last five years; however, it remains unclear whether consumer demand will meet the supply. High prices for hemp, driven primarily by demand for use in producing CBD, relative to other crops, have driven increases in planting. Producer interest in hemp production is largely driven by the potential for high returns from sales of hemp flowers to be processed into CBD oil.”

In past posts we’ve discussed how the 2018 Farm Bill and the USDA require that Cannabis sativa L. must have a THC level no greater than 0.3% to be considered hemp. But assuming that we have a legal hemp crop – do we know if it is safe?

The cannabis plant is an example of a bioaccumulator, meaning that it absorbs chemical substances such as pesticides at a faster rate than it can remove them. This is a key reason why cannabis-derived products need to be so carefully monitored and tested – bioaccumulators retain many toxins, which can be found in their end products (including, in the case of cannabis, in hemp). An obvious example is heavy metals from soil, which can cause serious health concerns. To ensure products are safe for public consumption, growers and manufacturers must carefully and regularly test products for toxins at every stage. 

A study performed by V. Angelova, et al. (2003)¹ demonstrated that when flax, hemp and cotton were grown in contaminated soil containing 200 mg/kg of lead, the resulting hemp flower contained 45 mg/kg of lead (roots = 39 mg/kg, stems = 24 mg/kg, leaves = 17 mg/kg, fiber = 6 mg/kg and seeds contained 8 mg/kg of lead). According to the World Health Organization, “there is no level of lead exposure that is known to be without harmful effects” and lead poses a variety of health risks when inhaled or consumed, including damage to the brain and central nervous system. While it is most dangerous for young children, lead can also cause serious risks for adults (and can be passed from mother to fetus during pregnancy), making testing crucial.

If you are a grower, you definitely want to have your soil tested prior to planting your expensive hemp seed, as contamination could render your product unusable. If you are a buyer of hemp flowers or CBD it is your responsibility to have your product tested for heavy metal contamination, to ensure your products are safe for public consumption.

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¹Angelova, V., Ivanova, R., Delibaltova, V., Ivanov, K., 2004. Bio-accumulation and distribution of heavy metals in fiber crops (flax, cotton, and hemp). Ind. Crops Prod. 19, 197