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Lost in the Marijuana Debate: Its Impact on Water Treatment Systems

Columns appearing on the service and this webpage represent the views of the authors, not of The University of Texas at Austin.

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The debate over the consequences of increased consumption of both legal and medicinal marijuana has drowned out any discussion of the impact there could be on the natural environment, particularly on our water supplies. We need to better understand how the chemical makeup of marijuana is affected as it goes into our treatment systems and back into the environment as effluent.

The legal marijuana market is expected to be worth $22 billion by 2022. In June 2018, the U.S. Food and Drug Administration approved Epidiolex, a marijuana-based drug developed for the treatment of a rare form of epilepsy. FDA approval of any drug inevitably leads to a dramatic rise in its consumption levels. Epidiolex is no different. Sales in the U.S. are expected to exceed $1.1 billion by 2022. That’s a 1,100% increase in consumption levels in less than 10 years.

As marijuana consumption grows, the release of its chemicals through human excretion will increase, and they inevitably will end up in our natural and engineered water systems. This is nothing new.

Every year unique pharmaceuticals and personal care products are introduced by the health care industry, the byproducts of which eventually find their way into our rivers, streams, lakes and oceans. All are potentially harmful, but some are higher risk than others.

For example, methadone, a common narcotic that is often provided as a substitute to heroin addicts, is not a carcinogen in itself, but after going through the treatment system and getting exposed to chlorine, it can transform to nitrosodimethylamine (NDMA), which is carcinogenic.

More recently, it was discovered when an X-ray contrast agent, iopamidol, is released into our treatment systems, it gets transformed and releases iodine from its molecular structure. Iodine then reacts with natural organic matter that is already present in the treatment system and produces disinfection byproducts that are extremely toxic and carcinogenic.

In other words, we continue adding names to a growing list of emerging contaminants found in our water supplies. A recent addition to that emerging contaminants list is something known as halogenated methanesulfonic acid, a new class of organic micropollutant produced from an approved drug — now prevalent in the water cycle. Cannabinoids can introduce similar compounds during their passage through engineered treatment systems.

Responding to the unknown risks caused by the increased use of any new medicine isn’t exactly straightforward. But we are faced with a uniquely different set of variables with marijuana that serve to further exacerbate the complexity of this problem.

Marijuana is already being illegally consumed for recreational purposes, a factor that makes it impossible to be certain of mass production levels. It doubles up the problem of knowing how much is being consumed as well as which compounds are causing more harm than others.

That’s because marijuana compounds, or cannabinoids, are one of the most understudied classes of emerging contaminants in our water systems. Preliminary results demonstrate that some can produce halogenated organics that are toxic and potentially carcinogenic.

The most common pharmaceuticals already excreted into our water treatment systems include antibiotics, anticonvulsants, antidepressants, beta-blockers, analgesics, anti-inflammatory drugs, hormones and psychostimulants. Most of these, however, have been studied in detail, and their transformation pathways are well understood. Marijuana, on the other hand, has a unique chemical structure making it highly reactive to disinfectants and other chemicals that are present in our water and wastewater treatment systems, such as chlorine, iodine, bromine and other oxidants.

We are putting ourselves at risk by not considering how transformation processes in the environment can change the chemical makeup of marijuana. Understanding the transformation pathways will equip pharmacists with the information required to redesign drugs containing these molecules to avoid chemical components within the drug that are prone to producing toxic byproducts. We need to test the efficacy of our treatment processes for removing these compounds and their byproducts so that these do not end up in our environment.

Navid Saleh is an assistant professor of civil, architectural and environmental engineering at The University of Texas at Austin.

A version of this op-ed appeared in The Hill.

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