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EarthTalk - What are the environmental impacts of the legalization of marijuana?

© iStock

Roddy Scheer & Doug Moss

Dear EarthTalk:

What are the environmental impacts of the widespread legalization of marijuana in recent years?

Mac Styles, Tallahassee, FL

Cannabis is an increasingly popular recreational and medicinal drug that is capable of producing psychogenic effects. As more states legalize cannabis for some medicinal and recreational uses, cannabis production is on the rise.

On average, cannabis requires double the amount of water than food staples like corn, soybean and wheat. Over 60 percent of marijuana grown in the United States originates from California. Additionally, California produces nearly 75 percent of the nation's fruits and nuts and over 33 percent of its vegetables. Californian agriculture is significantly supported by aquifers, surface water diversion, springs and rivers. The rising demand for cannabis may exacerbate water scarcity, divert freshwater from essential agriculture and municipal needs, and harm water ecosystems by altering stream flows.

PROMO 64J1 Plant - Marijuana Leaf Neon Sign - iStock - Nikolay Evsyukov

© iStock - Nikolay Evsyukov

A single pound of commercial marijuana product correlates to over 4,600 pounds of carbon dioxide (C02) emissions produced. Additionally, cannabis plant matter has been found to contain high concentrations of biogenic volatile organic compounds (BVOCs), especially monoterpenes, which have been linked to increases in ground-level ozone pollution and particulate matter that can lead to severe health issues. Further, cannabis cultivation is often enhanced by pesticides and ammonia-rich fertilizers that are used to supplement the plant’s high nitrogen requirement. The ammonia frequently volatilizes into the atmosphere, bonding with nitrogen oxides to produce particulate matter. Runoff from these inputs also causes soil acidification, water eutrophication, oxygen depletion and harm to aquatic life.

Indoor planting facilities require significant energy for lighting, heating, ventilation and dehumidification. One 2012 study even attributed “the energy consumption for this practice in the United States at 1 percent of national electricity use, or $6 billion each year.” Back then, only 16 states had legalized marijuana for medicinal use. Today, that number has risen to 38 states, suggesting that current energy consumption for indoor cannabis production is likely even higher.

Several foundational changes could make cannabis crops more sustainable. Many states that have legalized cannabis have not established energy standards for indoor cultivation facilities. By mandating LED bulbs instead of metal halide or fluorescent bulbs, policymakers can initiate energy reduction. However, this is not always feasible. Facilities located in cooler areas sometimes rely on the heat generated by non-LED bulbs to keep temperatures warm enough for the cannabis to grow.

In the early days of the cannabis industry, it was widely believed that growers had to use reverse osmosis (RO) to remove heavy metals and sodium from water before applying it to their crops. Roughly half of the water that was put through RO was discarded as wastewater. Yet, testing showed tap water works similarly without impacting product quality, prompting a shift away from RO.

Some facilities are transitioning their root media from traditional, non-recyclable 'stone wool' to a coconut-fiber-based product. Coconut fiber offers improvements in water retention and filtration, allowing plants to maintain a cleaner root environment and reduce watering frequency. Moreover, coconut fiber promotes better aeration and drainage, preventing waterlogging that can lead to root rot.

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