Reducing Heavy Metals in Commercial Cannabis with Ozonated Water

July 25, 2019

Conscientious growers who have been careful to sell what they thought was safe, uncontaminated cannabis products are being blindsided by California regulations.

Over the last few years, California and other states have been continuing to lower the bar for legal access to marijuana. As of July 2019, 10 states and Washington, D.C. have fully legalized the recreational use of marijuana. Dozens more have legalized the use of marijuana for medicinal use. The result is that in 2018, American marijuana companies generated $9 to $10 billion in sales in 2018, and will exceed that figure in 2019.

Given that the full value of the American cannabis industry—legal and black market combined—is believed to be approximately $50 to $55 billion, there is still immense growth potential for the industry.

But, there’s a problem.

Many marijuana growers are running into issues with state product testing requirements for pesticides, chemicals, fungi, but most of all, heavy metals.

When California fully legalized marijuana in 2018, it also tightened safety requirements for commercially sold cannabis products. As of July 1, 2018, all marijuana sold in the state must meet strict testing requirements.

Throughout 2018, all marijuana products were required to be tested for potency, as well as the presence of a variety of contaminants, including:

  • Pesticides
  • Microbial impurities (E. coli, Salmonella, and a variety of fungi)
  • Solvents
  • Processing chemicals and foreign materials

The stakes for passing these tests are quite serious. If a batch of cannabis goods fails to past any regulatory compliance testing, it cannot be sold. Failed goods must either be destroyed, or the owner must grow through a lengthy and costly remediation process. When testing requirements first went into effect, 20% of goods failed product testing. While cannabis growers quickly got their acts together, the failure rate was still quite high—around 14% by the end of 2018.

But then growers were hit with another complication, as beginning in 2019, the state of California implemented a third tier of required laboratory testing for the presence of mycotoxins—poisons produced by certain types of fungi—and heavy metals, particularly cadmium, arsenic, lead, and mercury.

Many growers have been very careful to utilize green, ‘eco-friendly’ ways of controlling pests and fertilizing their crops, which has allowed them to avoid issues with tests for fungi, pesticides, solvents, and other chemicals. But growers are already running into serious issues when it comes to fungal and heavy metal contamination.

But heavy metal contamination is proving to be a particularly vexing issue for growers. Many commercially available fertilizers have measurable levels of heavy metals. Even organic growers run into trouble, as organic fertilizers like bat guano and fish oil are also often contaminated with heavy metals. Some labs have seen heavy metal levels 10 to 20 times the maximum allowed by law.

Conscientious growers who have been careful to sell what they thought was safe, uncontaminated cannabis products are being blindsided by California regulations. And the issue isn’t limited to the state of California. States that have recently implemented or are currently implementing the mandatory testing of heavy metals and mycotoxins include Arizona, Colorado, Connecticut, Massachusetts, Minnesota, Nevada, Oklahoma, and Washington.

The trend is clear. Commercial marijuana growers will not be able to sidestep the complications imposed by lab testing for heavy metals and other contaminants by simply ignoring the California market. As states adopt and formalize standards for the legal sale of marijuana products, they will also impose increasingly state product testing requirements.

Growers must find a way to reduce levels of heavy metals and other contaminants in their crops. But how?

Ozone water purification systems make it simple and cost effective to reduce heavy metal levels in cannabis and other cultivated crops.

Water purity and filtration is crucial in any agricultural operation. But this particularly the case with the cultivation of marijuana and other crops and indoor crops. This is in part because marijuana is particularly vulnerable to fungal infestations—water supplies contaminated with fungal spores or bacteria can devastate a crop.

But traditional large-scale approaches to reducing heavy metal levels are inappropriate for agricultural applications. For instance while wastewater treatment plants—and some home and well water treatment systems—sometimes use reverse osmosis, this wastes a great deal of water. More critically, it also produces a waste stream with very high concentrations of heavy metals, which requires careful disposal. Other systems rely on ion exchange technologies, but these systems tend to be high maintenance and also filter out beneficial minerals, such as calcium, which are crucial to healthy plant development.

Chemical-based approaches, such as chlorinating irrigation water, can be used to reduce the presence of toxic heavy metals. This is because chlorine is an oxidizer. When a heavy metal is oxidized, it forms a less soluble and bioavailable chemical compound—typically in the form of a metallic oxide or hydroxide. But high levels of heavy metals require correspondingly high levels of chorine, higher than what is typical in municipal drinking water. Such levels of chlorine are toxic to both plants and beneficial soil organisms, which makes chlorination an unworkable solution for cannabis cultivation and other agricultural activities.

This is where ozone water treatment comes in. Ozone is an extremely powerful oxidizer, far more powerful than chlorine. When water is treated with ozone, which significantly increases the levels of dissolved oxygen in the water, bacteria, fungi, and other harmful organisms are immediately sanitized and broken down. In addition, harmful heavy metals and other minerals are also oxidized, precipitating them out of the water as harmless chemical compounds.

In the case of a cannabis cultivation or other agricultural applications, while irrigation water has high levels of dissolved oxygen, this water can reduce high levels of heavy metals introduced into the soil via the use of organic fertilizers and other contaminated soil treatment products.

One of the benefits of ozone water treatment is that while ozone is extremely powerful, it is also short-lived. When ozone is dissolved in water that is 70 degrees Fahrenheit has a half-life of less than 20 minutes. This means it does its job, killing harmful organisms and oxidizing heavy metals, and then rapidly breaks down and dissolves into water and surrounding air.

If your cannabis cultivation business or other agricultural operation is looking for a non-toxic, cost-effective way to reduce the levels of heavy metals and other harmful contaminants in your crops, ask us about our agricultural ozone water treatment systems. Our systems can be scaled up for operations of any size, and shipped to your location ready to install as a complete turnkey system. Contact Watson Well to learn more!

We can count on them more than any other contractor or service provider we know!

Don Watson and his family have been providing experienced and reliable service to our well-water system since 2011. In those seven years, Watson Well has made a number of timely emergency service calls at any time of day and night, upgraded our water system, and rehabilitated our well.

Mr and Mrs R.W. Goodlake

Eureka CA

Thank you Watson Well for saving our well!

When our well stopped producing water this summer, I called Watson Well. They used a special pump and opened up the well from 67’ to 132’. While inspecting the well with a video camera, they found that the wells steel casing had deteriorated in a number of places leaving large holes where sand and gravel were continuing to enter the well. They immediately installed a new liner and gravel packed the well. Our well has never produced this much water volume in twenty years of living on this property. We are also noticing a tremendous improvement in the quality of the water.

Susan Ashford

Don, his sons, and employees are all very knowledgeable and professional and did our projects at a very reasonable cost.

As Public Works Director for the Bear River Band of the Rohnerville Rancheria, I have contracted with Watson Well on five different projects for the tribe, here in Loleta, CA. Their company has completely replaced both of our main water systems submersible pumps and piping, which was not an easy task, as those wells are very deep. These projects were done very quickly and efficiently, while still maintaining a potable water supply to everyone at all times. They have the tools and equipment to not only handle the small jobs, but large jobs like this also. They have also installed three water softening units for us, as our water is very hard. These are big commercial units and all are working flawlessly. They have also developed a small rural water system for us on a piece of property the tribe recently purchased, to supply water to livestock. All of the work they have done for us is doing what they said it would do, without any problems or issues. Don, his sons, and employees are all very knowledgeable and professional and did our projects at a very reasonable cost. They stand behind their work and are only a phone call away. I would highly recommend Watson Well for any water project, no matter what the size, if you want it done right, on time and on budget, you won’t be disappointed.

Mike Flockhart, Director of Public Works

Bear River Band of the Rohnerville Rancheria

Thank you so much for the excellent response and care we have received. Your crew was courteous, prompt, clean, knowledgeable and very hard working!

It is hard to believe that it has been 9 months since I called you with an “out of water” problem on our property. It is not the call that any one on a well wants to make during a record breaking drought. You were here in a very short time and after taking in all the normal diagnostics you were concerned about us being dry but not convinced it was a true dry well. I think we were very fortunate that you had the ability to put a camera down our well to see what was happening and came up with a plan to rehabilitate our well after you discovered our weep holes for the well were plugged with iron bacteria, calcium and stuff. It gave us hope that we could get this reliable well up and running. You pulled the pump and line and determined that pump was fine. Once that was clear you put in the proper chemicals and literally scrubbed our well pipe of the “stuff” and found that our well was over 200’ deep. Water flowed and once the junk was sucked out of the well bottom and the chemicals neutralized we had 18’ more water which put us at over a 50’ column of water, of course this was fantastic. While here, all new water line and electrical wire was reinstalled and new electronics that were more current and a vast improvement of what we had. Since then the water keeps flowing with generous amounts and quality.

John and Elizabeth Ennis


I can only offer my highest praise for Don and his employees; thus I rank them 10 out of 10.

During the past two years, Watson Well has designed, constructed, and maintained a number of different projects at my home. These include new water storage tanks, a water treatment system, new piping from the pump house to the residence along with separate lines and faucets for untreated water; and a complex rain water catchment system including tanks, piping and faucets to different locations, all while providing flexibility directing the water to different areas as needed. Don Watson and his crew worked efficiently and coordinated the different aspects of the jobs in an effective manner. All systems continue to operate as expected without any problems. Don was always extremely helpful and receptive to new ideas which he easily incorporated into the projects.

Charles Compton

California Groundwater Association
National Groundwater Association

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