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Strengthen Supply Chain Management with an Integrated ERP & CMS

By Daniel Erickson
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Success in the cannabis industry is driven by a company’s ability to adapt to an ever-changing market and meet the demands of the evolving consumer. Selecting the right business management solution to handle the complexities of the growing cycle as well as daily operations and compliance requirements necessitates diligent research. Ensuring that the selected technology solution has a centralized database in a secure platform designed to reinforce quality throughout company operations is essential in today’s competitive industry. An ERP solution with integrated CMS capabilities helps businesses strengthen supply chain management by seamlessly incorporating cannabis cultivation with day-to-day company operations to efficiently deliver seed to sale capabilities and meet marketplace demands.

What are ERP & CMS?

Enterprise resource planning (ERP) is a business system in which all data is centralized – including finances, human resources, quality, manufacturing, inventory, sales and reporting. A cultivation management system (CMS) is an extension of an ERP solution to manage cannabis greenhouse operations, including growing, inventory and labor needs. A CMS maintains a detailed level of tracking to account for continuous cannabis growth periods that require extensive monitoring and incur a multitude of expenses. In an integrated solution, both the ERP and CMS data are managed under the same secure database to provide a forward and backward audit trail of all business processes. This visibility encompasses the entire supply chain from the management of supplier relationships to distribution – including growing, cultivating, extracting, manufacturing and shipping.

How do ERP & CMS strengthen supply chain processes?

Tracks individual plants and growth stages – By tracking plant inventories at the individual plant level in real-time with a unique plant identifier, greenhouse operations are optimized – monitoring the entire lifecycle of the plant throughout the germination, seedling, vegetative and flowering stages. Audit trails maintain regulatory compliance, including information such as terpene profiles and THC and CBD potency. Monitoring genealogy, mother and cloning, crossbreeding, plant genetics and clone propagation are key to success in this industry. Strain tracking is equally important, including identifying which strains are performing best, producing the most yield and how they are received by the marketplace. Tracking of the entire supply chain includes the recording of plant health, harvesting techniques, production, growth, costs, lab testing and batch yields – without any gaps in information.

PlantTag
A plant tagged with a barcode and date for tracking

Optimizes growing conditions to increase yields – By automatically documenting and analyzing data, insights into plant and greenhouse activities create streamlined processes for an optimal cannabis cultivation environment. This includes the monitoring of all growing activities such as space, climate, light cycles, moisture content, nutrient applications, fertilizer and other resources, which all have an effect on plant growth and yields. Most importantly, labor costs are monitored, as it is the highest expense incurred by growers. In an industry for which many companies have limited budgets, enabling efficient greenhouse planning, automation and workflows reduces overhead costs.

Integrates with regulatory compliance systems – Compliance is a mandatory part of the cannabis business, and many companies haven’t expended the effort to ensure their processes are meeting regulations. This has placed their licensing and business at risk. An integration that automates the transfer of required reporting information from the ERP to state government approved software such as METRC, Biotrack THC and Leaf Data Systems to ensure regulatory compliance is imperative. This streamlined process assures that reporting is accurate, timely and meets changing requirements in this complex industry.

Facilitates safety and quality control – With an ERP solution tracking all aspects of growing, manufacturing, packaging, distribution and sales, safety and quality are effectively secured throughout the supply chain. Despite the lack of federal legality and regulatory guidelines, proactive cannabis producers can utilize an ERP’s automated processes and best practices to ensure safe and consistent products. By standardizing and documenting food safety procedures, manufacturers mitigate the risk of cannabis-specific concerns (such as aflatoxins, plant pesticide residue, pest contamination and inconsistent levels of THC/CBD potency) as well as dangers common to traditional food manufacturers (such as improper employee procedures and training) for those in the edibles marketplace. Food safety initiatives and quality control measures documented within the ERP strengthen the entire supply chain.

Maintains recipes and formulations – In manufacturing, to achieve product consistency in regards to taste, texture, appearance, potency and expected results, complex recipe and formula management is a necessity – including monitoring of THC and CBD percentages. The calculation of specific nutritional values to provide accurate labeling and product packaging provides necessary information for consumers. Cannabis businesses have to evolve with the consumer buying habits and marketplace saturation by getting creative with their product offerings. With integrated R&D functionality, the expansion of new and innovative edibles, beverages and forms of delivery, as well as new extractions, tinctures, concentrates and other derivatives, helps to meet consumer demands.

Handles inventory efficiently – Established inventory control measures such as tracking stock levels, expiration dates and product loss are effectively managed in an ERP solution across multiple warehouses and locations. Cannabis manufacturers are able to maintain raw material and product levels, reduce waste, facilitate rotation methods and avoid overproduction to control costs. With the use of plant tag IDs and serial and lot numbers with forward and backward traceability, barcode scanning automatically links product information to batch tickets, shipping documents and labels – providing the ability to locate goods quickly in the supply chain if necessary in the event of contamination or recall. The real-time and integrated information available helps mitigate the risk of unsafe products entering the marketplace.

Food processing and sanitation
By standardizing and documenting food safety procedures, manufacturers mitigate the risk of cannabis-specific concerns

Utilizes user-based software permissions – Access to data and ability to execute transactions throughout the growing stages, production and distribution are restricted to designated employees with proper authorization – ensuring security and accountability throughout the inventory chain.

Manages supplier approvals – Assurance of safety is enhanced with the maintenance of detailed supplier information lists with test results to meet in-house quality and product standards. Quality control testing ensures that critical control points are monitored and only approved materials and finished products are released – keeping undeclared substances, harmful chemicals and impure ingredients from infiltrating the supply chain. When standards are not met, the system alerts stakeholders and alternate vendors can be sought.

Delivers recall preparedness – As part of an edible company’s food safety plan, recall plans that include the practice of performing mock recalls ensures that cannabis businesses are implementing food safety procedures within their facilities. With seed to sale traceability in an ERP solution, mitigating the risk of inconsistent, unsafe or contaminated products is readily maintained. Integrated data from the CMS solution provides greater insight into contamination issues in the growth stages.

An ERP solution developed for the cannabis industry with supporting CMS functionality embodies the inventory and quality-driven system that growers, processors, manufacturers and distributors seek to strengthen supply chain management. Offering a centralized, secure database, seed to sale traceability, integration to compliance systems, in-application quality and inventory control, formula and recipe management functionality and the ability to conduct mock recalls, these robust business management solutions meet the needs of a demanding industry. With a variety of additional features designed to enhance processes in all aspects of your cannabis operation the solution provides a framework to deliver truly supportive supply chain management capabilities.

From MedTech to Cannabis: A Q&A with Jennifer Raeder-Devens

By Aaron G. Biros
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Project Yosemite, a cannabis product innovation and brand development company, announced earlier this month the appointment of Jennifer Raeder-Devens as their new Chief Scientific Officer. Raeder-Devens is a veteran of the MedTech industry, working for companies like Becton Dickinson, Cardinal Health, Medtronic and 3M.

Prior to joining Yosemite, she was the Vice President of Research & Development at Becton, Dickinson, where she oversaw product development and technology strategies to launch infection prevention products including the ChloraPrep first-in-the-US sterile solution patient preoperative topical antiseptic. She was previously the Vice President of R&D, Strategy and Innovation at Cardinal Health. She’s also held roles at Medtronic, 3M Drug Delivery Systems and 3M Skin Health Division and she has a number of patents in drug delivery and medical devices.

Jennifer Raeder-Devens, Chief Scientific Officer at Project Yosemite

In November of 2018, Project Yosemite launched their first product, OLO, which is an infused, controlled-release sublingual strip. Part of Raeder-Devens’ new role at the company is the continued development and expansion of the OLO sublingual strip technology platform. Andrew Mack, CEO and founder of Project Yosemite, says he’s thrilled to have Raeder-Devens on the team. “Jennifer is an extremely accomplished scientist and engineer with extensive experience driving innovation and R&D in the pharmaceutical and medical device industries,” says Mack.

We caught up with Jennifer over the phone to talk about her background in the MedTech space, why she decided to jump ship to join the cannabis industry and what she’s excited to work on now.

Cannabis Industry Journal: Can you tell us about your background, including your work with 3M and Medtronic? 

Jennifer Raeder-Devens: I’m coming directly from Becton Dickinson, a global med tech company, where I supervised the development of drug-device combination products for topical antiseptics. I spent about 10 years there, mostly in topical drug and combination product development. Prior to that, I was at 3M and Medtronic working in drug-device combination products. At 3M, I was supervising a team of technology developers for the 3M Drug Delivery Systems business. I had experience working with designing and manufacturing transdermal, nasal, buccal and inhalation drug delivery mechanisms for pharmaceutical partners.

I worked on implantable drug delivery systems at Medtronic, which included working on the biocompatibility of things like pacemakers and drug infusion pumps and optimizing them to reduce infection and enhance healing after the implantation procedure.

CIJ: What made you consider joining the cannabis industry? 

Jennifer: With my work in topicals, transdermal and inhalation drug delivery, I had an easy understanding of the different routes of administration we see today in the cannabis industry. And so, from the technology standpoint, I thought this was a place I could contribute to immediately. And then what got me really excited about it was thinking about cannabis, and just like any other drug, with oral drug delivery, you’ve got first class metabolism and side effects from the 11-Hydroxy-THC that are undesirable and you’d rather not have delivered through the gut.

OLO sublingual strips have a 10-minute onset time

I got excited when I saw the development of things like sublingual strips that were focusing on alternatives to smoking that would preserve that relatively fast onset and mitigate some of the side effects of edibles.

The other thing I really like about the cannabis industry: Previously I have been very focused on known drugs that are already approved and repurposing them into a new delivery system. What really interests me about the cannabis industry is the active cannabinoids and terpenes are somewhat known and somewhat unknown, so there is this really interesting challenge there of trying to separate the wheat from the chaff in terms of producing therapeutic effects.

It is a really interesting space where the indications of certain molecules are evolving along with the delivery technology. So, it is a really exciting and eye-opening way to take the next step in my career and have this wide-open space in front of me, both in terms of the different cannabinoids, their effects and the delivery systems we can use.

CIJ: How might you be prepared, given your background, for some of the challenges in the cannabis space?

Jennifer: I think the challenges in cannabis delivery are not different from the challenges in pharmaceutical drug delivery. It’s just that we have this additional complexity of the entourage effect. We can be engineering not just the main ingredient of THC, but also all the other cannabinoids and terpenes. So, for example, with my background in infection prevention, we build a product that we know reduces the risk of infection, but we are really challenged to actually prove it reduces the risk of infection. We have a similar situation in the cannabis industry, where we can get the THC, or CBG or CBN where we want it to go, but then we are really challenged to figure out how we can find, what we call in the pharmaceutical industry, a surrogate end point for efficacy, so that we can test that product and really believe that when we put the product on the market, even though we haven’t tested thousands of users or conducted large randomized clinical trials, that the effect will be shown. We are networking and partnering with a good scientific community to build the right product and do some testing at a small scale that really demonstrates the product achieves the effect that we are really looking for.

CIJ: Can you tell us a little about your new role with Project Yosemite?

Jennifer: My job description falls into three buckets: The first part is that we are forming a scientific advisory board and we are working with some of the leading cannabinoid researchers around the country and around the world. These are the people identifying whether or not certain cannabinoids could reduce cancer cell metabolism or whether cannabinoids contribute to weight loss or diabetes control and other things of that nature. We are trying to reach as far upstream as we can to grasp the emerging understanding of the performance of cannabinoids and terpenes in the endocannabinoid system. So, part of my job is to chair that scientific advisory board, get the thought leaders together in the room and have them bring their knowledge and explore with our own knowledge what cannabis can really do.

The OLO sublingual strips

I have worked in topical, transdermal, buccal, nasal, inhalation drug delivery. In the second bucket of my job, we are trying to understand a given indication or experience that our users want to have, what would be the right route for them. We are challenging our sublingual delivery mechanism to see how fast of an onset we can really get. Right now, we are at 10 minutes for drug delivery in sublingual and we are still trying to get an even faster onset time for the sublingual strip.

For other indications, like chronic pain, we may want to think about a sustained release, so sort of aligning the different indications with which different cannabinoids and terpenes will work for it and see which delivery platform will work for what we are trying to accomplish in each indication.  So, we do not plan to remain solely a sublingual strip company, but will build out additional delivery platforms as we develop new indications.

Right now, we are working upstream with the growers and the processors to get cannabis oil and extracts. Some of the growers are working on different genetics in their cultivars to grow plants that have different ratios of different cannabinoids that we know from the emerging research will have an impact on people’s experience. Now we are working with growers to really get ahead of the curve on how to formulate products with various cannabinoids.

We have an R&D team in house that I supervise. We are always working with our production team to make small improvements such as the faster onset and the dissolution rate and things like flavors, which covers a downstream focus as well.

Taxes & Cannabis: 280E, R&D Credits, 199A & Qualified Opportunity Funds: Part 2

By Zachary Gordon, Jason Hoffman
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Editor’s Note: This is the second piece in a two-part series delving into tax issues. Part one discussed tax code 280E as it pertains to cannabis businesses. Part two will go into research and development credits, 199A and a discussion of risk as it relates to Qualified Opportunity Zones. 


While 280E is the most influential code section for the cannabis industry, structuring never happens in a vacuum. There are many open questions that each business must answer for themselves without court adjudication. We believe that among the riskiest of questions is whether a cannabis business can claim research and development credits.

There is no clear legal authority that either allows these credits or disallows them but certainly utilizing such credits comes at great risk. At the beginning of this article we talked about Congress and the purpose of 280E. Congress’s intention was to make sure that only the minimum required tax deductions were available to Schedule 1 and 2 sellers. A cannabis business receiving a research and development credit would not be with the intension of Congress. While the credits would be computed based on COGS expenditures, at this time we do not believe that a cannabis business should take this credit. Disallowance of COGS would create a constitutional challenge which is why Congress allowed the COGS deduction. Disallowance of Research and Development Credits does not open up the same constitutional issue since the credit is not part of COGS although calculated based on COGS expenditures. 280E states very clearly that credits arising from other code sections are disallowed in the entirety.

More recently the Tax Cut and Jobs Act (TCJA) opened up new issues for cannabis companies that are still unfolding. Two of the most publicized are Qualified Opportunity Funds and Section 199A, the 20% deduction (Qualified Business Deduction).

The 199A deduction allows eligible pass-through entities to claim an additional deduction of 20% of the income (subject to certain limitations) at the individual level potentially lowering the tax rate from 37% to 29.6%. While the American Institute of Certified Public Accountants (AICPA) and others have asked the IRS to clarify if 280E would make a cannabis business ineligible, the final regulations on the subject did not address this issue. There are other significant limitations and hurdles in 199A regulations that any business would have to first pass to be considered for the rate deduction. If a cannabis business meets all other eligibility and limitation criteria, should the pass-through income to their investors be qualified income under 199A? The answer will depend on whether the courts will treat this “deduction” as falling under the general prohibition of 280E.

We believe that there is a reasonable chance that the courts will allow the 199A deduction for cannabis companies. That does not mean, however, that we advise cannabis companies to claim this on their pass-through returns as Qualified Business Income. Much like everything else, it depends on the particular business and the risk profile that management is willing to tolerate. This is one area of tax law that is sure to be challenged in court. The more risk-averse business should pass on claiming this deduction on their returns, but monitor development with an eye to amending at a later date if favorable precedent emerges. If the amounts are large enough, consideration should be given to applying for a Private Letter Ruling, but that also has its own tax risks.

Another new tax incentive that was in the TCJA was Section 1400Z or Qualified Opportunity Zones (QOZ). The incentive allows for the deferral of capital gains until December of 2026. The use of 1400Z also results in up to a 15% decrease in capital gains tax- and tax-free appreciation if all requirements are met. While the IRS has only released proposed regulations and we anticipate significant changes to them when they are released as final, there was nothing in the proposed regulations limiting cannabis businesses from using Qualified Opportunity Funds (QOF) in their structure. It is interesting to note that the TCJA and proposed regulations did list other types of businesses that could not make investments under 1400Z along with all its benefits. Liquor stores, golf courses and sun tan parlors were among those listed but cannabis growers and dispensaries were not.

As the industry continues to mature, new issues and precedents will require CPAs and attorneys to find new solutions to best serve the industry.Using Opportunity Zones to entice investors sounds like a great opportunity, but there are significant risks. The first risk is that the proposed regulations, while currently proposed, may not be final. There is always a chance that the IRS will take a different position when the final regulations are released and add cannabis to the type of businesses that do not qualify. Another risk, and one that was previously mentioned as part of 199A and other areas of structuring, is that the IRS and the courts can always disagree with the taxpayer’s position. This is a new area of tax law and will eventually be litigated. The loss of the Opportunity Zone benefits can significantly change the return to the investors and lead to other issues.

All of these issues come into play when structuring businesses in this industry. These issues must be evaluated as they pertain to the business needs. This can be very complex and requires a great deal of research for each business opportunity. We have found that professionals operating in this industry like to know about all of their options. The most important thing we can do for the industry is to continue to educate the professionals working in it.

Accountants should be available to assist their clients and their clients’ attorneys with structuring techniques aimed at asset protection and minimizing 280E disallowances. Accountants should also be ready to speak to the questions outlined above and be prepared to explain the risks associated with each choice. As the industry continues to mature, new issues and precedents will require CPAs and attorneys to find new solutions to best serve the industry.

Stratos: Quality, Expansion & Growth in Multiple Markets

By Aaron G. Biros
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Jason Neely founded Stratos in 2014, when he and a small group of people left the pharmaceutical industry in search of a new endeavor in the cannabis marketplace. The concept was straightforward: Apply pharmaceutical methodologyof production to cannabis products. Back then, Stratos offered a range of THC-infused tablets in the Colorado market.

Brenda Verghese, vice president of research & development

Brenda Verghese, vice president of research & development, was one of five people on staff when Stratos launched. Now they have about 30 team members. Consumers were looking for a cannabis product that would be consistent and reliable every time, taking the guesswork out of infused products dosage. That’s where Brenda Verghese found her skillset useful.

Transitioning to the pharmaceutical industry right out of college, Verghese started her career as a chemist and worked her way up to the R&D business development sector. “I specializedin formulations and taking a product from concept to commercialization in the pharmaceutical space,” says Verghese. “Jason Neely approached me with the idea of a cannabis company and focusing on making products as effective and consistent as possible, so really bringing pharmaceutical science into the cannabis space. In the matter of 4 years we grew substantially, mainly focusing on the efficacy of products.”

Behind the scenes at packaging and labeling Image credit: Lucy Beaugard

Soon after the success of their THC products became apparent, Stratos launched a CBD line, quickly growing their portfolio to include things like tinctures and topicals as well. According to Verghese, they are hoping that what’s been established on the THC side of their business as far as reproducibility and consistency is something that consumers will also experience on the CBD side. “Quality and consistency have definitely driven our growth,” says Verghese. “That is what consumers appreciate most- the fact that every tablet, tincture or swipe of a topical product is going to be consistent and the same dose every time.” This is what speaks to their background in the pharmaceutical sciences, FDA regulation has taught the Stratos team to create really robust and consistent formulations.

Quality in manufacturing starts at the source for Stratos: their suppliers. They take a hard look at their supply of raw materials and active ingredients, making sure it meets their standards. “The supplier needs to allow us to do an initial audit and periodic audits,” says Verghese. “We require documentation to verify the purity and quality of oil. We also do internal testing upon receipt of the materials, verifying that the COAs [certificates of analysis] match their claims.”

Process validation in action at the Stratos facility
(image credit: Lucy Beaugard)

Verghese says maintaining that attention to detail as their company grows is crucial. They implement robust SOPs and in-process quality checks in addition to process testing. They test their products 5-6 times within one production batch. Much of that is thanks to Amy Davison, director of operations and compliance, and her 15 years of experience in quality and regulatory compliance in the pharmaceutical industry.

Back in August of 2018, Amy Davison wrote an article on safety and dosing accuracy for Cannabis Industry Journal. Take a look at this excerpt to get an idea of their quality controls:

Product testing alone cannot assess quality for an entire lot or batch of product; therefore, each step of the manufacturing process must be controlled through Good Manufacturing Practices (GMP). Process validation is an aspect of GMPs used by the pharmaceutical industry to create consistency in a product’s quality, safety and efficacy. There are three main stages to process validation: process design, process qualification and continued process verification. Implementing these stages ensures that quality, including dosing accuracy, is maintained for each manufactured batch of product.

Fast forward to today and Stratos is looking at expanding their CBD products line significantly. While their THC-infused products might have a stronger brand presence in Colorado, the CBD line offers substantial growth potential, given their ability to ship nationwide as well as online ordering. “We are always evaluating different markets and looking for what suits Stratos and our consumer base,”says Verghese.

Heavy Metals Testing: Methods, Strategies & Sampling

By Charles Deibel
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Editor’s Note: The following is based on research and studies performed in their Santa Cruz Lab, with contributions from Mikhail Gadomski, Lab Manager, Ryan Maus Technical Services Analyst, Laurie Post, Director of Food Safety & Compliance, and Charles Deibel, President Deibel Cannabis Labs.


Heavy metals are common environmental contaminants resulting from human industrial activities such as mining operations, industrial waste, automotive emissions, coal fired power plants and farm/house hold water run-off. They affect the water and soil, and become concentrated in plants, animals, pesticides and the sediments used to make fertilizers. They can also be present in low quality glass or plastic packaging materials that can leach into the final cannabis product upon contact. The inputs used by cultivators that can be contaminated with heavy metals include fertilizers, growing media, air, water and even the clone/plant itself.

The four heavy metals tested in the cannabis industry are lead, arsenic, mercury and cadmium. The California Bureau of Cannabis Control (BCC) mandates heavy metals testing for all three categories of cannabis products (inhalable cannabis, inhalable cannabis products and other cannabis and cannabis products) starting December 31, 2018. On an ongoing basis, we recommend cultivators test for the regulated heavy metals in R&D samples any time there are changes in a growing process including changes to growing media, cannabis strains, a water system or source, packaging materials and fertilizers or pesticides. Cultivators should test the soil, nutrient medium, water and any new clones or plants for heavy metals. Pre-qualifying a new packaging material supplier or a water source prior to use is a proactive approach that could bypass issues with finished product.

Testing Strategies

The best approach to heavy metal detection is the use of an instrument called an Inductively Coupled Plasma Mass Spectrometry (ICP-MS). There are many other instruments that can test for heavy metals, but in order to achieve the very low detection limits imposed by most states including California, the detector must be the ICP-MS. Prior to detection using ICP-MS, cannabis and cannabis related products go through a sample preparation stage consisting of some form of digestion to completely break down the complex matrix and extract the heavy metals for analysis. This two-step process is relatively fast and can be done in a single day, however, the instruments used to perform the digestion are usually the limiting step as the digesters run in a batch of 8-16 samples over a 2-hour period.

Only trace amounts of heavy metals are allowed by California’s BCC in cannabis and cannabis products. A highly sensitive detection system finds these trace amounts and also allows troubleshooting when a product is found to be out of specification.

For example, during the course of testing, we have seen lead levels exceed the BCC’s allowable limit of 0.5 ppm in resin from plastic vape cartridges. An investigation determined that the plastic used to make the vape cartridge was the source of the excessive lead levels. Even if a concentrate passes the limits at the time of sampling, the concern is that over time, the lead leached from the plastic into the resin, increasing the concentration of heavy metals to unsafe levels.

Getting a Representative Sample

The ability to detect trace levels of heavy metals is based on the sample size and how well the sample represents the entire batch. The current California recommended amount of sample is 1 gram of product per batch.  Batch sizes can vary but cannot be larger than 50 pounds of flower. There is no upper limit to the batch sizes for other inhalable cannabis products (Category II).

It is entirely likely that two different 1 gram samples of flower can have two different results for heavy metals because of how small a sample is collected compared to an entire batch. In addition, has the entire plant evenly collected and concentrated the heavy metals into every square inch of it’s leaves? No, probably not. In fact, preliminary research in leafy greens shows that heavy metals are not evenly distributed in a plant. Results from soil testing can also be inconsistent due to clumping or granularity. Heavy metals are not equally distributed within a lot of soil and the one small sample that is taken may not represent the entire batch. That is why it is imperative to take a “random” sample by collecting several smaller samples from different areas of the entire batch, combining them, and taking a 1 g sample from this composite for analysis.


References

California Cannabis CPA. 12/18/2018.  “What to Know About California’s Cannabis Testing Requirements”. https://www.californiacannabiscpa.com/blog/what-to-know-about-californias-cannabis-testing-requirements. Accessed January 10, 2019.

Citterio, S., A. Santagostino, P. Fumagalli, N. Prato, P. Ranalli and S. Sgorbati. 2003.  Heavy metal tolerance and accumulation of Cd, Cr and Ni by Cannabis sativa L.. Plant and Soil 256: 243–252.

Handwerk, B. 2015.  “Modern Marijuana Is Often Laced With Heavy Metals and Fungus.” Smithsonian.com. https://www.smithsonianmag.com/science-nature/modern-marijuana-more-potent-often-laced-heavy-metals-and-fungus-180954696/

Linger, P.  J. Mussig, H. Fischer, J. Kobert. 2002.  Industrial hemp (Cannabis sativa L.) growing on heavy metal contaminated soil: fibre quality and phytoremediation potential. Ind. Crops Prod. 11, 73–84.

McPartland, J. and K. J McKernan. 2017.  “Contaminants of Concern in Cannabis: Microbes, Heavy Metals and Pesticides”.  In: S. Chandra et al. (Eds.) Cannabis sativa L. – Botany and Biotechnology.  Springer International Publishing AG. P. 466-467.  https://www.researchgate.net/publication/318020615_Contaminants_of_Concern_in_Cannabis_Microbes_Heavy_Metals_and_Pesticides.  Accessed January 10, 2019.

Sidhu, G.P.S.  2016.  Heavy metal toxicity in soils: sources, remediation technologies and challenges.   Adv Plants AgricRes. 5(1):445‒446.