Heavy Metals Part 1: Arsenic

Has Arsenic been weighing heavily on you? You aren't the only one! In the first part of a 5-part series on heavy metals, Abraxas Labs tackles de-mystifying Arsenic, its sources, and approach to keeping your heavy metals levels in control.

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While Abraxas Labs makes the best effort to ensure that all of the informational material is up-to-date, the dynamic nature of the regulatory landscape of the industry renders it necessary for you to verify that any steps that you follow are, in fact, relevant to the most recent regulations in force.

Remember: it is ultimately your responsibility to ascertain the validity of any information source. To help you in this process, please make sure that you at the very least take the following precautions:

  1. Check the date of the article published by Abraxas Labs
    1. We regularly review our articles to make sure they are still applicable, so the date will be updated each time the article is reviewed 
    2. If you know that new regulations have been released since the article was published, make sure that you verify with the source (e.g. METRC or OMMA) or consult your attorney if you are still unclear as to the applicability of the material
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      1. Phone: 918-924-5164
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Arsenic: Introduction

Learning from a Certificate of Analysis that you may have a problem with your product is never a pleasant kind of surprise. It can be costly and extremely difficult to trace, not to mention the effects heavy metals have on the end-user's health. To complicate the situation further, one of the unique properties of the cannabis plant is its ability to readily uptake heavy metals from its environment. In fact, it is so good at heavy metals uptake that it has been grown in contaminated environments just for this purpose, a processes referred to as phytoremediation. Interestingly (yet hardly surprisingly) the ability of the plant to uptake heavy metals is driven in large part by its genetics. How is this helpful you ask? Great question!

Let's say you had the unpleasant experience of receiving a COA that showed readings of heavy metals that were above the reporting limit for the State of Oklahoma. There is no way to "remediate" this in Oklahoma, but you certainly do not want this to carry over into your next harvest, so you really need to trace the cause. Where do you start? The answer is very much dependent on your operation. As we discuss below, fish-based and ocean-based products, living soil (under specific conditions) are two of the more common culprits that we have observed.

Great! So the logical answer is test your soil and nutrients, correct? Well, yes, but that's not all. Due to the heavy genetic influence of the plant, combined with the plethora of variables affecting the metals content in the plant, it is decidedly difficult (virtually impossible) to know exactly what a specific heavy metals content in soil or nutrients will have on the content in the final plant product. We do  know that the roots of the plant are much more resilient to heavy metals exposure (likely to the nature of the pH therein), while their accumulations in leaves and stems has far more detrimental effects on the plant's vitality and growth.

Granted, this does not mean that you should skip testing the environmental variables affecting the plant. In fact, we encourage you -- as soon as you realize that heavy metals are likely to be a problem -- to establish a baseline of metals content in media that are likely to be most influential. Why? Because while you may not know what a reading of "X" PPM in soil means "Y" PPM in plant (again, genetic and environmental variables at play make such a direct comparison essentially impossible), you will know that for the plant genetics of your specific plants cultivated within your environment, using your SOPs had a specific reading of PPM (found on page 3 or page 4 of your Abraxas Labs COA), which corresponded to a specific PPM reading in the soil (or water, or nutrients). This does not provide a magic resolution to your problem, but now you have a start. If the level of metals in your (for example) soil stays the same or decreases during the next harvest, while the levels in the plant increase, the chances of that variable (e.g. soil) being the cause have just decreased. In this way, the level of energy that you are expanding to find your source will be more targeted towards the more probable causes, increasing your chances of finding the source quicker and losing less capital to identify the sources. With this in mind, let's consider some potentially helpful facts.

The most common sources of arsenic exposure in humans are primary ingestion of arsenic-contaminated food and water; which gets its Arsenic from...wait for it...contaminated soil where the crops is grown, and various sources of water contamination, such as water contaminated by bedrock containing arsenic, mining, and various sources of industrial pollution. In general, meat, fish, and poultry account for 80% of dietary arsenic intake.

Fish, bivalve shellfish, and algae also contain arsenic in the form of arsenobetaine and arsenocholine, sometimes referred to as “fish arsenic” which is an organic form of arsenic. Fish arsenic or organic arsenic has low toxicity to humans and is rapidly excreted in urine. However, one form of seaweed, hijiki, reportedly contains high levels of inorganic arsenic. Why differentiate between the organic & inorganic form of arsenic? For starters, inorganic arsenic is more toxic in humans than organic forms of arsenic.

While inorganic arsenic is a more toxic form of arsenic in humans, Oklahoma Medical Marijuana Authority (OMMA) and the current state regulations, require analytical laboratories testing medical cannabis for release for transfer or sale of the product to report arsenic as total arsenic. In other words, the OMMA makes no differentiation between, or calls for speciation and determination of, the arsenic source; all sources of arsenic in the final product tested add towards the failure threshold of 0.2 ppm (inhalable products failure threshold).

Subjective assessment of the data at Abraxas Labs suggests a positive association between the levels of heavy metals in client samples and use of sea kelp as a nutritional additive. Namely, levels of arsenic, cadmium, and lead appear to have positive association with the use of sea-based products.

Caution: these are observations made in a qualitative manner, with no statistical analysis performed. We will post these results are we collect enough data, but mention it here in case it is helpful to anyone facing these issues.


  1. P. Linger, J. Müssig, H. Fischer, J. Kobert, Industrial hemp (Cannabis sativa L.) growing on heavy metal contaminated soil: fibre quality and phytoremediation potential, Industrial Crops and Products, Volume 16, Issue 1, 2002, Pages 33-42, ISSN 0926-6690, https://doi.org/10.1016/S0926-6690(02)00005-5.
    1. Abstract: Hemp (Cannabis sativa L.) was used to examine its capability as a renewable resource to decontaminate heavy metal polluted soils. The influence of heavy metals on the fibre quality was of special interest. Determination of heavy metal content was carried out by means of atomic absorption spectroscopy (AAS). Four different parts of the plant were examined: seeds, leaves, fibres and hurds. In each case, the concentration relation was Ni>Pb>Cd. However, the heavy metal accumulation in the different parts of the plant was extremely different. All parts of hemp plants contain heavy metals and this is why their use as a commercially utilisable plant material is limited. We found that the highest concentrations of all examined metals were accumulated in the leaves...
  2. Ahmad, R., Tehsin, Z., Malik, S.T., Asad, S.A., Shahzad, M., Bilal, M., Shah, M.M. and Khan, S.A. (2016), Phytoremediation Potential of Hemp (Cannabis sativa L.): Identification and Characterization of Heavy Metals Responsive Genes. Clean Soil Air Water, 44: 195-201. https://doi.org/10.1002/clen.201500117
  3. Agency for Toxic Substances and Disease Registry (2016). "Addendum to the Toxicological Profile for Arsenic." Atlanta, GA USA. https://www.atsdr.cdc.gov/toxprofiles/Arsenic_addendum.pdf.
  4. Chung, J. Y., Yu, S. D., & Hong, Y. S. (2014). Environmental source of arsenic exposure. Journal of preventive medicine and public health47(5), 253.
  5. Rose, M., et al., “Arsenic in seaweed--forms, concentration and dietary exposure”. Food Chem Toxicol, 2007. 45(7): p. 1263-7.
  6. Punshon T., Jackson B.P., Meharg A.A., Warczack T., Scheckel K., Guerinot M.L. Understanding arsenic dynamics in agronomic systems to predict and prevent uptake by crop plants. Sci. Total Environ. 2017;581–582:209–220.