This is the fourth article in series of articles on the differences between outdoor versus indoor grown cannabis. In this article, we discuss heavy metals. This article begins with the understanding that heavy metal contamination has spread broadly over the globe and that there is a need to arrest this trend.
For farmers, chemical fertilizers, human sewage (BioSolids), and manure from animals given metal laden feed all contribute to the build up of heavy metals in our soils and the subsequent contamination of our crops. Furthermore, due to poor stewardship/naiveté, the soils in some areas of the country have been badly contaminated such that crops grown in these areas will likewise be contaminated. And finally, even organic farmers with relatively clean soil need to be careful about the materials they use as the case in New Zealand demonstrates wherein phosphate fertilizers were made using rock from the island of Nauru containing high amounts of the heavy metal cadmium.
Heavy Metals in Chemical Fertilizers
In Screening Evaluation of Heavy Metals in Inorganic Fertilizers they write “the presence of heavy metals in inorganic (chemical) fertilizers is well established (US EPA 1999a; CDFA 2004; WSDA 2007)… Analytical testing of a wide range of fertilizer products shows that some phosphate and micronutrient fertilizers, and liming materials contain elevated levels of arsenic, cadmium, and lead compared to other fertilizer types (e.g., nitrogen, potash, gypsum)”. To get a sense for the level of heavy metal contamination in chemical fertilizers, on the Washington State Department of Agriculture (WSDA) website are the tabulated Metals Concentration in Fertilizer Sampled by WSDA. So OK, we know that chemical fertilizers contain heavy metals and we have some sense for the levels of these metals in fertilizers from the WSDA data. Let’s see if we can get a better sense for the degree of contamination.
Industry Safe Levels of Heavy Metals in Chemical Fertilizers
AAPFCO - The Heavy Metal Rule |
||
Metals |
ppm per 1% P |
ppm per 1% Micronutrient |
Arsenic |
13 |
112 |
Cadmium |
10 |
82 |
Cobalt |
136 |
2,228 |
Lead |
61 |
463 |
Mercury |
1 |
6 |
Molybdenum |
42 |
300 |
Nickel |
250 |
1,900 |
Selenium |
26 |
180 |
Zinc |
420 |
2,900 |
- Fertilizers with a phosphate guarantee; but, no micro-nutrient guarantee Multiply the percent guaranteed P2O5 (phosphate) in the product by the values in the table to obtain the maximum allowable concentration of each metal. The minimum value for P2O5 utilized as a multiplier shall be six.
- Fertilizers with one or more micro-nutrient guarantees; but, no phosphate guarantee Multiply the sum of the guaranteed percentages of all micro-nutrients in the product by the value in the appropriate column in the Table to obtain the maximum allowable concentration (ppm) of each metal. The minimum value for micro-nutrients utilized as a multiplier shall be one.
- Fertilizers with both a phosphate and a micro-nutrient guarantee
- Multiply the guaranteed percent P2O5 (phosphate) by the value in the appropriate column. The minimum value for P2O5 utilized as a multiplier shall be 6. Then,
- Multiply the sum of the guaranteed percentages of the micro-nutrients by the value in the appropriate column. The minimum value for micro-nutrients utilized as a multiplier shall be one.
- Then, utilize the higher of the two resulting values as the maximum allowable concentration (ppm) of each metal.
For the sake of brevity, I’ll focus my attention on the heavy metal arsenic and leave it up to you to look at other metals. So what are the levels of heavy metals in chemical fertilizers? For that we can look at Metals Concentration in Fertilizer Sampled by WSDA. In the WSDA data related to arsenic, one of the more egregious fertilizers is KGRO Super Bloom with 136 mg/kg (ppm) of arsenic. Is this level “safe” per AAPFCO?
To answer this, we look up KGRO Super Bloom and find that this is a phosphate only 10-54-10 fertilizer. Knowing this, we can then use the table and rules above. Per AAPFCO, the allowable limit of arsenic for this particular fertilizer works out to be 54×13=702 ppm! So according to AAPFCO, it’s “safe” (136<702). But is it really? Let's look at arsenic from a different vantage point - in terms of natural background levels of heavy metals in soils.
Levels of Heavy Metals in Chemical Fertilizers Relative to Natural Soil Levels
Keeping up with our focus on arsenic, in Arsenic Cleanup Criteria for Soils in the US and Abroad, the range of natural “background” levels of arsenic in the soil is listed as being from 0.039mg/kg (ppm) in Wisconsin all the way up to 40mg/kg (ppm) for other states. All soil has some level of heavy metals in them and these are simply the natural, uncontaminated “background” levels for any given location. Using this information along with WSDA data in mg/kg (ppm), we can get a sense of the degree to which a given chemical fertilizers may lead to a build up of a given heavy metal in soils – in our case, arsenic. Note: Heavy Metals and Gardens has a table to help get a sense for safe levels of various heavy metals.
Before going any further, it’s worth noting that heavy metals do not go away over time – except when they’re taken up by plants or through targeted remediation. In other words, anytime a material like a chemical fertilizer, that has a higher level of a given heavy metal than the soil, is added to the soil, the concentration of the toxic metal builds up in the soil. So alright, let’s get back to the arsenic example.
To get a sense for how toxic a chemical fertilizer is, we need to compare the natural background level of a heavy metal in the soil to the chemical fertilizer in question. In Wisconsin, the background level of arsenic is really low, 0.039 mg/kg (ppm). However, in looking over the WSDA data, nearly all the chemical fertilizers listed have higher concentrations of arsenic. Fertilizers with a higher concentration would increase the level in the soil when added to the soil. Of course, the rate of build up would depend on the amount applied, the difference in concentrations, soil conditions, pH, and the like, but they would nonetheless build.
For examples, if Miracle-Gro Water Soluble Azalea with 0.2 mg/kg (ppm) of arsenic was applied, the build up would be relatively slow compared to KGRO Super Bloom with 136 mg/kg (ppm). Let’s try to get a better sense for the degree of build up. To do this, let’s assume that 1 ft3 of KGRO Super Bloom (weight of Super Bloom is 18.3 kg/ft3 based upon the box dimensions and listed weight) is worked into the top 8-inches of our loamy Wisconsin soil (weight of loamy soil is 36.5kg/ft3).
Let’s see over what area that amount of fertilizer would need to be applied in order to potentially double the level of arsenic to 0.078 mg/kg (ppm) in our Wisconsin soil. The math works out to about 140-foot by 140-foot area (19,600 ft3), or about 1/3rd of an acre. That’s a pretty large area of land. In other words, this chemical fertilizer would rapidly increase background levels of arsenic.
Now I would have ended the conversation here but by wife, who is an graduated with a degree in Agricultural Engineer, insisted I further quantify the application rate. In the USDA Data and Statistics for 2018 Vegetable Chemical Use in 2019 they list an average application rate for phosphate at 80 lbs/acre (36.3 kg/acre) per year for tomatoes. Tomatoes, you might ask? Well, there isn’t any data for cannabis and tomatoes are purported to be similar to cannabis in care – close enough for this discussion.
From above, we know that Super Bloom weighs 18.3 kg/ft3 and has an N-P-K ration of 10-54-10. In other words, it’s 54% phosphate by weight. To apply 80 lbs (36.3 kg) per acre, we need to use roughly ((36.3/18.3)/0.54)= 3.7 ft3 of this fertilizer per acre. Again from above, we know that applying 1 ft3 of Super Bloom over roughly 1/3rd of an acre potentially doubles the background levels of arsenic in Wisconsin. At 80 lbs/acre, we’re apply somewhat more than this amount. In other words, chemical fertilizers have the potential to increase heavy metals in the soil rather quickly – Super Bloom at this rate may very well double arsenic background levels in Wisconsin in less than a year.
OMRI Organic Safe Levels of Heavy Metals
A third way to approach getting a sense for the degree of potential harm heavy metals in chemical fertilizer pose is to look at the Organic Materials Review Institute (OMRI) safety guidelines. OMRI determines what materials may be used in certified organic production. The Rodale Institute states that, “OMRI requires heavy metals testing for many types of fertilizer products. If the test reveals that heavy metals exceed a certain concentration, the product may be either OMRI Listed with a ‘Caution’ statement, or potentially considered ineligible for OMRI listing. The following table provides an overview of the threshold levels“.
Level 1 = level at which OMRI issues a ‘Caution’ statement for a given product based upon the potential for long-term contamination
Level 2 = level at which a product is ineligible for the OMRI Products List due to risk of soil contamination
Getting back to our arsenic analysis, OMRI says that compost with more than 10 mg/kg (ppm) is problematic. If you remember, Miracle-Gro Water Soluble Azalea has 0.2 mg/kg (ppm) of arsenic and KGRO Super Bloom has 136 mg/kg (ppm). Given that the average weight of compost is 24 kg/ft3 and knowing that Super Bloom weighs 18.3 kg/ft3, this means that the OMRI data equates to a safe level for chemical fertilizers of roughly (10×24/18.3)= 13 mg/kg (ppm). This is much lower than AAPFCO 702 mg/kg (ppm) and is consistent with certified organic standards being more conscientious.
Taking this all in, the agricultural industry limits for heavy metals appear to be very high. Depending on the background levels of the soil and level of contamination of the chemical fertilizer, less than a years worth of fertilizer could potentially double background levels. In addition, while OMRI levels are much more limiting, it’s essential that growers pay careful attention to heavy metal contamination.
Heavy Metals in Sewage Sludge
With savings of $200 per acre, it’s no wonder some farmers are using composted human waste (aka sewage sludge, BioSolids) instead of chemical fertilizers. Surprised? That’s right; farmers are putting human waste on their fields!
In it’s wisdom, the EPA approved BioSolids in 1993. In terms of heavy metals, the EPA regulated that BioSolids are to be tested for a paltry number of heavy metals – nine to be exact. To get a sense for the toxicity of BioSolids, understand that the EPA allows relatively high heavy metal concentrations in BioSolids and “according to Natural News, BioSolids are also loaded up with “appreciable concentrations of polybrominated diphenyl ether (PBDE) flame retardants, triclosan, an antibacterial agent, nonylphenol detergent breakdown components, and other things“. This is not nice stuff.
Heavy Metals in Feed Additives
If you’re like me, you’ll be surprised to learn that heavy metals are intentionally put in livestock feed! In the case of arsenic, it is fed to chickens, turkeys, and pigs purportedly to prevent parasites. Copper is fed to pigs to fatten them up. In Accumulation of Copper and Zinc From Liquid Manure in Agricultural Soils and Crop Plants they write, “A comparison between the metal contents of liquid manure and normal heavy metal concentrations in soils demonstrates that the copper content in pig slurries is 10–40 times higher than in soil, whereas the zinc content in pig and calf slurries is 10–25 times higher”. In other words, heavy metals in feed additives end up in the manure at fairly high levels.
So what does this mean for cannabis? Well, we now know that manure from conventional farming is often contaminated with heavy metals. When this manure is applied to cannabis fields, depending on the soil, rate of application, and other factors, these heavy metals end up in the cannabis buds to varying levels. Furthermore, this is an issue for both conventional and organic farms. I say this because organic farmers are allowed to apply conventional animal waste to their land. I know; it makes no sense. The sad truth is that buying “certified organic” does not necessarily mean the heavy metal levels will be low.
Happily, at Organic Entourage, we do not bring in manure from other farms. The dairy compost we use comes from certified organic cows that are fed exclusively off of our certified organic land. Late spring through late fall, the cows graze on organic hay and alfalfa in the fields. During the colder months, they are fed the same from large bales set aside during harvest along with certified organic corn – they need the extra energy to keep warm.
In A Survey of Selected Heavy Metal Concentrations in Wisconsin Dairy Feeds they write, “Lowest heavy metal concentrations were found in homegrown alfalfa hay and haylage, and corn grain and silage. Highest metal concentrations were found in purchased feeds, particularly mineral supplements”. We’re doing everything we can to keep heavy metals low in our soil and in our cannabis.
Having said this, the unfortunate reality is that virtually all soil is contaminated to some degree with heavy metals. In today’s world, it is impossible to grow product without some level of contamination. We do everything we can, but all products have some level of contamination.
In addition to using only certified organic feed from our lands, the dairy makes an effort to properly compost their manure. This is done by adding carbon and aerating (turning) the piles in order to promote oxygen-loving microbial growth. These oxygen-loving (aerobic) micro-organisms are both beneficial to plants and people. The composting process is far from perfect at this point, but efforts are being made to construct a large roof soon. This will help keep the piles drier and promote better microbial growth.
Composting is not only important because it invigorates soil and plant life. In addition, organic matter in the compost often helps bind heavy metals in the soil. The graph below from Kansas University shows a notable reduction in lead contamination in Swiss chard, tomatoes, and carrots when grown in soils with higher amounts of organic matter. In our humble estimation, consumers concerned with heavy metals are best served by informed growers.
Land Polluted with Heavy Metals
While virtually all soil is contaminated with some level of heavy metals, parts of the country are so badly laden with heavy metals that they really shouldn’t be used for agriculture. For example, the lands around Los Angeles, Chicago, and New York City are loaded up with lead (Pb). This is a result of all of the traffic in these highly populated areas during the 70’s when leaded gasoline was allowed. Cannabis grown in these soils will have higher levels of lead. Is it any wonder that cannabis vaporizers are “plagued with incidences of lead contamination”? Reading Heavy Metal Labs
Alright, we’ve finished the discussion on heavy metals. Let’s take a minute and look at the heavy metals report for our CBD hemp at Organic Entourage. What you’ll see is that, just like virtually all other food products, there are small amounts of heavy metals in our product. We’re not perfect. And yes, we know that any good marketer would tell us we’re nuts to disclose this information – especially since it’s well within limits. However, we fervently stand behind our commitment to transparency and believe in the intelligence of our customers.
Since our focus is on providing excellent product and nurturing the land, it was important for us to quantify our heavy metal results. Just how bad/good are they? To answer this requires looking at multiple guidelines for reference. There is no definitive source. Furthermore, it’s actually a complex question that really should take into consideration what other exposures a person is subject to, the food type the metal is in, the method of intake, and so on. At best, we can only get a sense for where we stand. Let’s look at some points of reference.
World Health Organization 2001 Maximum Heavy Metals Limits |
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Heavy Metal |
Soil (ppm) |
Veggies (ppm) |
Arsenic |
12.0 |
0.43 |
Cadmium |
1.4 |
0.20 |
Chromium |
64.0 |
2.30 |
Cobalt |
40.0 |
n.a. |
Lead |
70.0 |
0.30 |
Mercury |
n.a. |
n.a. |
Nickel |
50.0 |
0.20 |
Copper |
n.a. |
n.a. |
Iron |
n.a. |
n.a. |
Manganese |
n.a. |
n.a. |
Selenium |
n.a. |
n.a. |
Zinc |
n.a. |
n.a. |
World Health Organization 2014 Maximum Heavy Metals Limits |
||
Heavy Metal |
Soil (ppm) |
Veggies (ppm) |
Arsenic |
20 |
n.a. |
Cadmium |
3 |
0.10 |
Chromium |
100 |
n.a. |
Cobalt |
50 |
50.00 |
Lead |
100 |
0.30 |
Mercury |
n.a. |
n.a. |
Nickel |
50 |
67.00 |
Copper |
100 |
73.00 |
Iron |
500 |
425.00 |
Manganese |
2000 |
500.00 |
Selenium |
10 |
n.a. |
Zinc |
300 |
100 |
International Standards for Food 2011 Maximum Heavy Metals Limits |
||
Heavy Metal |
Limit (ppm) |
|
Arsenic - solids not fish |
1.4 |
|
Cadmium - cereal/veggie |
0.1 |
|
Chromium - cereal/veggie |
1 |
|
Cobalt |
n.a. |
|
Lead - all solids |
6 |
|
Mercury - all solids |
0.5 |
|
Nickel |
n.a. |
|
Copper |
n.a. |
|
Iron |
n.a. |
|
Manganese |
n.a. |
|
Selenium |
n.a. |
|
Zinc |
n.a. |
|
New Standard in Consumer Safety |
||
| Verified A+++
Lead < 0.025 ppm Cadmium < 0.1 ppm Arsenic < 0.62 ppm Mercury < 0.006 ppm |
Verified A++
Lead < 0.05 ppm Cadmium < 0.25 ppm Arsenic < 1.25 ppm Mercury < 0.012 ppm |
|
| Verified A+ Lead < 0.12 ppm Cadmium < 0.5 ppm Arsenic < 2.5 ppm Mercury < 0.025 ppm |
Verified A Lead < 0.25 ppm Cadmium < 1 ppm Arsenic < 5 ppm Mercury < 0.050 ppm |
|
| Verified B Lead < 0.5 ppm Cadmium < 2 ppm Arsenic < 10.0 ppm Mercury < 0.1 ppm |
Verified C Lead < 1 ppm Cadmium < 4 ppm Arsenic < 20.0 ppm Mercury < 0.2 ppm |
|
| Verified D Lead < 2 ppm Cadmium < 8 ppm Arsenic < 40.0 ppm Mercury < 0.4 ppm |
Verified F Is anything worse than "D" |
|
In addition, we have a heavy metal standard from the Consumer Wellness Center shown above. Consumer Wellness Center is headed by Mike Adams. Setting Mr. Adam’s politics aside, this seems like a reasonable standard in light of the World Health Organization (WHO) data. Along side is the 2017 Cannabis Heavy Metal table from Analysis of Cannabis and Hemp Products for Heavy Metals. The table shows heavy metal levels found in 18 different cannabis concentrates. Unlike the other data, these are not limits but the actual levels in various products. Note: It’s important to realize that the cannabis data is in parts-per-billion (ppb) and not parts-per-million (ppm) as in all the other data. To convert ppb to ppm, simply move the decimal point three places to the left (19 ppb = 0.019 ppm).
With this data in mind, we can now look at the 2019 heavy metals results for Organic Entourage. What we see is that of the four heavy metals tested, Cadmium and Mercury, were below the detectable limit of 0.05ppm. Of the other two metals, Arsenic tested at 0.05 ppm and Lead tested at 0.06 ppm. In looking at the World Health Organization and International Standards, the limit for Arsenic ranges between 0.43 and 1.4 ppm while the limit for Lead ranges between 0.30 and 6. Based upon these standards, the level for Arsenic at Organic Entourage is between 8-28 times less than limits and Lead is between 5-100 times less than limits. Using this data, our levels are quite low.
In addition, we can also look at the heavy metals results for Organic Entourage based upon the other two tables shown. In terms of the “New Standard in Consumer Safety”, we rate very close to an A++ and in terms of cannabis test results, we fall right in the middle compared to concentrates. In other words, a lot of cannabis product on the market has low levels of heavy metals. That’s great.
So this is the reality of the world we live in today. Our heavy metal numbers are very low but not zero. I suppose we could put in a roadbed to the top of a remote and uninhabited mountain, mow down the vegetation, terrace the hillside, truck in soil, install holding tanks for irrigation, and so on as we’ve seen done. How wonderful to be in such a remote location.
I’m guessing locations like these have even lower lead levels due to their previously pristine habitat. On the other hand, they may be higher in mercury due to their elevation since mercury is carried on prevailing winds from coal power plants. When it comes down to it and having been exposed to the plight of small family farm first hand, we think it’s a bit sad that perfectly good farmland is passed over for these types of locations.
Outdoor Versus Indoor Cannabis Series
