1One plant, four very different products

Previous parts of this series covered powders and bee products, followed by tablets and capsules. This part looks at products made from hemp, Cannabis sativa. Part 7 covers botanicals.

Hemp takes up cadmium, lead, nickel and other metals from the soil. How much reaches each part of the plant depends on the growing conditions and on the plant tissue.

A 2021 review of field studies found several milligrams of cadmium per kilogram in hemp leaves and stems when the plants were grown on contaminated soil. The roots contained more, while the seeds contained less. Even so, a relatively small fraction of the metal taken up by the plant can still produce a significant concentration in a product.

Hemp seeds, hemp seed oil and ground or defatted hemp seed have a history of consumption in the EU and are not treated as novel foods. Hemp extracts and products containing CBD or other non-psychoactive cannabinoids are different: they fall under the EU novel-food framework, and none had been authorised at the time this article was written.

The heavy-metal rules are a separate matter. Regulation (EU) 2023/915 sets maximum levels for lead, cadmium, mercury and arsenic in food. Where a limit applies, it is expressed in milligrams per kilogram of the product as sold.

The applicable limit depends on the product category. The regulation identifies those categories by individual rows of its table, which we refer to by their row numbers below.

The main finding is simple:

• Hemp seeds, hemp seed oil and hemp protein: cadmium is the main concern.
• CBD oils and capsules: lead is the main concern based on the market surveys we found.
• CBD isolate and distillate: there is not enough published data to identify one metal as the main concern.
• Hemp flower for smoking: there is no EU heavy-metal limit; in the published Italian surveys we found, lead was the metal most likely to exceed the US inhalable limits.

2Hemp seeds, hemp seed oil and hemp protein

The metal

For hemp seed products, cadmium is the main concern.

The EU maximum level for cadmium in the relevant oilseed category is only 0.10 mg/kg. This is the lowest limit discussed in this article.

Hemp seed can contain considerably more.

In a 2011 field trial in western Romania, five approved hemp varieties were grown on soil containing more cadmium than the Romanian soil limit of 1 mg/kg. The whole seeds contained 1.3 to 4.0 mg/kg of cadmium. That is 13 to 40 times the EU oilseed limit.

The average concentrations were 1.9 mg/kg for Zenit and 3.4 mg/kg for both Armanca and Silvana. In two varieties, foliar phosphate fertiliser increased seed cadmium by 20–50 %.

The opposite result is also possible. A survey of 21 hemp seed lots from north-western Turkey found cadmium at only a few hundredths of the EU limit and no detectable lead. That study was available to us only as an abstract.

The difference between these results is important. The amount of cadmium in a commercial seed lot is likely to depend more on the growing conditions, particularly the soil, than on the hemp variety itself.

Lead is different. There is no lead maximum level for oilseeds, although lead does have a limit for oils. It is tested as part of the panel in any case.

Where it comes from

The main source is the soil.

Cadmium occurs naturally in the parent rock and can also enter agricultural soils through phosphate fertilisers, where it is present as an impurity of phosphate rock.

The plant takes up cadmium through its roots. Some of it moves into the shoots and a smaller amount reaches the seed.

We found no published measurement that separates cadmium in the hemp seed hull from cadmium in the kernel. We therefore do not give separate figures for the two.

There is also an important difference between seed, oil and protein.

In sunflower seed, a published conference report states that cadmium concentrates in the meal after crushing, while relatively little enters the oil. This is because cadmium is associated mainly with the protein and mineral fraction rather than the fat.

We have not found a comparable measurement for hemp seed. We therefore treat the same behaviour in hemp as an expectation, not as a measured result.

If that expectation holds, the same seed would produce:

• the lowest cadmium concentration in the oil;
• a higher concentration in the remaining press cake;
• and therefore potentially the highest concentration in hemp protein or hemp flour.

The number

Hemp seed is not named separately in the cadmium table of Regulation (EU) 2023/915. It falls within the regulation's oilseed category through the product classification in Regulation (EC) No 396/2005, where hemp seeds are entry 0401140.

The applicable row is therefore 3.2.11.1, which sets cadmium at 0.10 mg/kg for the relevant oilseeds.

There are separate, higher limits for some named oilseeds. These range from 0.15 mg/kg for rapeseed to 1.20 mg/kg for poppy seed.

There is no corresponding oilseed row for lead or mercury.

The regulation also contains a special provision for seed intended for crushing and refining. When the pressed seed is subsequently placed on the market as food, the concentration change caused by processing must be taken into account (Article 3).

This matters for hemp protein and hemp flour.

If pressing reduces the mass of the seed, while most of its cadmium remains in the press cake, the cadmium concentration in the cake increases. The regulation therefore allows the original oilseed limit to be multiplied by a processing factor.

For example, if a seed contains 30 % oil and pressing leaves approximately 70 % of the original mass as cake, the theoretical concentration factor would be about:

1 / 0.70 = 1.43

A seed containing 0.10 mg/kg cadmium would therefore correspond to roughly 0.14 mg/kg in the cake.

That is an illustration, not a regulatory factor to use automatically. The factor should be based on the actual seed and cake and should be supported by measurements when required.

Hemp seed oil has no cadmium row. Its relevant heavy-metal limit is instead the lead limit for fats and oils: 0.10 mg/kg (row 3.1.18).

The THC limits are separate and apply to the relevant hemp product categories (rows 2.6.1 to 2.6.3):

• hemp seeds: 3.0 mg/kg;
• ground and defatted hemp seed and other products made only from hemp seed: 3.0 mg/kg;
• hemp seed oil: 7.5 mg/kg.

These values are expressed as THC plus 0.877 × THCA.

When a hemp protein or hemp seed oil product is sold as a food supplement, the supplement limits apply instead (rows 3.1.28, 3.2.21.1 and 3.3.2):

• lead: 3.0 mg/kg;
• cadmium: 1.0 mg/kg;
• mercury: 0.10 mg/kg;
• no EU maximum level for arsenic in this category.

The same hemp protein can therefore be subject to different limits depending on whether it is sold as a food or as a food supplement.

When to test

For hemp seed: test each seed lot, preferably separately for each field or supplier, with particular attention to cadmium.

For hemp protein or press cake: test the material after pressing, because this is where cadmium may become concentrated.

For hemp seed oil: test each oil lot for lead.

The result should then be assessed together with the applicable limit and the measurement uncertainty. See Part 3 for an explanation of how to read the test result.

3CBD oils and capsules

The metal

For CBD oils and capsules, lead is the main concern based on the largest market surveys we found.

One US study analysed 202 CBD products bought online in late 2021. The products included tinctures, gummies, vape products and topicals. The samples were analysed for metals by ICP-MS in an accredited laboratory.

Lead was detected in 42 of the 202 products, at concentrations ranging from 8.3 to 27,150 µg/kg.

Five products exceeded a regulatory threshold. All five exceeded it because of lead.

Arsenic was detected in six products, with a maximum of 57.4 µg/kg. Cadmium was detected in four products, with a maximum of 56.4 µg/kg. Mercury was not detected.

The highest lead result was 27 mg/kg. That is nine times the EU food-supplement limit of 3.0 mg/kg.

A second US survey, carried out by the FDA, analysed 133 hemp and CBD products. We have the abstract rather than the full paper. It also found lead most frequently. Cadmium was found mainly in chocolate-containing products, where the cocoa appeared to be the source.

Where it comes from

A CBD oil has at least two potential sources of metals:

1. the hemp extract;
2. the carrier oil.

The extract is made from flower and leaf. These parts of the plant generally receive more of the metals taken up from the soil than the seed.

Extraction can also change what is transferred from the plant into the final extract.

One study compared ethanol, isopropanol and supercritical CO₂ extraction using the same high-CBD hemp cultivar. The researchers measured 24 elements.

The alcohol extracts contained more of several mineral elements, including potassium, magnesium, phosphorus and sulfur, than the CO₂ extracts.

However, cadmium, lead and arsenic did not differ between the extraction methods, and all were below the California limits in the extracts studied.

This gives us useful information about extraction, but it does not answer every question. In particular, the study did not test whether a flower containing a high concentration of lead would necessarily produce an extract with a high concentration of lead.

We found no study that answers that question.

The same caution applies to filtration and winterisation. These processes remove waxes and particles, but we found no data showing how effectively they remove metals that are already dissolved.

The carrier oil matters too. The carrier oil can be a significant source of lead simply because it makes up most of the finished product.

Olive oil, medium-chain triglyceride oil and hemp seed oil are covered by the fats-and-oils lead limit of 0.10 mg/kg.

Consider a finished CBD oil containing 90 % carrier oil and 10 % extract.

If the carrier contains 0.10 mg/kg lead, it contributes approximately 0.09 mg/kg of lead to the finished product.

For the finished product to reach the EU supplement limit of 3.0 mg/kg, the 10 % extract would then need to contain approximately 30 mg/kg of lead.

The highest result in the market survey was 27 mg/kg in a finished product, showing that concentrations of this order have been measured in commercial CBD products.

The number

For a CBD oil or capsule sold as a food supplement, the EU limits are (rows 3.1.28, 3.2.21.1 and 3.3.2):

• lead: 3.0 mg/kg;
• cadmium: 1.0 mg/kg;
• mercury: 0.10 mg/kg;
• no EU maximum level for arsenic.

These limits apply to the finished product as sold.

The carrier oil has its own lead limit of 0.10 mg/kg. An oil exceeding that limit cannot be used as an ingredient in a food product.

For US sales, the applicable limits can be lower. California sets a lead limit of 0.5 µg/g for non-inhalable cannabis products, while Colorado sets 1 µg/g for products taken orally.

When to test

The most useful points to test are:

Crude extract or distillate: before dilution, when contamination from the plant or extraction process can still be traced to the supplier.

Carrier oil: each lot, for lead.

Finished CBD oil: once for each formulation, and again when the formulation or a significant supplier changes.

4CBD isolate and distillate

The metal

For CBD isolate and distillate sold as ingredients, we cannot identify one metal as the main concern.

The reason is simple: we could not find published measurements of arsenic, cadmium, mercury or lead in these materials as ingredients.

The large survey mentioned above included products made from CBD isolate, but these were finished tinctures, gummies and vape products rather than measurements of the isolate itself.

So what can we say?

We can describe what the purification processes are expected to do to metals, but these statements should be treated as process chemistry, not measurements.

Where it comes from

A distillate is produced by evaporating cannabinoids from a crude extract under reduced pressure and then condensing them.

Metal salts do not normally evaporate under these conditions. They therefore remain mainly in the residue.

An isolate is produced by crystallising CBD from a solvent. During crystallisation, many dissolved impurities remain in the mother liquor rather than entering the crystals.

Both processes are therefore expected to reduce the amount of metal carried forward from the plant.

But neither process guarantees a low metal concentration.

Contamination can also be introduced later through:

• solvents;
• filter aids;
• reactor surfaces;
• drying equipment;
• other parts of the manufacturing process.

The metal result of an isolate or distillate therefore tells you something about the manufacturer's process, not simply about the original hemp.

If the manufacturer changes its solvent, equipment or process, the result can change.

The number

CBD isolate and distillate do not have a specific heavy-metal row of their own in Regulation (EU) 2023/915.

The limits apply to the finished food or food supplement.

For example, if an isolate makes up 2 % of a finished supplement, it would need to contain about 150 mg/kg of lead for the finished product to reach the EU supplement limit of 3.0 mg/kg.

That does not mean 150 mg/kg is an acceptable limit for the ingredient. It is simply a calculation showing how the concentration in an ingredient relates to the concentration in the finished product.

For the ingredient itself, the useful number is the laboratory result: the measured concentration of each metal together with the laboratory's limit of quantification.

When to test

Test once per manufacturer and bulk lot.

Repeat the test when there is a significant change in:

• manufacturer;
• solvent;
• equipment;
• purification process.

5Hemp flower for smoking

The metal

There is no EU maximum level for heavy metals in hemp flower sold for smoking.

Hemp flower sold for smoking is not treated as food under Regulation (EU) 2023/915, so the food contaminant limits do not apply.

The laboratory can still report total arsenic, cadmium, mercury and lead in the dried flower. Those results then need to be compared with the limits used by the relevant market or customer.

In the two Italian surveys we found, lead was the metal most likely to exceed the US inhalable limits.

The larger study analysed 72 dried flower samples from six varieties grown in four Italian regions in 2022.

The median lead concentration was 0.03 mg/kg and the mean was 0.14 mg/kg.

The samples from Apulia were higher, ranging from 0.31 to 0.79 mg/kg. Two samples, from the Finola and Tiborszállási varieties, exceeded 0.5 mg/kg, the US inhalable limit.

Cadmium, arsenic and mercury remained below the inhalable limits in every sample.

The results also showed an important pattern: geographical origin separated the samples more clearly than variety did.

A second Italian survey analysed 31 flowers from several regions. We have the abstract rather than the full paper. It also reported lead above the US limits for both oral and inhaled products, along with several other elements above the inhalable limits.

Where it comes from

Flower is an above-ground part of the plant, like the leaf.

Field studies show that leaves and stems can contain more of the metals taken up by hemp than the seeds.

The Italian data illustrate how much the growing location can matter. The same six varieties produced lead concentrations of only a few hundredths of a milligram per kilogram in one region and up to 0.79 mg/kg in another.

The field can matter more than the variety.

The number

There is no EU heavy-metal limit for hemp flower sold for smoking.

Where a numerical limit is required, one useful comparison is provided by the US state limits for inhalable cannabis.

California, in section 15723 of its cannabis regulations, sets the following action levels for inhalable cannabis and cannabis products:

• cadmium: 0.2 µg/g;
• lead: 0.5 µg/g;
• arsenic: 0.2 µg/g;
• mercury: 0.1 µg/g.

A batch that fails "shall not be released for retail sale".

Colorado, in Rule 4-115 of its marijuana rules, uses the same four limits for inhaled products and applies them to flower, trim, concentrates, pre-rolls and hemp products. The same four numbers appear in the Italian survey as the US Pharmacopeia inhalation limits for a consumption of 10 g of product a day.

For products that are eaten, the limits differ between California and Colorado. California allows 0.5 µg/g of cadmium, 0.5 of lead, 1.5 of arsenic and 3.0 of mercury; Colorado allows 0.5, 1.0, 1.5 and 1.5.

The important point is therefore to identify the market and the intended use before deciding which limit applies.

When to test

Test each harvest lot, separately for each field where possible.

For US inhalable products, compare the results with the applicable inhalable limits.

For products sold in the EU, where there is no EU heavy-metal limit for smoking flower, the relevant specification should come from the customer, contract or destination market.

6One table to keep

If you want a simple working rule, keep this table.

The simple rule is:

Different hemp products create different metal risks. Test the material at the point where the risk is introduced or concentrated, and assess the result against the limit that actually applies to the product and market.