Heavy metals in kratom: limits, testing, EU standards

In brief

Kratom, like any plant material, may contain heavy metals originating from soil, water or the drying process. In analytical practice, five main elements are monitored: lead (Pb), cadmium (Cd), mercury (Hg), arsenic (As) and nickel (Ni). The limits are set primarily by Commission Regulation (EU) 2023/915 on maximum levels of contaminants in food and by the pharmacopoeial standards USP <232> for elemental impurities.

Which metals are monitored

Lead (Pb)

Enters the plant from soil, atmospheric deposition (especially in areas with historical contamination from tetraethyl-lead petrol) and during processing. It is among the elements most frequently exceeding the limit in dried plants.

Cadmium (Cd)

Accumulates in the leaves from contaminated soils, especially near phosphate fertilisers and mining activities. Cadmium is monitored strictly in plant materials.

Mercury (Hg)

A less common problem in plant raw materials, but monitored because of possible contamination near incinerators and chemical plants. In Indonesian production it may be related to gold mining in the vicinity of Kalimantan.

Arsenic (As)

A natural occurrence in some soils (especially alluvial ones); it can accumulate in plants. Inorganic arsenic, which has higher toxicity than organic, is monitored.

Nickel (Ni)

Monitored primarily as a contaminant from the metal surfaces of processing machines (grinding equipment, conveyors). In raw leaf, nickel tends to be at low concentrations; in industrially processed powder it may be higher.

Limits under EU 2023/915 and USP

For guidance we state the limits used in practice as a reference; the specific classification of kratom in Czech legislation follows from the PML regime under 167/1998 Coll., which may set its own limits in its implementing decree.

EU Regulation 2023/915 (food framework, indicative for plant raw materials)

• Lead (Pb): 3.0 mg/kg for food supplements containing plants,
• Cadmium (Cd): 1.0-3.0 mg/kg depending on the type of plant raw material,
• Mercury (Hg): 0.1 mg/kg for food supplements,
• Inorganic arsenic: 1.0 mg/kg for food supplements.

USP <232> (pharmacopoeial limits of elemental impurities, oral route)

• Lead (Pb): 5 μg/g (PDE 5 μg/day),
• Cadmium (Cd): 5 μg/g,
• Mercury (Hg): 30 μg/g,
• Arsenic (As): 15 μg/g,
• Nickel (Ni): 200 μg/g.

The specific values are updated; the COA should state against which version of the standard the result is assessed.

How they get into the leaf

The main routes of contamination:

• Soil accumulation - the tree draws trace elements, including metals, from the soil. Soils near mining activities, along roads and in flooded areas may have a higher content of Pb, Cd, As.
• Water - irrigation with contaminated surface water.
• Atmospheric deposition - near incinerators, chemical plants and busy roads.
• Processing - contact with the metal surfaces of grinding and packaging lines (nickel, possibly chromium).

The measurement method (ICP-MS)

ICP-MS (Inductively Coupled Plasma Mass Spectrometry) is the reference method for determining heavy metals in plant raw materials. The procedure:

1. a sample of 0.2-0.5 g of dry matter,
2. microwave digestion in nitric acid (HNO₃) with hydrogen peroxide,
3. making up with demineralised water to a reference volume,
4. measurement by ICP-MS with an internal standard (typically ¹⁰³Rh, ¹¹⁵In),
5. quantification against a calibration series.

The limit of quantification (LOQ) for most elements is below 0.01 mg/kg, which is an order of magnitude below the legislative limits. More in the article HPLC and ICP-MS - laboratory methods for kratom analysis.

Frequently asked questions

What is the lead limit in plant raw materials?

Under EU Regulation 2023/915, typically 3.0 mg/kg for food supplements containing plants. The pharmacopoeial limit under USP <232> is 5 μg/g.

Is mercury a common problem?

Generally less common in plant raw materials. In Indonesian areas neighbouring informal gold mining the problem may be greater, which is why mercury is monitored as standard.

Why is nickel checked?

Nickel is an indicator of contamination from processing (grinding machines, metal surfaces). A high value signals a technological problem, not primarily contamination of the raw material.

Can heavy metals be removed from the finished powder?

From a practical standpoint, no. The metals are firmly bound in the plant matrix. The key is control at the input (choice of the raw-material source, not subsequent "cleaning").

References

• Commission Regulation (EU) 2023/915 on maximum levels of certain contaminants in food.
• USP <232>. Elemental Impurities - Limits. United States Pharmacopeia.
• USP <233>. Elemental Impurities - Procedures. United States Pharmacopeia.