Heavy Metals in Supplements: How to Read the Numbers

Quick answer on heavy metals in supplements

Lead, arsenic, cadmium and mercury are present in trace amounts in essentially every plant and mushroom grown in soil, because they are present in soil. The meaningful question is never whether a botanical product contains any, but how much, measured against what limit, by which method. A certificate of analysis that reports the measured value beside the specification limit lets you answer that. One that reports only "Pass" does not.

Why they are there at all

Plants and fungi take up what is around them. Roots and mycelium draw water and dissolved minerals from soil, and some of what dissolves is lead, cadmium or arsenic — naturally occurring in the earth's crust, and added to in places by historical industry, mining or atmospheric deposition.

This means the levels vary by where something was grown rather than by how carefully it was made. Root crops and mushrooms tend to pick up more than leaves or fruit, simply because of what they are and where they sit.

It also means nobody can produce a botanical product with zero. A brand claiming no heavy metals whatsoever is describing a detection limit, not an absence.

Understanding ppm and ppb

Results are usually reported in parts per million, written ppm, or occasionally parts per billion, ppb.

One part per million is one milligram per kilogram. For scale, that is roughly one second in eleven and a half days. One part per billion is a thousand times smaller again.

So a lead result of 0.01 ppm is ten parts per billion. Whether that is reassuring depends entirely on the limit it is being measured against — which is why a number without its specification is not information.

What the limits are

There is no single federal maximum for heavy metals in dietary supplements generally. Instead, several reference points are used, and knowing which one a brand is citing is useful.

United States Pharmacopeia general chapters set elemental impurity limits widely used as industry specifications. Many manufacturers write their own tighter internal specifications on top.

California's Proposition 65 sets separate thresholds that trigger a warning requirement rather than a sale prohibition. These are set deliberately conservatively, with a substantial margin below the level at which effects have been observed, which is why products carrying the warning are not necessarily unsafe and products without it are not necessarily cleaner.

The practical consequence: compare the measured result to the stated specification on that particular certificate, and treat cross-brand comparisons carefully unless both are reporting against the same limit.

How the testing is done

The standard method is inductively coupled plasma mass spectrometry, abbreviated ICP-MS. It ionises the sample in a plasma torch and separates the resulting ions by mass, which allows extremely low detection limits for individual elements.

On a certificate you will often see it cited alongside a USP general chapter reference, which specifies how the procedure should be carried out.

Where the test was run matters too. An independent laboratory, ideally ISO 17025 accredited, is a different proposition from an in-house bench — the distinction set out in what is a certificate of analysis.

What to actually do with this

Ask for the certificate matched to your lot number, then do one comparison: result against specification.

A result an order of magnitude or more below the limit is a different situation from one just inside it. Both pass. Only the numbers tell you which you have. We publish ours, with limits and methods alongside, on our testing page.

And treat "heavy metal free" as a marketing phrase rather than a chemical statement, for the reasons above. The more informative claim is a number. This is part of the broader argument in how to choose a supplement brand.

Frequently asked questions

Do all supplements contain heavy metals? Botanical and mushroom products grown in soil contain trace amounts, because soil contains them. The question is the quantity relative to a specification limit.

What does ppm mean on a certificate of analysis? Parts per million, equivalent to one milligram per kilogram. A result of 0.01 ppm is ten parts per billion.

Which heavy metals are supplements tested for? Most commonly lead, arsenic, cadmium and mercury, usually by inductively coupled plasma mass spectrometry under a USP method.

Is a Proposition 65 warning a sign a product is unsafe? Not necessarily. Proposition 65 thresholds are set conservatively and trigger a warning requirement rather than a prohibition. Their absence is also not evidence a product is cleaner.

What is ICP-MS? Inductively coupled plasma mass spectrometry, the standard analytical method for measuring trace elements, capable of detecting individual metals at very low concentrations.

Can a supplement be heavy metal free? Not literally. A claim of zero describes the limit of detection of the instrument rather than a true absence. A stated measured value is the more honest figure.

Sources

United States Pharmacopeia. General Chapter <730> Plasma Spectrochemistry.

United States Pharmacopeia. General Chapter <232> Elemental Impurities — Limits.

California Office of Environmental Health Hazard Assessment. Proposition 65 Safe Harbor Levels.

National Institutes of Health, Office of Dietary Supplements. Dietary Supplements: What You Need to Know.

These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.