Heavy Metals in Supplements: How Brands Test and Determine Compliance With Applicable Limits

Supplement brands test for heavy metals by sending finished products or raw materials to an accredited laboratory for elemental analysis, usually by inductively coupled plasma mass spectrometry (ICP-MS). The lab reports the concentration of lead, arsenic, cadmium and mercury in the sample. The brand then converts each result into a daily exposure figure using the serving size and the maximum servings per day on the label. It then compares that daily figure against the limits that apply in each market where the product sells.

No single number defines compliance. U.S. regulations require each brand to set and verify its own contaminant specifications, while pharmacopeial standards, California Proposition 65, Health Canada, the European Union and retailer programs each publish different thresholds. A product can pass one benchmark and miss another. Understanding how the testing works, and how the limits differ, is the foundation of a defensible heavy metals program.

What Are Heavy Metals in Supplements?

Heavy metals in supplements are toxic elements, chiefly lead, arsenic, cadmium and mercury, that enter dietary supplements through contaminated soil, water, botanical raw materials, mineral ingredients or processing equipment. They serve no nutritional purpose. Regulators and standards bodies limit them because they accumulate in the body over time and can harm the nervous system, kidneys and reproductive health.

What U.S. Regulation Requires

The FDA's dietary supplement Good Manufacturing Practice rule, 21 CFR Part 111, requires brands to control heavy metals but does not publish numeric limits for most finished supplements. Under 21 CFR 111.70, a manufacturer must establish specifications for components and finished batches, including limits on contamination that may adulterate the product. Under 21 CFR 111.75, manufacturers must verify those specifications using scientifically valid methods before releasing a batch.

In practice, this means the brand chooses its own numeric limits and must be able to justify them. FDA has cited firms that skip this step. A 2024 FDA warning letter cited a manufacturer for failing to establish contamination limits for botanical components under 111.70. The agency has also used Import Alert 99-42 to detain Ayurvedic products considered likely to be injurious to health because of lead or mercury.

FDA does set numeric action levels in specific food categories. Its Closer to Zero initiative covers lead, arsenic, cadmium and mercury in foods, and the agency has published action levels for lead in processed foods for babies and young children. These do not apply directly to adult supplements, but they signal the agency's direction on toxic elements.

Which Heavy Metal Limits Apply to Supplements

Brands generally build their specifications around one or more of the following published standards. The limits below are drawn from the primary documents. Inclusion of a standard or program here is informational and does not constitute endorsement.

USP General Chapter <2232> (United States, voluntary)

The U.S. Pharmacopeia chapter Elemental Contaminants in Dietary Supplements is a widely referenced daily-dose benchmark in the U.S. industry. A USP presentation on <2232> lists the following permitted daily exposure (PDE) values for finished products, which brands should confirm against the current official chapter:

• Lead: 5 µg/day
• Cadmium: 5 µg/day
• Inorganic arsenic: 15 µg/day
• Total mercury: 15 µg/day
• Methylmercury: 2 µg/day

The same USP material lists individual component limits of 0.5 µg/g for lead and cadmium, 1.5 µg/g for inorganic arsenic and total mercury, and 0.2 µg/g for methylmercury. These apply when the product's maximum daily intake is 10 grams or less. USP notes that compliance is voluntary for supplements unless a product claims to meet USP or NF standards.

California Proposition 65 (warning requirement, not a ban)

Proposition 65 requires a warning when a product exposes California consumers to a listed chemical above a safe harbor level. It does not prohibit sale. The Office of Environmental Health Hazard Assessment (OEHHA) publishes these safe harbor levels:

• Lead: 0.5 µg/day (reproductive toxicity MADL); 15 µg/day (cancer NSRL, oral)
• Cadmium: 4.1 µg/day (oral MADL)
• Inorganic arsenic: 10 µg/day (oral cancer NSRL)

The 0.5 µg/day lead MADL is ten times lower than the USP PDE. Some consumer testing reports, including recent surveys of lead in protein powders, use Prop 65 as their pass/fail line. BSCG's analysis of the Consumer Reports protein supplement survey explains why results framed against Prop 65 differ from results framed against toxicological limits such as USP <2232>. Both are legitimate reference points, but they answer different questions.

Health Canada (Natural Health Products)

Health Canada's Quality of Natural Health Products Guide sets tolerance limits per kilogram of body weight per day and lists the following adult daily equivalents:

• Total arsenic: 10 µg/day (0.14 µg/kg bw/day); inorganic arsenic 2.1 µg/day
• Cadmium: 6 µg/day (0.09 µg/kg bw/day)
• Lead: 10 µg/day (0.14 µg/kg bw/day)
• Total mercury: 20 µg/day (0.29 µg/kg bw/day); methylmercury 2 µg/day

The guide states that if total arsenic exceeds the limit, the licence holder must run speciation testing to show inorganic arsenic stays within its tighter limit. It also explains why a single "total heavy metals" test at 10 ppm is not adequate protection on its own.

European Union (Regulation (EU) 2023/915)

The EU regulates heavy metals in food supplements by concentration rather than daily dose. Regulation (EU) 2023/915 sets maximum levels for food supplements of 3.0 mg/kg for lead, 1.0 mg/kg for cadmium (3.0 mg/kg for supplements consisting of 80 percent or more dried seaweed, seaweed products or dried bivalve molluscs), and 0.10 mg/kg for mercury. These are enforceable legal maximums. A product can meet the EU concentration limit and still exceed a U.S. daily-dose benchmark if the serving size is large.

NSF/ANSI 173 and other program-based limits

Third-party certification standards set their own contaminant limits. A draft of NSF/ANSI 173 filed with FDA proposed daily intake limits of 10 µg/day for arsenic, 6 µg/day for cadmium, and 20 µg/day for lead and mercury, alongside raw material concentration limits. This draft is not the current standard; the limits in force are those in the current edition of NSF/ANSI 173. Certification program limits vary and are not identical to USP or Prop 65. Brands seeking certification should review the specific limits a program applies.

Retailer requirements

BSCG's overview of the Amazon dietary supplement policy states that Amazon requires heavy metals testing for products in higher-risk categories. Sports nutrition, weight loss, sexual enhancement and joint health products face additional contaminant, label claim and drug testing requirements, with protocols conforming to NSF/ANSI 173 or USP standards. BSCG provides this testing through its network of ISO/IEC 17025-accredited laboratories.

How to Test Supplements for Heavy Metals: Step by Step

A defensible heavy metals testing program follows a consistent sequence. The steps below reflect 21 CFR Part 111 specification and verification requirements, USP <2232> compliance options and USP <233> analytical procedures.

1. Set written specifications before testing. Decide which limits apply to each product based on its markets (for example, USP <2232> for the U.S., Prop 65 for California labeling, EU 2023/915 for export). Record the limit, the unit and the rationale in the product specification.
2. Identify higher-risk ingredients. Botanical raw materials, seaweed and algae, marine oils, Ayurvedic preparations and shilajit have documented histories of elevated metals. USP's <2232> material describes a risk-based approach that considers the likelihood of contamination from source through manufacturing.
3. Test raw materials and finished products. Supplier certificates of analysis are a starting point, not a substitute. Part 111 requires the manufacturer to verify component specifications through its own testing or a documented, qualified supplier program.
4. Use a validated method at an accredited lab. USP <233> specifies closed-vessel digestion followed by ICP-OES (Procedure 1) or ICP-MS (Procedure 2). USP <233> also permits validated alternatives such as atomic absorption. ICP-MS is generally preferred for supplements because validated methods reach lower limits of quantitation across botanical and powder matrices, which matters when evaluating results against sub-microgram daily limits such as Prop 65.
5. Confirm the lab's limit of quantitation (LOQ) fits the specification. A result reported as "below LOQ" is only useful if the LOQ, once multiplied by the daily serving mass, falls under the specification limit. Request the LOQ in µg/g for the product matrix.
6. Request speciation when needed. Total arsenic and total mercury results assume the most toxic form. If a total result exceeds the inorganic arsenic or methylmercury limit, a validated speciation method (Health Canada recommends HPLC coupled with ICP-MS for arsenic) can distinguish the toxic species from less toxic organic forms.
7. Convert results to daily exposure and document the comparison. This calculation, covered in the next section, is where the compliance decision is made.
8. Repeat on a defined schedule. Metal content in botanical crops changes with harvest, region and season. Testing once at launch does not verify later lots.

Converting Lab Results to Daily Exposure

Laboratories report heavy metals as a concentration, usually in µg/g, mg/kg or ppm. These three units are equivalent: 1 mg/kg equals 1 µg/g equals 1 ppm. Daily-dose limits such as USP <2232>, Prop 65 and Health Canada require one further step.

Daily exposure (µg/day) = concentration (µg/g) × grams per serving × maximum servings per day on the label

USP's <2232> material states this directly as Result = MVSS × N, where MVSS is the measured amount per serving and N is the maximum daily intake in the labeling. Two worked examples show why serving size matters more than concentration alone.

• Botanical capsule. Lead result 0.4 µg/g, capsule fill 0.5 g, two capsules per day. Daily exposure = 0.4 × 0.5 × 2 = 0.4 µg/day. This is under the USP PDE of 5 µg/day and under the Prop 65 MADL of 0.5 µg/day.
• Protein powder. Lead result 0.05 µg/g, 30 g scoop, two scoops per day. Daily exposure = 0.05 × 30 × 2 = 3.0 µg/day. This is under the USP PDE of 5 µg/day but above the Prop 65 MADL of 0.5 µg/day, so a California warning evaluation is needed. The same powder would sit far below the EU concentration limit of 3.0 mg/kg.

The protein example illustrates a recurring pattern. Powders consumed in multi-gram servings can show very low concentrations and still produce daily exposures that trigger Prop 65. Capsules and tablets with small serving masses produce lower exposures at the same concentration. Health Canada's guide reaches the same conclusion, noting that a product with a large daily dose can produce unsafe exposure even when it meets a 10 ppm total heavy metals limit.

Reading a Certificate of Analysis for Heavy Metals

A certificate of analysis (COA) is only as reliable as the information it contains. When reviewing a supplier or lab COA for heavy metals, confirm the following elements are present:

• The analytical method (ICP-MS, ICP-OES) and the reference procedure (USP <233>, AOAC or equivalent)
• Units for each result and the LOQ for each element
• Whether arsenic and mercury results are total element or speciated
• The laboratory's ISO/IEC 17025 accreditation and the lot or batch number tested
• The specification limit the result was compared against, and the basis for that limit

A COA showing "lead: <1 ppm" from an unnamed method tells a brand little. For a 30 g serving taken twice daily, an LOQ of 1 ppm corresponds to an undetermined exposure anywhere up to 60 µg/day. That is twelve times the USP PDE. Detection capability has to match the limit being enforced.

How Third-Party Certification Programs Address Heavy Metals

Independent certification adds an external check on a brand's internal program, but scope varies. Some programs test only for banned substances and do not examine contaminants. Others include heavy metals as part of a broader quality review. A seal indicates heavy metals testing only when contaminant screening is expressly in the program's scope, a distinction BSCG explains in Certified vs Tested.

BSCG's Certified Quality program is one example of a contaminant-inclusive program. It tests one lot of each participating product annually for identity, label claims, heavy metals, pesticides, microbiological agents and the BSCG menu of 450+ drugs. Testing runs in ISO/IEC 17025-accredited laboratories, and BSCG states that testing follows methods and limits from AHPA, AOAC, NSF/ANSI 173, ICH Q3D, Health Canada, USP, EPA, FDA and other references, and that contaminant limits meet or exceed national or international guidelines. The program treats state thresholds such as Prop 65 as reported information rather than a certification pass/fail criterion.

For brands that need testing without certification, BSCG's a la carte testing services include a standard heavy metals panel for arsenic, cadmium, chromium, lead and mercury by ICP-MS, evaluated against the USP or NSF/ANSI 173 thresholds.

Other certification programs, including NSF Certified for Sport, Informed Sport and Informed Choice, define their own scopes. Brands should confirm directly with each program which contaminants it tests, how often, against which numeric thresholds, and whether raw materials or only finished products are covered. Inclusion of any program here does not constitute endorsement.

Where Heavy Metals Enter the Supply Chain

Knowing the source guides where to test. USP's background material on <2232> notes that ingredients from natural sources pick up metals from water, air pollution, soil, agricultural inputs and processing. The same material cites a survey of 109 herbal products in which 20 showed elevated cadmium and 4 showed elevated lead. It also reports a lead poisoning cluster linked to Ayurvedic medicines that mix metal ash with herbs.

Health Canada's guide identifies ingredients known to selectively accumulate specific metals: cadmium in certain plants, arsenic in certain algae, and mercury in marine oils. The guide states these products should be tested for individual metals rather than relying on a total heavy metals result. Contamination controls at the raw material stage, including supplier qualification and incoming testing, are an efficient control point.

BSCG's guide on supplement contamination risk mitigation covers these controls in more detail.

Frequently Asked Questions

What is the legal limit for heavy metals in supplements in the United States?

FDA does not publish a single numeric limit for heavy metals in adult dietary supplements. Under 21 CFR Part 111, each manufacturer must set its own contaminant specifications and verify them with scientifically valid testing. Many brands adopt USP <2232> permitted daily exposures (lead 5 µg/day, cadmium 5 µg/day, inorganic arsenic 15 µg/day, total mercury 15 µg/day) as their internal benchmark, and evaluate California Prop 65 safe harbor levels separately for warning purposes.

What test method is used for heavy metals in supplements?

USP <233> recognizes both ICP-OES and ICP-MS after closed-vessel acid digestion, and permits validated alternatives such as atomic absorption. ICP-MS is typically preferred for supplements because it reaches lower quantitation limits. Validated speciation methods separate inorganic arsenic from organic arsenic, or methylmercury from inorganic mercury, when total results exceed a limit.

How do you convert a heavy metals test result to a daily exposure?

Multiply the concentration in µg/g by the grams per serving and by the maximum servings per day on the label. A result of 0.1 µg/g lead in a 25 g serving taken once daily equals 2.5 µg/day. Since 1 ppm equals 1 mg/kg equals 1 µg/g, results in any of these units can be used directly in the formula.

Does Prop 65 mean a supplement is unsafe if it exceeds 0.5 µg of lead per day?

No. Proposition 65 is a California warning statute. Exceeding the 0.5 µg/day lead MADL requires a consumer warning; it does not make the product illegal or establish that it is unsafe. The MADL is a conservative reproductive-toxicity screening level, and USP <2232> sets a separate toxicological PDE of 5 µg/day.

How often should supplement brands test for heavy metals?

Part 111 requires that specifications be met for each finished batch, either through direct testing or through a documented, scientifically valid approach such as verified supplier testing combined with process controls. Ingredients from botanical, mineral or marine sources warrant more frequent testing because contamination varies by harvest and origin. BSCG Certified Quality requires annual finished-product testing.

Which supplement ingredients carry the highest heavy metal risk?

Documented higher-risk inputs include botanical raw materials, certain algae and seaweed (arsenic), marine oils (mercury), and traditional preparations such as Ayurvedic formulas and shilajit. Health Canada's guide and USP's <2232> background material both identify these categories. Risk-based testing focuses effort on these inputs first.

Summary

Testing for heavy metals in supplements is a two-part exercise: accurate measurement and correct interpretation. Measurement depends on a validated ICP-MS method at an accredited laboratory with a limit of quantitation suited to the target limit. Interpretation depends on converting concentration results to daily exposure and comparing them against every benchmark that applies in the product's markets.

The benchmarks are not interchangeable. USP <2232> and Health Canada express toxicological daily limits, Proposition 65 sets a much lower warning threshold, the EU regulates concentration, and certification programs apply their own scopes. U.S. law requires brands to choose, document and verify limits but leaves the numbers to the brand. A product's status therefore depends on which standard is being asked about, and a complete answer names the standard alongside the result.