Heavy Metals in Botanical Raw Materials: What USP <232> and <233> Require — and Why ICP-MS Is Non-Negotiable

In 2023, the FDA and the New York State Department of Health documented lead levels in turmeric supplements exceeding California’s Prop 65 threshold of 0.5 µg/day — in some cases by a factor of ten or more. The source wasn’t contaminated soil. Investigators traced it to lead chromate, a yellow pigment added post-harvest to enhance color in export markets. Turmeric wasn’t an anomaly. It was a case study in how quickly a botanical raw material can move through an international supply chain and arrive in a Midwest manufacturer’s warehouse with a certificate of analysis that says “lead: ND” — because the analytical laboratory generating that result used equipment that wouldn’t detect lead chromate at these concentrations.

That gap between what a COA says and what USP <233> actually requires is where compliance problems live.

What USP <232> Sets — and What It Doesn’t Resolve for Dietary Supplements

USP <232> Elemental Impurities — Limits establishes permitted daily exposure (PDE) values for 24 elemental impurities, classified by potential toxicity and route of administration. For oral drug products — and by extension, dietary supplements increasingly following this framework — the Class 1 limits are:

• Arsenic (As): 15 µg/day
• Cadmium (Cd): 5 µg/day
• Lead (Pb): 5 µg/day
• Mercury (Hg): 30 µg/day (inorganic)

These are daily exposure limits, not concentration limits in a raw material. That distinction matters enormously for raw material specifications. If a consumer takes three capsules per day and each capsule delivers 500 mg of ashwagandha root extract — 1,500 mg total — your raw material specification for lead needs to be tight enough that the finished dose stays under 5 µg. Work backwards: at 1.5 grams per day, that means your incoming spec should sit at or below approximately 3.3 ppm for lead. Now factor in that California’s Prop 65 MADL for lead is 0.5 µg/day — ten times more restrictive — and that specification tightens to roughly 0.33 ppm.

Here’s the complication: FDA has not issued a final binding rule requiring dietary supplement manufacturers to comply with USP <232>/<233>. DSHEA’s cGMP regulations under 21 CFR Part 111 require testing for identity, purity, strength, and composition — but leave manufacturers latitude in how they define “purity.” In practice, the supplement industry has increasingly adopted USP <232>/<233> as the operative standard, because it’s what FDA investigators reference during 483 observations, what large retail buyers require in their supplier questionnaires, and what any reasonable legal defense would need to point to if a product triggers a Prop 65 enforcement action.

The brands that are most exposed are usually smaller Midwest manufacturers who haven’t updated their raw material testing specifications in several years. They’re running quality programs written before USP <232>/<233> became widely expected, and they’re accepting supplier COAs generated to those older, more permissive standards.

Why ICP-MS Is the Required Method for USP <233> Compliance

USP <233> Elemental Impurities — Procedures defines how to measure elemental impurities. It recognizes two primary techniques: Inductively Coupled Plasma Mass Spectrometry (ICP-MS) and ICP-OES (Optical Emission Spectrometry). For routine compliance work — especially at the concentration levels relevant to Class 1 elements near their PDE thresholds — ICP-MS is the method of choice in accredited analytical laboratories, and for good reason.

ICP-MS routinely achieves detection limits below 1 part per billion (ppb) for most elements, with some configurations operating into the parts-per-trillion (ppt) range. ICP-OES is typically an order of magnitude less sensitive. For a botanical matrix — dense with polyphenols, alkaloids, and polysaccharides that can suppress or enhance elemental signals — that sensitivity difference is not academic. You need the headroom.

But the method is only as good as the sample preparation. USP <233> specifies closed-vessel microwave-assisted acid digestion as the standard preparation approach, and for good reason: open-vessel digestion at elevated temperatures loses volatile species, particularly arsenic (as AsH₃) and mercury. An analytical laboratory reporting “mercury: ND” after open-vessel digestion is not giving you a compliance-grade result. The mercury may simply have evaporated before analysis.

A USP <233>-validated test report includes: the specific digestion procedure, instrument type and calibration approach, detection limits explicitly stated for each element, spike recovery data demonstrating the method performed correctly in that specific matrix, and lot traceability linking results to the sample you submitted. If a supplier COA doesn’t include those elements, it documents nothing about the actual contamination risk in the material you received.

Which Botanical Raw Materials Carry the Highest Heavy Metal Risk

Not every ingredient warrants the same level of scrutiny. Based on documented contamination incidents, soil geochemistry, and supply chain history, five categories represent elevated risk for Midwest supplement brands.

Turmeric and curcumin extracts sit at the top of the list. As described above, lead chromate adulteration is well-documented and has resulted in FDA import alerts and state health department advisories. The lead isn’t incidental to the soil — it’s intentionally introduced in portions of the export supply chain to boost color scores. Standard heavy metals screening using ICP-MS will detect it; a COA based on portable X-ray fluorescence or older colorimetric methods may not.

Ashwagandha root (Withania somnifera) grown in certain agricultural districts of Rajasthan and Madhya Pradesh sits in naturally mineral-rich soil. Lead and cadmium bioaccumulation in root material from these regions has been documented in peer-reviewed literature. The risk is geological rather than intentional, but the result is the same.

Spirulina and chlorella can concentrate cadmium and inorganic arsenic from cultivation water. Freshwater spirulina grown in controlled ponds with tested input water is generally lower risk. Ocean-adjacent cultivation facilities near industrial areas are a different matter. Without knowing the water quality protocols at the cultivation site, a spirulina COA tells you very little.

Ayurvedic herbal blends present a distinct challenge. A 2008 study published in JAMA found that approximately 20% of Ayurvedic herbal medicine products purchased through US internet retailers contained detectable lead, mercury, or arsenic — concentrations that would in many cases exceed even the more permissive federal thresholds. Some traditional Rasa Shastra formulations intentionally incorporate heavy metals. These have no place in a DSHEA-regulated dietary supplement, but mislabeled or adulterated batches continue to surface in global B2B supply chains.

Rice protein concentrates carry inorganic arsenic as an inherent risk, a direct consequence of paddy cultivation methods where flooded fields mobilize naturally occurring arsenic from soil into the plant’s vascular system. For manufacturers sourcing rice protein as a plant-based protein component, arsenic speciation testing — distinguishing inorganic arsenic from organic forms — is worth including in the incoming QC program.

What a Compliance-Grade Incoming Heavy Metals Program Actually Looks Like

Most Midwest supplement brands are running some version of a heavy metals program. The gap is usually in the details.

Step 1 — Establish exposure-based raw material specifications. Don’t accept limits from a supplier’s spec sheet. Calculate the PDE-based limit for each Class 1 element using your intended daily dose, then add a safety factor — typically 50% below the calculated limit — to account for formulation variability and combined exposure from multiple ingredients. If you sell in California, use the Prop 65 MADL as your design target for lead, not USP <232>‘s PDE.

Step 2 — Test every incoming lot, not just qualification batches. Botanical raw materials have significant batch-to-batch variability. A supplier who qualified cleanly two seasons ago may be sourcing from a different agricultural region this harvest cycle. Annual supplier audits do not substitute for lot-level elemental testing.

Step 3 — Specify ICP-MS with closed-vessel digestion in your quality agreement. Your quality agreement with raw material suppliers should require elemental testing under USP <233> or an equivalent validated method using ICP-MS. If the supplier cannot provide documentation confirming the method, that COA has no evidentiary value for your compliance program.

Step 4 — Review the full method package, not just the result table. Request detection limits, spike recovery data, and instrument calibration records alongside the numerical results. A lead result of “0.08 ppm” is meaningful. A lead result of “ND” is only meaningful if the stated detection limit is published and appropriate for your specification — typically at or below 0.05 ppm for high-risk botanicals subject to Prop 65 scrutiny.

Our team receives botanical and raw material samples at our Countryside, IL facility and routes them through ICP-MS analysis under ISO 17025 accreditation, with full USP <233> documentation on every report. For most 24-element panels — all four Class 1 elements plus the Class 2 and Class 3 elements most commonly flagged in botanical matrices — results come back in 5 to 7 business days. That fits a standard incoming QC workflow without holding up production.

The point isn’t to generate paperwork. It’s to know — actually know — what’s in a raw material before it reaches your production floor, your retailer’s shelves, and a consumer who trusted the label.

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Written by Nour Abochama, VP Operations, Qalitex | Quality Consultant, Ayah Labs. Learn more about our team

Ship your sample to our Chicago facility — get a Qalitex CoA in 5–7 days. Contact us

Related from our network

• ICP-MS and USP <232>/<233> Testing for Dietary Supplements — Qalitex Laboratories provides ISO 17025-accredited elemental impurity testing with validated USP <233> methods and full method documentation for raw material and finished product qualification.
• Botanical Identity and Adulteration Screening — HPTLC and DNA barcoding services for botanical ingredient verification, available alongside ICP-MS heavy metals panels for complete incoming raw material qualification.