California Prop 65 vs. DSHEA Heavy Metal Limits: What Midwest Supplement Brands Must Get Right Before Selling Nationwide

Sixty-day notice letters from California private plaintiffs arrived at supplement companies at a rate of several hundred per year throughout 2023 and 2024 — and many of those companies had ICP-MS test results sitting in their quality files. The problem wasn’t that they skipped testing. It was that they’d tested against the wrong benchmark.

Federal DSHEA compliance and California Prop 65 compliance are not the same thing. For Midwest supplement brands that sell through Amazon, wholesale distributors, or their own e-commerce platforms, the gap between the two can land you in a settlement negotiation with a private plaintiff’s attorney before you’ve even realized there was a gap to close.

This matters especially for brands formulating with botanical raw materials. Plants bioaccumulate heavy metals from soil. Popular ingredients — turmeric, ashwagandha, spirulina, green tea extract — regularly test above California’s thresholds even when the raw material concentration looks modest on a µg/g basis. Understanding exactly what each standard requires, and how to use ICP-MS data to calculate per-serving exposure under both frameworks, is now a baseline competency for any QC program that sells nationally.

Two Standards, Two Very Different Numbers

The federal framework for heavy metals in dietary supplements is anchored primarily in USP <232> (Elemental Impurities — Limits) and USP <233> (Elemental Impurities — Procedures). USP <232> establishes Permitted Daily Exposures (PDEs) by route of administration. For the oral route, the four metals most relevant to botanical supplements are:

• Lead (Pb): 5 µg/day
• Cadmium (Cd): 2 µg/day
• Arsenic (As): 15 µg/day
• Mercury (Hg): 3 µg/day

These PDEs assume a conservative default daily intake of 10 grams of product when converting to concentration-based limits in µg/g. USP <233> specifies the ICP-MS methodology required to measure against them reliably.

California’s Proposition 65, administered by OEHHA (Office of Environmental Health Hazard Assessment), uses a completely different risk model. For each listed chemical, OEHHA establishes either a No Significant Risk Level (NSRL) for carcinogens or a Maximum Allowable Dose Level (MADL) for reproductive toxins. The safe harbor thresholds for the metals most commonly implicated in botanical supplement enforcement actions are:

• Lead (Pb): MADL = 0.5 µg/day
• Cadmium (Cd): NSRL = 4.1 µg/day
• Arsenic (inorganic): NSRL = 10 µg/day
• Methylmercury: MADL = 0.3 µg/day

Lead is the critical number. The Prop 65 MADL of 0.5 µg/day is ten times stricter than the USP <232> PDE of 5 µg/day. A product that clears the federal standard with room to spare can still require a Prop 65 warning — or attract an enforcement notice — if per-serving lead exposure exceeds half a microgram per day.

That gap exists for a reason. The USP PDE is derived from a pharmaceutical-grade health-protective assessment. OEHHA’s MADL uses a 1,000-fold uncertainty factor applied to reproductive toxicity data. Neither number is arbitrary, and neither is “wrong” from a scientific standpoint. But if you’re only running tests against one framework while selling product in California, you have an incomplete picture of your actual compliance status.

Why Botanical Ingredients Are the Highest-Risk Category

Heavy metals in dietary supplements aren’t primarily a manufacturing contamination problem — they’re an agronomic one. Plants absorb metals through root uptake from the soil profile, and the concentration in the finished raw material reflects the geological history and agricultural practices of the growing region. Processing, extraction, and encapsulation rarely reduce what’s already in the plant matrix.

Several botanical ingredients that dominate the current supplement market carry well-documented heavy metal profiles:

Turmeric (Curcuma longa): Lead contamination has been a persistent concern, particularly for material sourced from Bangladesh and parts of India, where lead chromate has historically been used as a post-harvest color enhancer. A 2021 study published in Environmental Research by researchers from the National Institutes of Health and Dartmouth linked turmeric consumption in a South Asian community to measurably elevated blood lead levels in adults and children. Even material that hasn’t been adulterated with lead chromate can carry elevated concentrations from high-lead soils.

Ashwagandha (Withania somnifera): Root material from Indian origin routinely shows measurable lead and cadmium. At standard label doses of 300–600 mg per serving, even modest µg/g concentrations can push per-serving lead exposure toward or past the 0.5 µg/day Prop 65 threshold.

Spirulina and chlorella: These algae-based ingredients can concentrate metals from their growth medium. Arsenic is a particular concern in spirulina produced in some freshwater cultivation systems, though speciation matters — organic arsenosugars behave very differently from inorganic arsenic, and Prop 65 applies specifically to inorganic arsenic compounds.

Green tea extract: Variable arsenic and lead depending on growing region, soil composition, and the concentration ratios used in extraction. A high-concentration extract amplifies whatever metal content was present in the raw plant.

The pattern across all of these is identical: the raw material concentration in µg/g looks small until you multiply it by your intended serving size and daily frequency. That calculation — not the µg/g figure on its own — determines your Prop 65 position.

The ICP-MS Calculation That Actually Matters

Running ICP-MS testing is necessary but not sufficient for Prop 65 substantiation. What converts raw analytical data into a defensible compliance position is the per-serving exposure calculation:

Daily Exposure (µg/day) = Concentration (µg/g) × Serving Size (g) × Servings per Day

For Prop 65 purposes, the safe harbor calculation defaults to 100% bioavailability unless you have product-specific bioavailability data from a validated study. That’s a conservative assumption, but without the study data, it’s what you use. Some matrices genuinely reduce metal bioaccessibility, but you can’t credit that in the exposure calculation without evidence.

Here’s a worked example. An ashwagandha root extract tests at 0.8 µg/g lead. The label dose is 600 mg once daily:

0.8 µg/g × 0.6 g × 1 serving/day = 0.48 µg/day

That lands just under the 0.5 µg/day MADL. But change the dosing to two 300 mg servings per day — the same total daily dose — and the result is identical, still compliant. Now change the incoming lot. The next shipment from the same supplier tests at 1.1 µg/g, well within most specifications:

1.1 µg/g × 0.6 g × 1 serving/day = 0.66 µg/day

Now you need a Prop 65 warning, or you need to change the label dose, or you need to reject the lot and source differently. And you only know that because you tested the specific lot and ran the calculation for your specific formulation.

This is why per-lot incoming ICP-MS testing matters for Prop 65 compliance. A qualification test from 18 months ago doesn’t represent the lot on your floor today. Botanical ingredient concentrations vary by crop year, growing season, and supplier sourcing practices in ways that can shift the calculation meaningfully.

For brands that need to demonstrate compliance to a retailer requiring Prop 65 substantiation — or in response to a 60-day notice — the testing data must originate from an ISO 17025-accredited analytical testing laboratory. Accreditation establishes method validation, measurement uncertainty quantification, and the chain-of-custody documentation that withstands legal scrutiny. Internal QC records or certificates from non-accredited facilities don’t meet the evidentiary standard in a Prop 65 enforcement proceeding.

What a 60-Day Notice Actually Means for a Midwest Manufacturer

Prop 65 enforcement is structurally unusual compared to most federal regulatory mechanisms. Government agencies play a secondary role — enforcement is primarily driven through a private attorney general mechanism. Any individual, law firm, or public interest organization can issue a 60-day notice of intent to sue if they believe a company is exposing California consumers to a listed chemical above safe harbor levels without a required warning.

The 60-day period is designed to allow the notified company to evaluate its exposure position and either remediate (add a warning, reformulate, or demonstrate compliance with data) or face litigation. The burden effectively shifts: the company must show, with data, that per-serving exposure is below the applicable MADL or NSRL.

Settlement economics in the supplement category are well-documented in the California Attorney General’s annual enforcement reports. Dietary supplements consistently appear among the top categories by number of notices issued. Settlements in supplement cases frequently fall between $25,000 and $150,000, plus plaintiff attorney fees — costs that often exceed the settlement amount itself. The underlying regulatory violation — selling a product above Prop 65 limits without a warning — is typically a per-day, per-unit violation that can accumulate quickly when calculated against sales volume.

The practical defense is not complicated, but it requires existing records. Per-lot ICP-MS data from an accredited analytical testing laboratory, a completed per-serving exposure calculation file, and documentation that the calculation was reviewed as part of each incoming lot disposition — that’s the file you need. If you don’t have a warning and your data shows you’re below the threshold, that file closes the enforcement action. If the data doesn’t exist, you’re negotiating from a much weaker position.

For Midwest supplement brands that have historically focused on Midwest retail distribution — where California-specific compliance wasn’t a daily operational concern — online sales change everything. The moment a California consumer places an order through your website or through a national e-commerce platform, Prop 65 applies to that transaction. Where your facility is located has no bearing on it.

A Practical Testing Program for Brands Selling Nationally

Translating all of this into an actual QC workflow for a botanical supplement manufacturer selling across state lines looks like four concrete steps:

1. Incoming raw material qualification: Test each new botanical ingredient at the raw material level. For each element of concern, run the per-serving exposure calculation at your intended label dose and compare against both USP <232> PDEs and the applicable Prop 65 MADL or NSRL. Document the result in the ingredient qualification file.

2. Per-lot incoming testing: For lead and cadmium at minimum — the two elements most commonly implicated in Prop 65 botanical enforcement actions — retest each incoming lot. The per-lot µg/g result must be inserted into your exposure calculation before the lot is released into production.

3. Finished product confirmation for high-risk botanicals: For products containing turmeric, ashwagandha, spirulina, or green tea extract, run finished product ICP-MS testing to confirm that no additional contamination was introduced during processing. Formulation interactions and manufacturing equipment can occasionally contribute trace contamination that wasn’t present in the raw material alone.

4. Formulation change review: Any change in botanical ingredient, lot source, daily dose, serving frequency, or target consumer population (adults vs. children) triggers a full recalculation and likely new raw material testing. A formulation change that seems cosmetically minor — adjusting a dose from 500 mg to 750 mg — can shift the per-serving exposure calculation across the Prop 65 threshold.

The accreditation requirement applies to each of these steps. Testing reports should provide µg/g results with stated measurement uncertainty, instrument detection limits, and a clear declaration of the accreditation scope under which the method was run. That documentation is what makes the data defensible.

If you’re shipping samples from the Chicago area, the logistics of a testing program like this don’t need to be complicated. Raw material and finished product samples can be received and logged locally, with ICP-MS analysis performed under ISO 17025 accreditation and a formal certificate of analysis returned within five to seven business days. Getting the data before lot disposition, rather than after the product has already moved, is the part that changes your exposure.

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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 Elemental Impurities Testing Under USP <232>/<233> — Qalitex Laboratories provides ISO 17025-accredited ICP-MS analysis for dietary supplement and botanical ingredient manufacturers, with CoA reporting formatted to support both federal and California Prop 65 compliance documentation.