Heavy Metals

Heavy metals — lead, arsenic, cadmium and mercury — are the most consequential contaminant class in dietary supplements. They occur naturally in botanicals (soil uptake), in minerals (geological origin) and in sea-derived ingredients (bioaccumulation), and they accumulate through industrial and agricultural pathways. The modern USP framework — chapters <232> Elemental Impurities — Limits, <233> Elemental Impurities — Procedures and <2232> Elemental Contaminants in Dietary Supplements — replaced the legacy <231> heavy metals colorimetric test with ICP-MS-based quantitative analysis and a Permitted Daily Exposure (PDE) framework.

USP <2232> sets the PDE for oral dietary supplements: lead 5 µg/day, arsenic (inorganic) 15 µg/day, cadmium 5 µg/day, mercury (inorganic) 15 µg/day, with the in-product concentration limit computed by dividing the PDE by the maximum daily dose. USP <233> defines the analytical methodology — ICP-MS as the primary technique (necessary for the typical low-ppb in-product limits), with explicit validation per ICH Q2(R1) and sample preparation by closed-vessel microwave digestion with concentrated nitric acid. Interference handling uses collision/reaction cell ICP-MS or triple-quadrupole instruments. Quantitation runs on internal standards, matrix-matched calibration and per-batch certified reference materials.

California Proposition 65 layers a separate consumer-warning regime above USP with the MADL for lead at 0.5 µg/day — ten times lower than the USP PDE — driving sourcing decisions for any product sold in California. A botanical at 0.5 ppm lead, dosed at 1 g/day, hits the MADL exactly. The defensible operating posture: USP <2232>-aligned spec per SKU with PDE-derived in-product limit, per-lot supplier COA verified by in-house or contract-lab ICP-MS retest, per-batch finished-product ICP-MS for high-risk SKUs (botanicals, minerals, sea-derived), CRMs in every analytical run, and cross-lot trending with alert thresholds at 50% of the spec. In V5 the USP-aligned spec, the supplier-origin per-lot ICP-MS history, the per-batch finished-product result and the parallel Prop 65 MADL exposure analysis live on the SKU spine — heavy metals stay below limit by design.