Everything you need to know
Heavy metals — arsenic, cadmium, lead, and mercury — are naturally occurring elements that can contaminate dietary supplements through soil, water, and agricultural practices. Understanding regulatory limits, which products carry the highest risk, and how testing works helps brands make informed decisions about their QC programs.
Which heavy metals are most concerning in dietary supplements?
The four heavy metals of primary regulatory concern in dietary supplements are: Lead (Pb) — can accumulate in bone and affect neurological development; California Prop 65 NSRL is 0.5 µg/day. Cadmium (Cd) — nephrotoxic; Prop 65 NSRL is 4.1 µg/day. Arsenic (As) — inorganic arsenic is a Group 1 carcinogen; Prop 65 NSRL is 10 µg/day (inorganic As only). Mercury (Hg) — neurotoxic; Prop 65 NSRL is 0.3 µg/day (methylmercury). FDA does not have specific action levels for heavy metals in finished dietary supplements, but Prop 65 applies to products sold in California.
Which supplements have the highest risk for heavy metal contamination?
Plant-based protein powders (rice protein, pea protein, hemp protein) tend to show the highest heavy metal levels — particularly arsenic in rice protein and cadmium in plant proteins generally. Other high-risk categories include: herbal supplements and adaptogens sourced from South Asia (ashwagandha, turmeric, spirulina); bone meal and collagen supplements; seafood-derived products (fish oil, krill oil, algae); soil-grown botanical ingredients; and baby formula or infant cereals made with rice or grain ingredients.
What are California Prop 65 limits for heavy metals in supplements?
California Proposition 65 establishes "No Significant Risk Levels" (NSRLs) for carcinogens and "Maximum Allowable Dose Levels" (MADLs) for reproductive toxicants. For the key supplement metals: Lead: 0.5 µg/day MADL (reproductive toxicant); Cadmium: 4.1 µg/day MADL; Arsenic (inorganic): 10 µg/day NSRL; Mercury (methylmercury): 0.3 µg/day MADL. These are daily exposure thresholds — testing labs calculate per-serving exposure based on your serving size and compare it to these thresholds to determine Prop 65 compliance.
What testing method is used for heavy metals in supplements?
The gold standard for heavy metals testing in supplements is ICP-MS (Inductively Coupled Plasma Mass Spectrometry). ICP-MS can detect arsenic, cadmium, lead, and mercury simultaneously at parts-per-billion (ppb) concentrations — sensitivity far below regulatory action levels. Samples are acid-digested before analysis to fully dissolve the matrix. For arsenic, speciation testing by HPLC-ICP-MS distinguishes inorganic arsenic (toxic) from organic arsenic forms (much less toxic), which is important for rice-based products where total arsenic may appear high but most may be organic.
How often should I test my supplement products for heavy metals?
At minimum, you should test every production lot before release. For high-risk ingredients (rice protein, botanical herbs), consider incoming raw material testing as well as finished product testing. If your supplier provides COAs, periodically verify their results with your own independent testing — supplier COAs should be confirmed, not assumed. Brands selling in California under Prop 65 should test each lot and maintain records to demonstrate compliance.
What is the Consumer Reports / Clean Label Project standard for protein powder heavy metals?
Consumer Reports tested protein powders in 2010 and 2018, finding some products with lead, cadmium, and arsenic near or above Prop 65 thresholds. The Clean Label Project applies stricter proprietary benchmarks: their heavy metals standard is <0.1 ppm lead, <0.1 ppm arsenic, <0.1 ppm cadmium, and <0.1 ppm mercury in finished product. Our ICP-MS method can detect well below these thresholds. Order a protein powder heavy metals test.