Heavy metals in supplements are a quiet quality problem, and California's Prop 65 label is one clue a buyer can learn to read. The label is not a verdict. It is a notice about a listed chemical, and the real answer sits in the lab data behind the product.
This guide covers what Prop 65 is, how its safe harbor levels work, what one 2018 protein powder study found, and what test records a buyer can ask a brand to show.
What Prop 65 is
Prop 65 is the common name for the Safe Drinking Water and Toxic Enforcement Act of 1986. California voters passed it as a citizen initiative, with 63 percent of the vote. The state keeps a list of chemicals known to cause cancer or reproductive harm. Lead is on it.
The law does not ban any product. It says a business must give a clear and reasonable warning before it knowingly exposes someone in California to a listed chemical. That is why it is often called a right to know law.
The law covers sellers outside California too, if their products reach buyers there. Government agencies are exempt, and so are businesses with nine or fewer employees.
Sources: California Attorney General, Proposition 65 frequently asked questions (oag.ca.gov/prop65/faq)
How safe harbor levels work
A business does not need a warning if its product stays under a set exposure level. The state calls these safe harbor levels. Two kinds matter here.
For chemicals that cause cancer, the level is the "no significant risk level." It is set so that no more than one extra cancer case would be expected in 100,000 people exposed over a 70-year lifetime. For chemicals that cause reproductive harm, the level is the "maximum allowable dose level." It is the highest exposure with no observed effect, divided by 1,000.
Lead is the best known example. The state's own Q&A notes that a product can meet a federal standard and still need a Prop 65 warning if buyers would take in more than 0.5 micrograms of lead per day from it. The test is about what a person is exposed to, not only what is in the powder.
Some chemicals have no set safe harbor level. In that case the business has to show its own exposure falls under the thresholds in the law, or give the warning.
Sources: California Attorney General, Proposition 65 frequently asked questions (oag.ca.gov/prop65/faq); OEHHA, Current Proposition 65 No Significant Risk Levels and Maximum Allowable Dose Levels (oehha.ca.gov)
What a warning has to say
The state also has safe harbor wording for the warning itself. Updated rules took effect on August 30, 2018. Under the state's regulation, a warning must name at least one of the listed chemicals, and it must be shown so that an ordinary shopper is likely to see, read and understand it. A business can add context, such as where the exposure comes from or how to lower it. It cannot add words that weaken the warning.
The rules also allow a short form for small packages. It uses the word WARNING, names cancer, reproductive harm or both, and points to the state website P65Warnings.ca.gov.
So a label is a legal notice. It tells you a listed chemical may be present at a level that needs a warning, or that the seller chose to warn to be safe. It does not tell you how much, in which lot, or how that compares with similar products. For that you need data.
Sources: Cal. Code Regs. tit. 27, sections 25601 to 25603 (Cornell Legal Information Institute, law.cornell.edu); California Attorney General, Proposition 65 frequently asked questions (oag.ca.gov/prop65/faq)
What one 2018 study found
In February 2018 the nonprofit Clean Label Project released a study of 134 top-selling protein powders. It bought them from stores and online sellers and sent them to Ellipse Analytics, a private lab in Denver. The project tested for lead, mercury, cadmium and arsenic, and also for BPA, a plastics chemical.
It reported that 53 of the 134 products had "substantially elevated" levels of at least one of the tested contaminants. Plant-based powders did worse. In its results, 75 percent of them had measurable lead, and on average they held about twice as much lead per serving as other powders. About 10 percent of whey powders were above health guidelines for lead. None of the egg-based powders tested contained lead.
Treat these numbers with care. The study had not finished peer review when it came out, and the project's own health guidelines, not Prop 65 levels, set the bar. Still, it shows why buyers ask for lot level data. A product type can carry risk even when the brand name looks clean.
Sources: Food Safety News, "Heavy metals found in 40 percent of protein powders tested," February 28, 2018 (foodsafetynews.com)
What to ask a brand to show
You do not need a chemistry degree to ask good questions. These five are a practical start. They are editorial advice, not a legal test.
A certificate of analysis for heavy metals. It should list lead, cadmium, arsenic and mercury as separate lines, not one pass or fail stamp.
The lot number. A report must match the lot in your hand. Plant-sourced raw materials can vary from one harvest to the next, so one old report proves little.
Results with units and limits. Look for a number, a unit and the limit it was judged against. "Not detected" should come with the detection limit, since a weak test can miss small amounts.
The method and the lab. A named method and a named lab let you check the work. An accredited lab, such as one holding ISO/IEC 17025, is a good sign.
Third-party testing. A report from an outside lab carries more weight than a brand's own summary.
If a brand carries a Prop 65 warning, ask the same questions. If it carries none, do not assume the product has been tested. A missing warning can mean low levels, a small business, or no testing at all.
The limits of any single check
No one label settles this. A Prop 65 notice shows a legal duty, a test report shows one lot, and a study shows one group of products on one date. Together they give a fair picture. Alone, each can mislead.
This article is general information. It is not medical advice, and it does not rate any brand.
Sources: California Attorney General, Proposition 65 frequently asked questions (oag.ca.gov/prop65/faq); Food Safety News, February 28, 2018 (foodsafetynews.com)