Understanding heavy metal regulations like Prop 65

In California, Proposition 65Opens in a new tab warnings are nearly impossible to avoid. They appear in parking garages, on coffee cups, and across grocery aisles from protein powders to even organic spinach. If you steered clear of every product bearing the label, you’d be severely limiting your diet. But Proposition 65 was designed to inform consumers about potential exposures to certain chemicals, not to declare that a product is unsafe.

So what does that warning actually mean?

Earlier in this series, we explored why trace metals in today’s foods are far lower than in the past and introduced the principles that distinguish toxic exposure from harmless trace presence.

Now we’ll break down where the heavy metal regulations — specifically Proposition 65 — come from, how safety limits are set, and why even safe foods sometimes carry warnings. 

What Is Proposition 65? A Brief History

In the early 1980s, California found that over 100 Silicon Valley wellsOpens in a new tab were contaminated with toxic chemicals from semiconductor manufacturing.

Frustrated that state agencies had failed to adequately address the problem, California residents voted on and passed the Safe Drinking Water and Toxic Enforcement Act of 1986Opens in a new tab. 

This law mandates the state to maintain a list of chemicalsOpens in a new tab “known to cause cancer, birth defects or other reproductive harm” and requires that businesses either:

• Prove that exposure to these chemicals is below state-defined “safe harbor” levels, OR
• Provide a “clear and reasonable warning”

The Safe Drinking Water and Toxic Enforcement Act of 1986 — often referred to as Prop 65 — was aimed at preventing contamination of drinking water and protecting consumers from significant chemical exposures. 

But as the list of regulated substances expanded from a few dozen to around 900 chemicals, the warning requirements grew. With advances in testing technology capable of detecting substances at parts per billion, everyday products began to qualifyOpens in a new tab — including those containing trace amounts of naturally-occurring elements like lead or cadmium.

Fast-forward to today and what began as an environmental safeguard is one of the most misunderstood consumer warnings in the country.

How Are Prop 65 Safety Limits Calculated?

A Prop 65 warning doesn’t mean a product is dangerous. It means the product exceeded California’s extremely cautious threshold. But what is California’s threshold?

A warning is required when exposure to a listed chemical exceeds the state's "safe harbor" level — limits that already include large safety marginsOpens in a new tab. For reproductive toxicants, that level sits 1,000 times below the no observable effect levelOpens in a new tab identified in toxicology studies. For cancer risk, a warning must be given when exposure to a chemical could cause at least one case of cancer for every 100,000 people exposedOpens in a new tab.

These levels are set by California’s Office of Environmental Health Hazard AssessmentOpens in a new tab (OEHHA) in two steps: 

Step 1: A scientific organization approved by OEHHA reviews toxicology data to determine the no observable effect levelOpens in a new tab (NOEL) for reproductive harms, the “maximum level of exposure at which a chemical has no observable reproductive effect” or no significant risk levelOpens in a new tab for cancer, “the level of exposure that would result in not more than one excess case of cancer in 100,000 individuals exposed to the chemical over a 70-year lifetime.”

Step 2: The NOEL number is then divided by additional safety factors to account for human variability and long-term exposure, resulting in limits intentionally far below any level expected to pose real-world risk.

Here’s what that looks like in practice:

• California’s limit for leadOpens in a new tab: 0.5 micrograms/day — derived by taking the no observable effect level (NOEL) from toxicology studies and dividing it by 1,000-fold.
• FDA’s limit for leadOpens in a new tab: 2.2 µg/day for children, 8.8 µg/day for women of childbearing ageOpens in a new tab, and 12.5 µg/day for the general adult populationOpens in a new tab — roughly 4 to 25 times higher than California's. FDA also builds in a safety margin: 10x below levels that pose a “potential health concern,” versus Prop 65's 1,000x margin.

So a product that exceeds California’s threshold may still be well within federal safety limits. The difference reflects California’s modeling assumptions and extra safety margins, not actual health hazards.

In other words, a Prop 65 warning doesn’t automatically mean danger.

Why a Prop 65 Warning Doesn’t Mean a Product Is Dangerous

An extra safety margin sounds like a good thing, but Prop 65’s thresholds are so far below any demonstrated risk that warnings now appear on everything from coffee to seafood to wooden furniture. 

The result isn’t necessarily greater safety; it’s greater confusion.

The key thing to remember is that a Prop 65 label is a legal disclosure, not a scientific statement of danger. It’s required when estimated exposure exceeds California's safe harbor level, but companies may also apply it based on the presence of a listed chemical alone, without estimating exposure at all. Either way, the label doesn't tell you a product is harmful.

In most foods, human exposure to harmful chemicals is far below levels that raise concern. Many whole foods naturally contain trace amounts of substances that appear on the Prop 65 list simply because of how they’re grown, processedOpens in a new tab, harvested, or cooked — from minerals absorbed in soil to compounds formed through heat.

CocoaOpens in a new tab, spinachOpens in a new tab, seaweedOpens in a new tab, and root vegetablesOpens in a new tab can all contain measurable levels of metals like lead or cadmium, even though they’re widely recognized as safe and nutrient-dense.

Ironically, a truly “toxin-free” diet would mean eliminating most fresh foods and eating mostly high-calorie and low-fiber ultra-processed products — the very foods driving today’s metabolic health crisisOpens in a new tab.

And the obsession with eliminating all exposure overlooks a basic biological principle: small amounts of stress can be beneficial. Known as hormetic stressOpens in a new tab, this concept reflects how low-level challenges can, in some cases, strengthen cellular defenses and build resilience to larger impacts over time. There hasn’t been much research on Prop 65 chemicals and hormetic stress in people, but preliminary evidenceOpens in a new tab suggests that exposure to low levels of some heavy metals can, for example, boost cells’ ability to protect themselves from various stressors.

Why Are Prop 65 Warnings on Everything?

Today, the Prop 65 list includes about 900 chemicals. Because private individuals and law firms can file Prop 65 lawsuits and collect a portion of the civil penalties (aka, make a profit), the system unintentionally incentivizes over-warningOpens in a new tab. To avoid litigation, some companies may choose to label products even when exposure is negligible, especially since fines can reach up to $2,500 per violation per day.

As a result, consumers encounter warnings on many everyday items that are unlikely to pose a meaningful health risk, from vegetables and coffee cups to makeup and cookware. That’s why a Prop 65 label, on its own, shouldn’t be a deciding factor. Context and credible science matter far more than a blanket warning.

This challenge echoes one of toxicology’s most famous ironies. Dr. Bruce Ames — creator of the Ames TestOpens in a new tab, a breakthrough tool for detecting mutagenic compounds — watched as results from his own invention were taken out of context. The test (which is extraordinarily sensitive) flagged mutagenic activity in coffee. But instead of treating those findings as preliminary screens that require context and dose considerations, some people and headlines leapt to conclusions that coffee causes cancerOpens in a new tab.

Ames spent much of his later career explaining that detection isn’t danger. The world is full of compounds that can trigger a positive result in a lab test, but that doesn’t mean they pose a real-world risk at the amounts people actually encounter. 

His message was simple: Don’t confuse the ability to detect a trace hazard with evidence that it can cause harm.

It’s the same misunderstanding that fuels Prop 65 over-warning today — a tendency to “major in the minors” by focusing on what we can detect instead of what meaningfully impacts health.

When every trace becomes a trigger for alarm, genuine risks fade into the background. The result isn’t greater safety, but greater confusion about what deserves your time, money, and energy in the pursuit of health.

How to Tell Which Food Safety Warnings Matter

Next time you are at the grocery store, ask yourself three simple questions:

• Is it sold nationwide? If you can buy it in stores across the U.S., it probably meets federal safety standards. The Prop 65 warning reflects California’s uniquely strict limits — as an overly-cautious warning — not a safety issue.
• Does every brand have a warning? Look at the shelf. If ALL the dark chocolate bars, ALL the canned tuna, or ALL the coffee has the warning, it's probably about unavoidable trace amounts, not unsafe products.
• Is it a whole food from nature? Seafood, leafy greens, root vegetables, nutsOpens in a new tab, and chocolate contain naturally-occurring trace minerals from soil and water. The warning doesn't mean they’re unsafe to eat or should be avoided.

A simple rule of thumb: If it's a normal grocery store item that's been sold for years, it's probably safe despite the warning.

There are a couple of events that would warrant attention.

Product recalls or contamination events: This refers to situations where a government agency (FDA, USDA, or California regulators) identifies a real safety problem like Salmonella in peanut butter or lead in candy. These are actionable warnings that indicate an actual health risk. For updates and notices on specific recalls or events you can check: 

• Recalls.govOpens in a new tab
• FoodSafety.govOpens in a new tab 
• FDA websiteOpens in a new tab
• U.S. Consumer Product Safety Commission (CPSC)Opens in a new tab 

Industrial exposure (e.g., water, occupational settings): This points to scenarios where people might encounter high levels of a chemical in the course of work or from environmental contamination like lead from a factory or contaminated drinking water. You can refer to websites and tools like:

• U.S. Environmental Protection Agency (EPA)Opens in a new tab
• State-level environmental agencies (Google yours!)
• EPA's ECHO Notify programOpens in a new tab 
• National Environmental Public Health Tracking Network (CDC)Opens in a new tab 

But foods or products with Prop 65 labels don’t automatically mean you need to avoid them. Instead, focus on overall diet quality and nutrient density. Prioritize variety and balance, not trace detection. And remember that in most cases your body can naturally detoxify a large portion of the heavy metals you’re exposed to.

The takeaway isn’t to ignore safety, but to interpret warnings wisely. Understanding the difference between real risk and regulatory noise lets you make informed, confident choices.

Next in the Series: “How to Read a Toxicology ReportOpens in a new tab”. Learn how toxicologists assess exposure levels, what “parts per billion” means, and how to interpret toxicology reports yourself.

This was the third article in our six-part "Toxicology in Context: Heavy Metals" series. Want to read the other articles? Check them out below: 

• A brief history of heavy metalsOpens in a new tab
• Toxic metals vs. toxicology: Why dose mattersOpens in a new tab
• How to read a toxicology report: What does parts per billion mean?Opens in a new tab
• Does your body absorb heavy metals? Bioavailability explainedOpens in a new tab
• Mechanisms of detoxification: How the body clears heavy metalsOpens in a new tab

FAQs

Q: What does a Proposition 65 warning mean?

A Prop 65 warningOpens in a new tab means a product may expose consumers to a listed chemical above California's "safe harbor" exposure level. For reproductive toxicants, California's safe harbor levels include a 1,000-fold safety factor below the no-observed-effect level (NOEL)Opens in a new tab used in toxicology studies. Prop 65 warnings are legal disclosures of presence, not scientific statements of danger. A product that exceeds California's threshold can still be well within federal safety limits set by the FDA.

Q: Why do so many everyday products carry Prop 65 warnings?

A: The Prop 65 list now includes about 900 chemicals, and California's thresholds are so cautious that they capture naturally-occurring trace amounts in whole foods like cocoaOpens in a new tab, spinachOpens in a new tab, seaweedOpens in a new tab, and root vegetablesOpens in a new tab. Because private individuals and law firms can sue and collect a portion of the penalties (which are up to $2,500 per violation per day), companies may label products preemptively to avoid litigation even when exposure is negligible.

Q: How are Prop 65 safety limits calculated?

A: California's Office of Environmental Health Hazard AssessmentOpens in a new tab (OEHHA) first identifies the no observable effect levelOpens in a new tab (NOEL) for reproductive harms from toxicology studies, then divides that number by 1,000 to account for human variability and long-term exposure. The result is a threshold intentionally far below any level expected to pose real-world risk. For lead, California's daily limit is 0.5 micrograms — derived by dividing the no-harm level by 1,000. For cancer risk, the no significant risk level is calculated based on the chemical exposure level that would cause at least one case of cancer for every 100,000 people exposed. 

Q: How is Prop 65 different from FDA safety limits?

A: The FDA's lead limitsOpens in a new tab are 2.2 micrograms per day for children and 8.8 micrograms per day for women of childbearing age — roughly 4 to 25 times higher than California'sOpens in a new tab. The FDA also builds in a safety margin (10x below what could cause concerning blood lead levels), but California's is up to 1,000 times more conservative on top of that.

Q: Does a Prop 65 warning mean I should avoid a product?

A: Not on its own. A few quick questions can help you decide: Is it sold nationwide? Does every brand of that product carry the warning? Is it a whole food from nature? If yes to those, the warning is almost certainly flagging unavoidable trace amounts of heavy metals. Product recalls such as those from the FDAOpens in a new tab or CPSCOpens in a new tab are a different category — those reflect identified health risks and are worth paying attention to.

Q: Why do whole foods like spinach and cocoa contain heavy metals?

A: Plants absorb trace minerals from soil and water as they grow. Some of those minerals — like lead and cadmium — appear on the Prop 65 list. Their presence reflects how food is grown, not contamination or poor quality. Many of the foods most likely to trigger a warning (leafy greens, root vegetables, seafood, cocoa) are also among the most nutrient-dense.

Originally published May 2026; updated July 2026