Prop 65 Exposure vs MADL Calculator
California Proposition 65 requires a clear and reasonable warning when a product exposes people to a listed chemical above the safe harbor level. This calculator does the exposure arithmetic so you can decide whether a warning, a reformulation or a better test is the next step.
Your numbers
Concentration of the listed chemical in the product or material, micrograms per gram.
Mass of product a user ingests or that transfers to skin per use.
Use 100 for ingestion of the whole mass; lower values for dermal transfer from a wipe study.
Take the value for your chemical and route from the OEHHA safe harbor table. Lead reproductive MADL is 0.5 ug/day.
Your results
Prop 65 exposure assessment follows OEHHA regulations (Title 27 CCR section 25821 and related). Use the reasonably anticipated rate of exposure for the product and a qualified toxicologist for defensible claims. This tool is a screening aid, not legal advice.
Daily exposure vs concentration
Sweeps Chemical concentration in product from 0 to 10, holding your other inputs fixed.
Chemical data on your item master
Optional expert review of how to hold test results and chemical specs against ERP items.
Optional. The tool and every export work without this. No spam.
How to use it
Start with the analytical result for the chemical in the product. Enter the amount of product a person ingests or contacts per use and the number of uses per day. If the route is dermal, use a transfer fraction from a wipe or migration study; for ingestion leave it at 100%. Enter the safe harbor level for the chemical and the endpoint: a MADL for reproductive toxicity or an NSRL for cancer risk. The tool returns exposure, the share of the level and the highest concentration that avoids a warning.
- Use the OEHHA table for the current level
- Pick the endpoint that gives the lower level if the chemical has both
- Use the realistic upper-bound use pattern
The method
Daily exposure equals concentration times mass per use times uses per day times the fraction that reaches the person. If that exposure is at or below the safe harbor level, a warning is not required for that chemical and route. The inverse gives the specification limit you can write into a purchase order: maximum concentration equals the level divided by the daily mass transferred. Safe harbor levels are not the only defence, but they are the most direct one.
- Exposure = conc x mass x uses x transfer
- Max conc = level / daily mass transferred
- Reduction = 1 - level / exposure
Worked example
A product has 2 ug/g of lead and a user ingests 5 g once a day, so exposure is 10 ug/day against a lead reproductive MADL of 0.5 ug/day. That is 2,000% of the level and a warning would be needed. The maximum concentration would be 0.1 ug/g, a 95% reduction. The chart shows how steeply exposure rises with concentration, which helps when you negotiate a specification with a supplier.
Common mistakes
Teams often use the level for the wrong route or endpoint, or copy a value from an old list. Another mistake is using average rather than reasonably anticipated use, or ignoring that a sold-in-California product can reach the state through a distributor. Keep the evidence, the date of the level you used and the use assumptions together in the technical file so you can defend the decision if a notice of violation arrives.
Frequently Asked Questions
What is a MADL?
A maximum allowable dose level is the safe harbor level for chemicals that cause reproductive toxicity, given in micrograms per day. Exposure at or below the MADL does not require a Prop 65 warning for that chemical.
What is an NSRL?
A no significant risk level is the daily intake that is calculated to result in no more than one excess case of cancer in 100,000 individuals exposed over a 70 year lifetime. It is the cancer-endpoint equivalent of a MADL.
Does a warning protect me from all claims?
A compliant warning reduces the risk of a notice of violation for that exposure, but it must meet the content and delivery rules of the regulation. It is not a substitute for reducing exposure where that is possible.
Where do I get the safe harbor value?
OEHHA, California's Office of Environmental Health Hazard Assessment, publishes the MADL and NSRL tables on its Proposition 65 website. Use the current version and record the date you consulted it.
Netray can help you attach test results and chemical specifications to the item records in your ERP so Prop 65 decisions are traceable by part number.
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