OEHHA to Adopt two New MADLs for n-Hexane



California’s Office of Environmental Health Hazard Assessment (OEHHA) is about to finalize a Safe Harbor Level for the chemical n-hexane, adding another regulatory level to the State of California’s Proposition 65 Chemical list.

N-hexane is used as a low-temperature filler in thermometers, as an extraction solvent and also as a degreasing compound.

N-hexane was added to California’s Proposition 65 list as a reproductive toxicant on December 15, 2017.

The safe harbor level for n-hexane is also called the maximum allowable dose level (MADL). The MADL is a regulatory level that denotes the maximum exposure level for which a Proposition 65 warning is required.

OEHHA has recommended the adoption of two MADLs for n-hexane at:

28,000 micrograms per day, for oral exposure and

20,000 micrograms per day for inhalation exposure.


Maximum Allowable Dose Levels (MADL) are the safe harbor levels for reproductive toxicants or chemicals otherwise identified causing birth defects or other reproductive or developmental harm.  

OEHHA has not set safe harbor levels for the majority of chemicals listed under Proposition 65.  The agency has not been able to assess risk for nearly 600 chemicals of the approximately 900 chemicals on the Proposition 65 list.

Another term for a safe harbor levels term is a No Significant Risk Levels (NSRLs) which is used to denote cancer-causing chemicals.  If chemical users can show that exposures from a chemical fall below an NSRL for the chemical in question they are not required to provide Proposition 65 warnings.

No Significant Risk Levels (NSRLs) for carcinogens means that exposure to chemicals at this level would cause only one case of cancer in every 100,000 people in over 70 years. Lead is one of many carcinogens with an NSRL set by the OEHHA.

Proposition 65 does not require warnings if a listed chemical that is discharged is below their safe harbor levels.

The warning requirement takes effect one year after the chemical is listed under Proposition 65.

Because n-Hexane was listed by OEHHA on December 15, 2017, the compliance date will take effect on December 15, 2018, and Proposition 65’s warning requirements will take effect at that time.

Public comments related to the proposed MADLs must be submitted to OEHHA by November 19, 2018.

About Jack Schatz

Jack Schatz began writing about Proposition 65 and other U.S. environmental laws since 1994. He has also written extensively about Consumer Product safety as well. He is the publisher and co-author of the 2013 and 2017 editions of the Proposition 65 Handbook.
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