Cardno ChemRisk Scientists Publish Paper to Derive a Prop 65 NSRL for 2-Nitropropane

Posted on Behalf of  Lindsey Garnick

Posted on behalf of Lindsey Garnick

We are pleased to share with you an article our colleagues recently published in the Journal of Applied Toxicology, titled Derivation of Cancer No Significant Risk Levels for 2-Nitropropane and Screening Safety Assessment for Spray ProductsThe study is available here:

In this study, No Significant Risk Levels (NSRLs) were derived for 2-nitropropane (2-NP), in the absence of a California published NSRL. In January 1988, the State of California listed 2-Nitropropane (2-NP) (CAS number 79-46-9) as a chemical known to cause cancer under Proposition 65. Although 2-NP is listed on the Prop 65 list, currently no Safe Harbor Level exists for this chemical. Benchmark Dose (BMD) modeling was performed using hepatocellular carcinoma incidence data from four 2-NP single exposure inhalation studies in Sprague-Dawley rats. Additionally, a safety assessment was performed based on estimated consumer inhalation exposure to 2-NP during indoor application of paint from a spray can. For the exposure assessment, three key factors were analyzed: the 2-NP residual concentration in the spray paint product, the mass of spray paint used, and the frequency of use. 

A cancer potency factor was determined from the results of the BMD modeling, and then the NSRL was calculated using a lifetime cancer risk of 10-5. The inhalation and oral derived NRLSs are 67 µg/day and 32 µg/day, respectively.

Based on the screening exposure assessment, potential consumer exposure to 2-NP from indoor application of paint from a spray can does not exceed our proposed inhalation NRSL, therefore, a warning label is not needed for spray can products containing 2-NP as a minor contaminant.

The current study focused on the inhalation route of exposure due to the nature of the product scenario being evaluated. Future studies could evaluate the exposure from dermal routes as well as alternative use scenarios.  In deriving the NSRL, we used a model averaging approach to reflect the use of the best science in the concentration response analysis. Additional sensitivity analyses are planned to highlight the impacts of using current risk assessment best practices versus the single mode choice approach defined in the current NSRL Derivation guidance.

If you have any questions or would like further information, please contact Andy Maier.