On February 19, 2016, the California Office of Environmental Health Hazard Assessment announced its adoption of a Proposition 65 No Significant Risk Level (NSRL) of 146 micrograms per day for diisononyl phthalate (DINP). This means that exposures to DINP above 146 micrograms per day require a warning under Proposition 65. The NSRL, adopted as a formal regulation under Proposition 65, will be effective as of April 1, 2016.
DINP is a plasticizer used in a variety of products and has been a favorite target among Proposition 65 private enforcers. OEHHA listed the chemical as a carcinogen on December 20, 2013. With hundreds of Proposition 65 chemicals still awaiting the development of an NSRL (for carcinogens) and Maximum Acceptable Dose Levels (for reproductive toxicants), it is remarkable OEHHA has moved so quickly to adopt an NSRL for this chemical.
OEHHA had proposed this NSRL on January 2, 2015. A number of public comments were submitted, including comments from the American Chemistry Council, Consumer Specialty Products Association and Exxon Mobil. One of the key scientific disputes presented by the commenters was whether the incidence of mononuclear cell leukemia (MNCL) in a particular rat species exposed to DINP should be considered in developing the NSRL. The rat species, designated Fischer 344, has a known incidence of MNCL even in the absence of chemical exposures. The commenters also argued that MNCL is not a relevant predictive model for human disease. After reviewing these and other related comments, OEHHA concluded that it was appropriate for it to consider studies showing an increased incidence of MNCL in Fisher 344 rats exposed to DINP.
The Chanler Group, a well-known private Proposition 65 enforcer law firm, also submitted comments urging OEHHA to adopt a lower level of 70 micrograms per day. Whether or not members of the public, NGOs and the regulated community agree with the adopted NSRL, an established NSRL at least provides more concrete guidance to businesses evaluating whether their products require a warning.