Understanding NSRL and MADL

Considering the No Significant Risk Levels (NSRLs) and Maximum Allowable Dose Levels (MADLs) is essential. These thresholds define the limits for exposure to cancer-causing chemicals and compounds causing reproductive toxicity, providing a safe harbor for consumers. If the exposure levels or emissions to drinking water sources remain below these thresholds, they are exempted from Proposition 65 scrutiny.

Notably, enforcement proceedings sometimes lead to negotiated exposure levels established through settlement agreements. This regulatory landscape aims to balance public health and commerce.

Charting the Path: Prioritizing NSRL Development for Carcinogens

The Office of Environmental Health Hazard Assessment (OEHHA) plays a vital role in Proposition 65 implementation, particularly in setting safe harbor limits, including NSRLs. These limits, outlined in Sections 25705 and 25709 of the California Code of Regulations, Title 27, help determine the necessity of Proposition 65 warnings.

Priority Substances for NSRL Development:

• 1. Antimony trioxide
• 2. Ethylene oxide
• 3. 1-Bromopropane

The changes to the proposed regulations and the inclusion of additional documents directly impact the risk assessment, with the risk level for Antimony trioxide recently considered negligible.

The Evolution of Antimony Trioxide’s NSRL:

Antimony trioxide, a substance under the Proposition 65 microscope, has evolved in its NSRL. The OEHHA has taken measured steps to modify the proposed NSRL for Antimony trioxide in Title 27, California Code of Regulations, section 25705(b)(1). This modification and the inclusion of significant documents in the rulemaking file reflect a commitment to evidence-based decision-making.

The journey began on August 26, 2022, when OEHHA initially published a Notice of Proposed Rulemaking in the California Regulatory Notice Register (CRNR), introducing the regulation. Concurrently, an Initial Statement of Reasons provided insights into the proposal. This marked the commencement of a 45-day public comment period, running from August 26 to October 11, 2022, allowing stakeholders to weigh in on the matter. (See below for details on the proposed rulemaking and the public comments received.)

Deciphering the Rationale Behind the Proposed Modification

The rationale behind the proposed modification stems from the valuable feedback OEHHA received during the comment period for the initial proposal. Notably, comments highlighted variations in the absorption rate of Antimony trioxide through oral and inhalation exposure routes.

The scientific literature, including assessments by authoritative bodies such as the European Commission (2008), ATSDR (2019), WHO (2003), IARC (1989), and studies like those conducted by Boreiko and Rossman (2020), has provided crucial insights. Additionally, toxicokinetic data from studies such as Gross et al. (1955), Groth et al. (1986), Hiraoka (1986), Newton et al. (1994), Sunagawa (1981), and Westrick (1953) have also played a pivotal role.

OEHHA concluded that accurately calculating the NSRL for oral exposure was not feasible due to ambiguity surrounding absorption rates and differences between inhalation and oral exposure. As a result, OEHHA has proposed to designate the NSRL with an “(inhalation)” tag, thereby narrowing its focus to inhalation exposure. It is important to note that this adjustment allows for the potential creation of an NSRL for oral administration in the future, as long as sufficient data is available.

Proposition 65’s NSRLs and MADLs are essential benchmarks in protecting public health while allowing for economic activity. As exemplified by the Antimony trioxide case, the continuing evolution of these thresholds shows OEHHA’s commitment to evidence-based decision-making and continuous improvement in safeguarding Californians from harmful substances.

Reference: https://oehha.ca.gov/proposition-65/general-info/priority-list-development-proposition-65-no-significant-risk-levels