California Considers Listing Titanium Dioxide Nanoparticles and Other Chemicals as Reproductive Toxicants
California’s Office of Environmental Health Hazard Assessment’s (OEHHA) Proposition 65 Developmental and Reproductive Toxicant Identification Committee (DARTIC) will hold a virtual public meeting on Dec. 10 to consider comment and review its Prioritization Document where it considers classifying 22 chemicals as reproductive toxicants for the purpose of labeling under Proposition 65 (Prop 65). Titanium dioxide nanoparticles — ultrafine particles 1 – 100 nanometers (nm) in diameter — are among the chemicals under OEHHA’s consideration for Prop 65 listing.
If OEHHA finalizes listing, manufacturers of products containing one or more of these chemicals must provide warnings on product labels within one year. Under Prop 65, individuals must provide warnings prior to exposure to a chemical identified by the State of California to cause cancer or reproductive harm. The duty to warn applies to most individuals causing an exposure, including product manufacturers, employers and individuals causing exposures in an affected area. Prop 65 requires the State of California maintain a list of chemicals that are known to the State to cause cancer, birth defects or other reproductive harm, or both. The list includes over 900 chemicals since it was published in 1987.
The state can add chemicals to the Prop 65 list using four mechanisms: 1) the State’s qualified expert mechanism; 2) formally required to label mechanism; 3) labor code listing mechanism; and 4) authoritative body mechanism.
Last month, ACA filed comments with OEHHA urging the agency not to list titanium dioxide nanoparticles under Prop 65.
In its comments, ACA notes that paint manufacturers may use nanoscale titanium dioxide as a filter for ultra-violet light to protect binding agents in a paint matrix; however, ACA underscored that the extent of use in paints is unknown and that it may not be common.
Because no studies associate reproductive toxicity with use of products containing nanoscale titanium dioxide, ACA asserted its belief that a Prop 65 listing is not supported at this time. This is especially true for use in paint products, since any nanoscale material is bound in a matrix and rendered unavailable during use. Any releases from weathering, sanding, demolition or disposal are expected to be negligible.
Particles bound in a paint matrix do not pose a hazard
ACA urged DARTIC to consider that wetted mixtures, such as paint, containing hazardous chemicals typically pose no hazard. OEHHA has recognized that particles bound in a paint matrix do not pose a hazard during application. Studies cited in the prioritization document do not support the proposition that nanoscale titanium dioxide in paint would increase the likelihood of reproductive toxicity in users of paint products. OEHHA’s listing of crystalline silica and titanium dioxide as a carcinogen in Proposition 65, recognize that chemicals bound in a paint matrix do not pose a hazard. In considering availability for exposure of titanium dioxide, the International Agency for Research on Cancer (IARC) recognizes that “No significant exposure to primary particles of titanium dioxide is thought to occur during the use of products in which titanium dioxide is bound to other materials, such as in paints.”
ACA also noted that IARC reached a similar conclusion when considering carcinogenicity of carbon black: “End-users of these products (rubber, ink or paint) are unlikely to be exposed to airborne carbon black particles, which are bound within the product matrix.”
As such, ACA asserts that listing titanium dioxide nanomaterials for use in paint products
under Prop 65 is unwarranted.
Nanoscale titanium dioxide does not pose a significant hazard during abrasion
ACA stressed to OEHHA that any concern related to particles in wetted mixtures usually occur from sanding and abrasion after application. OEHHA’s listing of titanium dioxide and crystalline silica as Proposition 65 carcinogens is limited to “airborne, unbound particles of respirable size.” Moreover, since particles are bound in a matrix, any respirable particles typically do not contain pure form of the particle at issue, minimizing any risk posed by that chemical.
ACA pointed to a study that considers hazards associated with nanoscale titanium dioxide in paint particles where the authors conclude that hazards of nanoscale titanium dioxide in dried paint particles cannot be predicted based on hazards of pristine nanoscale titanium dioxide. The authors also note that amounts of nanoscale titanium dioxide from dried paint particles are negligible.
Specification of particle dimensions would assist in identifying products with nanoscale titanium dioxide
For clarity, ACA suggested that OEHHA harmonize California’s definition of nanoscale titanium dioxide with particle parameters identified in the U.S. Environmental Protection Agency’s (EPA) Nanoscale Materials Reporting Rule. The EPA definition specifies that:
- Particles manufactured or processed in a form where any particles, including aggregates and agglomerates, are in the size range of 1-100 nanometers (nm) in at least one dimension; and
- Are solid at 25 °C and standard atmospheric pressure.
Companies applied this definition in 2017 when identifying reportable products under the rule. Should DARTIC recommend listing, harmonizing California’s definition would assist companies that are already familiar with USEPA’s definition. U.S. EPA also provides some additional clarity by noting particle size must apply to at least one dimension.
For the aforementioned reasons, including insufficiency of studies indicating reproductive toxicity of nanoscale titanium dioxide as used in products, ACA urged DARTIC not to recommend listing nanoscale titanium dioxide under Prop 65 at this time.
Contact ACA’s Riaz Zaman for more information.