Read more about California’s Proposition 65, also known as
The Safe Drinking Water and Toxic Enforcement Act of 1986 requires
California businesses to provide warnings about significant exposures to
chemicals that can cause cancer, birth defects, or other reproductive
harm.

Proposition 65: The Safe Drinking Water and Toxic Enforcement Act of
1986

What is Prop 65? CA Prop 65 compiles a list of chemicals that cause
cancer, birth defects, or other reproductive harm, and requires
businesses to provide warnings about significant exposures to the  listed
chemicals and never knowingly discharging significant amounts of listed
chemicals into sources of drinking water.

Why is Prop 65 Significant to Environmental Justice? Prop 65 provides
warnings for people in California if they may be exposed to a chemical
that causes cancer or reproductive harm, and communities burdened by
Multiple sources of pollution or contamination often include the listed
chemicals. Proposition 65 requires businesses, including construction
and development companies, to have clear exposure warnings posted.
Developers will typically try to conceal that they are building on top
of historical contamination, and while Prop 65 cannot stop them, and does
not halt the use or exposure of any chemical, it can warrant an
investigation into the chemicals people may be exposed to when on or
near the site.

Then link these for additional information (both attached):
Prop 65 Training Presentation
Prop 65 Facthseet