The reason why toasters have a Prop 65 warning is because toasters can contain small amounts of chemicals that are listed under California's Proposition 65 warning.
California's Proposition 65 requires warning labels to be placed on products which can expose consumers to chemicals that are known to cause reproductive harm or cancer.
Even if the exposure to those chemicals are minimal it still is required.
The toaster may contain chemicals that are present in the metal components or plastic parts of the toaster.
One possible group of chemicals is called phthalates and might trigger the Prop65 warning.
Phthalates are often used on plastic and other items, including many electrical cords, The chemical maintains plastic's elasticity, so it prevents cracking and prolongs the usable life.
Some types of household appliances may expose you to chemicals that are on the Proposition 65 list.
These chemicals can possibly cause cancer and/or birth defects or other reproductive harm.
The California Proposition 65 requires businesses to determine if they must provide a warning about significant exposure to listed chemicals.