Aren't some acrylics toxic because they're made with heavy metals, like cadmium?

Some colors, such as cadmiums are toxic. There are alternatives, such as "cadmium hues," but if you're using true cadmium, there is some toxicity. Because the pigment is bound in the acrylic polymer there is no way for particles of pigment to enter your body through the air. The pigment stays imbedded within the polymer. To avoid skin contact, however, you could use latex gloves. If you sand a lot, especially with a orbital sander, consider getting a mask to keep the air you are breathing particulate free.