Engine exhaust and some of its constituents, and some dust created by power sanding, sawing, grinding, drillingandotherconstructionactivities contains chemicals known to the State of California to cause cancer, birth defects and other reproductive harm. Some examples of these chemicals are:
Crystallinesilicafrombricks.
Cementandothermasonryproducts. 
Arsenicandchromiumfromchemically treatedlumber.
Your risk from these exposures varies, dependingonhowoftenyoudothistype of work. To reduce your exposure to these chemicals: ALWAYS work in a well ventilated area, and work with approved safety equipment, such as dust masks that are specially designed to filter out microscopic particles.