Brake dust is the result of your brake pads wearing down during normal driving. Small flakes of material will begin to slough off onto your wheels and the surrounding brake system. Once it's on your wheels, it can be quite a project to remove. Not only that, but brake dust is extremely hazardous to aquatic life, so it is important to take care when cleaning.
Steps for how to remove brake dust:
1. Move your car into a shaded location out of the direct sun.
2. Spread some microfiber towels underneath the car's wheels and tires where you will be cleaning. This is to catch any run-off.
3. Select an all purpose degreaser that does not contain acids or other petrochemical solvents.
4. Spray wheels and allow the degreaser to penetrate for about 2 minutes.
5. Gently scrub wheels with a microfiber cloth on soft brush.
6. Dry wheels with a microfiber towel.
7. Apply a metal polish or spray wax to help seal the wheels from future brake dust accumulation.