A3.2.7 Continued…


Heavy Metal Pollution from Roads

Road water run off may include more heavy metals than you might think. Studies in the USA have found that half of the zinc and copper contribution to the environment from urbanization is from cars. Brakes release copper, while tyre wear releases zinc. Motor oil also tends to accumulate metals as it comes into contact with surrounding parts as the engine runs, so oil leaks become another pathway by which metals enter the environment.

On the road surface, most heavy metals become bound to the surfaces of road dust or other particulates. During precipitation, the bound metals will either become soluble (dissolved) or be swept off the road with the dust.

Studies have revealed high levels of the following metals in road water runoff:

  • Lead: leaded petrol, tyre wear, lubricating oil and grease, bearing wear.
  • Zinc: tyre wear, motor oil, grease, brake emissions, corrosion of galvanized parts.
  • Iron: car body rust, engine parts.
  • Copper: bearing wear, engine parts, brake emissions.
  • Cadmium: tyre wear, fuel burning, batteries.
  • Chromium: air conditioning coolants, engine parts, brake emissions.
  • Nickel: fuel, lubricating oil, brake emissions.
  • Aluminium: car body corrosion .