Sources of highway pollutants include vehicles (exhaust emissions, fuel losses, lubricant losses, and tire wear), litter, spills, pavement wear (concrete and asphalt), atmospheric deposition (dust fall and precipitation), and roadway maintenance operations (herbicides, salt, and road repairs). (Folkeson, 1994, Barret et al., 1995).
The main categories of highway runoff pollutants include suspended particles, oxygen-consuming pollutants, petroleum products, nutrients, heavy metals, organic pollutants, and microorganisms. (Folkeson, 1994).
The pollutants most frequently found are bacteria, cadmium, chlorine, chromium, copper, floatable litter, iron, hydrocarbons, lead, nickel, nitrogen, particulates, phosphorus, sodium, and zinc. Overall the pollutants are also analyzed for their biological and chemical oxygen demand placed on the receiving water.
Primary sources of some of the constituents of roadway runoff are:
1. Copper - metal parts wear (bearings, engine parts, plating, brake linings), fungicides and insecticides.
2. Nitrogen and Phosphorus - dust fall from the atmosphere, fertilizers, sediments.
3. Lead - deposits from leaded gasoline (no longer in use), tire and bearing wear, lubricants, and dust fall.
4. Floatable Litter - litter discarded by pedestrians or from vehicles, litter and debris falling from truck beds, spills.
5. Particulates - pavement wear, vehicles, atmosphere, maintenance, abrasives (used for snow and ice), sediment.
6. Bacteria - soil, bird and animal droppings, livestock wastes.
7. Zinc - tire wear, lubricants.
(Kearfott, 2005).