3. Pollutant sources

The expression "pollutant origin" is ambiguous. It can refer either to the primary sources responsible for the production of these pollutants, or to the deposit from which they are mobilized at the time of rainfall. Urban industrial activity, for example, is a source of various substances. Industrial emissions can be airborne, and the pollutants produced can be found either in atmospheric deposits during dry weather, or in rainwater itself. Emissions can also take the form of aqueous discharges, and the pollutants are found either in wastewater or in deposits in sewer systems.

We have chosen to present the results by deposit, as this breakdown is the least difficult for researchers to analyze, and therefore the one for which knowledge appears most solid. However, we will indicate the most likely sources, deposit by deposit.

The distinction...