the number of vehicles moving along roads, or the amount of aircraft, trains, or ships moving along a route
Traffic
waste material or things that are no longer wanted or needed
Rubbish
damage caused to water, air, etc. by harmful substances or waste
Water pollution
the fact of a country or city, etc. having too many people for the amount of food, materials, and space available there:
Overpopulation
to become or to make something become smaller in size, amount, degree, importance
REDUCE
to use something again:
Reuse
to sort and collect rubbish in order to treat it and produce useful materials that can be used again
recycle
