There are gaseous wastes into the air from domestic premises, vehicles and industrial premises. Most disposable wastes are in some form of solid or liquid or some form of slurry in between. Most solid waste is deposited on land (some at sea), but its chemical contents can "leach" through soils to contaminate water.

It is very difficult to say what is 'harmful' waste. That makes it difficult to find accurate figures for how much is produced - every country has different statistics.