Let me try some numbers:

The average household has 50 light bulbs, with an average life of 10 years. Each bulb contains 20mg of mercury, so the mercury waste from one household is 1 gram every decade. With a toxic TLV of 25 microgrammes per cubic metre, that is potentially 40,000 cubic metres of toxic mercury vapour.

There are 30 million households in the UK alone, so that represents 30 metric tonnes of mercury released every decade, enough to pollute over 1000 cubic kilometres per decade.