Wednesday, 29 February 2012

Challenging misperceptions around clean energy Part 2

Mercury Falling (apologies to Sting)

You may have read Emma's incisive comment on my previous post, questioning the relevance of US mercury emissions from power generation to the safety of CFLs here in Britain.  I agree!  The objective of my post was to put the case that the climate change resulting from (global) greenhouse gas emissions is a much greater threat to our safety than the trace amounts of mercury present in compact fluorescent lamps.  However, I used American data that didn't answer the question of how CFLs contribute to mercury pollution in Britain.

To put this right, I have examined the mercury emissions arising here in Britain from the Government's Carbon Emissions Reductions Target (CERT) programme, that funded the free distribution and subsidised retail sale of CFLs.  Rightly or wrongly, I am excluding any mining and manufacturing emissions of mercury in the production of these bulbs, since that took place outside the UK.

Compact fluorescent lamps (CFLs) of up to 20 watts contain under 5 milligrams (mg) of mercury, the metal vapour that emits ultra-violet light when the bulb is running.  This U-V light excites the white phosphor coating inside the tubes of the CFL, causing the phosphor to fluoresce, and that's how fluorescent lighting works, in a nutshell!  The typical quantity of mercury in a modern CFL is around 4mg mercury, commonly described as "enough to cover the writing tip of a biro".

Up to 350 million compact fluorescent lamps were distributed under CERT between 2008 and 2010, containing around 1.4 Tonnes of mercury in total.  Each is expected to last up to 10 years and to be recycled appropriately at end of life - in which case there is no mercury leakage from CFLs.  In practice, some of these lamps break and many are thrown in the bin when they stop working, releasing their trace of mercury to the environment.

To estimate the release of mercury from these 350 million CFLs, I have assumed that (1) 10% of them fail each year, for 10 years, giving an average working life of 5 years, and (2) HALF these CFLs are broken or binned, rather than being recycled properly.  In this case, 17.5 million of those CFLs supplied under CERT will be broken each year, for 10 years, releasing around 70 kg of mercury a year to the environment.

How does this compare with other sources of mercury emissions here in the UK?  The 2009 National Atmospheric Emissions Inventory  shows that 7.35 Tonnes of mercury were reported to be released in that year.  Some of the sources were: 3.9 T from manufacturing and chemical industries, 1.5 T from cremation and clinical waste incineration, 1.3 Tonnes from power generation and 360kg from landfill.

So the amount of mercury released each year from the CFLs distributed under CERT represents just under one percent of the total annual emissions of this toxic metal in Britain.  We are all exposed to this pollution, principally through our diets - because mercury enters the foodchain - and particularly if we eat the top marine predators like tuna and swordfish.  But the quantities we ingest are minuscule and the risk they present to most of us is, frankly, trivial in comparison with the certain dangers of manmade climate change for us and our descendants.

We live in a 4-bedroom detached house.  Shockingly, it has around 120 bulbs installed!  I first surveyed the energy use of lighting in our home five years ago, when we had 34 energy-saving CFLs and 92 incandescent lights - including halogen lamps.  We now have about 80 CFLs fitted and have replaced almost all the remaining incandescent bulbs with clean, bright LED lighting.  Our electricity usage has halved over the same period, largely through fitting energy-efficient appliances including lighting.

I also have a small, medical thermometer containing mercury, that we used to put in our babies' mouths when they were unwell.  The thermometer contains 2 - 3 times as much mercury as all the CFLs in my house.  I am sad to say that climate change is a far greater threat to my grown-up babies' wellbeing than that thermometer ever was.

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