Wednesday, 17 July 2013

Monitoring mercury in the atmosphere

Edinburgh is the venue for the International Conference on Mercury as a Global Pollutant later this month (28 Jul - 2 Aug 2013), and CEH's John Kentisbeer will be among the scientists presenting at the event. Here John tells us a bit more about mercury and also why and how CEH monitors its presence in the atmosphere.

Why does the Centre for Ecology & Hydrology monitor mercury in the atmosphere? Put simply, because it is a poisonous pollutant that needs to be better understood and controlled.

Mercury is a special metal because it is a liquid at ambient temperature and pressure, leading to its nickname of quicksilver. This liquid mercury easily turns to vapour and can exist in the atmosphere for up to a year. It can enter the atmosphere through natural processes, such as volcanic eruptions, but humans add to this by making chemicals, burning coal, disposing of mercury-containing waste, as well as gold mining and many other processes. Have you ever heard of the phrase "Mad as a hatter"? It comes from using mercury in the manufacturing of felt hats in the 19th century. Nowadays, mercury is used in all manner of fluorescent light bulbs and you may even have some in your mouth if you have a filling!

Mapping mercury concentrations in air over Europe

Of course there has always been mercury in the atmosphere, but not as much as there is now. Gold rushes since the 16th century and processes linked to the industrial revolution are among ways that humans dramatically increased the amount of mercury in the atmosphere, leading to a peak in the 1980s before control measures were introduced, curbing emissions and allowing levels in the atmosphere to fall. They have been pretty constant since the mid-1990s.

The reason we should all care about mercury in the atmosphere is that it is one part of the global mercury cycle. It doesn't just stay in the atmosphere; it can be deposited to land and water directly, and in rain. This allows it to accumulate in the environment where it can have a detrimental effect by being transformed into a more reactive form, such as methylmercury. Methylmercury is highly toxic and is easily absorbed in the bodies of animals and humans. If methylmercury enters a lake, it will be absorbed by small fish through their diet, and when the small fish are eaten by bigger fish the methylmercury moves to the bigger fish; this carries on right up the food web, until you get to humans, a process called bioaccumulation. This can result in significant mercury exposure in humans and lead to Minimata disease, which can cause serious neurological damage, insanity, paralysis and, in extreme cases, death. It affects animals too - in one outbreak in Japan it was called "dancing cat fever" because of the effects on cats. For this reason, many countries advise their citizens how much of certain fish, such as tuna, they should eat.

UK monitoring

CEH monitors mercury at eleven sites across the UK to assess the rural background levels. We monitor both the mercury in the atmosphere, as well as mercury in rainfall. Mercury can be present in the atmosphere in three forms: it can be a gas, it can be part of a molecule or it can be stuck to particles. Mercury gas can be present in the atmosphere for up to a year, while mercury as a compound or stuck to a particle has a much shorter lifetime and is easily removed by rain. Gaseous mercury can be changed in the atmosphere to the other two types, but this is generally thought to be quite a slow process. Our monitoring, undertaken on behalf of the UK governments, forms part of a European and global programme for monitoring mercury in the atmosphere to help understand local, regional and global trends.

CEH's atmospheric monitoring site at Auchencorth Moss in Scotland

In order to work out how much mercury is in the air, we have to capture it, which we do using gold. We pass air across a gold surface, to which the mercury sticks as it forms an amalgam. Once we have finished sampling a known volume of air, we heat the gold up and the mercury is released from the surface and is sent to the analyser, which uses ultraviolet light to calculate the mass of mercury in the sample. We can then work out the original concentration in air.

Typically background concentrations of gaseous mercury in the northern hemisphere are about 1.4 - 1.7 nanograms per cubic metre of air. That is 0.0000000014 grams, which seems really small, but these small amounts can accumulate to cause potentially harmful effects. We monitor mercury in air every five minutes at two sites, one at Auchencorth Moss in Midlothian, Scotland and the other at Harwell in Oxfordshire, England. At the other sites, we have low volume samplers which sample Total Gaseous Mercury (TGM), comprising gaseous elemental mercury and mercury-containing compounds, for two-week periods.

A low-volume Total Gaseous Mercury sampler

Our data show that average concentrations of mercury in the south-east of the UK are higher than in the north-west. This would be consistent with the urbanisation of the UK, but also with air containing mercury coming from the European mainland. Using the five-minute data and local wind speed and direction, we can even start to pinpoint possible local emission sources, such as coal-fired power stations or crematoria.

By understanding the sources and their influence on atmospheric mercury, we provide evidence to policy makers to help them make informed decisions on the problems we face. When control measures designed to reduce emissions are introduced, we can then monitor the impact and their effectiveness.

CEH also measures mercury content in soils as part of the UK Countryside Survey, which allows us to better understand how mercury enters and leaves soils, and its impact on the soil environment. Additionally, CEH scientists at Bangor also coordinate the ICP Vegetation programme (the International Cooperative Programme on Effects of Air Pollution on Natural Vegetation and Crops) which surveys the concentration of heavy metals, including mercury, in mosses across Europe.

We also operate the Predatory Bird Monitoring Scheme, which examines the concentrations of pollutants in certain dead birds as a way of identifying risks to wildlife and potentially humans. Mercury is one of the chemicals monitored as part of this programme as it is thought to be a contributing factor to the decline of some bird species.

  • Find out more about CEH's various monitoring activities with the links below. And if you are in the Edinburgh area, the International Conference on Mercury also has a public open day. Come along to the Lomond Suite, Edinburgh International Conference Centre, 150 Morrison Street, on Sunday 28 July between 2pm-4.30pm.

John Kentisbeer

Additional information

UK Pollutant Deposition: Heavy Metal Monitoring

UK Countryside Survey

Predatory Bird Monitoring Scheme

ICP Vegetation

2013 International Conference on Mercury as a Global Pollutant website 

Staff page of John Kentisbeer at CEH

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