Science: Plants that tell a sad tale of pollution

Lichens can reveal much about air quality. Sanjida O'Connell reports

Professor Mark Seaward, of the environmental sciences department at Bradford University, has a list of every lichen spotted in the British Isles in the past 300 years. Amateur and professional lichenologists scour the country and send sightings to Professor Seaward, who enters the location of each finding on his computer. He likens it to train-spotting. Esoteric though they seem, lichens carry an important message - they are perfect monitors of air pollution.

William Nylander, a Scandinavian, was the first to suggest that lichens might indicate air quality, in 1861. His observation was confirmed in 1896, when he noticed that all lichens had disappeared from the Jardin du Luxembourg in Paris due to air pollution.

Professor Seaward was the first to notice the reappearance of lichens in the Jardin in 1990. They were a few millimetres wide and had taken about two years to reach that size.

Because of their sensitivity to air pollutants, lichens can chart the extent of pollution. Maps showing sightings of lichens sensitive to sulphur dioxide display a coffin pattern between Liverpool and London where none survives. The Clean Air Acts of 1956 and 1968 helped to reduce the intensity of air pollution in our cities, but the policy resulted in widespread blanket pollution, since gases are dispersed more efficiently from factories and power stations, many of which are outside cities.

Professor Seaward seems to know many of his 1,900 maps off by heart. He can rapidly call up on his computer the distribution of a lichen which grows only on gravestones, while another map has a scattering of white dots indicating extinction. "Some lichens are tolerating pollution, but only because they are thriving in the absence of competition," he says.

Lichens can incorporate heavy metals into their bodies. Several years ago, there was a lichen that was only found in Scotland. It grew on stones rich in heavy metals, including lead. Now, because of car emissions, it has moved south to colonise most of Britain.

The train-spotting mentality pays off. In the late l970s, Professor Seaward examined the level and type of radioactive elements in lichens in Poland. The amount was four times higher than normal because of the Poles' habit of burning lignite (brown coal).

In April 1986, the Chernobyl disaster released radioactive material for 10 days, depositing radionuclides throughout Europe. Professor Seaward was the only person who knew what the background levels of radiation were in Poland. He returned to find that the lichens he had measured previously had absorbed radioactive caesium extremely efficiently - caesium is chemically similar to potassium, which is an essential nutrient. Levels of radioactivity had increased 165 times.

Professor Seaward had thought lichens were harmless, but he was proved wrong. He is now working on lichens attacking Italian frescoes and monuments, in collaboration with Dr Howell Edwards from the department of chemical technology at Bradford.

Professor Seaward says frescoes at the Palazzo Farnese near Rome will be obliterated within 15 years. They were painted in the 1600s, so why are the lichens attacking them now? It may be due to changes in the type of pollution in Italy, and the fact that maintenance has not been as intensive as it was before the war. Also, the frescoes have been repainted, but the paint formula was different from the original one, which had kept the lichens at bay.

Lichens are two organisms living together - a fungus and an alga. The alga photosynthesises, making carbohydrate from sunlight, and the fungus acts like a placenta. On the frescoes, the fungus forms a crust by reacting with chemicals in the paint - to remove the lichen, the whole paintwork will also be lifted off. Using a microprobe, a laser is beamed at the lichen and its chemical composition is analysed, without disrupting the lichen and consequently damaging the painting.

Professor Seaward and Dr Edwards are testing how much of this crust the lichens produce under different conditions in the lab. "If we can find the answer," Professor Seaward said, "we can start to consider ways of controlling the environment around the frescoes."

Start your day with The Independent, sign up for daily news emails
ebooks
ebooksA celebration of British elections
  • Get to the point
Latest stories from i100
Have you tried new the Independent Digital Edition apps?
Independent Dating
and  

By clicking 'Search' you
are agreeing to our
Terms of Use.

iJobs Job Widget
iJobs General

Ashdown Group: Marketing Manager (B2B) - Romford - £40,000 + car

£35000 - £40000 per annum + car and benefits: Ashdown Group: Marketing Manager...

Ashdown Group: Helpdesk Analyst - Devon - £20,000

£18000 - £20000 per annum: Ashdown Group: Helpdesk Analyst - Devon - £20,000 ...

Ashdown Group: Data Scientist - London - £50,000 + bonus

£35000 - £50000 per annum + generous bonus: Ashdown Group: Business Analytics ...

Ashdown Group: IT Project Coordinator (Software Development) - Kingston

£45000 - £50000 per annum: Ashdown Group: IT Project Coordinator (Software Dev...

Day In a Page

General Election 2015: ‘We will not sit down with Nicola Sturgeon’, says Ed Balls

'We will not sit down with Nicola Sturgeon'

In an exclusive interview, Ed Balls says he won't negotiate his first Budget with SNP MPs - even if Labour need their votes to secure its passage
VE Day 70th anniversary: How ordinary Britons celebrated the end of war in Europe

How ordinary Britons celebrated VE Day

Our perception of VE Day usually involves crowds of giddy Britons casting off the shackles of war with gay abandon. The truth was more nuanced
They came in with William Caxton's printing press, but typefaces still matter in the digital age

Typefaces still matter in the digital age

A new typeface once took years to create, now thousands are available at the click of a drop-down menu. So why do most of us still rely on the old classics, asks Meg Carter?
Discovery of 'missing link' between the two main life-forms on Earth could explain evolution of animals, say scientists

'Missing link' between Earth's two life-forms found

New microbial species tells us something about our dark past, say scientists
The Pan Am Experience is a 'flight' back to the 1970s that never takes off - at least, not literally

Pan Am Experience: A 'flight' back to the 70s

Tim Walker checks in and checks out a four-hour journey with a difference
Humans aren't alone in indulging in politics - it's everywhere in the animal world

Humans aren't alone in indulging in politics

Voting, mutual back-scratching, coups and charismatic leaders - it's everywhere in the animal world
Crisp sales are in decline - but this tasty trivia might tempt back the turncoats

Crisp sales are in decline

As a nation we're filling up on popcorn and pitta chips and forsaking their potato-based predecessors
Ronald McDonald the muse? Why Banksy, Ron English and Keith Coventry are lovin' Maccy D's

Ronald McDonald the muse

A new wave of artists is taking inspiration from the fast food chain
13 best picnic blankets

13 best picnic blankets

Dine al fresco without the grass stains and damp bottoms with something from our pick of picnic rugs
Barcelona 3 Bayern Munich 0 player ratings: Lionel Messi scores twice - but does he score highest in our ratings?

Barcelona vs Bayern Munich player ratings

Lionel Messi scores twice - but does he score highest in our ratings?
Martin Guptill: Explosive New Zealand batsman who sets the range for Kiwis' big guns

Explosive batsman who sets the range for Kiwis' big guns

Martin Guptill has smashed early runs for Derbyshire and tells Richard Edwards to expect more from the 'freakish' Brendon McCullum and his buoyant team during their tour of England
General Election 2015: Ed Miliband's unlikely journey from hapless geek to heart-throb

Miliband's unlikely journey from hapless geek to heart-throb

He was meant to be Labour's biggest handicap - but has become almost an asset
General Election 2015: A guide to the smaller parties, from the the National Health Action Party to the Church of the Militant Elvis Party

On the margins

From Militant Elvis to Women's Equality: a guide to the underdogs standing in the election
Amr Darrag: Ex-Muslim Brotherhood minister in exile still believes Egypt's military regime can be replaced with 'moderate' Islamic rule

'This is the battle of young Egypt for the future of our country'

Ex-Muslim Brotherhood minister Amr Darrag still believes the opposition can rid Egypt of its military regime and replace it with 'moderate' Islamic rule, he tells Robert Fisk
Why patients must rely less on doctors: Improving our own health is the 'blockbuster drug of the century'

Why patients must rely less on doctors

Improving our own health is the 'blockbuster drug of the century'