London soil pollution worst on former Blitz bomb sites

First published on Chemistry World, 15.01.18

Study links heavy metal enrichment to destruction of housing in 1940s


The UK capital’s soil bears a poisonous legacy from the Blitz bombing campaign – with calcium, lead and zinc pollution highest in the most heavily damaged areas.

Researchers from the British Geological Survey found that anomalous high calcium, lead and zinc levels in some parts of London were caused by the distribution of building dust and debris following the large-scale destruction of historic housing stock. These elements were widely used in paints, piping and mortar during the construction boom of the 19th century.

The presence of large quantities of calcium, the main ingredient of lime, in central London soil had been previously observed. Don Appleton, a geochemist at the British Geological Survey in Nottingham, and his colleague Mark Cave, were determined to find out why.

‘Traditional mortar contains a lot of lime, so if a building would be destroyed then the dust would spread in the surrounding area,’ Appleton explains. ‘We were thinking, was [the calcium enrichment] related to bomb sites?’

The team compared data on soil pollution with a map of the 31,373 sites bombed by the Luftwaffe – Nazi Germany’s air force – between October 1940 and June 1941. Areas bombarded in the 1940s had levels of calcium, lead and zinc that were up to 1.75 times higher than in areas built-up after the war or those that escaped the bombing.

(a) Number of bomb sites, (b) GM Pb (mg kg−1) 1km grid squares for sectors of the GLA with both soil chemistry and bomb site data underlain by Brickearth, River Terrace deposits or Thames Group clays

Source: © University of Portsmouth licensed under a Creative Commons Attribution- NonCommercial-ShareAlike

The bomb sites from the Blitz (left) correlate with the pollution of London’s soil with the poisonous metal lead (right)


Other built-up areas of London, however, also showed elevated heavy metal levels, if not quite as high as those bombarded during the Blitz. Appleton says that some of these metals, especially lead, are distributed by exhaust fumes from cars. The researchers found that lead enrichment in London soil increases with proximity to roads as well as bomb sites, hinting at a more complex pattern of pollution. ‘If you get closer to roads, that’s where the buildings are,’ Appleton says. ‘That makes it sometimes difficult to work out what exactly is the major cause.’

Heavy metal pollution is dangerous to human health, especially children who might ingest lead or zinc while playing on polluted land. Vegetables grown on such soil, for example in urban gardens, can also have enriched levels of toxic metals.

However, the chemical make-up of London’s soil provides some protection. London was built on large chalk deposits, which increases the pH of the soil and locks up heavy metals, says Mike Fullen, a soil technology professor at the University of Wolverhampton. ‘Even though these metals are there, it is not easy for them to get into the biological system.’

Many British cities are built on the most fertile land, as this is where ancient farming communities settled. The Thames terrace, for example, has some of the richest soil in England, but is now mostly covered by Heathrow Airport. As a result, even if land is subsequently freed, it loses much of its fertility due to urban pollution.

While the removal or chemical cleaning of soil is expensive, Fullen’s team are working on developing cheaper and environmentally friendly methods to remove heavy metals. In China, students from the University of Wolverhampton are planting carnations on soil polluted with cadmium. The plants act as so-called hyper-accumulators by drawing toxic materials into their roots.

Fullen says this method could be used on London’s brownfield sites, and even in parks created on former bomb sites. ‘If you are not looking to reuse the land straight away, the cheapest option is to plant something that will soak up the toxins, and that can then be burned in a safe place,’ he says.


Shipping pollution hotspots mapped with real-time data

First published on SciDev.Net, 30.08.17

Coastal areas around South East Asia suffer the most from pollution caused by ship traffic, according to a global study that estimates shipping emissions based on real-time, local activity for the first time.

The study, published this month (19 August) in Atmospheric Environment, sheds light on forces at play in a region where shipping pollution is believed to cause up to 24,000 deaths a year. The researchers put together a detailed picture of the emissions of around 300,000 commercial vessels for the year 2015. They found  that three of the six most polluted harbours – Singapore, Hong Kong and Shanghai – are in South East Asia.

The Malacca Strait, the Eastern China Sea and the Yellow Sea have the world’s highest concentration of shipping emissions, the authors said.

“In some harbour areas shipping can cause severe health effects and premature deaths.”

Lasse Johansson

They used data from the global Automatic Identification System (AIS), which requires all ships larger than 300 tonnes to regularly report their position. This is significant because it records where ships have been and when, allowing a more precise estimate of shipping pollution compared to previous studies.

The team from the Finnish Meteorological Institute joined around 8 billion AIS data points to cover more than a billion kilometres travelled by commercial ships worldwide in 2015. By combining this data with information on vessel size, engine type and fuel used, they managed to draw a high-resolution image of shipping pollution, particularly highly dangerous small-particle pollution less than 2.5 micrometres in diameter.

The consequences of inhaling these pollutants are serious, says lead author Lasse Johansson, a research scientist at the institute. “In some harbour areas shipping can cause severe health effects and premature deaths.” A 2007 study showed that small-particle emissions from ships lead to an estimated 60,000 premature deaths globally each year.

The situation in South East Asia is compounded by the large number of unregistered local vessels, according to Johansson, which were not included in the study. Globally, the researchers identified  76,000 vessels for which no technical data, such as the ship’s size or type of fuel used, could be obtained.

Together, these vessels travelled a distance that accounts for only 3.5 per cent of all recorded shipping kilometres, but Johansson says their local impact should not be underestimated. “Near coastal cities the [emission] contribution of these vessels can still be larger than the overall contribution might suggest,” he says.

Registered ships were responsible for 93 per cent of small-particle emissions and 91 per cent of the carbon dioxide emissions covered by the study.

Part of the large concentration of shipping emissions in the region is explained by the rapid economic growth of countries in the Association of South East Asian Nations (ASEAN),which is fuelled by  export of consumer goods. The ASEAN nations’ GDP grows by an average 6 per cent annually, according to the OECD, with 74 per cent of the region’s exports travelling by sea  to non-ASEAN countries.

South East Asia also suffers from high shipping emissions because its location exposes it to the densest and most frequent shipping traffic in the world.

Aretha Aprilia, a civil engineer from Indonesia and former coordinator at the UN Environment Programme, tells SciDev.Net that regional efforts to curtail shipping emissions have been “a huge challenge”.

“To date, not much attention has been given to the issues regarding emissions from shipping, and this needs to shift,” says Aprilia. “It is a prerequisite to have more legally binding regulations that are enforced from the countries.”

The study suggests that pollution control areas, where carbon dioxide and fine particle emissions from ships are subject to strict rules, can work if enforced. “Yet these can be costly for ship owners,” says Johansson. He suggests that poorer nations should look at alternatives, like re-routing large ships and planning their infrastructural development in order to mitigate pollution. “For instance in Helsinki, where I live, the cargo terminals were relocated well outside of the city.”