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|  Nitrogen friend or foe ?
Friend and foe: nitrogen pollution’s little-known environmental and human health threats Quote:
Billions of people owe their lives to nitrogen fertilisers – a pillar of the fabled Green Revolution, which averted global famine in the 20th century – but few are aware that nitrogen pollution from fertilisers and other sources has become a major environmental problem that threatens human health and welfare in multiple ways.
“It’s been said that nitrogen pollution is the biggest environmental disaster that nobody has heard of,” said Dr Alan Townsend, a professor of ecology and evolutionary biology, at the meeting of the American Chemical Society in Denver, Colorado, USA, last month.
Townsend called for greater public awareness of nitrogen pollution and concerted global action to control it. “Awareness has grown, but nitrogen pollution remains such a little-recognised environmental problem because it lacks the visibility of other kinds of pollution. People can see an oil slick on the ocean, but hundreds of tons of nitrogen spill invisibly into the soil, water and air every day from farms, smokestacks and automobile tailpipes. But the impact is there – unhealthy air, unsafe drinking water, dead zones in the ocean, degraded ecosystems and implications for climate change. But people don’t see the nitrogen spilling out, so it is difficult to connect the problems to their source.”
Townsend described the scope and the intensification of the nitrogen pollution problem as “startling”. Nitrogen inputs into the terrestrial environment have doubled worldwide during the past century. This increase is due largely to the invention and widespread use of synthetic fertiliser, which has revolutionised agriculture and boosted the food supply.
The concern focuses on so-called “reactive” nitrogen. Air contains about 78% nitrogen. This nitrogen is unreactive, or “inert”, and is thus unavailable to plants. In 1909, German chemist Fritz Haber developed a way to transform this unreactive gas into ammonia, the active ingredient of synthetic fertiliser. By 2005, human activity was producing about 180 million tonnes of reactive nitrogen each year.
“A single atom of reactive nitrogen can contribute to air pollution, climate change, ecosystem degradation and several human health concerns,” Townsend said. Damage to the ecosystem includes water pollution and reduced biological diversity, including the loss of species.
Although the full extent is currently unknown, nitrogen pollution can harm human health. Reactive nitrogen is a key contributor to air pollution, including the formation of ground-level ozone, which is a well-known health risk. Recent estimates suggest that nitrogen-related air pollution costs the USA well over US$10b a year in both health costs and reduced crop growth. And although less well studied, high nitrogen levels in water can cause a variety of health concerns, ranging from the effects of drinking water nitrate to the potential to alter the risks of several human diseases.
Increased nitrogen levels also have implications for climate change. One the one hand, they lead to more warming via the greenhouse gas nitrous oxide. On the other hand, they can reduce warming by fuelling extra plant growth and by forming substances called reflective aerosols in the atmosphere.
“The net effect of these processes remains uncertain, but appears to result in minor cooling presently,” Townsend said. However, excess nitrogen also has large and clear consequences for air and water pollution.
“Climate change is expected to worsen each of these problems worldwide, but reduction of nitrogen pollution could go a long way toward lessening such climate-driven risks. We’re just now starting to recognise the scope of the problem. But the good news is that there are many opportunities for us to lessen the problems.”
Possible solutions include technologies that remove or reduce reactive nitrogen formation during fossil fuel burning, and incentives to encourage farmers to be more efficient with their fertiliser use, such as subsidies that reward the use of environmental practices that reduce nitrogen levels.
Several other solutions exist for improving the efficiency of agricultural nitrogen use. “In many ways, we already know how to do it – the problems are largely about finding the political and cultural means to implement these new practices,” he said.
| Sydney Environmental & Soil Laboratory
Source: Friend and foe: Nitrogen pollution's little-known environmental and human health threats |
20th September 2011, 11:48 AM
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