The production of goods for consumers in rich nations leaves a deep footprint in the form of potentially-dangerous nitrogen pollution in developing countries, a study said Monday.
Reactive nitrogen, generated in large part by fuel combustion and agriculture -- mainly fertiliser use -- can contribute to air and water pollution, climate change and acid rain.
A study in the journal Nature Geoscience said many developed nations had a sky-high nitrogen pollution "footprint" -- much of it left far away in the developing world.
A "footprint" is the amount of reactive nitrogen emitted during the production, consumption and transportation of goods and services used in a particular country, regardless of where production took place. "High-income nations are responsible for more than 10 times the emissions of the poorest nations," study co-author Arunima Malik of the University of Sydney said in a statement.
Emissions per person ranged from over 100 kilogrammes (220 pounds) per year in nations like Hong Kong and Luxembourg, to less than seven kilogrammes in Papua New Guinea, Ivory Coast and Liberia.
"These differences reflect wealthy consumers' preference for animal products and highly processed food," wrote the research team.
"We conclude that substantial local nitrogen pollution is driven by demand from consumers in other countries," they added.
The study claims to be the first to trace the flow of nitrogen emissions along international trade routes.
Nitrogen (N2) is a key building block of all life on Earth and is the most abundant element in the atmosphere -- crucial for plant growth. Reactive nitrogen is a less stable form which binds with other chemicals to cause smog, for example, or nitrogen oxide -- a poisonous gas belted out by diesel cars.
Based on a global trade database of 188 countries, the study showed the bulk of nitrogen emissions in 2010 came from industry and agriculture, which accounted for 161 teragrams (trillion grammes), while 28 Tg was produced by consumers -- mainly from sewage.
Consumption in the United States, China, India and Brazil, was responsible for nearly half the world's nitrogen pollution, they added.
Commenting on the paper, James Galloway of the University of Virginia and Allison Leach of the University of New Hampshire, pointed out that developed countries such as Japan, Germany, Britain and the US had a reactive nitrogen footprint "twice as large as the amount... directly released in their own countries."There was much consumers could do to change the trend.
"For countries such as the United States, if consumers ate according to the national and international protein recommendations and reduced food waste by 50 percent, their total nitrogen footprint would decrease by over 35 percent," the duo wrote.