Nitrogen pollution in many developing countries is down to the high demand for consumer goods exported to middle- and high-income nations, a study has found.
The study analysed the supply chains of 15,000 trade sectors to calculate the nitrogen footprints of 188 countries, and found that consumption in four - Brazil, China, India and the United States - is responsible for almost half of global nitrogen pollution. Among other problems, this pollution contributes to climate change, soil and water acidification, and causes respiratory problems in humans.
"We wanted to see how nitrogen flows along international trade supply chains, from ... hotspots of nitrogen pollution to where the products are consumed," says Arunima Malik, a sustainability researcher at the University of Sydney in Australia and coauthor of the study published in Nature Geoscience last week (25 January).
Harmful nitrogen compounds are released into the atmosphere as a result of human activities such as fossil fuel burning, manufacturing and adding fertiliser to soil. The researchers found that the poorest developing countries tend to be net exporters of goods that create a lot of nitrogen pollution, as goods such as meat and textiles are sold to be consumed elsewhere.
Jan Willem Erisman, an environmental researcher who studies nitrogen cycles at VU University Amsterdam in the Netherlands, sees some uncertainty in the study's data due to missing calculations for natural processes that absorb the harmful gas.
But, he says, the overall results agree with findings from other region-specific studies, and show for the first time how substantial nitrogen emissions are for certain countries. The next step should be to add the social and environmental damage caused by these emissions into the cost of each product, he adds.
At the moment, "the nitrogen emitted to the atmosphere and groundwater ... is not taken into account in the nitrogen flow of the product," says Erisman.
Pakistan, for example, is identified in the paper as having a below-average nitrogen footprint because its per capita consumption of nitrogen-rich goods is relatively low. But its economic reliance on exporting items such as cotton, wool and clothing put it in the top ten for nitrogen emissions generated by producing goods for export.
This illustrates the study's finding that, even though demand for nitrogen-rich goods is often lower in developing countries than developed ones, poorer nations still have to deal with most of the related health and environmental consequences of producing such items.
Mahmood Khwaja, a senior advisor at Pakistan's Sustainable Development Policy Institute, says that, while addressing nitrogen pollution may not be a high priority for the country, steps should be taken to resolve the root cause.
"Exporting our environmental capital must be stopped with promotion of cleaner production, recycling of waste and the best in-house environmental practices and awareness raising," he says.
Malik agrees that better consumer awareness in developing nations could reduce nitrogen pollution in the supply chain. She and her coauthors also call for an international convention to regulate global nitrogen emissions.