Fixing the nitrogen cycle

15th June 2023


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Dr Calum Preece

Dr Calum Preece, environmental market manager at Elementar UK, explains why new methods are needed to tackle the global threat of nitrogen pollution.


When it comes to assessing the key environmental challenges facing the world, nitrogen pollution is sometimes overlooked, despite the significant risks it poses to the stability of the global biosphere. Nitrate pollution threatens global water quality and acts as a key accelerant of climate change, creating a pressing need for new and better ways to tackle the problem.

Although the risks created by nitrate pollution are well-known, meaningful action cannot be taken without a sound scientific understanding of the root causes and sources of this pollution. Historically, this has been held back by the difficulties associated with testing and analysing sources and transformation of environmental nitrogen. However, new methods are now emerging that could simplify this process and greatly expand our understanding of how to combat this threat.

The scale of the nitrate pollution problem

Statistics from the UN Environment Programme show that around 120 million tonnes of reactive nitrogen are created by anthropogenic activities annually, and that nearly two-thirds of this nitrogen can be classed as pollution.

Nitrate - a reactive form of nitrogen produced by a range of biological and chemical processes - is a key driver of this. Although a certain amount of nitrate is required by plants and crops for growth, the burning of fossil fuels and overuse of artificial fertilisers to replenish nitrates in soil is increasing environmental nitrate to excessive levels, which is negatively impacting our air, water, soil, marine and coastal areas, and the wider atmosphere.

Dr Leonard Wassenaar is a senior researcher in stable isotope ecology and hydrology at WasserCluster Lunz Biological Station. From 2012 to 2021, he was a laboratory and section head for isotope hydrology at the International Atomic Energy Agency (IAEA) in Vienna. He told Elementar that the global nitrate pollution problem has been “60 or 70 years in the making”, and driven in large part by the industrialisation of agriculture and fertiliser production.

There are a number of ways in which this problem manifests:

  • Nitrate leaching - nitrates leach from sewer faults and animal waste created by livestock farming into groundwater supplies, polluting aquifers and drinking wells. Drinking water with high nitrate content has been linked with an increased risk of cancer and foetal development problems
  • Nitrate runoff - excess nitrate runs off into surface waters, which increases the nutrient availability of the water and causes toxic algal blooms and eutrophication. This leads to hypoxia and vast marine dead zones in coastal areas and at sea
  • Nitrogen oxides in the atmosphere - Nitrogen oxides (NOx) are formed through the combustion of fossil fuels, and from industrial and agricultural processes. Among them is nitrous oxide (N2O), a greenhouse gas with around 300 times more warming potential than CO2

Dr Wassenaar notes: “The big problem is that once nitrate is in groundwater, you cannot get it out. There is no way we can treat all of the affected groundwater, and groundwater has a long residence time - from decades, to hundreds, to thousands of years. Once you have polluted it, there is no turning the clock back.”

As the global population grows, so too does the scale of activity in the agricultural sector, which means that the impact of nitrate pollution is only likely to worsen. Indeed, the consequences of this can be seen across the world:

  • ● The European Commission has referred both Spain and Belgium to the European Court of Justice for failing to take sufficient action on nitrate pollution, violating the terms of the EU Nitrates Directive
  • ● ClientEarth and WWF have launched a legal complaint against the UK’s Environment Agency for failing to monitor and enforce laws designed to address nitrogen pollution from farms across England

The difficulties of understanding the sources of nitrate pollution

For any meaningful action to be taken against nitrate pollution, industries and lawmakers need to know which areas are being worst affected by the pollution, what the sources of the pollutants might be, and what actions will be needed to counteract them.

There are a number of challenges that make this difficult to achieve in practice. Most notable is the fact that nitrates are naturally occurring compounds, which means that the nitrate found in the environment may come from natural or manmade sources: while some is generated from fertiliser usage and sewage leaks, nitrate may also be created through the mineralisation of soil, or from the nitrification of naturally-occurring ammonia or urea in animal manure.

As such, when analysing environmental nitrate trends, laboratories need to have methods available for identifying which sources are anthropogenic, and which are natural. This can be achieved using stable isotope analysis, a process that involves converting dissolved nitrate samples into N2O and examining the unique isotope signatures that help to distinguish nitrates from different environmental sources.

However, historically, the number of labs that have actually been able to perform this research has been prohibitively small, because of the significant challenges associated with preparing samples for analysis. For decades, the most common approach to nitrate isotope analysis has depended on a highly complex process involving specially cultivated bacteria, which only a few dozen laboratories in the world are able to do. The only viable alternative has been a separate chemical approach that relies on toxic and heavily restricted reagents.

Dr Wassenaar explains: “In my career over the last 10 years, it was a real pain to get samples done. There was never a lab available, because there were so few; the backlog was six months to a year; and, of course, the price was high. It became a barrier to further research.”

How new analytical methods can help turn the tide on nitrate pollution

With the scope of the environmental challenges posed by nitrate pollution and the urgent need for more accessible analysis methods in mind, Dr Wassenaar co-created a new breakthrough sample preparation technique. It has the potential to greatly simplify nitrate isotope sample preparation, and empower more laboratories worldwide to contribute to the fight against nitrate pollution.

Developed alongside Dr Mark Altabet, the titanium (III) reduction method uses simple, established and affordable techniques to prepare samples for analysis within 24 hours. It utilises cheap, safe reagents that are easy to dispose of and readily available, with minimal manual work required.

Dr Wassenaar explained: “You put a couple of tens of microlitres of titanium (III) chloride solution in with your sample, cap it and let it sit for 12 to 24 hours, and it's done. It’s very easy, can be done in any laboratory, and uses only microlitres of titanium.

“I think it costs less than $6 in materials, compared to over $100 for older methods; I would predict the cost will come way down, which then opens up the accessibility to do new science because it is so much more affordable.”

Dr Wassenaar’s hope is that the new method is efficient and cost-effective enough that isotope analysis of nitrate samples could become a mainstream option for national monitoring networks in future. Potentially, this could accelerate the development of new and better-targeted national strategies for tackling nitrate pollution in the most effective ways possible.

He added: “That is a dream application for us. Whether that happens or not is up to each government, and usually, it comes down to cost and what information they can get out of it. But it would be nice.”

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Please note: the views expressed in this blog are those of the individual contributing member and are not necessarily representative of the views of IEMA or any professional institutions with which IEMA is associated.

Image credit: Shutterstock

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