Dr Calum Preece on breaking down the practical barriers for nitrate analysis
Nitrogen pollution is one of the key environmental challenges facing the world at present. Although this topic does not always attract the same level of attention as carbon emissions, it is a trend that nevertheless threatens the stability of the global ecosystem, meaning that significant investment is needed for measures to monitor and address the problem.
This dangerous pollution trend poses a significant threat to water quality, is a key accelerant of climate change and requires careful application of proven analytical techniques to understand and mitigate the underlying causes. However, this area of research has typically had high barriers to entry due to the costs and challenges associated with the sample preparation, particularly for nitrate isotope analysis.
Now, innovative new methods are emerging that promise to help break down these barriers and empower more laboratories around the world to contribute to this vital research, which could help turn the tide on nitrogen pollution in future.
The importance of increasing analytical capacity for nitrogen pollution
Maintaining balance in the global nitrogen cycle depends on a healthy balance of environmental nitrogen inputs and outputs. However, human activity is currently generating excessive quantities of nitrate - a highly reactive form of nitrogen - through excessive burning of fossil fuels, or overuse of artificial fertilisers to replenish nitrates in the soil. This is leading to poisoning, eutrophication and toxic algal blooms within water sources, and an atmospheric increase in nitrous oxide, a potent greenhouse gas.
There is a significant need for major international action to address these issues and bring nitrate pollution under control, particularly in emerging economies that depend on heavy industry or intensive agriculture. However, because the nitrogen cycle is so intricate and complex, the exact impact of anthropogenic inputs on the natural balance is hard to quantify without a strong foundation of research and analysis.
Methods such as stable isotope analysis are crucial to this, allowing researchers to separate different sources of nitrate and determine what the most significant causes of nitrate pollution might be. This enables stakeholders to identify the sources, sinks and cycling of nitrogen throughout terrestrial, atmospheric and marine ecosystems. As these pollution problems are getting worse, international analysis and research capacity will need to be scaled up to help create viable and well-targeted solutions.
The barriers to labs investing in nitrate analysis
At present, the stable isotope analysis forms a key facet of environmental nitrogen research. However, for many smaller or less well-resourced laboratories, it has not been possible to take part in this field of research due to the high technical barriers to entry that have been present up until now.
Stable isotope analysis requires dissolved nitrate samples to be converted to N2O prior to analysis. This is because nitrate cannot be directly analysed using isotope-ratio mass spectrometry (IRMS). The sample preparation process, which must be free from isotopic fractionation, allows researchers to assess δ15N and δ18O values within the sample and provide key insights into its environmental origins.
Both established techniques for converting nitrate to N2O pose significant technical challenges. One of the methods involves microbiological sample preparation, which requires special denitrifying bacteria to be cultivated in idealised conditions; not every laboratory is able to achieve this, creating a major entrance hurdle for smaller labs wanting to start nitrate analysis.
Alternatively, labs may utilise a chemical approach that relies on reagents like cadmium and sodium azide. Although this approach does not have the same setup requirements, the hazardous nature of these reagents means that thorough risk assessments need to be carried out when purchasing or disposing of the materials.
How the new titanium method can improve accessibility for nitrate analysis
Because of these drawbacks, there has been a significant gap in the market for a simpler and more accessible sample preparation approach. This breakthrough has since come in the form of research by Dr Mark Altabet and Dr Leonard Wassenaar, who published a paper in 2019 on a new single-step conversion process that uses titanium (III) chloride to reduce dissolved nitrate to N2O gas in septum sealed sample vials.
This new method offers a number of important advantages compared to previously established techniques. It avoids the need for hazardous reagents or fragile bacterial cultures, while the sample preparation process takes only a few minutes and produces fully prepared samples within 24 hours.
Moreover, the titanium method can be performed using basic laboratory infrastructure, meaning that even novice labs are now able to perform high-quality isotopic analysis of dissolved nitrate, utilising reagents that are safe to use, easy to dispose of and readily available. As a result, isotopic analysis of dissolved nitrate in environmental samples becomes simpler and faster than ever before.
At present, UN data shows that around 120 million tonnes of reactive nitrogen are created by anthropogenic activities each year, with nearly two-thirds of this being classifiable as pollution. It is clear that the global issues caused by nitrogen-containing compounds are only going to get worse without significant scientific and industrial investment in new solutions, based on a strong bedrock of reliable research. As such, new methods that can facilitate nitrogen research and make the techniques more accessible to smaller labs will be crucial to worldwide efforts to solve these pressing problems.
Dr Calum Preece is Environmental Market Manager at Elementar UK