We look at a rapid new method for source apportionment of nitrate pollution in waterways, using ABB’s OA-ICOSTM GLA451-N2OI3 multi-isotope analyser.
ABB recently published a new application note for their OA-ICOSTM GLA451-N2OI3 multi-isotope analyser. Using an innovative method, the instrument can now be used to determine the sources of aquatic nitrogen pollution. In this post, we break it down, looking at why such analysis is needed, how it can now be performed, and the many advantages of the new approach.
The problem of nitrogen pollution
The United Nations label nitrogen pollution as one of the world’s most pressing pollution issues. Nitrogen is essential for life – which is why it’s a key component of agricultural fertilisers. It’s a fundamental constituent of proteins, DNA, and light-absorbing chlorophyll. To feed a growing population and counteract environmental degradation, nitrogen fertiliser use has increased many-fold in recent decades.
However, much of the nitrogen fertiliser applied to fields seeps into waterways, where it disrupts natural nutrient equilibria. Animal manure and deposition of atmospheric pollution are also sources of nitrogen in rivers, lakes, and seas. Here, it triggers excess algal growth (“eutrophication”), which reduces the oxygen available for other organisms. So-called algal blooms may also release harmful toxins, which can contaminate food sources.
Nitrogen pollution can also make drinking water unsafe, particularly for infants. This is a problem in areas of intensive agriculture or large urban centres with insufficient sewage systems. The World Health Organisation (WHO) has Guidelines for Drinking Water Quality (GDWQ), which include limits for nitrogen compounds. In this context, detailed measurement and understanding of nitrogen pollution in water is critical.
A new way to track nitrogen pollution
What should be measured?
In water, nitrogen pollution is typically in the form of nitrate ions, which are made up of nitrogen and oxygen atoms. To determine the ions’ origins (“source apportionment”), you can investigate the makeup (or, subatomic particles) of the individual atoms.
Atoms of the same element which have slightly different numbers of subatomic particles (specifically, neutrons) are called isotopes. An element’s isotopes are found in varying amounts in different areas of the environment. For example, the proportion of the “heavy” oxygen isotope (18O) is slightly higher in the atmosphere than in seawater (16O is the “normal” oxygen isotope).
So, what does this mean for nitrate pollution? Depending on where they came from, nitrate ions will contain different proportions of isotopes. For example:
- Nitrogen fertiliser production utilises nitrogen and oxygen from the air, so nitrates from fertiliser pollution reflect proportions of nitrogen and oxygen isotopes you’d find in the atmosphere.
- Nitrate pollution from manure and sewage contains different nitrogen and oxygen isotope proportions due to the actions of microorganisms.
The instrument
ABB’s OA-ICOSTM GLA451-N2OI3 measures oxygen (δ¹⁸O and δ¹⁷O) and nitrogen (δ¹⁵N) isotopes. It uses patented Off-Axis Integrated Cavity Output Spectroscopy (OA-ICOS) technology. In simple terms, this involves injection of the sample into a small cavity that has mirrors at either end. Light is bounced between the two mirrors. At the correct wavelength, the sample will absorb the light, and the reduction in light reaching a detector indicates the concentration of the sample.
The new method
The GLA451-N2OI3 is optimised for the measurement of isotopes in nitrous oxide gas. However, the International Atomic Energy Agency (IAEA), in collaboration with the University of Massachusetts, has developed a new method for its use in analysing nitrogen pollution in rivers, lakes, and seas. The method uses a form of titanium chloride to convert the nitrates in water samples to nitrous oxide gas. It’s referred to as the “Ti method”. Read ABB’s new application note detailing the solution.
The implications of a new standard of analysis
This new method is significant. Traditionally, nitrate isotopologue (molecules or ions containing isotopes) analysis involves toxic chemicals and multi-step conversions – non-conducive to the rapid, repeated analyses required in water quality monitoring.
Use of the GLA451-N2OI3 enables direct, rapid, automated, and simultaneous analysis of δ¹⁵N, δ¹⁸O, and δ¹⁷O in gas derived from nitrates, with minimal sample preparation. This facilitates:
- Discrimination between organic waste, synthetic fertiliser, and atmospheric deposition pollution sources.
- Identification of natural bioremediation processes such as bacterial denitrification.
- Examination of the impacts of changes in agricultural land use or fertiliser optimisation practices – which is not possible with concentration values alone.
- Development of targeted strategies to manage nitrogen pollution and mitigate its harmful effects on people and the environment.
To discuss the ABB OA-ICOSTM GLA451-N2OI3 or our other isotope analysers, please get in touch with Lewis John, Cura Terrae Air’s UK Sales Manager for Scientific Applications.
