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"Isotope tools are very powerful to measure nutrients in water, but historically their use has been very difficult, hampered by cost and accessibility. The new technique allows scientists to run more samples and much more cheaply for large-scale studies. I think it is a game changer," "Isotope tools are very powerful to measure nutrients in water, but historically their use has been very difficult, hampered by cost and accessibility. The new technique allows scientists to run more samples and much more cheaply for large-scale studies. I think it is a game changer," said Leonard Wassenaar, hear of the IAEA Isotope Hydrology Section.

The International Atomic Energy Agency and the University of Massachusetts have developed a new method for tracing the origin of nitrogen pollution in lakes, seas, and rivers. Their nuclear-derived analytical tool provides a cheaper, safer, faster way to determine whether excessive nitrogen compounds in water stem from agriculture, sewage systems, or industry, which will aid prevention and remediation efforts.

Nitrogen has been widely used as fertilizer since the mid-1900s. "One of the major global problems in terms of water quality is that we have been overfertilizing our landscapes for decades, either with manure or synthetic fertilizers," said Leonard Wassenaar, head of the IAEA Isotope Hydrology Section. "All of these nutrients, particularly nitrogen forms such as nitrates, are seeping into groundwater and eventually into rivers, lakes, and streams."

Excessive nitrate levels increase algae growth that can lead to toxic blooms. These also sink to the bottom of lakes, feeding bacteria and creating "dead zones." Wassenaar said, scientists "now see more fish kills, where thousands of fish float to the surface because the bottom of the lake where they normally dwell is depleted of oxygen from this rain of organic material."

The new method, presented at a recent IAEA International Symposium on Isotope Hydrology and published in the international journal Rapid Communications in Mass Spectrometry, measures the amount and proportion of nitrate stable isotopes in water. Nitrogen has two stable isotopes with different weights; because the weight difference is not the same in human waste or fertilizers, for example, the isotopes can be used to identify the source.

"Isotope tools are very powerful to measure nutrients in water, but historically their use has been very difficult, hampered by cost and accessibility. The new technique allows scientists to run more samples and much more cheaply for large-scale studies. I think it is a game changer," Wassenaar said.

The new method uses a form of titanium chloride – a salt – to convert nitrate in a water sample to nitrous oxide gas. From this gas, the isotopes can be analyzed with equipment such as a mass spectrometer or laser. Current methods use genetically modified bacteria or cadmium for the nitrous oxide conversion, making them costly and limited to few very specialized laboratories.

"It's a relatively simple method for what used to be very complex and expensive process," said collaborator Mark Altabet, professor of estuarine and ocean sciences at the University of Massachusetts Dartmouth's School of Marine Science and Technology. Sample analysis costs five to 10 times less than before, and it takes only minutes to prepare samples. Altabet plans to use the method to study the impact of measures to control pollution in Long Island Sound, which was heavily impacted by excessive nitrate in the past.