After a four-year coordinated research project involving 14 countries to develop and test new isotope-based methods for tracing nitrate pollution in river and groundwater systems led by the International Atomic Energy Agency, a report has been published describing the outcomes. The countries that participated in the study were Argentina, Australia, Burkina Faso, Cameroon, Ecuador, Finland, France, Greece, Italy, Malaysia, Nigeria, Pakistan, Spain, and Ukraine.

The final report on the project, Improving the Understanding of Nitrate Sources in Freshwater Systems Through Linking Isotopes and Contaminants of Emerging Concern, describes how scientists combined the analysis of nitrogen and oxygen isotopes in nitrate pollutants with measurements of hydrochemical "contaminants of emerging concern"-such as pharmaceuticals, artificial sweeteners, and other compounds associated with human activity-to accurately trace pollution sources in freshwater systems.

According to the IAEA, the use of the complementary isotope and contaminant tracers allowed the researchers "to distinguish between different sources of nitrate [including agricultural, animal-derived, and human-derived sources] and better understand how nitrogen moves through aquatic environments. The integrated approach provided greater confidence in source identification than any single monitoring method alone."

The final report offers expert guidance for water managers, scientists, and environmental practitioners regarding "the monitoring, management and remediation of water pollution in human-impacted environments," the IAEA said.

Nitrate pollution: The study was prompted by international concern over nitrate pollution, which the IAEA describes as "an increasing threat to rivers, lakes, and groundwater worldwide." Nitrate (NO₃) is a compound that occurs naturally in air, soil, and water and is essential for plant and animal growth and survival. However, industrial nitrates that find their way into the environment from fertilizers, food additives, pharmaceuticals, and other industrial products can lead to excessive concentrations of the compound, which can cause serious environmental and health problems.

Identifying the sources of nitrate contamination is crucial to solve this problem. However, because of the complex biological and chemical transformations that nitrogen undergoes as it moves through the environment, identification can be challenging, which is why the IAEA initiated the study.

Study overview: Scientists used the combined isotope and contaminant analyses to link nitrate contaminants to urban wastewater, agricultural activities, and legacy nitrogen in soils and groundwater in the 14 countries that participated in the study.

The scientists frequently detected such wastewater-related nitrate indicators as caffeine, pharmaceutical compounds, and the artificial sweetener sucralose, providing strong evidence that human-derived contamination was the cause of the elevated nitrate concentrations. Those chemical tracers were particularly useful in distinguishing wastewater sources from agricultural and natural sources, especially in such highly urbanized environments as the Kifissos River Basin near Athens, Greece.

The IAEA report also sheds light on the environmental processes that control nitrogen concentrations in aquatic systems. For example, the isotope-based data allowed for a better understanding of such natural microbial processes as nitrification and denitrification, which, depending on local conditions, can either increase or decrease nitrate concentrations.

Another research advancement described in the report is the use of analytical tools like machine learning and Bayesian statistical methods to analyze seasonal and regional patterns in nitrate contamination and transport. According to the report, this type of information can provide water managers with a stronger scientific basis for their decisions.

Astrid Harjung, an IAEA isotope hydrologist who participated in the study, summed up the report by saying, "This multi-tracer approach transforms how we understand water quality by providing greater clarity on pollution sources, transport pathways, and environmental processes in river systems that influence both terrestrial and downstream marine ecosystems. It enables scientists, policymakers, and water managers to make informed decisions that support pollution reduction, ecosystem protection, and the sustainable management of water resources."

Asunción Romanelli of Argentina's National Scientific and Technical Research Council and the National University of Mar del Plata emphasized that the combination of analytical techniques in the study allowed the researchers to improve the "ability to identify contamination sources and transport pathways, generating scientific evidence that can support more effective water-resource management."