A life cycle assessment approach for nitrogen footprint quantification: the reactive nitrogen indicator.

Among the environmental issues that have recently catalyzed the attention of the scientific world, we must undoubtedly include the perturbation in the biogeochemical flows of nitrogen and phosphorus, which have been identified as one of the major risks on a global scale, also considering its social implications, since the use of macronutrients is essential to guarantee the food needs of the world population. In this context, there is a growing interest in the evaluation of the environmental impact related to this issue, particularly with regard to the effects of changes in the nitrogen cycle and the methods for quantifying them. In the latter field, several researches have recently been developed focusing on the indicator known as the nitrogen footprint, associated with the environmental releases of reactive nitrogen. This study proposes an innovative method to quantify the reactive nitrogen emissions of a product system through the reactive nitrogen indicator; the method is designed using as a reference the requirements of the international standards ISO 14040 and ISO 14044, in order to be aligned with the operating procedures of the life cycle assessment technique, thus differing from the previous approaches to calculate the nitrogen footprint. As part of the study, the proposed method is applied to calculate the reactive nitrogen emissions of a set of agricultural and livestock supply chain products, using secondary inventory data from an internationally recognized database. A validation of the method was also carried out by comparing references in the literature regarding the nitrogen footprint accounting for the same products, generally obtaining a good level of agreement. The proposed method, due to its reproducibility, ease of application and completeness, can therefore be usefully applied to any product system for the calculation of reactive nitrogen emissions, thanks to an innovative approach that meets the requirements of life cycle assessment.