A critical review of criticality methods for a European Life Cycle Sustainability Assessment

The beginning of the 21st century is marked by the fourth industrial revolution, which could be a great opportunity for a sustainable technological transformation. The key role of these technologies in the development of a more sustainable future implies the need for the evaluation and monitoring of both supply risks as well as environmental and social impacts of a number of raw materials in the supply chain. These raw materials that are important to the economy and might be under supply risk are referred to as Critical Raw Materials (CRMs) in the EU. The integration of Life Cycle Sustainability Assessment (LCSA) - well established for sustainability evaluation - and Criticality Assessment (CA) – increasingly used as governance tool - is therefore consequent to support decision-making regarding efficient use those natural resources. Based on a critical review of CA methods within and outside the framework of an LCSA, this research aimed to investigate the compatibility of CA methods with the life-cycle approach. The methods range from specific CA methodologies (e.g., NRC (USA) and EC-CA (EU)) to the existing methods integrating CA and LCSA (e.g., ESSENZ and GeoPolRisk). The evaluation of the methods was based on a set of criteria (e.g., acceptance and credibility) and further analysis of compatibility with frameworks from ISO 14040-44 and UNEP-SETAC. The current challenges for integration in the field are identified, namely: interpretation of criticality within the three pillars of sustainability (social, economic or environmental); the incompatibility among inventories and the characterization of material’s criticality; arbitrariness in the interpretation of what is “critical”; and the uncertainty intrinsic to CA models. Potential solutions towards the operationalization of criticality indicators in a product-oriented LCSA include the definition of the impact pathway of criticality in LCSA, the linkage of criticality indicators to product/technological flows, the use of intermediate indicators (supply risk and economic importance), the characterization of criticality at the normalization and weighting step, and addressing uncertainties in an LCSA. Further works of this research will explore the solutions proposed.