Anticipatory life cycle assessment of gold nanoparticles production: Comparison of milli-continuous flow and batch synthesis

The demand of gold nanoparticles (AuNPs) is growing steeply as a result of the remarkable advances in the applications of this product in the healthcare and diagnostics sectors. To this end, having an efficient and sustainable production system is of paramount importance for achieving low environmental impacts and avoiding depletion of capitals. In this respect, the present work gives insights on the environmental impact and costs of the production of AuNPs for nano-enabled medical applications, by looking at two production technologies: the conventional batch production and an innovative milli-continuous flow production, currently at lab scale. Life Cycle Assessment (LCA) and cost assessment are used to evaluate the sustainability and economics of the continuous-flow technology in an anticipatory fashion; this means capturing the environmental impacts and production costs of the emerging technology before it reaches full-scale and is deployed. The aim is to prevent waste of resources in the process development and avoid having a non-optimized final system, which would lead to high costs and reduce competitiveness. The milli-continuous flow production was subjected to a scale up/out-analysis enabling the comparison with the batch production, already established at large scale. The life cycle of both production systems is described, and the results of the assessment comprise a normalisation analysis, which frames the environmental impacts of the gold nanoparticles production in the European context, a scenario analysis, a comparative analysis and a hotspot analysis. The results show that significant advantages can be gained from the adoption of the continuous-flow production in place of the batch system, both in terms of environmental impact and production costs. Specifically, the environmental impact is reduced in terms of human toxicity (cancer effect), ecotoxicity of freshwater and depletion of gold resources; these impact categories were identified as the main carrier of the environmental impact in the conventional production. The main contributors to savings for the flow production are primarily milder cleaning procedures, reduction of hazardous wastes produced, and less labour required for the operation and control of the process. Finally, the depletion of gold resources associated to the production of AuNPs emerges as a major issue. It is hardly addressable by using second-hand gold, and this calls for the necessity of recycling the product at the end of its life cycle or complementing AuNPs with alternative nano-products. (C) 2020 Elsevier Ltd. All rights reserved.