Global environmental impacts of silver nanoparticle production methods supported by life cycle assessment

Considering their antimicrobial, electrical and optical properties, silver nanoparticles (AgNPs) are the most common type of engineered nanomaterials found in consumer products. AgNPs may be synthesized through multiple methods, including chemical, biological and physical techniques; however, literature suggests that the manufacturers prefer to use physical and chemical methods (85 %) rather than biological. This work presents cradle-to-gate life cycle impact assessments in order to evaluate global environmental impacts of six different AgNPs synthesis routes (two chemical and four physical) along with thirteen different inventories and a mass based functional unit of 1 kg of AgNPs. Results are then combined with the annual global AgNPs production estimates, and global environmental impact calculations are performed based on both optimistic and skeptical estimations. Since AgNPs production volumes are forecasted to increase drastically, industrial scale AgNPs syntheses are modeled and future life cycle impacts are projected using three different scale-up factors. Furthermore, given that each industry has specific preferences for properties of AgNPs (i.e. size, surface area) and those are dependent on the synthesis methods, industry based environmental impact projections are developed for industries where the majority of AgNPs are used such as textiles; coatings, paints and pigments; consumer electronics and optics; cosmetics; medical and packaging. Results show that scaling up may reduce the environmental emissions up to 90 % globally, and up to 83 % per industrial sector which suggest that the global environmental impact of AgNPs may vary significantly as a function of the synthesis method, scale, and desired product application. © 2020 Elsevier B.V.