Developing physicochemical property-based ecotoxicity characterization factors for silver nanoparticles under mesocosm conditions for use in life cycle assessment

Abstract

Global production and consumption of silver nanoparticles (nAgs) are forecasted to increase due to their applications in modern technologies. This situation raises concerns related to their environmental and human health consequences, as nAgs potentially will be released to the environment during and/or at the end of the product life cycles. Environmental impacts due to the raw materials and manufacturing of nAgs are examined throughout the literature using cradle-to-gate life cycle assessments. However, calculating nano-specific emissions resulting from nAg release is occasionally overlooked, or modeled as ionic silver, due to the lack of widely accepted characterization factors (CFs) to define the associated impact. The current study seeks to calculate CFs for nAgs by combining the principles of colloidal science with the USEtox model to be integrated to cradle-to-grave life cycle assessments. In order to control the variables while modeling the fate and behavior of nAgs, data from published mesocosm conditions are used. Effect and fate factors for CFs are calculated considering certain physicochemical properties of nAgs in the mesocosm and the composition of aquatic media. Additionally, two different scenarios are computed where the hetero-aggregation is modeled as either a removal or a transformation process, which significantly changes the final results. Considering different scenarios, a CF range is proposed as 2.19 × 10³–2.34 × 10⁵ PAF m³ day kg⁻¹ (PAF: potentially affected fraction) for polyvinylpyrrolidone (PVP)-coated nAgs. Moreover, as a result of sensitivity analysis, it is found that the characteristics of the suspended particulate matter largely affect the fate of nAgs under both scenarios. Results suggest that using ionic silver to model nAg release will potentially overestimate the environmental impacts.