Regionalized aquatic ecotoxicity characterization factor for zinc emitted to soil accounting for speciation and the transfer through groundwater

Abstract

The goal of this study is to calculate regionalized fate and characterization factors for zinc (Zn) emitted to soil considering the Zn transfer through groundwater in USETox and Zn speciation in soil, groundwater, and surface water using regionalized soil, subsoil, and freshwater parameters. Partition coefficients for Zn in soil and water and effect factors (EF) are calculated using the WHAM7 software. Soil and watershed maps are intersected with a geographic information system software to obtain native geographic resolution. USETox is modified by linking (a) the soil with subsoil and groundwater compartment and (b) subsoil and groundwater compartment to the freshwater compartment. Soil to water fate factors (FFsw) for each native resolution cell are calculated using these soil, subsoil, and watershed partition coefficients with the modified version of USETox. These specific FFsw’s are multiplied with bioavailability factors (BF) and effect factors (EF) to generate characterization factors (CFsw) for all the native resolution cells. The results obtained at the native resolution scale are aggregated at different more operational regionalization scales: country, continent, and global level, with the corresponding spatial variability determination. The newly obtained results are compared with the default values of USETox. Regionalized freshwater ecotoxicity characterization factors for Zn emitted to soil have a global spatial variability of 3 orders of magnitude. The aggregated global value is in the same order of magnitude with the default USETox value. The spatial variability of soil to water fate (FFsw) and the characterization factors (CFsw) for Zn within each watershed are quantified. The results are illustrated on a world map for all the native resolution cells. With the exception of Europe, all the regional and continental FFsw and CFsw varied over 2 orders of magnitude. The inclusion of the transfer through groundwater for Zn soil emissions in fate and in characterization calculation along with the Zn speciation allow better prediction of the potential impacts in freshwater systems. The spatial variability of Zn CFsw at continental scale is close to the uncertainty of USEtox’s CFsw (2 orders of magnitude), meaning that using a continental level CFsw seems a reasonable compromise between a too intensive data collection and imprecise impact assessment.