Fate of transition metals in PO₄-based in vitro assays: equilibrium modeling and macroscopic studies

Abstract

Through macroscopic experiments and thermodynamic modeling, this work demonstrates the precipitation and oxidation of transition metals in phosphate-based in vitro assays.

Precipitation of aqueous transition metals in particulate matter during the dithiothreitol (DTT) oxidative potential assay

“…For the precipitation experiments, SRM-1648a extract was added to the DTT assay at three concentration levels (Table 1), which were selected according to the range of Fe concentrations measured in ten urban areas across the US using accepted PM lter sampling and extraction protocols. 36,49,50 The concentrations of the remaining elements were calculated based on the dilution factor (DF) and the elements' concentration in the SRM-1648a extract. Note that the Cu concentration for samples 1, 2, and 3 and Mn concentration for samples 1 and 2 were below the DL for the colorimetric analysis.…”

“…Note that the Cu concentration for samples 1, 2, and 3 and Mn concentration for samples 1 and 2 were below the DL for the colorimetric analysis. To maintain the relevance of Mn and Cu concentrations to that in PM lter extracts (0.058 mM Mn and 0.06 mM Cu), 36,49,50 increasing the SRM-1648a sample concentrations above the DL for Mn and Cu was not preferred. Also presented in Table 1 are metal solubilities and saturation indexes (SI) determined by MINEQL 36,81 under the DTT assay conditions (0.1 M TOTPO 4 , T ¼ 37 C, pH ¼ 7.4 and ionic strength ¼ 0.22 M).…”

“…To maintain the relevance of Mn and Cu concentrations to that in PM lter extracts (0.058 mM Mn and 0.06 mM Cu), 36,49,50 increasing the SRM-1648a sample concentrations above the DL for Mn and Cu was not preferred. Also presented in Table 1 are metal solubilities and saturation indexes (SI) determined by MINEQL 36,81 under the DTT assay conditions (0.1 M TOTPO 4 , T ¼ 37 C, pH ¼ 7.4 and ionic strength ¼ 0.22 M). The modeling approach used is based on our previous work 36 (thermodynamic data are presented in Table S7, † and detailed results from thermodynamic modeling are presented in Tables S8 and S9 †).…”

“…Also presented in Table 1 are metal solubilities and saturation indexes (SI) determined by MINEQL 36,81 under the DTT assay conditions (0.1 M TOTPO 4 , T ¼ 37 C, pH ¼ 7.4 and ionic strength ¼ 0.22 M). The modeling approach used is based on our previous work 36 (thermodynamic data are presented in Table S7, † and detailed results from thermodynamic modeling are presented in Tables S8 and S9 †). In Table 1, metals with an asterisk (Al, Ca, Fe, Mn, and Pb) indicate species that can theoretically precipitate (i.e., those with a positive saturation index (SI)).…”

“…[39][40][41] In our prior study, the thermodynamic predictions were validated at high aqueous metal concentrations with experiments during which visible precipitates formed. 36 However, metal precipitation has not been demonstrated at lower metal concentrations (<50 mM) representative of PM samples (i.e., aqueous lter extracts). The reactivity of metals and PM, including the generation of ROS, vary due to their phase (aqueous vs. solid) and oxidation state.…”