Abstract
Abstract. Determination of transition metals in ambient aerosols is important due to their toxicity to human health. However, the traditional measurement techniques for metal analysis are often costly and require sophisticated instruments. In this study, we developed and verified relatively low-cost liquid spectrophotometric methods for the measurements of iron (Fe) and copper (Cu), the two most abundant transition metals in ambient fine particulate matter (PM2.5). For Fe analysis, we utilized a ferrozine-based colorimetric method, which has been frequently used for water-soluble (WS) Fe determination, and further extended this approach for the measurement of total Fe (water-soluble + water-insoluble). In this method, Fe is quantified through the formation of a light-absorbing ferrozine–Fe(II) complex (absorbance at 562 nm). A similar colorimetric method, which forms a bathocuproine–Cu(I) complex absorbing light at 484 nm, was developed and examined for measurement of WS and total Cu. These methods were applied to 24 h integrated filter samples collected in urban Atlanta. Based on PM2.5 ambient aerosols, total and water-soluble Fe and Cu concentrations were in good agreement with inductively coupled plasma mass spectrometry (ICP-MS) measurements (slopes 1.0±0.1, r2>0.89). The water-soluble components, operationally defined as those species in the aqueous filter extract that pass through a 0.45 µm filter, were further characterized by ultrafiltration, which showed that roughly 85 % of both the Fe and Cu in the water-soluble fraction was composed of species smaller than nominally 4 nm.
Highlights
Transition metals are known to contribute to airborne particle toxicity and can cause a wide range of adverse health effects (Chen et al, 2018; Gonet and Maher, 2019)
Water-soluble species are operationally defined and are obtained though aqueous dissolution of collected aerosols followed by liquid filtration of the extract solution, which is roughly analogous to the process particles undergo when deposited in the respiratory-tract-lining fluid
A new approach for the measurement of WS Cu and total Cu has been developed and tested based on liquid spectrophotometry. It follows a similar method for quantifying WS Fe
Summary
Transition metals are known to contribute to airborne particle toxicity and can cause a wide range of adverse health effects (Chen et al, 2018; Gonet and Maher, 2019). Water-soluble species are operationally defined and are obtained though aqueous dissolution of collected aerosols followed by liquid filtration of the extract solution (typical filter pore sizes of 0.22 or 0.45 μm), which is roughly analogous to the process particles undergo when deposited in the respiratory-tract-lining fluid. Metals measured in this fraction can include molecules and colloidal nanoparticles that are more readily bioavailable than insoluble species. Studies have found that water-soluble transition metals, including water-soluble (WS) Fe and Cu, have stronger adverse health associations than the corresponding water-insoluble components
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