Enhanced Gastric/Lung Arsenic Bioaccessibility from Lignite Fly Ashes: Comparing Bioaccessibility Rates with Multiple Environmental Matrices

Abstract

Inorganic arsenic (As), a carcinogenic element to humans, is among the most dangerous and flammable substances that coal-burning plants could release. When coal is burned, large portions of arsenic are captured on fly-ash (FA) particles, but it could also contribute significantly to stack emissions of fine fly-ash particles. The aim of this study was to evaluate the oral and respiratory bioaccessibility of arsenic in lignite fly-ash (LFA) samples, and their contribution to total As exposure. Arsenic bioaccessibility fractions via ingestion and inhalation showed significant differences, suggesting the presence of highly soluble As-bearing phases in the studied LFA samples. The bioaccessible As fractions (BAF%) in the simulated gastric fluids (UBM protocol, ISO 17924:2018) showed a range of 45-73%, while the pulmonary bioaccessibility rates in the simulated lung fluid (artificial lung fluid (ALF)) exhibited significantly enhanced levels ranging from 86% to 95%. The obtained arsenic bioaccessibility rates were compared with previous data for multiple environmental matrices such as soil and dust-related materials, revealing that LFA exhibited significantly higher bioaccessibility (%) for the inhalation pathway.

Keywords: Greece; arsenic; bioaccessibility; gastric; lignite fly ash; mineralogy; respiratory.

Figure 3

Arsenic concentrations (mg kg⁻¹) in the <250 and <10 μm size fractions, and a comparison of the obtained As contents with published data ¹ [10], ² [17], ³ [49], ⁴ [48].

Figure 1

Representative XRD patterns of Ca-rich (Sample AD, top) and Si-rich (Sample MG1, bottom) fly-ash samples of the two different studied size fractions. An: anhydrite, Bsn: bassanite, C: calcite, Etr: ettringite, Ghl: gehlenite, Gps: gypsum, Ht: hematite, L: lime, Prt: portlandite, Pl: plagioclase, Q: quartz. The concentration units of pXRF results are given in the inlets.

Figure 2

Representative SEM images of the studied fly-ash samples.

Figure 4

Arsenic bioaccessibility (in mg kg⁻¹) of lignite fly-ash samples in (left) gastric (G)/gastrointestinal (GI) and (right) lung fluids.

Figure 5

Arsenic bioaccessibility (%) of lignite fly-ash samples in gastric and lung fluids.

Figure 6

Heat maps of Pearson’s correlation coefficients matrix for (left) gastric and (right) lung As bioaccessibility and selected geochemical parameters. Correlations in red are positive and in green are negative. p < 0.01 significance is marked in bold, and p < 0.05 in underlined.

Figure 7

Comparison of As bioaccessible fractions (%) between LFA and other environmental materials. Data for other coal FAs are from Jin et al. [38], for soil, road dust, and house dust are from Kelepertzis et al. [54], and those for fine surface dust (FSD) are from Morais et al. [55]. The box is determined by the 25^th and 75^th percentiles. The whiskers (−) are determined by the 5^th and 95^th percentiles. Additionally, the minimum (*), median (line), mean (□) and maximum (*) values are presented. Green boxes: this study; Yellow boxes: other FAs; Red boxes: other materials.