Effects of soil pH and organic carbon content on in vitro Cr bioaccessibility in Ultisol, Alfisol, and Inceptisol

Yang-Xiao-Xiao Shi; Jia-Qi Cui; Feng Zhang; Ke-Wei Li; Jun Jiang; Ren-Kou Xu

doi:10.1016/j.chemosphere.2023.139274

Effects of soil pH and organic carbon content on in vitro Cr bioaccessibility in Ultisol, Alfisol, and Inceptisol

Chemosphere. 2023 Sep:336:139274. doi: 10.1016/j.chemosphere.2023.139274. Epub 2023 Jun 19.

Authors

Yang-Xiao-Xiao Shi¹, Jia-Qi Cui², Feng Zhang², Ke-Wei Li¹, Jun Jiang², Ren-Kou Xu³

Affiliations

¹ State Key Laboratory of Soil and Sustainable Agriculture, Institute of Soil Science, Chinese Academy of Sciences, P. O. Box 821, Nanjing, China; University of Chinese Academy of Sciences, Beijing, 100049, China.
² State Key Laboratory of Soil and Sustainable Agriculture, Institute of Soil Science, Chinese Academy of Sciences, P. O. Box 821, Nanjing, China.
³ State Key Laboratory of Soil and Sustainable Agriculture, Institute of Soil Science, Chinese Academy of Sciences, P. O. Box 821, Nanjing, China; University of Chinese Academy of Sciences, Beijing, 100049, China. Electronic address: rkxu@issas.ac.cn.

PMID: 37343637
DOI: 10.1016/j.chemosphere.2023.139274

Abstract

Hexavalent chromium (Cr(VI)) is a toxic heavy metal and its mobility and bioaccessibility in soils are influenced by soil properties. In this study, the soil pH and organic carbon contents of Ultisol, Alfisol, and Inceptisol were adjusted before they were polluted with 230 mg kg^-1 Cr(VI). Alkaline digestion, sequential extraction, and an in vitro experiment were conducted to study the valence state, species, and bioaccessibility of Cr in the soils. The results showed that a high soil pH was not favorable for reduction of Cr(VI); therefore the Cr(VI) and exchangeable Cr contents were positively related to soil pH. Soil organic carbon promoted the reduction of Cr(VI). Almost all Cr(VI) was reduced to Cr(III) when the soil organic carbon content reached 10 g kg^-1. Chromium bioaccessibility in simulated gastric and intestinal phase solutions was influenced by Cr(VI) and Cr(III) adsorption/desorption, dissolution/precipitation, and redox reactions. Chromium bioaccessibility differences between the gastric and intestinal phases were associated with the Cr(VI)/Cr(III) ratio. Acidic conditions and a high organic carbon content promoted the conversion of Cr(VI) to Cr(III). When soil pH was increased from 4.01 to 5.85, Cr(VI) in Alfisol without the addition of humic acid increased from 96.38 to 174.78 mg kg^-1, the exchangeable Cr proportion increased from 9.7% to 22.6%, and Cr bioaccessibility increased from 41.29% to 49.14% in the gastric phase and from 41.32% to 48.24% in the intestinal phase. When the organic carbon content increased from 3.95 to 9.28 g kg^-1 in Alfisol, Cr(VI) content decreased from 167.66 to 20.52 mg kg^-1, which led to a decrease in Cr bioaccessibility from 49.15% to 13.8% in the gastric phase and from 45.85% to 7.67% in the intestinal phase. Therefore, acidic conditions and increasing soil organic carbon levels can reduce the health risk posed by Cr in soils.

Keywords: Cr species; Cr valence state; Cr/Cr(VI) bioaccessibility; Soil organic carbon; Soil pH.

MeSH terms

Carbon / chemistry
Chromium / chemistry
Soil Pollutants* / analysis
Soil* / chemistry

Substances

Soil
Carbon
chromium hexavalent ion
Soil Pollutants
Chromium