Study of Chromium Bioavailability Using Different Extractants in Different Agricultural Soils in Libya (Tarhuna District)

Enageh Abdalgader; Ismail Ben Sulaiman; Noureeyah Alazraq; Omar Algeidi

doi:10.69667/ajs.261002

Authors

Enageh Abdalgader Department of Chemistry, Faculty of Education-Janzour, Tripoli University, Tripoli, LIBYA Author https://orcid.org/0000-0002-4985-0714
Ismail Ben Sulaiman Department of Chemistry, Faculty of Education-Janzour, Tripoli University, Tripoli, LIBYA Author https://orcid.org/0000-0003-3041-3124
Noureeyah Alazraq Department of Chemistry, College of Science, Tarhuna, Azzaytuna University, Tarhuna, LIBYA Author https://orcid.org/0000-0002-3912-7725
Omar Algeidi Department of Chemical Engineering, Faculty of Engineering, Sabratha University, LIBYA Author https://orcid.org/0009-0002-5629-0775

DOI:

https://doi.org/10.69667/ajs.261002

Keywords:

Chromium Bioavailability, Calcareous Soils, Extractants, pH Effect, Ammonium Oxalate, Libyan Agriculture

Abstract

Chromium (Cr) bioavailability in calcareous agricultural soils is strongly influenced by soil properties and extraction conditions, yet limited data exist for Libyan soils. This study aimed to evaluate the extractability of Cr using eight single extractants (deionized water, EDTA, ammonium acetate, ammonium chloride, ammonium oxalate, hydroxylamine HCl, calcium chloride, and magnesium chloride) at three pH values (4.91, 6.00, and 10.14) across six soils from the Tarhuna district, Libya, representing high‑carbonate (>30% CaCO₃) and low‑carbonate (<3% CaCO₃) groups. Total Cr concentrations averaged 6.03 mg/kg in low‑carbonate soils (0–10 cm depth) and 6.91 mg/kg in high‑carbonate soils (40–50 cm depth). Extractable Cr ranged from 0.014 mg/kg (CaCl₂, pH 4.91) to 0.225 mg/kg (NH₄OAc, pH 10.14), corresponding to 0.21–3.73% of total Cr. Based on established Cr speciation chemistry, extraction at pH 10.14 is expected to favor solubilization of Cr(VI) anionic species, whereas acidic to neutral pH (4.91–6.00) favors release of Cr(III) species; direct speciation analysis was not performed in this study. Ammonium oxalate at pH 6.00 yielded the highest extraction (3.71% of total Cr), while ammonium acetate at the same pH gave the lowest (0.41%). Extraction curves (Figures 1–8) showed marked differences between high‑ and low‑carbonate soils, particularly with deionized water, reflecting Cr(VI) retention by CaCO₃ under alkaline conditions. Alkaline pH (10.14) preferentially extracted Cr(VI) as anionic species, whereas acidic to neutral pH (4.91–6.00) favored Cr(III) release. Correlation analysis (n=42) revealed weak positive relationships between EDTA‑extractable Cr and organic matter (r up to 0.176) and weak negative relationships with CaCO₃ (r down to –0.266), indicating that other factors (e.g., clay content, oxide mineralogy) also contribute to Cr retention. Although absolute extraction values were low, the extractable Cr concentrations (0.014 to 0.225 mg/kg) fall within ranges reported to influence plant uptake in sensitive species, suggesting potential ecological relevance under specific conditions.