Geochemical Speciation and Potential Mobility of Heavy Metals in Agricultural Soils of Cross River State, Nigeria: A Visual MINTEQ Modelling Approach
Potential Mobility of Heavy Metals in Agricultural Soils of Cross River State, Nigeria
DOI:
https://doi.org/10.67254/0wt7n564Keywords:
Heavy metals; Visual-MINTEQ; Geochemical speciation; mobility; groundwater; mineral saturation.Abstract
This study evaluated the geochemical speciation, aqueous behaviour, and potential mobility of selected heavy metals in agricultural soils from twelve farm locations across the Yakurr and Biase Local Government Areas of Cross River State, Nigeria, using the Visual MINTEQ geochemical modelling software. Soil samples were collected from Ekori, Adim, Akpet, Umon, Abini, Agwagune, Mkpani, Idomi, Inyima, Ugep, Nko, and Abaribara, and analysed for Cu, Ni, Zn, Cr, Mn, Fe, Pb, Cd, and As using atomic absorption spectrophotometry. The measured physicochemical parameters exhibited substantial spatial variability, with soil pH ranging from 4.0 to 6.9 and moisture content ranging from 70% to 99%. Elevated concentrations of Ni, Pb, Cd, and As were observed at Idomi, Inyima, and Ugep, while Cu concentrations remained below the WHO drinking water guideline across all locations. Visual MINTEQ modelling revealed that under the prevailing near-neutral water chemistry (pH 6.29-6.77), the investigated metals occurred predominantly as dissolved free ions and carbonate complexes. The calculated ionic strength ranged from 0.00134 to 0.00584 mol/L, while free-ion activities varied considerably among farms. Malachite saturation indices were consistently negative (−0.9 to −4.1), indicating undersaturation and a low likelihood of spontaneous copper mineral precipitation. The model further indicated that Cd, Pb, and Cu could persist in dissolved forms under the existing geochemical conditions, thereby increasing their potential availability for transport and biological uptake. These results show that total metal concentrations alone do not adequately describe environmental mobility, as aqueous speciation, pH, ionic strength, and mineral saturation strongly influence metal behaviour. The findings underscore the potential risk of continued metal mobility and groundwater contamination in the investigated agricultural environments, highlighting the need for integrated geochemical assessments in environmental monitoring programmes
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The data supporting the findings are contained in this article of this study and are available from the corresponding author upon reasonable request.
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