Soil properties and bioavailability of heavy metals in soils of orange orchards in north-eastern Mexico

Abstract

Soil pollution by heavy metals has increased due to anthropogenic activities, particularly agriculture, where intensive agrochemical use contributes to contaminant accumulation. Evaluating metal bioavailability is essential to understand potential risks in cultivated soils. This study aimed to assess the presence of heavy metals (Cu, Cd, Cr and Pb) in orange orchard soils by analysing their bioavailable concentrations and the soil physicochemical properties influencing their bioavailability. An exploratory soil sampling was conducted, collecting 60 soil samples from six orchards in the Municipality of Hidalgo. Samples were processed using diethylenetriaminepentaacetic acid extraction and quantified by Flame Atomic Absorption Spectrophotometry. Six soil physicochemical properties were also evaluated. Descriptive statistical parameters and Spearman’s correlation analysis were applied to assess the relationship between variables. The bioavailable concentrations of HMs followed the order Cu > Cr > Pb > Cd, with ranges of 1.1–3.2, 0.1–0.8, 0.2–0.4 and 0.04–0.2 mg/kg, respectively. Significant correlations were observed between particle density and bulk density, porosity, pH and electrical conductivity and the bioavailable concentrations, suggesting a significant association between these properties and heavy metal bioavailability. These findings demonstrate that soil physicochemical properties strongly influence metal mobility and highlight the need for continuous monitoring in agricultural areas. Changes in management practices could alter these properties and increase metal bioavailability, potentially raising toxicological risks.