Trace Elements in Soils, Their Uptake by Crops and Potential Health Risks: Insights From a Legacy Mining Area in Oruro, Bolivian Altiplano

Abstract

A geochemical study was conducted in the legacy mining area in Oruro, the Bolivian Altiplano to examine the distribution of trace elements (TEs) in agricultural soils and their uptake by crops. The pseudo-total, bioavailable fractions of TE and sequential extraction fraction of As contents were determined in soils. The pseudo-total concentration of TEs in soils suggests naturally elevated background levels. The strong correlation (p < 0.01) between Feregia/Mnregia-Asregia, Curegia, and Znregia suggests that secondary iron oxides play a key role in adsorbing these TEs. Species linked to carbonates are also present, but negative (r = -0.51; p < 0.01) correlation between soil pH and AsDTPA suggests that the retention of TEs in carbonate is not dominant. The chelate diethylene-triamine-pentaacetic acid (DTPA) method extracted less than 2% of total As, whereas sequential fractionation reported up to 12% as potentially mobilized (F1–non-specifically-bound + F2–specifically-bound), posing a risk of transfer to crops or groundwater. As, Cd and Pb tend to accumulate in soils by binding to amorphous and crystalline Fe oxide surfaces. Arsenic levels in beans and alfalfa (0.19 mg/kg), barley (0.17 mg/kg), and peeled potatoes (0.11 mg/kg), Cd levels in beans (0.03 mg/kg), alfalfa (0.017 mg/kg), barley (0.012 mg/kg), and peeled potatoes (0.023 mg/kg), remained within Chilean, FAO, WHO, and European regulatory limits. However, Pb concentrations exceeded permissible limits in beans (0.32 mg/kg), and alfalfa (0.22 mg/kg); however peeled potatoes (0.16 mg/kg) and barley (0.16 mg/kg) remained below the threshold of European guidelines.