Potentially Toxic Element Accumulations and Soil-to-Plant Bioconcentration Patterns in Potato (Solanum tuberosum L.) Crops in Farmer-Managed Volcanic Agroecosystems of Ecuador

Potato (Solanum tuberosum L.) production on volcanic soils takes place in complex agricultural systems where natural soil properties and agricultural practices coexist and may be associated with trace element dynamics. This study evaluated the concentration and apparent transfer index of Pb, Cd, Hg, As, and Ni in the soil-potato system of Quero Canton, Tungurahua, Ecuador. Soil and whole-plant samples were collected from 20 georeferenced sites and analyzed using standardized methods and atomic absorption spectrophotometry. Soil chemical composition varied among sites and was characterized by elevated phosphorus and potassium contents. Pb and As concentrations in soil remained below guideline values for agricultural soils, whereas localized high concentrations of Cd, Hg, and Ni were observed. Mean concentrations in plant tissues were 0.28 mg/kg for Hg, 0.38 mg/kg for As, and 1.13 mg/kg for Ni, all of which were below reported phytotoxicity thresholds. Bioconcentration factors indicated generally limited soil-to-plant transfer. Hg showed the highest variability in BCF values. Principal component analysis showed that variation in the apparent transfer index was associated with pH, bulk density, and electrical conductivity. These findings highlight the importance of soil quality monitoring to support the management of potato production systems on volcanic soils.