Trace metals in high-Andean forages: differential dietary exposure in cattle, sheep, and alpacas, and lack of non-carcinogenic risk

Abstract

Trace metal accumulation in forage plants is a growing concern in mountain grazing systems, yet the relative importance of environmental and biological drivers remains poorly understood in the high Andes. This study evaluated trace metal concentrations in soils and cultivated forages along an altitudinal gradient (4,098–4,467 m a.s.l.) in the Junín region of central Peru and assessed potential dietary risks for livestock. Soil properties and concentrations of Zn, Cd, Cu, Mn, Pb, and Cr were determined in soils and four forage species (Avena sativa, Dactylis glomerata, Lolium multiflorum, and Lolium perenne) across eight plots. Dietary exposure was estimated using the Estimated Daily Intake (EDI), while non-carcinogenic risks for cattle, sheep, and alpacas were assessed through the Hazard Quotient (HQ) and Hazard Index (HI). Marked spatial variation in soil properties and trace metal concentrations was observed among plots, indicating that metal accumulation was primarily driven by local soil heterogeneity. Altitude was not associated with trace metal concentrations, and forage species showed no significant differences in metal accumulation (p > 0.05). Although sheep exhibited the highest EDI values, all HQ and HI values remained below 1. These findings demonstrate that fine-scale soil heterogeneity is a stronger determinant of trace metal accumulation than altitude or forage species identity in high-Andean forage systems. The study provides new evidence that current trace metal exposure levels do not represent a significant non-carcinogenic risk for cattle, sheep, or alpacas under the evaluated environmental conditions.