Toxin or Treat? Glacial Flour as a Source of Beneficial Micronutrients and Toxic Trace Elements for Crops

Micronutrient deficiencies in human diets, often exacerbated by soil degradation, pose a significant global health challenge. Glacial flour, fine sediments produced by glacial erosion, may offer a sustainable, low-cost solution to improve soil fertility and enhance micronutrient availability in crops. This study evaluates the potential of glacial flour soil amendments from glaciers with two contrasting lithologies—basaltic Sólheimajökull (Iceland) and metasedimentary Chhota Shigri (Himalaya)—to enrich soybeans (Glycine max var. Black Jet) with essential nutrients while assessing the risk associated with potentially toxic elements. In a controlled glasshouse experiment, soybeans were grown in artificial soils amended with five doses of glacial flour (0.5–20 T ha−1) and analysed for 18 elements. Results demonstrated enhanced uptake of key nutrients such as Zn, Fe, Mo, and Se, particularly in Icelandic glacial flour treatments, supporting the potential for crop biofortification. However, Himalayan flour led to arsenic (As) accumulation at higher doses, exceeding food safety limits. Multivariate clustering revealed two distinct element uptake behaviours: oxyanion-mediated and mimicking elements (Mo, Se, Sr, As) and those driven by plant demand (macronutrients, Fe, Mn, Zn). These findings highlight glacial flour’s potential for nutrient enrichment but also of potentially toxic elements, underscoring the need for source-specific screening to ensure safe agricultural application in deglaciating regions.