Impacts of fertilization on metal(loid) transfer from soil to wheat in a long-term fertilization experiment – using 87Sr/86Sr isotopes as metal(loid) tracer

Fertilizers are widely used to sustain food production but can alter soil chemistry and potentially contribute toxic metal(loid)s to agricultural systems. For the first time, this study examined the occurrence of select metal(loid)s (Zn, Sr, V, As, Cd, Pb, and U) alongside the ⁸⁷Sr/⁸⁶Sr isotope ratio in agricultural soil— both total and mobile pools— and wheat grain. Samples were collected from one of four fertilization treatments— mineral (NPK), organic (manure), combined mineral + organic, and unfertilized controls— within the 120-year Static Fertilization Experiment in Bad Lauchstädt, Germany. Fertilization treatments altered soil pH and organic carbon resulting in mineral fertilization lowering pH and increasing cation mobility (Cd, Zn, Sr), whereas organic fertilization increased pH and enhanced the mobility of non-cationic elements (V, As). These effects translated into higher Cd in mineral-fertilized wheat grain and higher As in mineral + organic wheat grain. Fertilization shifted the ⁸⁷Sr/⁸⁶Sr ratios in soils and wheat grains toward that of the applied fertilizers, with mineral and mineral + organic wheat grains inheriting the triple super phosphate signature (0.70778) and organic wheat grains matching manure (0.70883). The ⁸⁷Sr/⁸⁶Sr ratio in the mobile soil pool was correlated with mobile As, V, and P, demonstrating that the ⁸⁷Sr/⁸⁶Sr ratio reflects both fertilizer source and the mobility of select co-occurring metal(loid)s. Overall, this study demonstrates metal(loid) enrichment in soil and wheat from fertilization and establishes ⁸⁷Sr/⁸⁶Sr ratio as a robust tracer of fertilizer impacts. These findings underscore the need for targeted fertilization strategies to reduce contaminant accumulation in agroecosystems.