Differential uptake of Ag nanoparticle forms by wheat across field soils

Understanding the environmental risks of engineered silver nanoparticles (Ag NPs) is complicated by transformation processes which occur in soil, such as dissolution and sulphidation, generating diverse Ag forms, altering bioavailability and uptake by organisms. Despite this, integrated studies linking nanoparticle speciation to plant uptake in soil systems remain limited, and gaps persist in understanding Ag transformations as a function of soil type and their consequences for bioavailability. Using complementary techniques we compared the speciation (XAS and spICP-MS), bioavailability, and uptake of three Ag forms, two Ag NPs (Ag NP, Ag2S NP) and AgNO3 (all at 10 mg kg−1), in wheat (Triticum aestivum L) grown in three different field soils over 27 days. Results showed that Ag forms were differentially bioavailable (Ag NPs >/≈ AgNO3 > Ag2S NP), and that soil type can have a pronounced influence on the extent of Ag uptake (approx. 7- to 15-fold variation for NPs across soils). Notably Ag2S NPs, though considered “less mobile”, can be more bioavailable to wheat than other Ag forms in some soil contexts. XAS speciation analysis revealed slower transformation dynamics in Woburn soil that may influence the overall pool of bioavailable Ag. While no single soil property fully explained the observed patterns, these findings indicate that intrinsic nanoparticle properties alone are not always sufficient to predict environmental behaviour in soil systems.