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Silver nanoparticles (NPs) are used in more consumer products than any other nanomaterial and their release into the environment is unavoidable. Of primary concern is the wastewater stream in which most silver NPs are transformed to silver sulfide NPs (Ag₂S-NPs) before being applied to agricultural soils within biosolids. While Ag₂S-NPs are assumed to be biologically inert, nothing is known of their effects on terrestrial plants. The phytotoxicity of Ag and its accumulation was examined in short-term (24 h) and longer-term (2-week) solution culture experiments with cowpea (Vigna unguiculata L. Walp.) and wheat (Triticum aestivum L.) exposed to Ag₂S-NPs (0–20 mg Ag L⁻¹), metallic Ag-NPs (0–1.6 mg Ag L⁻¹), or ionic Ag (AgNO₃; 0–0.086 mg Ag L⁻¹). Although not inducing any effects during 24-h exposure, Ag₂S-NPs reduced growth by up to 52% over a 2-week period. This toxicity did not result …