Nutrient stoichiometry and concentrations influence silver toxicity in the aquatic macrophyte Lemna gibba

Though nutrients and silver often co-occur in aquatic ecosystems, the combined effects of these environmental stressors on aquatic plants are poorly understood. Such coexposures are important because nanosilver is increasingly released to the environment, and recent studies in aquatic systems indicate that nanosilver represents an environmental source of ionic silver (Ag(+)), which exerts relatively high acute toxicity to aquatic life. The primary objective of this study was to understand the effects of nitrogen (N) and phosphorus (P) concentrations and N:P ratios on the toxicity of ionic silver to the model aquatic macrophyte Lemna gibba over 7-d study periods. L. gibba were more sensitive to silver (e.g., lower EC50 values) when N and P concentrations were higher. In addition, greater ionic silver toxicity occurred under higher P-availability (e.g., lower N:P ratios). L. gibba frond number and fresh weight were also differentially affected across nutrient×silver treatment combinations. Such observations highlight the importance of considering site-specific nutrient conditions during the prospective and retrospective risk assessments and management of silver impacts to primary producers.