From microalgae to gastropods: Understanding the kinetics and toxicity of silver nanoparticles in freshwater aquatic environment.

Silver nanoparticles (AgNPs) are increasingly used in various consumer products and industrial applications, raising concerns about their environmental impact on aquatic ecosystems. This study investigated the physicochemical stability, trophic transfer, and toxic effects of citrate-coated AgNPs in a freshwater food chain including the diatom Cyclotella meneghiniana and the gastropod Lymnaea stagnalis. AgNPs remained stable in the exposure medium, with a minimal dissolution (<0.06%) after 24 h, indicating that particulate forms dominated during exposure. AgNPs inhibited the growth of C. meneghiniana without significantly affecting chlorophyll-a content or reactive oxygen species (ROS) production. Scanning electron microscopy revealed extracellular polymeric substance (EPS) secretion, which likely formed eco-coronas, reducing AgNPs bioavailability and oxidative damage. However, trace element analysis showed significant depletion of iron, manganese, and nickel, indicating early metabolic stress and redistribution of essential metals to support antioxidant defenses. In L. stagnalis, toxicokinetic analysis showed distinct patterns of Ag uptake and depuration across exposure routes. Waterborne and foodborne exposure resulted in similar and higher Ag accumulation compared to the combined group. Waterborne exposure showed the highest non-eliminable fraction and a bioconcentration factor (BCF) > 1, indicating efficient uptake and retention. Foodborne exposure exhibited a biomagnification factor (BMF) > 1, despite efficient elimination. Combined exposure had the highest depuration rate, with BCF >1 and BMF <1, reflecting reduced trophic transfer potential. Oxidative stress in L. stagnalis was highest during combined exposure, with increased ROS in hemolymph during uptake. Foodborne exposure caused prolonged immune stress, evidenced by elevated total antioxidant capacity (TAC) and protein levels. In the hepatopancreas, foodborne exposure during depuration led to increased lipid peroxidation and TAC, indicating oxidative and metabolic challenges specific to dietary exposure. These results highlighted the complex interactions of AgNPs with primary producers and consumers in freshwater ecosystems, emphasizing the need for multi-route assessments in nanoparticle risk evaluations.