Due to its strong antimicrobial properties, silver nanoparticles (AgNPs) are the most widely used nanomaterials in consumer products. Most nanomaterials "age" even under optimal storage conditions and their properties change over time. The main goal of this study was to investigate whether storage time of the dispersed AgNPs impacts their toxicity on saltwater aquatic organism, Artemia salina. Acute toxicity of freshly produced colloidal AgNPs as well as same product after six months storage in room temperature was evaluated using adult males and females brine shrimp during 48 hour tests. In each experiment, animals (ten per test vessel) were exposed in triplicate to 0, 10, 30, 50, 60, 75, 90, 100, 130, 170, 200 mg/L of nanoparticles. Water salinity was adjusted by using synthetic salt at 35 g/L and the temperature was adjusted to 24 °C using a water bath. The mortality rates were monitored at 24 and 48 hours and data were assessed using the EPA Probit analysis program to estimate median lethal concentrations (LC50). The calculated 48 h LC50 values of fresh and aged AgNPs for females were 35.86 ± 11.17 and 14.97 ± 9.84 mg/L, respectively. In the case of males, these values were 29.03 ± 9.73 and 10.96 ± 9.50 mg/L, respectively, for fresh and aged AgNPs. According to the results, it seems that aging of AgNPs over time increases their acute toxicity to both males and females Artemia. Different toxicity over the aging duration can be an important reason of the conflicting toxicity results which sometimes observed in the experiments on identical NPs, and the aging issue should therefore be considered in toxicology studies of nanomaterials.
