Use of nano-materials has increased in various aspects of human life. However, possible outbreak of nano-materials toxicity in humans and other organisms is one of the future challenges. Different chemical precursors which are used in chemical approaches for production of nano-materials may have secondary and sometimes toxic effects in living organisms. These secondary effects may be reduced in physical approaches due to not use of chemicals. To test this hypothesis, acute toxic effects of two types of silver nanoparticles (AgNPs) which were produced by physical (top-down) and chemical (bottom-up) methods on survival rate of Zebrafish (Danio rerio) were compared. According to the results, AgNPs produced by physical method were 38 times less toxic than ones generated by chemical method and therefore, the hypothesis was approved. The estimated 96 hr LC50 values of AgNPs produced by physical and chemical methods for zebrafish were 0.540 ± 0.032 and 0.014 ± 0.001 mg/L, respectively. According to these values and regarding the rules of European Union, both types of AgNPs are considered as highly toxic chemicals to aquatic organisms. Generally, AgNPs seems to have toxic effects on aquatic organisms regardless of the method used for their production, and so, their accidental or intentional entrance into the aquatic ecosystems should be inhibited.
