Despite the increasing use of nanomaterials, the possibility of their toxicity in human and other living organisms is one of the challenges of the future. Various chemicals which are used for the production of nanomaterials in chemical methods, itself may cause secondary toxic effects on organisms; conversely, lack of using those chemical in physical production methods, may possibly reduce mentioned secondary effects. To test this hypothesis, in the present study acute toxicity effects of two types of colloid silver nanoparticle (AgNPs) produced by top-down (physical) and bottom-up (chemical) methods were compared on the survival of zebrafish. In support of this hypothesis, the results showed that AgNPs produced by physical method are at least 38 times less toxic than AgNPs produced by chemical methods. 96-h LC50 values of AgNPs produced by chemical and physical methods for zebrafish were estimated to be equal to 0.014±0.001 and 0.540±0.032 mg.l-1 respectively; based on these values both studied AgNPs should be classified according to the rules adopted by the Europe Union, as highly toxic chemicals for aquatic organisms. In general it seems that silver nanoparticles, regardless of their production method, have toxic effects on aquatic organisms and so more attention appear to be necessary on the prevention of their accidental or intentional entry to the aquatic ecosystems.
