A comparative evaluation of acute toxicity of synthesized nano-silvers using two different procedures (biological and chemical reduction methods) and effect of silver ions on the bacteria Vibrio fischeri were investigated. The bacterial light inhibition test as a toxicological endpoint was used by applying of a homemade luminometer. To compare the toxicity effects as a quantitative parameter, after 5 min and 30 min exposure times, nominal effective concentration (EC) of chemicals and susceptibility constant (Z-value) were calculated. After 5 and 30 min contact times, the EC50 values of two silver nanoparticles and the EC20 values were about similar. The EC values of nanoparticles were larger than those of the silver ions. The susceptibilities of V. fischeri (L/mg) to the silver ions were greater than those of the nano silvers. According to the EC and Z values, the toxicity of silvers decreased in the following order: silver ions >> silver nanoparticles from chemical reduction method ~ silver nanoparticles from biological method.
