Effect of water hardness on the toxicity of a nonionic detergent to fish

Fish (trout and goldfish) were placed in treatment solutions of different water hardnesses containing ethoxylate (EO) detergents. Survival times were recorded, ¹⁴C-labelled EO was used to assess absorption. The toxicity of ethoxylates to fish acclimatised and treated in different water hardnesses, and the effect of cations on ethoxylate toxicity were also investigated, EO is slightly less toxic in hard water than in soft water. The hardness of the treatment solution has no marked influence on the amount of EO absorbed by the fish. Evidence suggests that there is little relationship between the composition of cations constituting a particular hardness and the toxicity of EO. Acclimatisation in different water hardnesses does not affect the susceptibility of fish to nonionic ethoxylate detergents.