RESPONSES OF GAMMARUS PU LEX (L.) TO MODIFIED ENVIRONMENT I. REACTIONS TO TOXIC SOLUTIONS

Heavy metal salts constitute a very serious type of pollution in freshwater oecause they being stable compounds are not readily removed by oxidation, pre cipitation or other processes. Jones (1937) using Polycelis nigra Ehrb. and Gam mar us pul ex (L.) investigated the toxicity of several metallic salts. He showed that the toxic effect at concentrations below isotonicity is due almost entirely to the cation, the toxicity of the anion being relatively small. At concentrations above isotonicity the anion and the osmotic pressure of the solution act as addi tional factors. Davies (1941) investigated the toxicity of zinc sulphate solutions to various aquatic animals and showed that the degree of toxicity varies consider ably among them, the lethal limit of concentration for Gammarus pulex being 0.8 mg/1. Most of the previous studies on the reaction behaviour of aquatic animals to dissolved toxic substances have been confined to fish (Shelford & Allee, 1913;