The toxicity of copper to certain nymphs of the Ephemeroptera

Abstract

The toxic effects of copper to three species of British Mayfly nymphs were studied. Those species were, Beatin rhodani, Ecdyonurus venosus and Rithrogena semicolorata. The study was divided into the following sections : 1. Toxicity tests. These were carried out so that a basic profile of copper toxicity in respect to concentration could be arrived at for each species. Tests were also carried out to determine the effects of complicating factors such as temperature, pH and water hardness on the basic profiles of toxicity. Threshold of toxicity concentrations were also determined using the toxicity test technique. It was found that B.rhordani is the most susceptible of the three species to copper, with R. semicolorata being the most tolerant. In all cases the extent of toxic effect bore a simple, direct relationship to the concentration of copper used. This toxic effect was made more acute by higher temperatures and low pH values, but was less acute in harder waters. In this part of the study the results were expressed as Tlm survival curves and probit analyses. A series of toxicity tests was also carried out to determine the effect of short exposure times to copper and it was found that complete recovery only occurred or is only possible in the case of low (less than 20mg/L copper sulphate) concentrations and exposures of less than six hours. 2. Serial sections of nymphs exposed to copper solutions were treated with Rubeanic acid which is a copper specific histological stain. This procedure identified areas of copper accumulation within the bodies of the nymphs. The distribution of copper was found to be as follows: a. Within the lumen and cells of the mid-gut. b. In parts of the central nervous system c. In other organs including the Malpighian tubles and the gill filaments.

3. The effect of copper on the rate of respiration as measured by oxygen consumption was studied using a sensitive micromanometer. It was found that in the case of E.venosus there was very little effect but that in the case of the other two species copper repressed the rate of oxygen consumption. These results related to the ecology of the respective species. 4. The rate of uptake of copper by the three species was measured using the radioactive isotope of copper, Cu64. Generally it was found that uptake is rapid up to sixteen hours. The fastest rate was for B.rhodani. An attempt was made to correlate these results with findings from earlier experiments in the study and some relationship was found to exist between the rate at which copper is taken up and the survival curves established by the toxicity tests in the first part of the study.