Effects of water hardness and metal concentration on a freshwater Tubifex tubifex muller

Abstract

The present investigation was designed to determine the effects of water hardness and heavy metals concentrations on a freshwater Tubifex tubifex. Very few data concerning the effect of water hardness on the acute toxicity of heavy metals are available on T. tubifex, which has been proposed as a test organism for ecotoxicological studies. The effect of water hardness on the toxicity of heavy metals is discussed. The acute toxicity of selected heavy metals to a freshwater T. tubifex Muller was determined in very soft, soft, hard and very hard (12, 45, 170 and 300 mg CaCO3L-1 total hardness, respectively) water. Percentage mortality of T. tubifex as influenced by heavy metals was studied in water of variable hardness. Water hardness had a significant effect on heavy metals toxicity. The concentrations of metals necessary to immobilize 50% of the test animals at 24, 48, 72, 96 hr were significantly different in soft and hard water. The 96 hr EC50 values for T. tubifex were higher in hard and very hard water compared with soft and very soft water. Median effective concentrations (EC50) and their 95% confidence limits were determined for cadmium, cobalt, chromium, copper, iron, lead, manganese, mercury, nickel, and zinc during exposure for 24, 48, 72 and 96 hr in four different water hardness. Hardness has a much smaller effect upon the acute toxicity of mercury than the other heavy metals tested. The results indicate that Cu, Cd, Hg and Zn induced autotomy of the caudal region and mucus production. It is concluded that water hardness parameters should be considered in establishing appropriate water quality criteria and standards for the protection of aquatic fauna and flora, and ultimately human health.