EXPERIMENTAL TOXICITY OF CHROMIUM TO TWO FRESHWATER CRUSTACEANS; DAPHNIA MAGNA AND MACRQBRACHIUM ROSENBERGII

Abstract

The analysis of the potential toxicity of chromium, was conducted on two aquatic model systems, namely the cladoceran Daphnia magna and the decapod Macrobrachium rosenbergii. Chromium was chosen since human activity has led to a conspicuous increase of this metal in the environment. The toxicity of chromium to Daphnia magna was evaluated on the basis of a 48-hr 50% lethal concentration (LC50)3 a 3-week LC50 and a 16% decrease in the number of bom young (reproductive impairment). The daphnids were exposed for concentrations ranging from 2 to 30 ig Cr/L from which 48 hr- LC50 was calculated both in absence and presence of EDTA, a chelating agent to be 8 and 27 |ig Cr /L, respectively. In the static- renewal systems, daphnids were exposed to sublethal doses (13, 16, 18,22 and 23 jag Cr/L) equivalent to LC10, LC20, LC25, LC35 and LC40, respectively, as deduced from the regression line for chromium toxicity for 48 hr. in the static system in presence of EDTA. The 3-week 16% reproductive impairment concentration for the metal ions was 17fig- Cr/L. At metal concentrations permitting survival but impairing reproduction (sublethal concentration), daphnids body length and weight were less than those of control animals. The concentration causing 50 % reproductive impairment was more or less the same as the 48-hr LC50 (in presence of EDTA), being 26 and 27 M-g Cr/L respectively. The 21-day LC50 was 16. 5 ngCr/L. The time of onset of reproduction ranged from 6 days in the control to 14 days in the highest concentration. The acute toxicity of chromium to the freshwater prawn Macrobrachium rosenbergii revealed that the 48-hr LC50 was 425 jigCr/L. Prawn juveniles were exposed in static-renewal systems for 45 days, to sublethal doses (210, 300, 325 and 375 ngCr/L) equivalent to LC10, LC25, LC30 and LC40 respectively, as deduced from the regression line for chromium toxicity for 48 hr in the static system. The results showed that juvenile prawn of initial weight 0.255±0.097 g, in higher concentration (375 i g Cr / L), had given a significant decrease (PO.05) from the control in final mean weight, weight gain, % weight gain, specific growth rate and survival, represented by 0.270 g, 0.015 g, 1.928, 0.127 and 33.3 % , respectively. Also prawn in different concentrations of chromium recorded the highest food conversion ratio represented by 3.76,6.39, 8.1 and 8.7, respectively, Amounts of total protein and lipids of both daphnids and prawns varied with the different concentrations. This study indicated that Daphnia magna was more sensitive to chromium than Macrobrachium rosenbergii and that bioassays with these two organisms are useful to assess the toxic potential of aquatic pollutants,