Abstract:
Effect of temperatures and heavy metals, namely copper, cadmium and lead on embryonic development and adult oysters (Crassostrea commercialis Iredale and Roughley) was investigated. Firstly, effect of temperatures and heavy metals on embryonic development of oysters from fertilized eggs to D-shaped stage were determined. On the effect of temperatures alone on the embryonic development of oysters, it was found that the period of development was shorten at higher temperature. At ambient temperature of 28 oC the period of development from fertilized eggs to D-shaped stage was 18 hours. At low temperature of 23.5 oC and at high temperature of 32.5 oC, the period of development were 23 and 12 hours respectively. It was found that the 48-h. EC50 values for copper at temperatures 23.5, 28.0 and 32.5 oC were 0.0049, 0.0094 and 0.0030 ppm. respectively. The 48-h. EC50 values for cadmium at the same temperatures were recorded at 0.2049, 0.5542 and 0.1847 ppm. respectively. This experiment showed that copper was more toxic to oyster embryos than cadmium. The toxicity of these metals was higher at the higher and lower temperatures comparing to the ambient temperature. Safety concentrations of copper and cadmium for embryonic development of oysters were 0.0002 and 0.0139 ppm. respectively. Secondly, the 96-h. LC50 of copper and cadmium for adult oysters at ambient temperature were reported 2.44 and 2.21 ppm. While the 96-h. LC50 values for copper at 23.5 and 32.5 oC were 10.64 and 1.45 ppm. respectively. For cadmium, the 96-h. LC50 values at the sametemperatures were 8.62 and 1.32 ppm. In conclusion, cadmium was more toxic to adult oysters than copper. The toxicity of these metals was higher at high temperature and lower at low temperature. Safety concentration of copper and cadmium for adult oysters were 0.1220 and 0.1105 ppm. respectively. The result on the effect of temperatures and lead on embryonic development of oysters showed that the 48-h. EC50 values for lead at temperatures 23.5, 28.0 and 32.5 oC were 0.3287, 1.1059 and 0.1569 ppm. Safety concentrations of lead for embryonic development of oysters was 0.0276 ppm. It should be noted that the actual lead concentration in the 1.0 ppm. dilution was lower than expected when detected after the experiment. The effect of temperatures and lead on adult oysters in this experiment can not be concluded due to the fact that lead precipilated in high concentration dilutions starting from 7 ppm. dilution. Thus the actual lead concentrations would be lower than expected. The oyster embryos were more sensitive to the toxicity of heavy metals than adult oysters. Thus, in order to set the criteria on water quality concerning heavy metal pollution, the effects of heavy metals on both the embryonic and adult stages of aquatic organisms should be considered.