Abstract
In the short-term bioassay using Porphyra yezoensis conchospores, it is basically important to clarify the most appropriate exposure period and end point to evaluate the effects of toxicants on the growth of Porphyra yezoensis conchospores. In this study, short-term bioassays (120 hours) were conducted on copper (Cu) and monochloramine (NH2Cl), which have different chemical characteristics. Three kinds of end points (survival ratio, germination ratio and growth ratio) at exposure periods every 24 hours were compared to define the most appropriate exposure period and end point.
The minimum LOECs (lowest-observed-effect concentration) for Cu occurred at exposure period of 96 hours in the three kinds of end points. The 96-h LOECs from the survival ratio, the germination ratio and the growth ratio were 0.046 ± 0.026mg Cu·l-1 (n=5), 0.033 ± 0.027mg Cu·l-1 (n=5), 0.021 ± 0.019mg Cu·l-1 (n=5), respectively. The minimum LOECs for NH2Cl occurred at exposure period of 96 hours in the survival ratio and the growth ratio of 0.093 ± 0.026mg Cl2·l-1 (n=5) and 0.038 ± 0.016mg Cl2·l-1 (n=5), respectively. The minimum LOEC (0.036 ± 0.000mg Cl2·l-1, n=5) for NH2Cl from the germination ratio occurred at the exposure period of 48 hours.
Therefore, taking into account of the simplicity of bioassay and its sensitivity to toxicants, it is concluded that the most appropriate exposure period and end point is 96 hours for Cu and 48 hours for NH2Cl judging from the end point of the germination ratio.
