Discrimination Of Excess Toxicity From Narcotic Effect:Influence Of Species Sensitivity On The Classification Of Modes Of Action

The toxicity data of2624chemicals to fish, D. magna, T. pyriformis and V. fischeri were used to investigate the excess toxicity. The results showed that47chemical classes were identified as same modes of action (MOAs) to all four species, but more than half of classes were identified as different MOAs. Difference in chemical MOAs is one of the reasons resulting in the difference in toxic effect to these four species. Other important reasons are the difference in sensitivity and bioconcentration of species. The most compounds identified as reactive MO A in four species are to V. fischeri. Some compounds can be easily absorbed into the bacteria, react with the DNA or proteins, disrupt the normal function of the cell and exhibit significantly great toxicity to the bacteria. On the other hand, the skin and lipid content of aqueous organisms can strongly inhibit the bio-uptake for some reactive compounds, resulting in less toxic effect than expected. D. magna is the most sensitive species and T. pyriformis is the least sensitive species in the four species. For the comparison of interspecies toxicity, we need to use same reference threshold of excess toxicity. However, some reactive compounds may be identified as baseline or less inert compounds for low sensitive species from the threshold developed from high sensitive species. The difference in the discrimination of excess toxicity to different species is not only because of the difference in MOAs for some compounds, but also due to the difference in sensitivity and bioconcentration.