Interspecies Mechanisms Study Of Toxic Action For Organic Pollutants Using Structure Classification Method

Interspecies correlation and comparing interspecies difference of toxicity and is a valuable method used to estimate toxicological data. It not only allows the prediction of toxicity to a number of other species but it is also helpful in the interpretation of mechanisms. Although some authors realized the differences between toxicities to different aquatic organisms and tried to develop interspecies correlations for these species, little attention has been paid to the theoretical considerations of toxic mechanism of action between species. Comparing interspecies difference of toxicity using structural classification method not only allows the discrimination of excess toxicity from narcotic, but it is also helpful in the interpretation of mechanisms. This paper based on a large number of industrial organic pollutants, through the study of the interspecies correlations of toxicity between eight species of aquatic organisms and comparing the toxic mechanism of action between two species, concluded main conclusions as followed:First, this study examines the interspecies correlations of toxicity between species of Vibrio fischeri, river bacteria, algae, Daphnia magna, carp, Tetrahymena pyriformis, fathead minnow and guppy. The results show that there are good interspecies correlations between marine bacterium and fresh water bacteria or fish and fish. It is suggested that compounds share the same bio-uptake and toxic mechanism of action between the species. On the other hand, poor interspecies relationships were found between toxicities to algae and T. pyriformis or D. magna. It is suggested that compounds have different toxic mechanisms of action between these species. Interspecies relationships can be improved by inclusion of the octanol/water partition coefficient or the energy of the lowest unoccupied molecular orbital. Benzoic acids show very different toxicity contributions to the three species, V. fischeri, D. magna and carp. They can be easily absorbed into the unicellular bacteria, V. fischeri. On the contrary, the skin and lipid content of multicellular organisms, such as D. magna and fish, can strongly inhibit the bio-uptake for ionisable compounds, which results in the different toxic effect between V. fischeri and D. magna or carp. Good correlation coefficients were observed between toxicities to V. fischeri and D. magna or fishes by inclusion of hydrophobic and ionization parameters.Second, the toxicity data of758chemicals to Daphnia magna and993chemicals to Tetrahymena pyriformis were used to discriminate the excess toxicity from narcotic effect levels of organic compounds and examine the similarity and difference of toxicity to different species. The result showed that mode of toxic action of chemicals is species dependent. The results showed that some classes (e.g. alkanes, alcohols, ethers, aldehydes, esters and benzenes) shared same modes of toxic action to both D. magna and T. pyriformis. However, some classes may share different modes of toxic action to T. pyriformis and D. magna (e.g. anilines and their derivatives). On this basis, We carried out linear regression analysis between log KOW and the toxicity for baseline or polor narcosis chemicals to D. magna and T. pyriformis, respectively. The toxic ratio (TR) calculated from baseline model over the experimentally determined values were used to measured the excess toxicity of different chemicals. For the interspecies comparison, same reference threshold need to be used between species toxicity. The excess toxicity indicates that toxicity enhancement is driven by reactive or specific toxicity. However, not all the reactive compounds exhibit excess toxicity. In theory, the TR threshold should not be related with the experimental uncertainty. The experimental uncertainty only brings the difficulty for discriminating the toxic category of chemicals. The real threshold of excess toxicity which is used to identify baseline from reactive chemicals should be based on the critical concentration difference inside body, rather than critical concentration outside body (i.e. EC50or IGC50). The experimental bioconcentration factors can be greatly different from predicted bioconcentration factors, resulting in different toxic ratios and leading to mis-classification of toxic category and outliers.Third, the24h acute immobilization toxicity of substituted phenols, anilines and benzoic acids was determined for the freshwater crustacean Daphnia magna under the condition of pH equal6,7.8and9. The fraction of neutral form (FO)was calculated for substituted phenols, anilines and benzoic acids at three different pH conditions. The toxicity and FO were higher for phenols and benzoic acids at lower pH values but they were higher for anilines at higher pH values. The toxicity data suggested that the effect of pH was most pronounced when pH-pKa was in the range of1to3for acids, and-3to1for bases. It is a important influencing factor of ionization for the toxicity of phenols. Inclusion of log FO with log KOW can improve the determinate coefficient of the phenols models. Ionization degree is very low for anilines at all three pH condition and neutral form is accounts for absolute advantage, so the effect of ionization to anilines is smaller than phenols. The correlation of the toxicity for benzoic acids and hydrophobicity parameter is very poor, and inclusion of EHOMO and the number of hydroxyl (NOH) with log KOW can improve the determinate coefficient of the models.