Abstract
Investigations on the relationship of toxicities between species play an important role in the understanding of toxic mechanisms to environmental organisms. In this paper, the toxicity data of 949 chemicals to fish and 1470 chemicals to V. fischeri were used to investigate the modes of action (MOAs) between species. The results show that although there is a positive interspecies correlation, the relationship is poor. Analysis on the excess toxicity calculated from toxic ratios (TR) shows that many chemicals have close toxicities and share the same MOAs between the two species. Linear relationships between the toxicities and octanol/water partition coefficient (log KOW) for baseline and less inert compounds indicate that the internal critical concentrations (CBRs) approach a constant both to fish and V. fischeri for neutral hydrophobic compounds. These compounds share the same toxic mechanisms and bio-uptake processes between species. On the other hand, some hydrophilic compounds exhibit different toxic effects with greatly different log TR values between V. fischeri and fish species. These hydrophilic compounds were identified as reactive MOAs to V. fischeri, but not to fish. The interspecies correlation is improved by adding a hydrophobic descriptor into the correlation equation. This indicates that the differences in the toxic ratios between fish and V. fischeri for these hydrophilic compounds can be partly attributed to the differences of bioconcentration between the two species, rather than the differences of reactivity with the target macromolecules. These hydrophilic compounds may more easily pass through the cell membrane of V. fischeri than the gill and skin of fish, react with the target macromolecules and exhibit excess toxicity. The compounds with log KOW > 7 exhibiting very low toxicity (log TR < –1) to both species indicate that the bioconcentration potential of a chemical plays a very important role in the identification of excess toxicity and MOAs.
Highlights
Information regarding aquatic toxicity is required in the assessment of the toxicity of organic chemicals to marine and freshwater organisms
Inspection of the characteristics of compounds suggests that fish are more sensitive to hydrophobic compounds and V. fischeri are more sensitive to hydrophilic compounds in toxicity
The linear relationships of the toxicities against log KOW with similar slopes and intercepts indicate that the CBRs are close to a constant both to fish and V. fischeri (i.e. CBRF % CBRVF) for neutral hydrophobic baseline compounds
Summary
Information regarding aquatic toxicity is required in the assessment of the toxicity of organic chemicals to marine and freshwater organisms. Discrimination of excess toxicity from narcotic level plays an important role in the study of modes of action (MOAs) for organic chemicals. The narcotic chemicals (baseline and less inert chemicals) have toxic effects through the disruption of the proper function of the cell membrane and can be quantified by using the hydrophobic parameter log KOW (octanol/water partition coefficient). Reactive chemicals exhibit significantly greater toxicity than that predicted from hydrophobicity alone due to the existence of a more specific interaction with organisms. For the identification of reactive compounds, the toxic ratio (TR) was employed to discriminate the excess toxicity from narcotic effect. The threshold of log TR = 1 which is based on the distribution of fish toxicity data is generally used to discriminate the excess toxicity from narcotic effect
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