Toxic Ratio as an Indicator of the Intrinsic Toxicity in the Assessment of Persistent, Bioaccumulative, and Toxic Chemicals

• Published in: Environmental science & technology 2004-07, Vol.38 (13), p.3659-3666
• Main Authors: Maeder, Valérie, Escher, Beate I, Scheringer, Martin, Hungerbühler, Konrad
• Format: Article
• Language: English
• Subjects: Animal, plant and microbial ecology; Animals; Applied ecology; Biological and medical sciences; Chemical contaminants; Cyprinidae - metabolism; Drug-Related Side Effects and Adverse Reactions; Ecotoxicology, biological effects of pollution; Fundamental and applied biological sciences. Psychology; Hazardous Substances - classification; Hazardous Substances - pharmacokinetics; Hazardous Substances - toxicity; Lethal Dose 50; Organic chemicals; Quantitative Structure-Activity Relationship; Ratios; Reference Standards; Techniques; Tissue Distribution; Toxicity; Water Pollutants, Chemical - classification; Water Pollutants, Chemical - pharmacokinetics; Water Pollutants, Chemical - toxicity
• ISSN: 0013-936X; 1520-5851
• DOI: 10.1021/es0351591

Persistence, bioconcentration, and toxicity (PBT) are important hazardous properties of organic chemicals. In PBT assessments, it is desirable that the three criteria P, B, and T are independent. However, this requirement is not fulfilled if an aqueous lethal concentration (LC50) is used as T indicator because LC50 includes both bioconcentration and intrinsic toxicity. Indicators for intrinsic toxicity such as the internal lethal concentration (ILC) are independent of a chemical's bioconcentration potential. However, ILC50 data are scarce and difficult to measure. Therefore, the toxic ratio (TR) is proposed here as an alternative. TR is defined as the ratio of a chemical's LC50 estimated from a QSAR for baseline toxicity and the experimental LC50 value. TR can also be interpreted as a measure of the ILC relative to the ILC for baseline toxicity. A TR of 10 separates specifically toxic chemicals from baseline toxicants. With some 800 chemicals, the practicability of classifying chemicals in terms of TR is demonstrated. Employing TR as toxicity indicator leads to different T scores for 30% of the chemicals studied. The baseline toxicity of hydrophobic compounds with TR < 10 does not receive a high T score but is still indicated by a high B score. The toxicity of specifically toxic hydrophilic substances is given additional emphasis by high TR values. These classification changes require that the interpretation of the B and T dimensions in PBT assessments is redefined.