Quantitative structure-toxicity relationships and volume fraction analyses for selected esters

Area of Science:

• Environmental Toxicology
• Ecotoxicology
• Quantitative Structure-Activity Relationships (QSAR)

Background:

• Esters are common environmental contaminants with varying toxicity.
• Understanding ester toxicity mechanisms is crucial for ecological risk assessment.
• Comparative toxicity studies in different organisms highlight species-specific responses.

Purpose of the Study:

• To compare the acute toxicity of aliphatic and aromatic mono- and diesters in two eukaryotic organisms.
• To elucidate the toxicological mechanisms of esters in Tetrahymena pyriformis (ciliates) and Pimephales promelas (fish).
• To develop and validate quantitative structure-activity relationships (QSARs) for ester toxicity.

Main Methods:

• Utilized two standard ecotoxicity assays: Tetrahymena pyriformis population growth impairment (IGC50) and Pimephales promelas mortality (LC50).
• Employed static 2-day and flow-through 4-day test systems, respectively.
• Analyzed toxicity data using quantitative structure-activity relationships (QSARs) based on 1-octanol/water partition coefficient (log Kow) and volume fraction (Vf).

Main Results:

• In Tetrahymena, esters exhibited toxicity consistent with nonpolar narcosis, with toxicity correlating strongly with log Kow.
• In Pimephales, in vivo hydrolysis significantly increased ester toxicity beyond nonpolar narcosis predictions, leading to a unique QSAR.
• Hydrolysis in fish created a non-reducing concentration gradient, enhancing toxicant uptake compared to thermodynamic equilibrium.

Conclusions:

• Ester toxicity mechanisms differ between ciliates and fish, primarily due to the role of in vivo hydrolysis in fish.
• QSAR models effectively describe ester toxicity, but species-specific metabolic processes like hydrolysis must be considered.
• Findings emphasize the importance of considering metabolic activation and uptake dynamics in environmental risk assessment of esters.