ASTM E1242-23 PDF

Overview

ASTM E1242-23: Standard Practice for Using Octanol-Water Partition Coefficient to Estimate Median Lethal Concentrations for Fish Due to Narcosis provides a standardized procedure for estimating the 96-hour median lethal concentration (LC50) of organic chemicals, specifically for the fathead minnow (Pimephales promelas). This practice applies to non-reactive and non-electrolytic organic chemicals that act through narcosis, as described by the Meyer-Overton toxicity relationship.

The method leverages the octanol-water partition coefficient (Kow), a widely used metric in environmental chemistry for assessing the hydrophobicity of chemicals, to estimate toxicity. This approach helps minimize the need for preliminary screening tests, conserving both time and biological resources in aquatic toxicology studies.

Key Topics

• Scope of Application:

  • Relevant for organic chemicals that are non-reactive, non-electrolytic, and whose primary toxicity mechanism is narcosis.
  • Examples of applicable chemicals include alcohols, ketones, ethers, simple halogenated aliphatics, aromatics, and aliphatic-substituted aromatics.
  • Excludes chemicals with toxiphores-structural components known for specific mammalian toxicity (e.g., cyanides, nitro groups, carbamates, organophosphates).

• Methodology:

  • Utilizes the octanol-water partition coefficient (Kow) to estimate a maximum 96-h LC50 value.
  • The estimation acts as a preliminary toxicity value before undertaking full-scale aquatic toxicity tests.

• Significance and Use:

  • Reduces the need for screening tests, thus limiting the number of fish required.
  • Saves time in aquatic toxicity assessments.
  • Assists in prioritizing the testing of chemical groups and can indicate if a chemical likely acts via the narcosis mechanism.

• Interpretation of Results:

  • If the estimated LC50 significantly exceeds measured LC50 values (by more than 0.3 times), narcosis is likely the main mode of action.
  • Lower experimental values than predicted may indicate alternative toxicity pathways or artifacts such as low solubility.

Applications

• Aquatic Toxicology:

  • Efficiently estimate acute toxicity of organic chemicals to fish, particularly fathead minnows, using physicochemical data rather than resource-intensive bioassays.
  • Provides a screening tool for environmental risk assessment by regulatory agencies, environmental consultants, and research laboratories.

• Chemical Prioritization:

  • Supports prioritizing substances for further detailed investigation by offering preliminary toxicity assessments.
  • Helps identify chemicals that may pose higher ecological risks due to narcosis-based toxicity.

• Environmental Risk Management:

  • Assists in early-stage hazard assessments and environmental impact studies.
  • Facilitates compliance with environmental safety regulations and standards in chemical manufacturing and use.

Related Standards

• ASTM E729: Guide for Conducting Acute Toxicity Tests on Test Materials with Fishes, Macroinvertebrates, and Amphibians
• ASTM E943: Terminology Relating to Biological Effects and Environmental Fate (withdrawn 2023)
• ASTM E1023: Guide for Assessing the Hazard of a Material to Aquatic Organisms and Their Uses
• ASTM E1147: Test Method for Partition Coefficient (N-Octanol/Water) Estimation by Liquid Chromatography (withdrawn 2013)

Practical Value

Utilizing the guidelines in ASTM E1242-23 streamlines aquatic toxicity testing for certain organic chemicals, enhancing efficiency in laboratory studies and supporting informed decision-making in environmental assessment and chemical management. Using Kow as a predictive tool simplifies the process of estimating fish toxicity, providing cost-effective and ethical alternatives to traditional bioassays. This standard is essential for professionals in environmental toxicology, regulatory compliance, and risk management seeking reliable and internationally recognized practices.