ISO 10634:2018

Overview

ISO 10634:2018 - "Water quality - Preparation and treatment of poorly water‑soluble organic compounds..." specifies standard techniques for introducing and maintaining poorly water‑soluble organic compounds (solubility ≲ 100 mg/L) in aqueous test vessels prior to biodegradability testing. The document addresses sample preparation and dispersion methods only; it does not define biodegradation test procedures themselves. It is intended to ensure reproducible sample introduction and improved comparability of biodegradability results across laboratories.

Key topics and technical requirements

• Scope: Applies to liquid and solid organic compounds with low water solubility. Techniques must be used while observing the experimental conditions of the standardized biodegradability methods.
• Preparation techniques covered:
  • Direct addition (recommended where feasible)
  • Ultrasonic dispersion (probe or bath) for non‑volatile liquids and solids
  • Adsorption/weighing onto inert support and subsequent transfer
  • Dispersion or solubilization using additives (e.g., non‑biodegradable solvents, emulsifying agents, mineral or silicone oils)
  • Combination of methods and parallel testing to assess method effects on bioavailability
• Analytical compatibility: The prepared test systems are intended for biodegradability tests based on CO2 evolution (ISO 9439) or oxygen demand (ISO 9408 / ISO 10707 closed respirometer). Methods measuring removal of dissolved organic carbon (DOC) are indicated as not appropriate for these preparations.
• Limitations and regulatory note: Some preparation methods (e.g., use of solvents or certain dispersants) may not be accepted by regulators when concluding on “ready biodegradability.” ISO 9439 is not suitable for volatile test compounds.
• Supporting elements: Preliminary tests to select emulsifier/mineral/silicone oil concentrations, guidance on apparatus and reagents, and examples of biodegradability curves (Annex A).

Applications and users

• Environmental testing laboratories performing biodegradability assessments
• Chemical manufacturers and formulators preparing data for regulatory dossiers
• Contract testing organizations and consultants advising on bioavailability and test design
• Regulators and risk assessors interpreting biodegradation data where low aqueous solubility complicates testing

Practical benefits include improved reproducibility of test introductions, structured selection of dispersion methods, and guidance to reduce artefacts from solvents or emulsifiers that can bias biodegradability outcomes.

Related standards

• ISO 9439 - Carbon dioxide evolution biodegradability test
• ISO 9408 - Ultimate aerobic biodegradability by oxygen demand
• ISO 10707 - Closed bottle biochemical oxygen demand method

Note: ISO 10634:2018 complements these standards by describing how to prepare poorly soluble compounds for subsequent, compliant biodegradability testing.