ISO 14593:1999

Overview

ISO 14593:1999 defines a laboratory method to evaluate the ultimate aerobic biodegradability of organic compounds in aqueous media by measuring biogenically produced inorganic carbon (CO2) in sealed vessels - commonly called the CO2 headspace test. The method quantifies mineralization to carbon dioxide (TIC/DIC) over time and expresses biodegradation as a percentage of the theoretical inorganic carbon (ThIC) derived from the compound’s formula. Typical tests run for about 28 days under controlled conditions.

Key topics and technical requirements

• Scope of applicability: suitable for organic substances that are water‑soluble, poorly water‑soluble (with dispersion measures per ISO 10634), volatile (with headspace management), and non‑inhibitory to the inoculum at test concentration.
• Measured endpoint: net increase in total inorganic carbon (TIC) in situ in sealed, gas‑tight vessels, giving a near‑real‑time measure of microbial CO2 production.
• Test conditions:
  • Incubation in the dark or diffused light at 20–25 °C (±2 °C).
  • Test concentration typically yields 2–40 mg/L TOC in medium (preferably 20 mg/L).
  • Standard test duration: ~28 days.
• Inoculum: mixed microbial population (commonly activated sludge); recommended suspended solids ~4 mg/L in final mixture (higher levels may increase blank CO2).
• Apparatus & reagents: carbon analyzer or TOC instrument with inorganic carbon capability, gas‑tight serum bottles (e.g., 160 mL), syringes, CO2‑free air supply (or 80% N2/20% O2), filtration (0.20–0.45 µm), and standard mineral medium.
• Data expression & validity: results reported as % of ThIC; include blanks, reference substances, and checks for inhibition. Test precision, lag phase, biodegradation and plateau phases are defined.

Practical applications

• Screening and regulatory evaluation of chemical biodegradability for environmental risk assessments.
• Product formulation and green chemistry R&D to compare mineralization potential of candidate molecules.
• Supporting environmental fate studies where mineralization (complete breakdown to CO2) is a critical endpoint.
• Assessing volatile or poorly soluble substances with appropriate headspace or dispersion measures.

Who should use this standard

• Environmental chemists, water quality laboratories, ecotoxicologists, regulatory agencies, and industrial R&D teams involved in biodegradability testing, environmental compliance, or product stewardship.

Related standards

• ISO 10634:1995 - preparation of poorly water‑soluble compounds for biodegradability testing
• ISO 15462 - alternative biodegradation methods
• ISO 8192 - methods for determining inhibitory effects on bacteria
• ISO 7827, ISO 9887/9888 - related biodegradation and DOC/toxicity procedures

Keywords: ISO 14593, CO2 headspace test, inorganic carbon analysis, ultimate aerobic biodegradability, water quality, TIC, ThIC, activated sludge.