ISO 16221:2001

Overview

ISO 16221:2001 - Water quality - Guidance for determination of biodegradability in the marine environment - provides standardized guidance for measuring the ultimate aerobic biodegradability of organic compounds in marine conditions. The International Standard adapts established freshwater biodegradation methods to static aqueous marine test systems, specifying how to prepare test mixtures with natural or artificial seawater, marine inocula and test compounds, and how to monitor biodegradation by summary endpoints (DOC, BOD, CO2, TIC).

Key topics and technical requirements

• Scope and applicability
  • Applies to organic compounds that are water‑soluble, poorly water‑soluble (with dispersion measures), volatile (with suitable conditions), and non‑inhibitory at chosen test concentrations.
  • Notes that these test conditions may not always deliver the maximum possible biodegradation, and alternative freshwater or low‑concentration methods may be needed for specific purposes.
• Five standardized methods (adapted from freshwater tests)
  • DOC die‑away test (ISO 7827) - measures removal of dissolved organic carbon.
  • Closed bottle test (ISO 10707) - measures biochemical oxygen demand (BOD).
  • Two‑phase closed bottle test (ISO 10708) - for poorly soluble substances.
  • CO2 evolution test (ISO 9439) - measures evolved carbon dioxide.
  • CO2 headspace test (ISO 14593) - measures total inorganic carbon (TIC) in sealed vessels.
• Test environment and controls
  • Incubation in the dark or diffused light at the specified test temperature (commonly 15–25 °C with minimal variation).
  • Use of natural or artificial seawater, appropriate inocula, reference compounds and blanks to assess validity and inhibitory effects.
• Endpoints and calculations
  • Express biodegradation as percent mineralization or relative to theoretical values (ThOD, ThCO2, ThIC) or measured summary parameters (DOC, BOD, CO2).
  • Guidance on validity criteria, reporting and interpretation is included.

Applications and users

ISO 16221 is intended for:

• Environmental testing laboratories conducting marine biodegradability testing
• Chemical and petrochemical manufacturers assessing marine fate of products (off‑shore use, spill scenarios)
• Regulatory agencies and consultants performing environmental risk assessment
• Research groups studying biodegradation processes in coastal and open seawater environments

Typical uses:

• Pre‑market screening for environmental compliance
• Product development and substitution decisions
• Marine ecotoxicology and persistence studies
• Supporting regulatory dossiers and environmental monitoring

Related standards

• ISO 7827 (DOC die‑away)
• ISO 9439 (CO2 evolution)
• ISO 10707 (closed bottle BOD)
• ISO 10708 (two‑phase closed bottle)
• ISO 14593 (CO2 headspace)
• ISO 14592 / ISO 15462 (related freshwater or low‑concentration biodegradation methods)

Keywords: ISO 16221, marine biodegradability testing, dissolved organic carbon (DOC), CO2 evolution, biochemical oxygen demand (BOD), seawater biodegradation, aerobic microorganisms, environmental fate.