ISO 19679:2020

Overview

ISO 19679:2020 specifies a laboratory test method for measuring the aerobic biodegradation of non‑floating plastic materials located at the interface between seawater and sandy marine sediment. The method quantifies biodegradation by analysing the amount of evolved carbon dioxide (CO2) and comparing it to the theoretical CO2 yield (ThCO2) calculated from the material’s total organic carbon (TOC). This is a simulation of benthic/sub‑littoral conditions (photic zone) where an item has sunk and settled on the seafloor surface. The standard does not cover plastics buried deeper in sediment.

Key topics and technical requirements

• Test principle: Closed‑vessel respirometric measurement of CO2 evolved during aerobic microbial degradation; results expressed as percent biodegradation against ThCO2.
• Test environment: Incubation in dark or diffuse light at a controlled temperature (preferably 15–25 °C, not exceeding 28 °C, ±2 °C). Systems must be free from vapours inhibitory to microorganisms.
• Materials and reagents: Use of natural or artificial seawater (example artificial recipe included in the standard) and sandy marine sediment; distilled/deionized water with DOC < 2 mg/L.
• Sample form and loading: Test specimens are typically films/disks laid on the sediment/water interface. Minimum test material concentration: 100 mg/L of seawater-plus-sediment (recommended 150–300 mg/L), corresponding to sufficient carbon for CO2 measurement.
• Sediment handling: Collection, storage (approx. 4 °C) and optional pre‑oxidation or pre‑conditioning of sediment/inoculum to reduce background respiration are described. Sediment carbon content should typically be in the 0.1–2% range.
• Apparatus and analysis: Biometer flasks (~250 ml recommended), CO2 absorption/analysis (e.g., Ba(OH)2 or KOH traps or instrumental CO2 analysers), analytical balance, pH meter. Calculation procedures for CO2 evolved and percent biodegradation are specified.
• Validity and reporting: Requirements for control/reference materials, blank corrections, plateau determination, visual inspection and full test reporting are included.

Applications and users

ISO 19679:2020 is used to:

• Evaluate marine biodegradability of non‑floating plastics (e.g., fishing gear, packaging that sinks or fouls and sinks).
• Support product claims, environmental risk assessment, research on polymer fate in coastal sediments. Primary users:
• Polymer manufacturers, environmental laboratories, certification bodies, academic researchers, and regulatory agencies concerned with marine litter and biodegradability.

Related standards

• ISO 18830 - oxygen‑consumption respirometric method (alternative measurement).
• ISO 14852 - CO2 respirometric methods for plastics (related principles).
• ISO 8245 - TOC analysis (for carbon content determination).
• OECD TG 308 (test apparatus examples) is also referenced for stirred systems.

Keywords: ISO 19679:2020, marine biodegradation, plastics, seawater/sediment interface, CO2 analysis, respirometric test, total organic carbon (TOC).