ASTM D6691-24a PDF

Full title and description

Standard Test Method for Determining Aerobic Biodegradation of Plastic Materials in the Marine Environment by a Defined Microbial Consortium or Natural Sea Water Inoculum (Designation: ASTM D6691-24a). This test method indexes the degree and rate of aerobic biodegradation of polymer materials exposed to marine microorganisms by measuring evolved carbon dioxide under controlled laboratory conditions.

Abstract

ASTM D6691-24a specifies a laboratory procedure to determine the aerobic biodegradation of plastics in seawater inocula (either a defined consortium or natural seawater) by measuring CO2 evolution relative to a positive reference material. The method is intended for comparative and indexing purposes and cautions against extrapolating short-term laboratory results to long-term environmental fate without appropriate qualification.

General information

• Status: Active (current standard; updated with amendment "24a").
• Publication date: 2024 (designation shown as D6691-24a; published/updated in 2024 with amendment dated April–June 2024).
• Publisher: ASTM International.
• ICS / categories: 13.030.99 (other standards related to wastes / marine environmental testing).
• Edition / version: D6691-24a (includes amendment "a"; revises D6691-17 / D6691-24).
• Number of pages: 5 pages.

Scope

This test method is applicable to polymer materials (including additives) containing at least 20% carbon that are not inhibitory to marine microorganisms and is conducted under controlled laboratory conditions to index potential biodegradability in biologically active marine environments. Biodegradation is quantified by measuring CO2 evolution and comparing it to theoretical CO2 production (ThCO2) and to a positive reference material. The standard notes there is no direct ISO equivalent and cautions about extrapolating laboratory results to environmental persistence.

Key topics and requirements

• Test principle: aerobic biodegradation measured by cumulative CO2 evolution from test specimens inoculated with either a defined marine microbial consortium or natural seawater inoculum.
• Applicability: polymers with ≥20% carbon content that do not inhibit the test inoculum.
• Controls and references: blank controls, positive reference material (e.g., cellulose or other accepted biodegradable reference), and instrumentation checks for CO2 measurement accuracy.
• Test conditions and duration: conducted under controlled laboratory temperature (method commonly run near 30 ± 2 °C) and typically run from about 10 to 90 days or until CO2 evolution plateaus, with flexibility to extend if biodegradation is slow.
• Data and reporting: conversion of measured CO2 to percent biodegradation using the test material's carbon content (ThCO2), presentation of biodegradation curves, and reporting of test conditions, inoculum source, and any deviations.
• Limitations and interpretation: designed as an index/test under simulated conditions—explicitly warns against direct extrapolation to real-world long-term environmental fate without supplementary evidence.

Typical use and users

Used by biodegradability testing laboratories, polymer and bioplastic manufacturers, product developers, environmental consultants, and regulatory bodies to screen and compare marine biodegradation potential of plastic formulations and additives. The method supports product claims assessment, research, and pre‑market evaluation but is normally combined with other tests and field data for environmental fate conclusions.

Related standards

Revises earlier ASTM D6691 editions (for example D6691-17); there is no single ISO equivalent specified in the standard. Related test methods and guidance documents addressing biodegradability in other environments (e.g., soil, compost, freshwater) or other measurement approaches (respirometric tests, disintegration tests) are often used alongside D6691 for a fuller assessment. Users commonly reference ASTM series standards on biodegradability and industry guidance when designing test programs.

Keywords

marine biodegradation, aerobic biodegradation, plastics, seawater inoculum, CO2 evolution, biodegradability test, ASTM D6691-24a.

FAQ

Q: What is this standard?

A: ASTM D6691-24a is a standardized laboratory test method for determining the aerobic biodegradation of plastic materials in a simulated marine environment by measuring evolved carbon dioxide from a defined microbial consortium or natural seawater inoculum.

Q: What does it cover?

A: It covers test setup, inoculum options, controls and references, measurement of CO2 evolution, calculation of percent biodegradation based on theoretical CO2 (ThCO2), reporting requirements, and limitations on interpretation—intended as an indexing/comparative laboratory method rather than a direct predictor of long-term environmental fate.

Q: Who typically uses it?

A: Testing laboratories, material manufacturers (including bioplastic developers), environmental consultants, and regulators evaluating marine biodegradability claims or comparing materials for research and product development.

Q: Is it current or superseded?

A: Current—ASTM D6691 has been updated and is shown in the catalog as D6691-24 with amendment "24a" (designation D6691-24a). It revises prior editions such as D6691-17; the document is actively maintained by ASTM. Users should confirm they have the latest edition/amendment before testing.

Q: Is it part of a series?

A: It is part of ASTM's suite of standards addressing biodegradability and environmental testing of polymers and plastics. While not formally a numbered series, users often apply D6691 alongside other ASTM/ISO/EN test methods for biodegradation and disintegration in different environments.

Q: What are the key keywords?

A: marine biodegradation, seawater inoculum, CO2 evolution, aerobic biodegradation, plastics testing, ASTM D6691-24a.