ASTM D6691 Aerobic Biodegradation of Plastic Materials in the Marine Environment by a Defined Microbial Consortium

ASTM D6691 determines the degree and rate of aerobic biodegradation of plastic materials when exposed to either a pre-grown population of at least 10 aerobic marine microorganisms of recognized genera or the native population found in natural seawater. The values are considered as a standard when expressed in SI units.

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ASTM D6691 Aerobic Biodegradation of Plastic Materials in the Marine Environment by a Defined Microbial Consortium

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Overview
Scope, Applications, and Benefits
Test Process
Specifications
Instrumentation
Results and Deliverables

Overview

ASTM D6691 describes a procedure for determining the extent and rate of aerobic biodegradation of plastics in a marine environment. The test procedure may employ a pure culture of known aerobic marine microorganisms or the natural microbial flora present in seawater.

The biodegradation process is followed by tracking the production of biogas, specifically carbon dioxide, as the polymer degrades. The data obtained indicate the amount of carbon from the polymer that is converted to biogas. All the data is presented in SI units. This is a common standard for assessing the environmental effects and biodegradability of plastic materials in marine environments.

Scope, Applications, and Benefits

Scope

ASTM D6691 evaluates:

Degree of aerobic biodegradation
Rate of biodegradation over time
Carbon conversion efficiency
Biogas (CO₂) evolution
Polymer breakdown in marine environments

The method applies to polymer materials that:

Contain at least 20% carbon
They are not inhibitory to marine microorganisms

Applications

Environmental impact assessment
Marine biodegradability studies
Plastic material development
Sustainable packaging evaluation
Regulatory compliance testing
Research and development
Quality control of biodegradable plastics

Benefits

Provides standardized biodegradation data
Quantifies biodegradation rate and extent
Supports eco-friendly material development
Helps assess marine environmental impact
Enables comparison of different polymers
Improves regulatory decision-making

Test Process

Sample Selection & Preparation

A representative plastic sample is selected, its carbon content is determined, and the specimen is accurately weighed.

Inoculum Preparation & Exposure Setup

The marine inoculum is prepared, and the samples are exposed in sealed test bottles.

Incubation & Biogas Measurement

Samples are incubated at 30 ± 2°C, and CO₂ evolution is monitored.

Data Collection & Analysis

Biogas production is recorded, and polymer carbon conversion is calculated.

Technical Specifications

Parameter	Details
Applicable Materials	Plastics with ≥20% carbon
Temperature	30 ± 2°C
Measurement Method	Closed respirometry
Output Units	SI units
Measured Outputs	CO₂ generation, biodegradation rate

Instrumentation Used for Testing

Respirometry system with CO₂ sensor
125 mL autoclave bottles with seal rings
Gas collection and measurement system
Controlled-temperature incubator or water bath
Analytical balance (±0.1 mg precision)
Data logging system

Results and Deliverables

Biodegradation rate curves
Total CO₂ evolution data
Percentage carbon conversion
Comparative polymer performance reports
Biodegradability assessment summary

Frequently Asked Questions

ASTM D6691 is an aqueous aerobic biodegradability test that determines the degree and rate of aerobic biodegradation of plastic materials in seawater.

The content of CO2 in biogas measurement aids in assessing the intensity and biodegradation rate of plastics in the marine environment based on the extent of degradation, which is a determinant of the resultant biodegradable impact.

The apparatus comprises a biogas production monitoring system, sample bottles, a gas-volume measuring and collection system, a water bath or a controlled environment shaker/incubator, and an analytical balance for weighing the test materials.

ASTM D6691 reports the degree and rate of aerobic biodegradation of polymeric materials by biogas (CO2) evolution and represents the amount of carbon in polymer converted to carbon in biogas.

The results of ASTM D6691 can guide the design and formulation of more biodegradable plastic materials, assisting manufacturers in producing products with lower environmental impact, particularly in marine applications.