ASTM D5988-18 Testing: Complete Guide to Determining Aerobic Biodegradation of Plastic Materials in Soil
What is ASTM D5988-18 Testing?
ASTM D5988-18 is a standard test method that outlines the determination of the aerobic biodegradation of plastic materials in soil. This procedure assesses the effectiveness and extent to which a plastic material is broken down by microorganisms under controlled environmental conditions that simulate natural soil environments.
It measures the conversion of carbon in the test material to CO₂, reflecting microbial activity and thus biodegradation. This enables researchers and manufacturers to evaluate the environmental impact and long-term degradability of plastics intended for disposal in soil environments.
Why is ASTM D5988 Testing Important?
As environmental concerns grow, understanding how plastics degrade in soil is essential for sustainable product development and regulatory compliance.
ASTM D5988 helps:
- Evaluate biodegradability claims for environmentally friendly or bio-based plastics.
- Assess the ecological impact of plastics intended for land disposal.
- Support product design and material selection for sustainable packaging, agricultural films, and disposable items, promoting environmentally friendly solutions.
- Comply with environmental standards and regulations, ensuring accurate labeling of biodegradable materials.
This method is widely recognized by regulatory agencies, research institutions, and manufacturers as a means to validate biodegradability performance.
Which Materials Can Be Tested Under ASTM D5988?
This test method applies to a broad range of organic plastic materials capable of being degraded by soil microorganisms, including:
- Biodegradable polymers (e.g., PLA, PHA, PBAT, PBS)
- Starch-based plastics and composites
- Natural polymers (e.g., cellulose, chitosan, lignin-based materials)
- Modified or blended plastics are intended to enhance biodegradation
- Control and reference materials (e.g., cellulose powder for comparison)
Materials can be in various forms, including films, pellets, powders, or molded specimens, depending on their intended end-use.
What Information Do ASTM D5988 Test Results Provide?
The ASTM D5988 test provides key biodegradation data, summarized as:
| Parameter | Unit | Description |
| CO₂ Evolution | mg or % | Amount of CO₂ produced due to biodegradation |
| Degree of Biodegradation | % | Portion of total organic carbon converted to CO₂ |
| Biodegradation Rate | % per day | The speed at which biodegradation occurs |
| Lag Phase | days | Time before significant microbial activity begins |
These results indicate whether a plastic is readily, partially, or slowly biodegradable in soil environments.
What Industries Use ASTM D5988 Testing?
ASTM D5988-18 testing is utilized across industries committed to sustainability and environmental compliance, including:
- Packaging: Biodegradable films, bags, and containers
- Agriculture: Mulch films, planting trays, and seed coatings
- Consumer Goods: Compostable utensils and disposable items
- Biomedical: Biodegradable implants or drug delivery systems
- R&D and Academia: Material innovation and life-cycle analysis studies
This test aids in product certification, eco-labeling, and environmental impact assessment.
What Equipment Is Used for ASTM D5988 Testing?
The test setup typically includes:
- Biodegradation vessels or respirometers for controlled incubation
- CO₂ measurement system (e.g., alkali absorption traps or infrared analyzers)
- Analytical balance for sample and CO₂ quantification
- Temperature and humidity control systems
- Reference and control soil containers
How Is the ASTM D5988 Test Performed?
Step-by-Step Procedure:
- Sample Preparation:
Plastic test materials are prepared in defined shapes or sizes, ensuring sufficient surface area for microbial action. A known carbon content is determined for accurate biodegradation calculation. - Soil Preparation:
Natural soil containing active microbial populations is collected, sieved, and characterized (pH, moisture, and organic content). It serves as the inoculum for biodegradation. - Incubation Setup:
Test materials are mixed or layered in the soil and placed in closed test vessels that allow airflow. Control samples (soil only and reference material) are also prepared. - Test Conditions:
The vessels are incubated under aerobic conditions (in the presence of oxygen) at 25°C ± 2°C or as specified. Moisture levels are maintained at 50–60% of soil water-holding capacity. - Monitoring CO₂ Evolution:
Throughout the test, the CO₂ produced by microbial respiration is periodically measured—typically using alkali traps or CO₂ analyzers. - Data Collection and Analysis:
The amount of CO₂ evolved from the test material is compared to the theoretical CO₂ that would result from complete oxidation of its organic carbon.
What Are the Standard Test Conditions?
| Parameter | Typical Condition |
| Temperature | 25°C ± 2°C |
| Moisture Content | 50–60% of water-holding capacity |
| Oxygen Level | Aerobic (ambient air exchange) |
| Duration | Up to 180 days (or until biodegradation plateaus) |
| Reference Material | Cellulose powder or equivalent |
| Control | Soil without test material |
Maintaining stable conditions ensures the production of accurate and reproducible results.
Key Properties Measured
ASTM D5988 measures the extent and rate of aerobic biodegradation of plastics by naturally occurring microorganisms in soil. The property being quantified is biodegradability, expressed as the percentage of organic carbon converted into CO₂ over time.
This test provides valuable insight into how a plastic behaves at the end of its life—especially in the case of materials being marketed as biodegradable or compostable.
Related Testing Methods
- ASTM D5338: Biodegradation under controlled composting conditions
- ASTM D5511: Anaerobic biodegradation of plastics in high-solids environments
- ASTM D6954: Degradability and safety assessment of oxo-degradable plastics
- ISO 17556: Determination of ultimate aerobic biodegradability in soil
Conclusion
ASTM D5988-18 provides a scientifically robust method for evaluating the aerobic biodegradability of plastics in soil environments, a key factor in assessing the environmental sustainability of polymer materials.
Measuring the evolution of CO₂ under controlled conditions, this test enables manufacturers and researchers alike to validate biodegradation performance, support eco-label claims, and inform the development of next-generation sustainable materials.
ASTM D5988 is a key resource for industries wanting to achieve environmentally responsible design, product validation, and compliance with global biodegradability standards.
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At the core of this breadth is our network of over 2,000 accredited labs in the USA, offering access to more than 10,000 test types. From advanced metrology (SEM, TEM, RBS, XPS) to mechanical, dielectric, environmental, and standardized ASTM/ISO testing, we give clients unmatched flexibility, specialization, and scale. You’re not limited by geography, facility, or methodology—Infinita connects you to the proper testing, every time.
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FAQs on ASTM D5988-18 Testing
What is the purpose of ASTM D5988-18 testing? The ASTM D5988-18 test is designed to determine the extent and rate of aerobic biodegradation of plastic materials in soil. It measures how microorganisms convert the carbon in plastics into carbon dioxide (CO₂) under controlled laboratory conditions that simulate a natural soil environment.
What does “aerobic biodegradation” mean? Aerobic biodegradation refers to the breakdown of organic materials by microorganisms in the presence of oxygen, resulting in the production of carbon dioxide (CO₂), water, and biomass. It indicates the natural degradability of plastics when exposed to soil microorganisms.
How is biodegradation measured in ASTM D5988? Biodegradation is quantified by measuring the amount of CO₂ evolved during the test period. The CO₂ produced is compared to the theoretical maximum CO₂ expected from complete oxidation of the test material’s organic carbon content, expressed as a percentage of biodegradation.
