Soil degradation characteristics testing is a laboratory-based evaluation that measures how materials, chemicals, and products biodegrade when exposed to natural soil environments under controlled aerobic or anaerobic conditions. This testing is essential for manufacturers of biodegradable plastics, agricultural films, lubricants, and organic compounds who need to substantiate environmental claims, achieve regulatory compliance, and support product certification. By quantifying biodegradation rates, transformation products, and ecological safety, these tests provide scientifically robust data for both market access and environmental risk assessment.
Technical Overview
Soil degradation characteristics testing refers to a family of laboratory procedures designed to quantify the rate and extent to which organic materials are broken down by soil microorganisms. Unlike industrial composting tests, which simulate controlled high-temperature conditions, soil degradation tests reflect ambient environmental conditions typical of agricultural fields, gardens, and natural land, making them directly relevant to real-world disposal and use scenarios.
During the test, a defined quantity of the test material is mixed into or placed in contact with a standardized soil inoculum. The soil is incubated under controlled temperature, moisture, and aeration conditions for a specified period, often ranging from several weeks to six months or longer. Degradation is monitored by measuring the amount of carbon dioxide evolved or oxygen consumed, which directly reflects microbial mineralization of the material into carbon dioxide, water, and biomass.
The resulting data are used to determine key degradation parameters, including the biodegradation percentage, lag phase duration, degradation kinetics, and the degree of disintegration. In many certification schemes, the test material must achieve a biodegradation level of at least 90 percent relative to a reference substance such as cellulose within a defined time frame. Accredited third-party laboratories conduct these tests in accordance with internationally recognized standards published by ISO, ASTM, OECD, EN, and GB organizations, ensuring that results are reproducible and acceptable to regulators, certification bodies, and downstream customers.
Testing Samples
Biodegradable Plastics and Polymers
Polylactic acid (PLA), polybutylene adipate terephthalate (PBAT), polybutylene succinate (PBS), polyhydroxyalkanoates (PHA), starch blends, and other bio-based or biodegradable polymer formulations are among the most frequently tested materials. Testing verifies whether these polymers achieve meaningful biodegradation in soil rather than only under industrial composting conditions.
Agricultural Mulch Films and Geotextiles
Biodegradable mulch films, which are plowed into the soil after the growing season, must demonstrate reliable soil degradation to avoid plastic accumulation in farmland. Soil burial testing supports conformity with agricultural film standards such as EN 17033 and related national specifications.
Lubricants and Functional Fluids
Hydraulic fluids, chain oils, two-stroke oils, and greases labeled as readily biodegradable are tested for their behavior in soil, complementing aquatic biodegradability data required by eco-label programs.
Organic Chemicals and Agrochemicals
Pesticides, fertilizers, soil amendments, and industrial chemicals are evaluated for their transformation pathways and persistence in soil, supporting environmental risk assessment and registration dossiers under frameworks such as OECD guidelines.
Textiles, Nonwovens, and Packaging
Natural fiber products, regenerated cellulose materials, and fiber-based packaging intended for soil contact or environmental release are tested to substantiate biodegradability claims and disintegration performance.
Testing Items
Soil degradation characteristics testing typically encompasses the following measurement endpoints:
- Ultimate aerobic biodegradation rate, expressed as the percentage of theoretical carbon dioxide released or theoretical oxygen demand consumed
- Biodegradation kinetics, including lag phase, biodegradation phase, and plateau phase analysis
- Disintegration degree, determined by mass recovery of residual material fragments after soil incubation
- Weight loss and physical fragmentation of the test material over time
- Molecular weight reduction of polymeric materials measured by gel permeation chromatography (GPC)
- Changes in mechanical properties such as tensile strength and elongation at break after soil exposure
- Transformation products and mass balance determination for chemicals tested under OECD 307
- Soil microbial activity and biomass indicators to confirm that the material does not inhibit soil biota
- Eco-toxicity screening, including seed germination, plant growth, and earthworm avoidance or survival tests
- Control parameters such as soil pH, moisture content, organic carbon, and microbial viability throughout the incubation period
Testing Methods
Testing is conducted using internationally standardized respirometric and soil-incubation procedures. The selection of method depends on the material type, intended application, and the regulatory or certification target.
ISO 17556 — Aerobic Biodegradability of Plastics in Soil
This method determines the ultimate aerobic biodegradability of plastic materials by measuring the oxygen demand in a closed respirometer or the amount of carbon dioxide evolved. Test materials are mixed with natural or synthetic soil and incubated, typically at 20 to 28 degrees Celsius, until the biodegradation curve reaches a plateau. Cellulose is used as the positive reference control.
ASTM D5988 — Aerobic Biodegradation of Plastic Materials in Soil
This standard test method measures carbon dioxide evolution from plastic materials buried in soil under controlled laboratory conditions. It is widely used in North America for evaluating compostable and biodegradable polymer claims and for research screening of new formulations.
OECD 307 — Aerobic and Anaerobic Transformation in Soil
This guideline is applied primarily to agrochemicals and industrial chemicals. Radiolabeled or non-labeled substances are incubated with several soil types, and the study quantifies primary degradation, mineralization, formation of transformation products, and half-life values for environmental fate assessment.
ISO 11266 and Related Guidance Standards
These documents provide general guidance on the design and interpretation of laboratory biodegradation tests in soil, covering inoculum selection, incubation conditions, sampling strategies, and data reporting.
National and Regional Standards
Chinese GB/T standards, European EN standards for biodegradable mulch films, and various national specifications harmonize with ISO and ASTM approaches. Accredited third-party laboratories select the appropriate standard combination based on the target market, whether for certification schemes, eco-labeling, or regulatory submission.
Typical test setups include static soil biometer flasks, dynamic respirometers with continuous carbon dioxide trapping, and automated oxygen uptake systems. Replicate vessels are prepared for each sampling interval, along with blank soil controls, positive controls such as cellulose, and reference soil to validate inoculum activity. Incubation may extend from 60 days up to 24 months depending on the expected degradation profile and the applicable standard.
Applications
Soil degradation test data serve a broad range of commercial, regulatory, and scientific purposes:
- Supporting certification of biodegradable and compostable products where soil biodegradation claims are required, complementing industrial composting standards such as EN 13432 and ASTM D6400
- Verifying the field performance of biodegradable agricultural mulch films and enabling compliance with agricultural plastic regulations
- Providing environmental fate data for the registration of pesticides, fertilizers, and industrial chemicals under national and regional regulatory programs
- Substantiating marketing claims for eco-labeled lubricants, detergents, and consumer products
- Guiding research and development of new biodegradable polymer formulations, plastic additives, and material modifications
- Assessing environmental risk associated with plastic accumulation, microplastic formation, and chemical persistence in terrestrial ecosystems
- Satisfying import market requirements where proof of terrestrial biodegradability is mandated for product entry
FAQ
What is the pass criterion for soil biodegradation testing?
Most certification schemes require the test material to reach at least 90 percent biodegradation relative to the cellulose positive reference, evaluated over a period that typically ranges from six months to two years depending on the applicable standard and product category.
How long does a soil degradation test take?
Standard incubation periods range from 60 days to 24 months. Polymers designed for rapid soil degradation may reach plateau within 90 to 180 days, whereas more resistant materials and chemical fate studies under OECD 307 may require extended incubation with multiple sampling intervals.
How does soil degradation testing differ from composting testing?
Composting tests simulate thermophilic industrial conditions with high temperatures, high moisture, and mature compost inoculum, while soil degradation tests use ambient-temperature natural soil with a lower and more diverse microbial population. Soil tests are generally more demanding and better reflect environmental release scenarios such as agricultural plow-in.
What types of soil are used in the tests?
Natural soils with documented properties such as pH, organic carbon content, water-holding capacity, and microbial biomass are used. OECD 307 studies typically require several soil types representing contrasting textures and pH values, whereas plastic biodegradation standards permit defined natural soils with verified biological activity.
Can aged or weathered samples be tested?
Yes. Pre-conditioning through UV weathering, thermal aging, or artificial disintegration is often performed to simulate environmental exposure prior to soil incubation, providing a more realistic assessment of end-of-life behavior.
Which industries benefit most from this testing?
Biodegradable plastics manufacturers, agricultural film producers, agrochemical developers, lubricant formulators, textile and packaging companies, and any organization making terrestrial biodegradability claims or preparing regulatory submissions benefit from accredited third-party soil degradation testing.