The standard "ISO 17556 Plastics - Determination of ultimate aerobic biodegradability of plastic materials in soil by measuring the oxygen demand or the amount of carbon dioxide evolved in a respirometer" published by the International Organization for Standardization (ISO) describes a method for determining the ultimate aerobic biodegradability of plastic materials in soil by measuring the oxygen demand or the amount of carbon dioxide evolved in a closed respirometer.
This method is designed to achieve an optimum degree of biodegradation by adjusting the moisture content of the test soil. If an unadapted soil is used as the inoculum, the test simulates the biodegradation processes that occur in a natural environment. If a previously exposed soil is used, the method can be used to investigate the potential biodegradability of a test material.
This method is valid for the following materials:
It may not be applicable to materials that inhibit the activity of microorganisms present in soil under test conditions. Inhibitory effects may be measured using an inhibition control or other suitable method. If the test material inhibits microorganisms in soil, a lower concentration of the test material, another soil type, or a previously exposed soil may be used.
A number of plastic materials and products are designed for applications that end up in or above ground. These are developed for applications where biodegradation is technically, environmentally, socially, or economically beneficial. Examples include agriculture (e.g., mulch film), horticulture (e.g., twine and clips, flower pots, needles), funeral materials (e.g., body bags), and recreation (e.g., plastic clay pigeons for shooting, hunting cartridges). In many cases, recovery or recycling of these plastic products is either difficult or not economically viable.
Several types of biodegradable plastics have been developed that are designed to biodegrade and decompose in situ at the end of their lifespan. Various international standards specify test methods for determining the ultimate aerobic or anaerobic biodegradation of plastic materials under aqueous or composting conditions. When considering the use and disposal of biodegradable plastics, it is important to establish a test method to determine the ultimate aerobic biodegradation of such plastic materials in soil.
In principle, this method is designed to obtain the optimum rate of biodegradation of a plastic material in a test soil by controlling the soil moisture and to determine the ultimate biodegradability of the material. The plastic material, which is the sole source of carbon and energy, is mixed with soil. The mixture is left to stand in a bottle for a period of time during which the amount of oxygen consumed ( BOD) or the amount of carbon dioxide released is determined. If the released carbon dioxide is absorbed, the amount of oxygen consumed can be determined, for example, by measuring the amount of oxygen required to maintain a constant gas volume in a respirometer vessel, or by automatically or manually measuring the change in volume or pressure (or a combination of both). An example of a suitable respirometer is included in the standard appendix (Appendix A).
The amount of carbon dioxide evolved is measured by passing carbon dioxide-free air over the soil at intervals related to the biodegradation kinetics of the test substance and then determining the carbon dioxide content of the air using a suitable method. The level of biodegradation, expressed as a percentage, is determined by comparing the amount of oxygen consumed with the theoretical oxygen demand or by comparing the amount of carbon dioxide evolved with the theoretical amount. The effect of possible nitrification processes on the amount of oxygen consumed should be considered.
The typical testing period is six months. The test may be shortened or extended until a plateau is reached, but the total testing period should not exceed two years. Unlike the ISO 11266 standard, which is used for various organic compounds, this standard is designed specifically to determine the biodegradability of plastic materials.
Incubation should be carried out in the dark or in diffused light in an enclosure free from vapors toxic to microorganisms and maintained at a constant temperature between 20 degrees and 28 degrees, preferably 25 degrees, plus/minus 2 degrees.
Before starting the tests, it's important to ensure that all glassware is thoroughly cleaned and free of any organic or toxic materials. Equipment used in these tests includes:
In short, the ISO 17556 standard defines a test method used to assess how effectively plastic materials biodegrade in natural soil environments.
With growing concerns about plastic pollution and sustainability, there's a growing need to ensure that plastics labeled as biodegradable actually break down in natural environments. This standard provides a standard laboratory procedure for assessing whether a plastic material can be considered biodegradable under aerobic (oxygen-rich) soil conditions.
This test helps to:
This testing method measures the ultimate aerobic biodegradability of plastic materials in soil by determining the amount of carbon dioxide released when microorganisms break down the plastic . The percentage of biodegradation is calculated by comparing the total amount of carbon dioxide produced to the theoretical maximum amount of carbon dioxide that could be produced if the plastic were completely biodegraded.
Materials that achieve greater than 90 percent biodegradation within the test period are generally considered highly biodegradable. Slower degradation rates may indicate that the material is not suitable for soil biodegradation claims. However, this standard does not define pass/fail criteria, only the method. Regulatory agencies or eco-labeling organizations may set their own threshold values based on this method.
As part of broader environmental efforts, this standard and similar standards support the circular economy by encouraging the development and use of materials that safely reintegrate into the natural environment. They help distinguish between truly biodegradable plastics and conventional plastics with misleading environmental claims.
As a result, the ISO 17556 standard plays a critical role in verifying the biodegradability of plastics in soil environments. By providing a scientifically sound method for measuring biodegradation, it helps protect consumers, guides industry innovation, and contributes to global sustainability efforts.
Our organization, which has been operating for many years and meticulously follows global developments in science and technology, employs a team of experienced professionals and a broad infrastructure to conduct testing, measurement, and analysis in a wide range of areas for businesses across all sectors. In this context, we also provide testing services in accordance with the ISO 17556 Plastics - Determination of the ultimate aerobic biodegradability of plastic materials in soil by measuring oxygen demand or carbon dioxide release in a respirometer.
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