Biodegradability Testings

Biodegradability testing

When you already know what does it mean “biodegradableBiodegradation is the breakdown of organic matter by microorganisms, such as bacteria and fungi. polymerA polymer is a substance or material consisting of very large molecules, or macromolecules, composed of many repeating subunits.”, you know WHERE it is biodegradableBiodegradation is the breakdown of organic matter by microorganisms, such as bacteria and fungi. and in which conditions, you should also ask HOW the biodegradability was measured.

The testing methods can be divided into two groups – physical methods and respirometry.

1) Physical methods

The main method of this group is simple weight loss measurement. The weight of the polymerA polymer is a substance or material consisting of very large molecules, or macromolecules, composed of many repeating subunits. in the beginning of the experiment is compared with weight of polymer after a period in selected environment. The main advantage of this method is the possibility to use it in natural environment. However, using this method, bioasimilation and mineralization of the polymerA polymer is a substance or material consisting of very large molecules, or macromolecules, composed of many repeating subunits. cannot be proven.¹

Other physical methods include visual evaluation, microscopy, spectroscopy, etc.

2) Respirometry

These methods measure oxygen consumed by bacteria during biodegradationBiodegradation is the breakdown of organic matter by microorganisms, such as bacteria and fungi. of the polymer or CO₂/CH₄ evolved.¹ The advantage is measuring the actual mineralization of the polymerA polymer is a substance or material consisting of very large molecules, or macromolecules, composed of many repeating subunits.. These methods can be proceeded only in laboratory using sophisticated equipment; thus, they poorly simulate natural conditions.

Misinterpretation of the measurements can lead to two major mistakes:²

Declaring biodegradability based on physical measurements, but not proving mineralization.
Blaming biodegradableBiodegradation is the breakdown of organic matter by microorganisms, such as bacteria and fungi. polymerA polymer is a substance or material consisting of very large molecules, or macromolecules, composed of many repeating subunits. not biodegradableBiodegradation is the breakdown of organic matter by microorganisms, such as bacteria and fungi., but not considering the type of environment for which the biodegradableBiodegradation is the breakdown of organic matter by microorganisms, such as bacteria and fungi. polymerA polymer is a substance or material consisting of very large molecules, or macromolecules, composed of many repeating subunits. was originally certified.

Stating whether the polymer is, or is not biodegradableBiodegradation is the breakdown of organic matter by microorganisms, such as bacteria and fungi. is complicated also because of the variety of methods used during the experiments. We have already discussed the high number of environmental conditions and material properties, which influence the biodegradability rate. If these variables are not properly corrected or discussed during the experiment, the results cannot be compared with measurements from other laboratories. Such results are irreproducible. This led the scientists to establish standard methods for biodegradability determination.

Standard methods and certifications

There are 3 standardized procedures:

Methods declaring the conditions and the process of the measurement

Methods that not only set the conditions, but also evaluate the outcomes – based on these methods, you can state whether the polymer is biodegradable, or not

Certificates – third party declarations

There are several ISO, OECD and ASTM standards. They are often overlapping or complementary and provide a set of rules how to measure biodegradability in various environments. These methods are very often criticized by the academics. Yet, they are the main and still best tool for the legislative. Valid methods (in 2021) are summarized in table 1.

The (standard) methods for biodegradability testing deal with these problems:¹

Source of microorganisms and the conditions – not enough variables are standardized, described and controlled in the normalized methods.
Shape and size of the product – most of the experiments use polymerA polymer is a substance or material consisting of very large molecules, or macromolecules, composed of many repeating subunits. as powder or thin foils. Powder degrades much faster than bigger object (e.g. a bottle); but we don’t know how much faster.
Additives – final products are usually not pure polymers of one kind. Thus, final formulas with all the additives must be tested for both biodegradability, and toxicity.
Experiment duration – short experiments do not provide valid information about the biodegradability rate. BiodegradationBiodegradation is the breakdown of organic matter by microorganisms, such as bacteria and fungi. can take several years – experiment proceeded in two weeks may lead in biased information. On the other hand, laboratory experiments run in relatively small volumes compared to the natural environments, where exchange of nutrients and metabolites is limited. Long cultivation poorly imitates natural conditions.
Correlation between laboratory experiment and the reality – laboratory experiments are more reproducible, but extrapolation of the laboratory result into natural environment can be misleading.
Insufficient characterization of the material – not only the external conditions, but also properties of the tested material itself influence the biodegradability.

Currently, the best accepted and probably most reliable are Vincotte OK biodegradableBiodegradation is the breakdown of organic matter by microorganisms, such as bacteria and fungi. certificates. As the only ones, they test also the toxicity of the polymerA polymer is a substance or material consisting of very large molecules, or macromolecules, composed of many repeating subunits. besides its biodegradability.

Now you know what are the perks of biodegradability measurements. Learn what is the biodegradability of PHA group of polymers.

Standard	Last revision	Name	Environment	Method
ISOInternational Organization for Standardization More 14851	2019	Determination of the ultimate aerobic biodegradability of plastic materials in an aqueous medium — Method by measuring the oxygen demand in a closed respirometer	Waste water and sewage sludge (aerobic)	O₂ consumption
ISOInternational Organization for Standardization More 14852	2018	Determination of the ultimate aerobic biodegradability of plastic materials in an aqueous medium — Method by analysis of evolved carbon dioxide	Waste water and sewage sludge (aerobic)	CO₂production
ISOInternational Organization for Standardization More 13975	2019	PlasticsMaterials with large molecular chains of natural or fossil raw materials, produced by chemical or biochemical reactions. More — Determination of the ultimate anaerobic biodegradationBiodegradation is the breakdown of organic matter by microorganisms, such as bacteria and fungi. of plastic materials in controlled slurry digestion systems — Method by measurement of biogasAnaerobic digestion More production	Waste water and sewage sludge (anaerobic)	CO₂ and CH₄ production
ISOInternational Organization for Standardization More 14853	2016	PlasticsMaterials with large molecular chains of natural or fossil raw materials, produced by chemical or biochemical reactions. More — Determination of the ultimate anaerobic biodegradationBiodegradation is the breakdown of organic matter by microorganisms, such as bacteria and fungi. of plastic materials in an aqueous system — Method by measurement of biogasAnaerobic digestion More production	Waste water and sewage sludge (anaerobic)	CO₂ and CH₄ production
ISOInternational Organization for Standardization More 17556	2019	PlasticsMaterials with large molecular chains of natural or fossil raw materials, produced by chemical or biochemical reactions. More — Determination of the ultimate aerobic biodegradability of plastic materials in soil by measuring the oxygen demand in a respirometer or the amount of carbon dioxide evolved	Soil	O₂ consumption and CO₂production
ASTM 5988 (Equivalent to ISOInternational Organization for Standardization More 17556)	2018	Standard Test Method for Determining Aerobic BiodegradationBiodegradation is the breakdown of organic matter by microorganisms, such as bacteria and fungi. of Plastic Materials in Soil	Soil	CO₂production
OECD 307	2002	Aerobic and Anaerobic Transformation in Soil	Soil	CO₂ evolution from radiolabelled polymerA polymer is a substance or material consisting of very large molecules, or macromolecules, composed of many repeating subunits. biodegradationBiodegradation is the breakdown of organic matter by microorganisms, such as bacteria and fungi. (¹⁴C)
EN 17033	2018	PlasticsMaterials with large molecular chains of natural or fossil raw materials, produced by chemical or biochemical reactions. More – BiodegradableBiodegradation is the breakdown of organic matter by microorganisms, such as bacteria and fungi. mulch films for use in agriculture and horticulture – Requirements and test methods	Soil
NF U 52-001 (French standard for mulch foils)	2013	BiodegradableBiodegradation is the breakdown of organic matter by microorganisms, such as bacteria and fungi. materials for use in agriculture and horticulture – mulching products – requirements and test methods	Soil
ISOInternational Organization for Standardization More 19679	2020	PlasticsMaterials with large molecular chains of natural or fossil raw materials, produced by chemical or biochemical reactions. More — Determination of aerobic biodegradationBiodegradation is the breakdown of organic matter by microorganisms, such as bacteria and fungi. of non-floating plastic materials in a seawater/sediment interface — Method by analysis of evolved carbon dioxide	Marine	CO₂production
ISOInternational Organization for Standardization More 22403	2020	PlasticsMaterials with large molecular chains of natural or fossil raw materials, produced by chemical or biochemical reactions. More — Assessment of the intrinsic biodegradability of materials exposed to marine inocula under mesophilic aerobic laboratory conditions — Test methods and requirements	Marine
ISOInternational Organization for Standardization More 18830	2016	PlasticsMaterials with large molecular chains of natural or fossil raw materials, produced by chemical or biochemical reactions. More — Determination of aerobic biodegradationBiodegradation is the breakdown of organic matter by microorganisms, such as bacteria and fungi. of non-floating plastic materials in a seawater/sandy sediment interface — Method by measuring the oxygen demand in closed respirometer	Marine	O₂ consumption
ASTM D7991	2015	Standard Test Method for Determining Aerobic BiodegradationBiodegradation is the breakdown of organic matter by microorganisms, such as bacteria and fungi. of PlasticsMaterials with large molecular chains of natural or fossil raw materials, produced by chemical or biochemical reactions. More Buried in Sandy Marine Sediment under Controlled Laboratory Conditions	Marine	CO₂production
ASTM D7473	2012	Standard Test Method for Weight Attrition of Plastic Materials in the Marine Environment by Open System Aquarium Incubations	Marine	Visual evaluation, weight loss
ASTM D6691	2009	Standard Test Method for Determining Aerobic BiodegradationBiodegradation is the breakdown of organic matter by microorganisms, such as bacteria and fungi. of Plastic Materials in the Marine Environment by a Defined Microbial Consortium or Natural Sea Water Inoculum	Marine	CO₂production
ISOInternational Organization for Standardization More 18606	2013	Packaging and the environment — Organic recyclingIt means the treatment of separately collected organic waste by anaerobic digestion and/or composting. More	Industrial compostingIndustrial composting is an established process with commonly agreed upon requirements (e.g. temperature, timeframe) for transforming biodegradable wa… More
ISOInternational Organization for Standardization More 17088	2012	Specifications for compostable plasticsPlastics that are biodegradable under composting conditions: specified humidity, temperature, microorganisms and timeframe. In order to make accurate … More	Industrial compostingIndustrial composting is an established process with commonly agreed upon requirements (e.g. temperature, timeframe) for transforming biodegradable wa… More
ISOInternational Organization for Standardization More 14855	2012	Determination of the ultimate aerobic biodegradability of plastic materials under controlled compostingComposting is the controlled aerobic, or oxygen-requiring, decomposition of organic materials by microorganisms, under controlled conditions. It reduc… More conditions — Method by analysis of evolved carbon dioxide	Industrial compostingIndustrial composting is an established process with commonly agreed upon requirements (e.g. temperature, timeframe) for transforming biodegradable wa… More	CO₂production
ASTM D5338 (Equivalent to ISOInternational Organization for Standardization More 14855)	2021	Standard Test Method for Determining Aerobic BiodegradationBiodegradation is the breakdown of organic matter by microorganisms, such as bacteria and fungi. of Plastic Materials Under Controlled CompostingComposting is the controlled aerobic, or oxygen-requiring, decomposition of organic materials by microorganisms, under controlled conditions. It reduc… More Conditions, Incorporating Thermophilic Temperatures	Industrial compostingIndustrial composting is an established process with commonly agreed upon requirements (e.g. temperature, timeframe) for transforming biodegradable wa… More
ASTM D6868	2019	Standard Specification for Labeling of End Items that Incorporate PlasticsMaterials with large molecular chains of natural or fossil raw materials, produced by chemical or biochemical reactions. More and Polymers as Coatings or Additives with Paper and Other Substrates Designed to be Aerobically Composted in Municipal or Industrial Facilities	Industrial compostingIndustrial composting is an established process with commonly agreed upon requirements (e.g. temperature, timeframe) for transforming biodegradable wa… More
ASTM D6400 (Equivalent to ISOInternational Organization for Standardization More 17088)	2019	Standard Specification for Labeling of PlasticsMaterials with large molecular chains of natural or fossil raw materials, produced by chemical or biochemical reactions. More Designed to be Aerobically Composted in Municipal or Industrial Facilities	Industrial compostingIndustrial composting is an established process with commonly agreed upon requirements (e.g. temperature, timeframe) for transforming biodegradable wa… More
ASTM D5526	2018	Standard Test Method for Determining Anaerobic BiodegradationBiodegradation is the breakdown of organic matter by microorganisms, such as bacteria and fungi. of Plastic Materials Under Accelerated Landfill Conditions	Landifill / bioreactor
EN 14995	2006	Evaluation of compostability – Test scheme and specifications	Industrial compostingIndustrial composting is an established process with commonly agreed upon requirements (e.g. temperature, timeframe) for transforming biodegradable wa… More
EN 13432European standard for the assessment of the compostability of plastic packaging products. More	2001	Packaging – Requirements for packaging recoverable through compostingComposting is the controlled aerobic, or oxygen-requiring, decomposition of organic materials by microorganisms, under controlled conditions. It reduc… More and biodegradationBiodegradation is the breakdown of organic matter by microorganisms, such as bacteria and fungi. – Test scheme and evaluation criteria for the final acceptance of packaging	Industrial compostingIndustrial composting is an established process with commonly agreed upon requirements (e.g. temperature, timeframe) for transforming biodegradable wa… More
EN 14045	2003	Packaging – Evaluation of the disintegration of packaging materials in practical oriented tests under defined compostingComposting is the controlled aerobic, or oxygen-requiring, decomposition of organic materials by microorganisms, under controlled conditions. It reduc… More conditions	CompostingComposting is the controlled aerobic, or oxygen-requiring, decomposition of organic materials by microorganisms, under controlled conditions. It reduc… More	Visual evaluation, weight loss
ISOInternational Organization for Standardization More 15985	2014	PlasticsMaterials with large molecular chains of natural or fossil raw materials, produced by chemical or biochemical reactions. More — Determination of the ultimate anaerobic biodegradationBiodegradation is the breakdown of organic matter by microorganisms, such as bacteria and fungi. under high-solids anaerobic-digestion conditions — Method by analysis of released biogasAnaerobic digestion More	Anaerobic	CO₂ and CH₄ production
ASTM D5511 (Equivalent to ISOInternational Organization for Standardization More 15985)	2018	Standard Test Method for Determining Anaerobic BiodegradationBiodegradation is the breakdown of organic matter by microorganisms, such as bacteria and fungi. of Plastic Materials Under High-Solids Anaerobic-Digestion Conditions	Anaerobic
NF T 51-800 (French standard)	2015	PlasticsMaterials with large molecular chains of natural or fossil raw materials, produced by chemical or biochemical reactions. More – Specifications for plasticsMaterials with large molecular chains of natural or fossil raw materials, produced by chemical or biochemical reactions. More suitable for home compostingComposting [bM 06/08] More	Home compostingComposting [bM 06/08] More
AS 5810 (Australian standard)	2010	Biodegradable plasticsBiodegradable plastics are plastics that are completely assimilated by the microorganisms present a defined environment as food for their energy. The … More – Biodegradable plasticsBiodegradable plastics are plastics that are completely assimilated by the microorganisms present a defined environment as food for their energy. The … More suitable for home compostingComposting [bM 06/08] More	Home compostingComposting [bM 06/08] More

Table 1 – standard methods for determining polymer biodegradability

References

¹Harrison, J. P., C. Boardman, K. O’Callaghan, et al. Biodegradability standards for carrier bags and plastic films in aquatic environments: a critical review. Royal Society Open Science. 2018, 5(5): 171792. doi: doi:10.1098/rsos.171792.

²Zumstein, M. T., R. Narayan, H.-P. E. Kohler, et al. Dos and Do Nots When Assessing the BiodegradationBiodegradation is the breakdown of organic matter by microorganisms, such as bacteria and fungi. of PlasticsMaterials with large molecular chains of natural or fossil raw materials, produced by chemical or biochemical reactions. More. Environmental Science & Technology. 2019, 53(17): 9967-9969. doi: 10.1021/acs.est.9b04513.