Biodegradability testing

When you already know what does it mean “biodegradable polymer”, you know WHERE it is biodegradable 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 polymer 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 polymer cannot be proven.1

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

2) Respirometry

These methods measure oxygen consumed by bacteria during biodegradation of the polymer or CO2/CH4 evolved.1 The advantage is measuring the actual mineralization of the polymer. These methods can be proceeded only in laboratory using sophisticated equipment; thus, they poorly simulate natural conditions.

Scheme: Biodegradation stages and comparison of methods used for biodegradability evaluation. Adapted from ref.1

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

  • Declaring biodegradability based on physical measurements, but not proving mineralization.
  • Blaming biodegradable polymer not biodegradable, but not considering the type of environment for which the biodegradable polymer was originally certified.

Stating whether the polymer is, or is not biodegradable 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 polymer 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. Biodegradation 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 biodegradable certificates. As the only ones, they test also the toxicity of the polymer besides its biodegradability.

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

StandardLast revisionNameEnvironmentMethod
ISO 148512019Determination of the ultimate aerobic biodegradability of plastic materials in an aqueous medium — Method by measuring the oxygen demand in a closed respirometerWaste water and sewage sludge (aerobic)O2 consumption
ISO 148522018Determination of the ultimate aerobic biodegradability of plastic materials in an aqueous medium — Method by analysis of evolved carbon dioxideWaste water and sewage sludge (aerobic)CO2 production
ISO 139752019Plastics — Determination of the ultimate anaerobic biodegradation of plastic materials in controlled slurry digestion systems — Method by measurement of biogas productionWaste water and sewage sludge (anaerobic)CO2 and CH4 production
ISO 148532016Plastics — Determination of the ultimate anaerobic biodegradation of plastic materials in an aqueous system — Method by measurement of biogas productionWaste water and sewage sludge (anaerobic)CO2 and CH4 production
ISO 175562019Plastics — 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 evolvedSoilO2 consumption and CO2 production

ASTM 5988

(Equivalent to ISO 17556)

2018Standard Test Method for Determining Aerobic Biodegradation of Plastic Materials in SoilSoilCO2 production
OECD 3072002Aerobic and Anaerobic Transformation in SoilSoilCO2 evolution from radiolabelled polymer biodegradation (14C)
EN 170332018PlasticsBiodegradable mulch films for use in agriculture and horticulture – Requirements and test methodsSoil 

NF U 52-001

(French standard for mulch foils)

2013Biodegradable materials for use in agriculture and horticulture – mulching products – requirements and test methodsSoil 
ISO 196792020Plastics — Determination of aerobic biodegradation of non-floating plastic materials in a seawater/sediment interface — Method by analysis of evolved carbon dioxideMarineCO2 production
ISO 224032020Plastics — Assessment of the intrinsic biodegradability of materials exposed to marine inocula under mesophilic aerobic laboratory conditions — Test methods and requirementsMarine 
ISO 188302016Plastics — Determination of aerobic biodegradation of non-floating plastic materials in a seawater/sandy sediment interface — Method by measuring the oxygen demand in closed respirometerMarineO2 consumption
ASTM D79912015Standard Test Method for Determining Aerobic Biodegradation of Plastics Buried in Sandy Marine Sediment under Controlled Laboratory ConditionsMarineCO2 production
ASTM D74732012Standard Test Method for Weight Attrition of Plastic Materials in the Marine Environment by Open System Aquarium IncubationsMarineVisual evaluation, weight loss
ASTM D66912009Standard Test Method for Determining Aerobic Biodegradation of Plastic Materials in the Marine Environment by a Defined Microbial Consortium or Natural Sea Water InoculumMarineCO2 production
ISO 186062013Packaging and the environment — Organic recyclingIndustrial composting 
ISO 170882012Specifications for compostable plasticsIndustrial composting 
ISO 148552012Determination of the ultimate aerobic biodegradability of plastic materials under controlled composting conditions — Method by analysis of evolved carbon dioxideIndustrial compostingCO2 production

ASTM D5338

(Equivalent to ISO 14855)

2021Standard Test Method for Determining Aerobic Biodegradation of Plastic Materials Under Controlled Composting Conditions, Incorporating Thermophilic TemperaturesIndustrial composting 
ASTM D68682019Standard Specification for Labeling of End Items that Incorporate Plastics and Polymers as Coatings or Additives with Paper and Other Substrates Designed to be Aerobically Composted in Municipal or Industrial FacilitiesIndustrial composting 

ASTM D6400

(Equivalent to ISO 17088)

2019Standard Specification for Labeling of Plastics Designed to be Aerobically Composted in Municipal or Industrial FacilitiesIndustrial composting 
ASTM D55262018Standard Test Method for Determining Anaerobic Biodegradation of Plastic Materials Under Accelerated Landfill ConditionsLandifill / bioreactor 
EN 149952006Evaluation of compostability – Test scheme and specificationsIndustrial composting 
EN 134322001

Packaging – Requirements for packaging recoverable through composting

and biodegradation – Test scheme and evaluation criteria for the final acceptance of packaging

Industrial composting 
EN 140452003

Packaging – Evaluation of the disintegration of packaging materials in practical

oriented tests under defined composting conditions

CompostingVisual evaluation, weight loss
ISO 159852014Plastics — Determination of the ultimate anaerobic biodegradation under high-solids anaerobic-digestion conditions — Method by analysis of released biogasAnaerobicCO2 and CH4 production

ASTM D5511

(Equivalent to ISO 15985)

2018Standard Test Method for Determining Anaerobic Biodegradation of Plastic Materials Under High-Solids Anaerobic-Digestion ConditionsAnaerobic 

NF T 51-800

(French standard)

2015Plastics – Specifications for plastics suitable for home compostingHome composting 

AS 5810

(Australian standard)

2010Biodegradable plasticsBiodegradable plastics suitable for home compostingHome composting 

Table 1 – standard methods for determining polymer biodegradability

References

1 Harrison, 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.

2 Zumstein, M. T., R. Narayan, H.-P. E. Kohler, et al. Dos and Do Nots When Assessing the Biodegradation of Plastics. Environmental Science & Technology. 2019, 53(17): 9967-9969. doi: 10.1021/acs.est.9b04513.