Plastics — Determination of specific aerobic biodegradation rate of solid plastic materials and disappearance time (DT50) under mesophilic laboratory test conditions

This document specifies a method to determine the specific aerobic biodegradation rate of solid, non-water soluble plastic materials under mesophilic conditions. NOTE The specific aerobic biodegradation rate (which, strictly speaking, is a specific mineralization rate, implying the assessment of the conversion of organic carbon into CO2 but neglecting biomass formation) is expressed as amount of carbon mineralized into CO2, per unit time, per unit area. The method described in this document does not provide information on the ultimate aerobic biodegradability of the tested samples. Biodegradability criteria for plastic materials under mesophilic conditions are provided for example by ISO 23517, and ISO 22403. The method described in this document shall be used to determine the DT50 only when the plastic material is proven to be intrinsically biodegradable using suitable standard specifications such as ISO 23517 and ISO 22403. Furthermore, the biodegradation rate determined on plastic materials whose ultimate biodegradation has not been proven, shall not be considered as a specific characteristic of the whole material. This document only considers the evolution of CO2 as direct measurement of mineralization of the tested sample. The method described in this document may be applied also to solid materials used as a reference. This document is not applicable for “marine, soil and freshwater biodegradable” claims of biodegradable plastic materials. For such purposes, see relevant product standards if available. NOTE Although results can indicate that the tested plastic materials and polymers will biodegrade under the specified test conditions at a certain specific aerobic biodegradation rate or DT50, the results of any laboratory exposure are not directly applicable to environmental compartments including soil, marine environments and limnic areas at the actual site of use or leakage.

Plastiques — Détermination du taux de biodégradation aérobie spécifique des matières plastiques solides et du temps de disparition (DT50) dans des conditions d'essai de laboratoire mésophile

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Status
Published
Publication Date
16-Jun-2022
Current Stage
6060 - International Standard published
Due Date
07-Jul-2023
Completion Date
17-Jun-2022
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INTERNATIONAL ISO
STANDARD 5148
First edition
2022-06
Plastics — Determination of specific
aerobic biodegradation rate of solid
plastic materials and disappearance
time (DT50) under mesophilic
laboratory test conditions
Plastiques — Détermination du taux de biodégradation aérobie
spécifique des matières plastiques solides et du temps de disparition
(DT50) dans des conditions d'essai de laboratoire mésophile
Reference number
ISO 5148:2022(E)
© ISO 2022
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ISO 5148:2022(E)
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© ISO 2022

All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may

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© ISO 2022 – All rights reserved
---------------------- Page: 2 ----------------------
ISO 5148:2022(E)
Contents Page

Foreword ........................................................................................................................................................................................................................................iv

Introduction .................................................................................................................................................................................................................................v

1 Scope ................................................................................................................................................................................................................................. 1

2 Normative references ..................................................................................................................................................................................... 1

3  Terms and definitions .................................................................................................................................................................................... 1

4 Principle ........................................................................................................................................................................................................................ 3

5 Apparatus .................................................................................................................................................................................................................... 3

5.1 Sieves ............................................................................................................................................................................................................... 3

5.2 Sieve shaker ............................................................................................................................................................................................... 4

5.3 Laser particle size analyser (i.e. laser diffraction instrument) .................................................................. 4

5.4 Micropore and chemisorption analyser ........................................................................................................................... 4

6  Determination of the specific surface area (SSA) of test sample .....................................................................4

6.1 General ........................................................................................................................................................................................................... 4

6.2 Powder test sample ............................................................................................................................................................................ 4

6.2.1 Sample preparation ......................................................................................................................................................... 4

6.2.2 Specific surface area determination ................................................................................................................. 4

6.3 Film/sheet test sample .................................................................................................................................................................... 6

6.3.1 Sample preparation ......................................................................................................................................................... 6

6.3.2 Specific surface area determination ................................................................................................................. 6

7 Determination of the net CO evolution ...................................................................................................................................... 7

8  Determination of the specific aerobic biodegradation rate and disappearance time ..............8

8.1 Determination of C disappearance .................................................................................................................................... 8

8.2 Determination of specific aerobic biodegradation rate ..................................................................................... 9

8.3 Determination of DT50 ................................................................................................................................................................... 9

9 Test report ...............................................................................................................................................................................................................10

Annex A (informative) Example for the determination of r and DT50 ................................................................11

SAB

Bibliography .............................................................................................................................................................................................................................16

iii
© ISO 2022 – All rights reserved
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ISO 5148:2022(E)
Foreword

ISO (the International Organization for Standardization) is a worldwide federation of national standards

bodies (ISO member bodies). The work of preparing International Standards is normally carried out

through ISO technical committees. Each member body interested in a subject for which a technical

committee has been established has the right to be represented on that committee. International

organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.

ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of

electrotechnical standardization.

The procedures used to develop this document and those intended for its further maintenance are

described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the

different types of ISO documents should be noted. This document was drafted in accordance with the

editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).

Attention is drawn to the possibility that some of the elements of this document may be the subject of

patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of

any patent rights identified during the development of the document will be in the Introduction and/or

on the ISO list of patent declarations received (see www.iso.org/patents).

Any trade name used in this document is information given for the convenience of users and does not

constitute an endorsement.

For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and

expressions related to conformity assessment, as well as information about ISO's adherence to

the World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see

www.iso.org/iso/foreword.html.

This document was prepared by Technical Committee ISO/TC 61, Plastics, Subcommittee SC 14,

Environmental aspects.

Any feedback or questions on this document should be directed to the user’s national standards body. A

complete listing of these bodies can be found at www.iso.org/members.html.
© ISO 2022 – All rights reserved
---------------------- Page: 4 ----------------------
ISO 5148:2022(E)
Introduction

Several test methods have been developed by ISO to measure the biodegradation degree of plastics.

Under aerobic conditions, the biodegradation reaction of a material is described by the following

reaction:
C + O → C + H O + C
M 2 CO 2 B
where

C is the organic carbon present in the test material (e.g. a polymer or a plastic material);

is the carbon evolved as carbon dioxide;

C is the carbon assimilated by microorganism and incorporated in the microbial biochemistry.

The test methods follow the biodegradation reaction by measuring either the oxygen uptake

(disappearance of the reactant) or the CO evolution (formation of the product). The test methods

return a biodegradation percentage (which, strictly speaking, is a "mineralization" percentage). This

value is the reaction yield percentage, i.e. the mass of carbon oxidised to CO during the reaction (actual

yield) in comparison with the maximum possible yield (theoretical yield). This is expressed as evolved

CO /theoretical CO , the latter value being the amount of CO obtained in case of total oxidation of the

2 2 2
original carbon present in the test substance.

A reliable test method for the determination of the C , i.e. the amount of C that has been assimilated in

B M
the biomass is not available at the date of publication.

The test methods are suitable for measuring the final degree of biodegradation but are not suitable for

measuring the biodegradation rate, because they do not take into account the surface area of the tested

sample. On the other hand, this document provides a guidance on how to measure the biodegradation

rate using existing test methods.

Biodegradation of solid, non-water soluble polymers and plastics is a heterogeneous reaction because

the polymer is in the solid state while microbes and enzymes are in the liquid phase. Even when the

tested material is exposed to solid matrices (e.g. compost, soil, marine sediment) the microbes are in

the liquid phase present within the solid matrix (e.g. micropores, macropores). Thus, the reaction of

biodegradation happens in the liquid/solid interphase and the available surface area can become a

limiting factor. It is a common knowledge that milling increases the biodegradation rate of a plastic

sample. The biodegradation speed, i.e. the CO evolution and the O uptake rates, is controlled by the

2 2

surface area of the tested sample. Therefore, biodegradation rate must be expressed as a function of the

available surface area, otherwise the information is pointless and paradoxical results can be obtained.

There is an increasing interest in determining the biodegradation rate and related parameters (such

as the disappearance time 50, DT50, i.e. the time within which the initial concentration of the test

substance is reduced by 50 %) in order to assess the risk in the case of accidental or deliberate leakage

of biodegradable plastics into the environment. Degradation of organic substances in the environment

influences exposure and, hence, it is a key parameter for estimating the risk of long-term adverse effects

on biota.

This document enables to determine the specific aerobic biodegradation rate i.e. the amount of carbon

mineralized per unit time per unit surface area, under the conditions defined by the applied test method.

The approach showed in this document is aimed to measure mineralization rate. It differs from

ISO 23832 that describes a test method for the determination of the physical degradation rate and

disintegration degree of plastic materials. On the other hand, ISO 22403 identifies the plastic materials

that show intrinsic biodegradability when exposed to marine inocula under mesophilic aerobic

laboratory conditions.
© ISO 2022 – All rights reserved
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INTERNATIONAL STANDARD ISO 5148:2022(E)
Plastics — Determination of specific aerobic
biodegradation rate of solid plastic materials and
disappearance time (DT50) under mesophilic laboratory
test conditions
1 Scope

This document specifies a method to determine the specific aerobic biodegradation rate of solid, non-

water soluble plastic materials under mesophilic conditions.

NOTE The specific aerobic biodegradation rate (which, strictly speaking, is a specific mineralization rate,

implying the assessment of the conversion of organic carbon into CO but neglecting biomass formation) is

expressed as amount of carbon mineralized into CO , per unit time, per unit area.

The method described in this document does not provide information on the ultimate aerobic

biodegradability of the tested samples. Biodegradability criteria for plastic materials under

mesophilic conditions are provided for example by ISO 23517, and ISO 22403. The method described

in this document shall be used to determine the DT50 only when the plastic material is proven to be

intrinsically biodegradable using suitable standard specifications such as ISO 23517 and ISO 22403.

Furthermore, the biodegradation rate determined on plastic materials whose ultimate biodegradation

has not been proven, shall not be considered as a specific characteristic of the whole material.

This document only considers the evolution of CO as direct measurement of mineralization of the

tested sample.

The method described in this document may be applied also to solid materials used as a reference.

This document is not applicable for “marine, soil and freshwater biodegradable” claims of biodegradable

plastic materials. For such purposes, see relevant product standards if available.

NOTE Although results can indicate that the tested plastic materials and polymers will biodegrade under the

specified test conditions at a certain specific aerobic biodegradation rate or DT50, the results of any laboratory

exposure are not directly applicable to environmental compartments including soil, marine environments and

limnic areas at the actual site of use or leakage.
2 Normative references

The following documents are referred to in the text in such a way that some or all of their content

constitutes requirements of this document. For dated references, only the edition cited applies. For

undated references, the latest edition of the referenced document (including any amendments) applies.

ISO 4591, Plastics — Film and sheeting — Determination of average thickness of a sample, and average

thickness and yield of a roll, by gravimetric techniques (gravimetric thickness)

ISO 4593, Plastics — Film and sheeting — Determination of thickness by mechanical scanning

3  Terms and definitions
For the purposes of this document, the following terms and definitions apply.

ISO and IEC maintain terminology databases for use in standardization at the following addresses:

— ISO Online browsing platform: available at https:// www .iso .org/ obp
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ISO 5148:2022(E)
— IEC Electropedia: available at https:// www .electropedia .org/
3.1
film

thin planar product of arbitrarily limited maximum thickness, in which the thickness is very small

compared to the length and width and which is generally supplied in roll form

Note 1 to entry: The arbitrary thickness limit can differ between countries and often between materials.

Note 2 to entry: The thickness of films is typically 0,01 mm to 0,3 mm.
[SOURCE: ISO 10210: 2012, 3.4]
3.2
pellet

small mass of preformed moulding material, having relatively uniform dimensions in any given batch

and used as feedstock in moulding and extrusion operations
Note 1 to entry: The average diameter of pellets can range from 1 mm to 5 mm.
[SOURCE: ISO 10210:2012, 3.5]
3.3
test material

product from which a test sample is taken and used to assess the biodegradability of a polymeric item

by means of standardized biodegradation tests
[SOURCE: ISO 10210:2012, 3.8]
3.4
specific surface area
SSA
ratio of the surface area of a sample of a solid material to its mass
2 -1
Note 1 to entry: It is expressed in square centimetres per gram (cm × g ).
3.5
lag phase

time, measured in days, from the start of a test until adaptation and/or selection of the degrading

microorganisms is achieved and the degree of biodegradation of a chemical compound or organic

matter has increased to about 10 % of the maximum level of biodegradation
[SOURCE: ISO 17556:2019, 3.6]
3.6
specific aerobic biodegradation rate
SAB

ratio of the mineralization rate coefficient, k, to the specific surface area, SSA (3.4)

-1 -2
Note 1 to entry: It is generally expressed in mmol C × day × cm .

Note 2 to entry: This is an assessment of the conversion rate of organic carbon into CO2 which neglects biomass

formation
3.7
disappearance time 50
DT50

time required for the concentration of the organic carbon of a sample of a solid material to decrease by

50 % of its original value
Note 1 to entry: It is generally expressed in days.
Note 2 to entry: DT50 is also called "dissipation time".
© ISO 2022 – All rights reserved
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ISO 5148:2022(E)
3.8
mineralisation rate coefficient

slope of the regression line representing the mineralization of a test material (3.3) versus time

Note 1 to entry: It is expressed as millimoles of C that are mineralized into CO per day (mmol C × day ).

4 Principle

The present document describes a method to determine the specific aerobic biodegradation rate and

disappearance time DT50 of solid, non-water soluble plastic materials.

The method described in this document can be considered as an additional extension ("add-on") of

the existing ISO standard test methods for measuring biodegradation of plastic materials in order to

determine the specific aerobic biodegradation rate.

This document only considers the evolution of CO as direct measurement of mineralization of the

tested sample. The specific aerobic biodegradation rate is intended as specific mineralization rate,

and it implies the assessment of the conversion of organic carbon of material into CO but neglecting

biomass formation. This rate is expressed as amount of carbon mineralized into CO , per unit time, per

-1 -2
unit area. It is measured as millimoles C× day × cm .

Thus, the DT50 as determined following this document is an underestimation of the true dissipation of

the tested materials, because conversion into biomass is not accounted for.

The method described in this document can be considered as an additional extension ("add-on"), i.e.

a method for the elaboration and expression of results, of the existing ISO and ASTM standard test

methods for measuring biodegradation of plastic materials under different test conditions:

— ISO 14852;
— ISO 17556;
— ASTM D5988;
— ISO 22404;
— ISO 19679;
— ISO 23977-1;
— ASTM D6691;
— ASTM D7991;

The present method makes it possible to determine the specific aerobic biodegradation rate and the

disappearance time 50 (DT50) of a test material when tested using existing ISO test methods for

biodegradation under mesophilic conditions in relation to surface area of test material.

5 Apparatus
5.1 Sieves

Sample powders with a specific particle size are obtained by using sieves of different sizes, to remove

the oversize and undersize fractions. The recommended sieve sizes are of 60 and 120 mesh (250 µm

and 125 µm) as specified in ISO 10210.
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ISO 5148:2022(E)
5.2 Sieve shaker

An automatic sieve shaker is recommended for the separation of the milled test sample powders. An

automatic sieve vibrator can accommodate more than two sieves and will produce more consistent

results than the manual use of sieves.
5.3 Laser particle size analyser (i.e. laser diffraction instrument)

Laser diffraction particle size analysers can be used to measure the sizes of particles of powder/granule

of test material, both in wet or dry dispersion. The laser diffraction method assumes a spherical particle

shape in its optical model. Particle size is calculated by measuring the angle of light scattered by the

particles as they pass through a laser beam. The applicable size range is approximately between 0,1 µm

to 3 mm, following ISO 13320.
5.4 Micropore and chemisorption analyser

The total surface can also be measured with instruments based on the BET method for the determination

of the specific surface area of solids by gas adsorption, according to ISO 9277.
6  Determination of the specific surface area (SSA) of test sample
6.1 General

The present method shall be applied to pellets of the plastics material under study, either milled (see

6.2) or converted in films (see 6.3) depending on the test method used for measuring biodegradation.

The specific surface area of a plastic sample (SSA) is the surface area per unit mass, it is an average and

2 -1
it is expressed as cm × g of sample.

The density of test material shall be known in order to calculate the SSA of a sample in powder form.

If a film/sheet is used as a sample, its thickness shall be known for the determination of its SSA.

6.2 Powder test sample
6.2.1 Sample preparation

Refer to ISO 10210:2012, 7.2, for milling of plastic pellets and preparation of a specific size fraction

from the powder.
...

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