EN ISO 17556:2019
(Main)Plastics - 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 (ISO 17556:2019)
Plastics - 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 (ISO 17556:2019)
This document specifies a method for determining the ultimate aerobic biodegradability of plastic materials in soil by measuring the oxygen demand in a closed respirometer or the amount of carbon dioxide evolved. The method is designed to yield an optimum degree of biodegradation by adjusting the humidity of the test soil.
If a non-adapted soil is used as an inoculum, the test simulates the biodegradation processes which take place in a natural environment; if a pre-exposed soil is used, the method can be used to investigate the potential biodegradability of a test material.
This method applies to the following materials:
— natural and/or synthetic polymers, copolymers or mixtures of these;
— plastic materials which contain additives such as plasticizers or colorants;
— water-soluble polymers.
It does not necessarily apply to materials which, under the test conditions, inhibit the activity of the microorganisms present in the soil. Inhibitory effects can be measured using an inhibition control or by another suitable method. If the test material inhibits the microorganisms in the soil, a lower test material concentration, another type of soil or a pre-exposed soil can be used.
Kunststoffe - Bestimmung der vollständigen aeroben Bioabbaubarkeit von Kunststoffmaterialien im Boden durch Messung des Sauerstoffbedarfs in einem Respirometer oder der Menge des entstandenen Kohlendioxids (ISO 17556:2019)
Dieses Dokument legt ein Verfahren zum Bestimmen der vollständigen aeroben biologischen Abbaubarkeit von Kunststoffmaterialien im Boden durch Messen des Sauerstoffbedarfs in einem geschlossenen Respiro-meter oder durch Messen der Menge des entwickelten Kohlendioxids fest. Das Verfahren ist entwickelt worden, um einen bestmöglichen Grad des biologischen Abbaus durch Einstellen der Feuchtigkeit des Prüfbodens zu erhalten.
Wenn ein nicht angepasster Boden als Inokulum verwendet wird, simuliert die Prüfung den biologischen Abbauprozess, der in einer natürlichen Umgebung abläuft; wird ein vorexponierter Boden verwendet, kann das Verfahren zum Untersuchen der potenziellen biologischen Abbaubarkeit eines Prüfmaterials ange¬wendet werden.
Dieses Verfahren gilt für folgende Materialien:
— natürliche und/oder künstliche Polymere, Copolymere oder deren Gemische;
— Kunststoffmaterialien, die Zusatzstoffe wie Weichmacher oder Farbmittel enthalten;
— wasserlösliche Polymere.
Dieses Verfahren gilt nicht notwendigerweise für Materialien, die unter Prüfbedingungen die Aktivität der im Boden vorhandenen Mikroorganismen beeinträchtigen. Inhibierungseffekte können durch Anwendung eines Inhibierungskontrollversuchs oder durch ein anderes geeignetes Verfahren gemessen werden. Wenn das Prüfmaterial die Mikroorganismen im Boden hemmt, kann eine geringere Konzentration des Prüfmate-rials, ein anderer Bodentyp oder ein vorexponierter Boden eingesetzt werden.
Plastiques - Détermination de la biodégradabilité aérobie ultime des matériaux plastiques dans le sol par mesure de la demande en oxygène dans un respiromètre ou de la teneur en dioxyde de carbone libéré (ISO 17556:2019)
Le présent document spécifie une méthode de détermination de la biodégradabilité aérobie ultime des matériaux plastiques dans le sol en mesurant la demande en oxygène dans un respiromètre fermé ou la quantité de dioxyde de carbone libéré. La méthode est conçue pour produire un taux de biodégradation optimal en ajustant l'humidité du sol d'essai.
Si un sol non modifié est utilisé comme inoculum, l'essai simule les processus de biodégradation qui ont lieu dans un environnement naturel; si un sol pré-exposé est utilisé, la méthode peut être utilisée pour étudier la biodégradabilité potentielle d'un matériau d'essai.
Cette méthode est applicable aux matériaux suivants:
— polymères, copolymères naturels et/ou synthétiques ou leurs mélanges;
— matériaux plastiques contenant des additifs tels que plastifiants ou colorants;
— polymères solubles dans l'eau.
Elle ne s'applique pas nécessairement aux matériaux qui, dans les conditions de l'essai, ont un effet inhibiteur vis-à-vis de l'activité des micro-organismes présents dans le sol. Les effets inhibiteurs peuvent être déterminés au moyen d'un contrôle de l'inhibition ou par une autre méthode appropriée. Si le matériau d'essai a un effet inhibiteur vis-à-vis des micro-organismes présents dans le sol, il est possible d'utiliser une concentration de matériau d'essai plus faible, un autre type de sol ou un sol pré-exposé.
Polimerni materiali - Ugotavljanje končne aerobne biorazgradljivosti polimernih materialov v zemlji z merjenjem porabe kisika v respirometru ali količine nastalega ogljikovega dioksida (ISO 17556:2019)
Ta dokument opisuje metodo za ugotavljanje končne aerobne biorazgradljivosti polimernih materialov v zemlji z merjenjem porabe kisika v zaprtem respirometru ali količine nastalega ogljikovega dioksida. Namen metode je doseči čim večjo stopnjo biorazgradljivosti s prilagoditvijo vlažnosti preskusne zemlje.
Če se kot inokulum uporabi neprilagojena zemlja, preskus simulira postopke biorazgraditve, ki potekajo v naravnem okolju; če se uporabi predhodno izpostavljena zemlja, se lahko metoda uporabi za preiskavo potencialne biorazgradljivosti preskusnega materiala.
Ta metoda zadeva naslednje materiale:
– naravne in/ali sintetične polimere, kopolimere ali njihove mešanice;
– polimerne materiale, ki vsebujejo dodatke, kot so mehčala ali barvila;
– polimere, topne v vodi.
Ne nanaša se nujno na materiale, ki pod preskusnimi pogoji zavirajo delovanje mikroorganizmov, prisotnih v zemlji. Zaviralne učinke je mogoče meriti na podlagi nadzora zaviranja ali z drugo ustrezno metodo. Če preskusni material zavira delovanje mikroorganizmov v zemlji, se lahko uporabi manjša koncentracija preskusnega materiala, druga vrsta zemlje ali predhodno izpostavljena zemlja.
General Information
Relations
Standards Content (Sample)
SLOVENSKI STANDARD
01-september-2019
Nadomešča:
SIST EN ISO 17556:2012
Polimerni materiali - Ugotavljanje končne aerobne biorazgradljivosti polimernih
materialov v zemlji z merjenjem porabe kisika v respirometru ali količine nastalega
ogljikovega dioksida (ISO 17556:2019)
Plastics - 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 (ISO 17556:2019)
Kunststoffe - Bestimmung der vollständigen aeroben Bioabbaubarkeit von
Kunststoffmaterialien im Boden durch Messung des Sauerstoffbedarfs in einem
Respirometer oder der Menge des entstandenen Kohlendioxids (ISO 17556:2019)
Plastiques - Détermination de la biodégradabilité aérobie ultime des matériaux
plastiques dans le sol par mesure de la demande en oxygène dans un respiromètre ou
de la teneur en dioxyde de carbone libéré (ISO 17556:2019)
Ta slovenski standard je istoveten z: EN ISO 17556:2019
ICS:
83.080.01 Polimerni materiali na Plastics in general
splošno
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
EN ISO 17556
EUROPEAN STANDARD
NORME EUROPÉENNE
May 2019
EUROPÄISCHE NORM
ICS 83.080.01 Supersedes EN ISO 17556:2012
English Version
Plastics - 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 (ISO 17556:2019)
Plastiques - Détermination de la biodégradabilité Kunststoffe - Bestimmung der vollständigen aeroben
aérobie ultime des matériaux plastiques dans le sol par Bioabbaubarkeit von Kunststoffmaterialien im Boden
mesure de la demande en oxygène dans un durch Messung des Sauerstoffbedarfs in einem
respiromètre ou de la teneur en dioxyde de carbone Respirometer oder der Menge des entstandenen
libéré (ISO 17556:2019) Kohlendioxids (ISO 17556:2019)
This European Standard was approved by CEN on 17 August 2018.
CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this
European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references
concerning such national standards may be obtained on application to the CEN-CENELEC Management Centre or to any CEN
member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by
translation under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC Management
Centre has the same status as the official versions.
CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania,
Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,
Turkey and United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2019 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 17556:2019 E
worldwide for CEN national Members.
Contents Page
European foreword . 3
European foreword
This document (EN ISO 17556:2019) has been prepared by Technical Committee ISO/TC 61 "Plastics"
in collaboration with Technical Committee CEN/TC 249 “Plastics” the secretariat of which is held by
NBN.
This European Standard shall be given the status of a national standard, either by publication of an
identical text or by endorsement, at the latest by November 2019, and conflicting national standards
shall be withdrawn at the latest by November 2019.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CEN shall not be held responsible for identifying any or all such patent rights.
This document supersedes EN ISO 17556:2012.
According to the CEN-CENELEC Internal Regulations, the national standards organizations of the
following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria,
Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, Former Yugoslav Republic of Macedonia,
France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta,
Netherlands, Norway, Poland, Portugal, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,
Turkey and the United Kingdom.
Endorsement notice
The text of ISO 17556:2019 has been approved by CEN as EN ISO 17556:2019 without any modification.
INTERNATIONAL ISO
STANDARD 17556
Third edition
2019-05
Plastics — 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
Plastiques — Détermination de la biodégradabilité aérobie ultime des
matériaux plastiques dans le sol par mesure de la demande en oxygène
dans un respiromètre ou de la teneur en dioxyde de carbone libéré
Reference number
ISO 17556:2019(E)
©
ISO 2019
ISO 17556:2019(E)
© ISO 2019
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting
on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address
below or ISO’s member body in the country of the requester.
ISO copyright office
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Phone: +41 22 749 01 11
Fax: +41 22 749 09 47
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii © ISO 2019 – All rights reserved
ISO 17556:2019(E)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 3
5 Test environment . 4
6 Materials . 4
7 Apparatus . 4
8 Procedure. 4
8.1 Preparation of the test material . 4
8.2 Preparation of the reference material . 5
8.3 Preparation of the test soil . 5
8.3.1 Collection and sieving of soil . 5
8.3.2 Preparation of standard soil . 6
8.3.3 Measurement of soil characteristics . 7
8.3.4 Adjustment of the water content and the pH of the soil . 7
8.3.5 Handling and storage of the soil . 7
8.4 Start-up and execution of the test . 7
9 Calculation and expression of results . 9
9.1 Calculation . 9
9.1.1 Percentage biodegradation from oxygen consumption values . 9
9.1.2 Percentage biodegradation from carbon dioxide evolved . 9
9.2 Expression and interpretation of results .10
10 Validity of results .10
11 Test report .10
Annex A (informative) Principle of a manometric respirometer (example) .12
Annex B (informative) Example of a system for measuring the amount of carbon dioxide
evolved .13
Annex C (informative) Examples of methods for the determination of evolved carbon dioxide .14
Annex D (informative) Theoretical oxygen demand (ThOD) .16
Annex E (informative) Example of a determination of the amount and the molecular mass
of water-insoluble polymer remaining at the end of a biodegradation test .17
Annex F (informative) Examples of long-term tests .18
Annex G (informative) Interlaboratory test .22
Bibliography .26
ISO 17556:2019(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 on 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 the following
URL: www .iso .org/iso/foreword .html.
This document was prepared by Technical Committee ISO/TC 61, Plastics, Subcommittee SC 14,
Environmental aspects.
This third edition cancels and replaces the second edition (ISO 17556:2012), which has been technically
revised. The main changes compared to the previous edition are as follows:
a) the unit for BOD, COD and DIC has been corrected (see Clause 3);
b) the formula for calculating the percent biodegradation has been modified (see 9.1.1);
c) the test period has been revised to two years at the longest (see Clause 4);
d) the number of replicates has been corrected to three (see 9.2).
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.
iv © ISO 2019 – All rights reserved
ISO 17556:2019(E)
Introduction
A number of plastic materials and products have been designed for applications ending up in or on
soil. They have been developed for applications where biodegradation is beneficial from a technical,
environmental, social or economic standpoint. Examples can be found in agriculture (e.g. mulching
film), horticulture (e.g. twines and clips, flower pots, pins), funeral items (e.g. body bags), recreation (e.g.
plastic “clay” pigeons for shooting, hunting cartridges), etc. In many cases, recovery and/or recycling of
these plastic items is either difficult or not economically viable. Various types of biodegradable plastics
have been developed which have been designed to biodegrade and disappear in situ at the end of their
useful life. Several International Standards specify test methods for determining the ultimate aerobic
or anaerobic biodegradation of plastic materials in aqueous or compost conditions. 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.
INTERNATIONAL STANDARD ISO 17556:2019(E)
Plastics — 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
WARNING — Appropriate precautions should be taken when handling soil because it might
contain potentially pathogenic organisms. Toxic test compounds and those whose properties
are unknown should be handled with care.
1 Scope
This document specifies a method for determining the ultimate aerobic biodegradability of plastic
materials in soil by measuring the oxygen demand in a closed respirometer or the amount of carbon
dioxide evolved. The method is designed to yield an optimum degree of biodegradation by adjusting the
humidity of the test soil.
If a non-adapted soil is used as an inoculum, the test simulates the biodegradation processes which take
place in a natural environment; if a pre-exposed soil is used, the method can be used to investigate the
potential biodegradability of a test material.
This method applies to the following materials:
— natural and/or synthetic polymers, copolymers or mixtures of these;
— plastic materials which contain additives such as plasticizers or colorants;
— water-soluble polymers.
It does not necessarily apply to materials which, under the test conditions, inhibit the activity of the
microorganisms present in the soil. Inhibitory effects can be measured using an inhibition control or
by another suitable method. If the test material inhibits the microorganisms in the soil, a lower test
material concentration, another type of soil or a pre-exposed soil can be used.
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 10390, Soil quality — Determination of pH
ISO 10694, Soil quality — Determination of organic and total carbon after dry combustion (elementary
analysis)
ISO 11274, Soil quality — Determination of the water-retention characteristic — Laboratory methods
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https: //www .iso .org/obp
ISO 17556:2019(E)
— IEC Electropedia: available at http: //www .electropedia .org/
3.1
ultimate aerobic biodegradation
breakdown of an organic compound by microorganisms in the presence of oxygen into carbon dioxide,
water and mineral salts of any other elements present (mineralization) plus new biomass
3.2
biochemical oxygen demand
BOD
mass concentration of dissolved oxygen consumed under specified conditions by the aerobic biological
oxidation of a chemical compound or organic matter
Note 1 to entry: It is expressed as milligrams of oxygen uptake per kilogram of test soil.
3.3
dissolved organic carbon
DOC
part of the organic carbon in water which cannot be removed by specified phase separation
Note 1 to entry: It is expressed as milligrams of carbon per litre.
−2
Note 2 to entry: Typical means of separation are centrifugation at 40 000 m⋅s for 15 min or membrane filtration
using membranes with pores of diameter 0,2 µm to 0,45 µm.
3.4
theoretical oxygen demand
ThOD
maximum theoretical amount of oxygen required to oxidize a chemical compound completely, calculated
from the molecular formula
Note 1 to entry: It is expressed as milligrams of oxygen uptake per milligram or gram of test compound.
3.5
theoretical amount of evolved carbon dioxide
ThCO
maximum theoretical amount of carbon dioxide evolved after completely oxidizing a chemical
compound, calculated from the molecular formula
Note 1 to entry: It is expressed as milligrams of carbon dioxide evolved per milligram or gram of test compound.
3.6
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 (3.8)
3.7
biodegradation phase
time, measured in days, from the end of the lag phase (3.6) of a test until about 90 % of the maximum
level of biodegradation (3.8) has been reached
3.8
maximum level of biodegradation
degree of biodegradation of a chemical compound or organic matter in a test, above which no further
biodegradation takes place during the test
3.9
plateau phase
time from the end of the biodegradation phase (3.7) until the end of the test
Note 1 to entry: It is measured in days.
2 © ISO 2019 – All rights reserved
ISO 17556:2019(E)
3.10
pre-conditioning
pre-incubation of soil under the conditions of the subsequent test in the absence of the chemical
compound or organic matter under test, with the aim of improving the performance of the test by
acclimatization of the microorganisms to the test conditions
3.11
pre-exposure
pre-incubation of soil in the presence of the chemical compound or organic matter under test, with the
aim of enhancing the ability of the soil to biodegrade the test material by adaptation and/or selection of
the microorganisms
3.12
water content
mass of water which evaporates from the soil when the soil is dried to constant mass at 105 °C, divided
by the dry mass of the soil
Note 1 to entry: This is simply the ratio between the mass of the water and that of the soil particles in a soil sample.
3.13
total water-holding capacity
mass of water which evaporates from soil saturated with water when the soil is dried to constant mass
at 105 °C, divided by the dry mass of the soil
3.14
total organic carbon
TOC
amount of carbon bound in an organic compound
Note 1 to entry: It is expressed as milligrams of carbon per 100 mg of the compound.
4 Principle
This method is designed to yield the optimum rate of biodegradation of a plastic material in a test soil
by controlling the humidity of the soil, and to determine the ultimate biodegradability of the material.
The plastic material, which is the sole source of carbon and energy, is mixed with the soil. The mixture
is allowed to stand in a flask over a period of time during which the amount of oxygen consumed
(BOD) or the amount of carbon dioxide evolved is determined. Provided the CO evolved is absorbed,
the BOD can be determined, for example, by measuring the amount of oxygen required to maintain
a constant gas volume in a respirometer flask, or by measuring either automatically or manually the
change in volume or pressure (or a combination of the two). An example of a suitable respirometer is
shown in Annex A. The amount of carbon dioxide evolved is measured at intervals dependent on the
biodegradation kinetics of the test substance by passing carbon-dioxide-free air over the soil and then
determining the carbon dioxide content of the air by a suitable method. Examples of suitable methods
are given in Annexes B and C.
The level of biodegradation, expressed as a percentage, is determined by comparing the BOD with
the theoretical oxygen demand (ThOD) or by comparing the amount of carbon dioxide evolved with
the theoretical amount (ThCO ). The influence of possible nitrification processes on the BOD has to
be considered. The normal test period is six months. The test may be shortened or extended until the
plateau phase (see 3.9) is reached, but the total test period shall not exceed two years.
Unlike ISO 11266, which is used for a variety of organic compounds, this document is specially designed
to determine the biodegradability of plastic materials.
ISO 17556:2019(E)
5 Test environment
Incubation shall take place in the dark or in diffused light in an enclosure which is free from vapours
toxic to microorganisms and is maintained at a temperature constant to within ±2 °C in the range
between 20 °C and 28 °C, preferably 25 °C.
6 Materials
6.1 Distilled water, containing less than 2 mg of DOC per litre.
6.2 Carbon dioxide absorber, preferably soda lime pellets.
7 Apparatus
Ensure that all glassware is thoroughly cleaned and, in particular, free from organic or toxic matter.
7.1 Closed respirometer, including test flasks and all other necessary equipment, located in a
constant-temperature enclosure or in a thermostatically controlled apparatus (e.g. a water-bath). An
example is described in Annex A.
Any respirometer capable of determining with sufficient accuracy the biochemical oxygen demand is
suitable, preferably an apparatus which measures and automatically replaces the oxygen consumed
so that no oxygen deficiency and no inhibition of the microbial activity occurs during the degradation
process.
7.2 Apparatus for measuring the amount of carbon dioxide evolved
7.2.1 Test flasks: glass vessels (e.g. conical flasks or bottles), fitted with tubing impermeable to
carbon dioxide to allow purging with gas, and located in a constant-temperature enclosure or in a
thermostatically controlled apparatus (e.g. a water-bath).
7.2.2 CO -free-air production system, capable of supplying CO -free air at a flow rate of several ml/
2 2
min to each test flask, held constant to within ±10 % (see example of system, including test vessels, in
Annex B). Alternatively, the incubation apparatus shown in ASTM D5988 may be used.
7.2.3 Analytical equipment for accurately determining carbon dioxide. Typical examples are
a carbon dioxide IR analyser, a dissolved inorganic carbon (DIC) analyser, apparatus for titrimetric
determination after complete absorption in a basic solution (see Annex C), and apparatus for the
gravimetric determination of carbon dioxide in accordance with ISO 14855-2.
7.3 Analytical balance.
7.4 pH-meter.
8 Procedure
8.1 Preparation of the test material
The test material shall be of known mass and contain sufficient carbon to yield a BOD or a quantity of
carbon dioxide that can be adequately measured by the analytical equipment used. Calculate the TOC
4 © ISO 2019 – All rights reserved
ISO 17556:2019(E)
from the chemical formula or determine it by a suitable analytical technique (e.g. elemental analysis or
measurement in accordance with ISO 8245) and calculate the ThOD or ThCO (see Annexes C and D).
NOTE Although elemental analysis is generally less accurate for macromolecules than for low-molecular-
mass compounds, the accuracy is usually acceptable for the purposes of calculating the ThOD or ThCO .
The amount of test material shall be sufficient to outweigh any variations in the background oxygen
consumption or any carbon dioxide evolved from the test soil: 100 mg to 300 mg of test material to
100 g to 300 g of soil is usually adequate. The maximum amount of test material is limited by the oxygen
supply to the test system. The use of 200 mg of test material with 200 g of soil is recommended unless
the soil contains an excessively large amount of organic matter.
When using test systems based on the determination of the carbon dioxide evolved, higher test material
amounts can be used (e.g. 2 500 mg for 200 g of soil) in order to increase the difference between the test
material CO production and the blank control CO production. Furthermore, a greater amount of test
2 2
material will be required if a final mass balance determination is to be carried out (see Annex E).
Pre-aeration of the test material or the addition of inert material is recommended, if necessary, to
reduce the respiration of the soil in the blank flasks.
The test material should preferably be used in powder form, but it may also be introduced in the form of
films, fragments or shaped articles.
Test samples may be reduced in size by means of cryogenic milling.
Experiments have shown that the ultimate degree of biodegradation is almost independent of the form
and shape of the test material. The speed of biodegradation, however, depends on the form and shape
of the material. Test materials of similar form and shape should therefore be used if different kinds of
plastic material are to be compared in tests of the same duration. If the test material is in the form of
a powder, small particles of known size distribution should be used. A particle-size distribution with
its maximum at 250 µm diameter is recommended. If the test material is not in powder form, the size
of the pieces of material should not be greater than 5 mm × 5 mm. Also, the size of the test equipment
used might depend on the form of the test material. It should be ascertained that no undesired changes
are caused in the test material due to the design of the equipment, such as grinders, used. Normally,
processing of the test material will not significantly influence the degradation behaviour of the material
(e.g. the use of powder in the case of composites).
Optionally, determine the hydrogen, oxygen, nitrogen, phosphorus and sulfur contents, as well as the
molecular mass of the test material, using, for example, size exclusion chromatography. Preferably,
plastic materials without additives such as plasticizers should be tested. When the material does contain
such additives, information on their biodegradability will be needed to assess the biodegradability of
the polymeric material itself.
For details on how to handle compounds with limited solubility in water, see ISO 10634.
8.2 Preparation of the reference material
Use as reference material a well-defined biodegradable polymer {microcrystalline-cellulose powder,
ashless cellulose filters or poly-(R)-3-hydroxybutyrate [(R)-PHB]}. If possible, the physical form and
size of the reference material should be comparable to that of the test material.
As a negative control, a non-biodegradable polymer (e.g. polyethylene) in the same physical form as the
test material may be used.
8.3 Preparation of the test soil
8.3.1 Collection and sieving of soil
Use natural soil collected from the surface layer of fields and/or forests. If the potential biodegradability
of the test material is to be assessed, this soil may be pre-exposed to the test material. Sieve the soil to
ISO 17556:2019(E)
give particles of less than 5 mm, preferably less than 2 mm, in size and remove obvious plant material,
stones and other inert materials.
It is important to remove organic solids, such as straw, as far as practicable because they can decompose
during the test and influence the results.
The soil may be pre-conditioned but, normally, pre-exposed soil should not be used, especially when
biodegradation behaviour in natural environments is being simulated. Depending on the purpose of the
test, however, pre-exposed soil may be used, provided that this is clearly stated in the test report (e.g.
percent biodegradation = x %, using pre-exposed soil) and the method of pre-exposure detailed. Pre-
exposed soil can be obtained from suitable laboratory biodegradation tests conducted under a variety
of conditions or from samples collected from locations where relevant environmental conditions exist
(e.g. contaminated areas or industrial treatment plants).
Record the sampling site, its location, the presence of plants or previous crops, the sampling date, the
sampling depth and, if possible, the soil history, such as details of fertilizer and pesticide application.
8.3.2 Preparation of standard soil
As an alternative to the natural soil described in 8.3.1, a standard soil may be used. The composition
of the standard soil is shown in Table 1. The use of standard soil is very useful in determining the
biodegradability of plastic materials in bulky soils (loamy or clayey soils), reducing handling and
aeration problems.
Table 1 — Standard-soil composition
Dry mass,
Constituent Remarks
g/kg
Industrial quartz Predominantly fine sand in which the size of more than 50 % of the parti-
700 g/kg
sand cles lies in the range 0,05 mm to 0,2 mm
Clay Kaolinite clay (containing not less than 30 % kaolinite) or calcium bentonite 100 g/kg
Natural soil See 8.3.1 160 g/kg
Use well-aerated compost from an aerobic composting plant. In order to
stabilize the microbial activity in the standard soil, it is recommended that
one-year-matured compost be used. If this is not possible, use a compost
Mature compost which has matured for a minimum of two-three months. The compost shall 40 g/kg
be homogeneous and free from large, inert objects, such as pieces of glass,
stones or pieces of metal. Remove them manually and then sieve the com-
post through a screen of mesh size about 2 cm to 5 cm.
To the soil specified in Table 1 are added the salts listed in Table 2, preferably dissolved in water and
preferably at the moment of adjustment of the water content (see 8.3.4).
Table 2 — Added salts
Constituent Molecular formula g/kg of soil
Potassium dihydrogenphosphate KH PO 0,2
2 4
Magnesium sulfate MgSO 0,1
Sodium nitrate NaNO 0,4
Urea CO(NH ) 0,2
2 2
Ammonium chloride NH Cl 0,4
A round-robin test was carried out to validate the standard soil (see Annex G).
6 © ISO 2019 – All rights reserved
ISO 17556:2019(E)
8.3.3 Measurement of soil characteristics
Knowledge of the soil characteristics is essential for full interpretation of the results of the study. It is
therefore recommended that at least the following tests be performed on the soil selected:
a) total water-holding capacity, in accordance with ISO 11274;
b) pH of the soil, in accordance with ISO 10390;
c) organic-matter content, in accordance with ISO 10694.
8.3.4 Adjustment of the water content and the pH of the soil
Adjust the water content of the soil to a suitable value for the test material by adding an appropriate
amount of water to the soil, or by drying the soil in the air in a shaded place followed by addition of an
appropriate amount of water. Adjust the pH of the soil to between 6,0 and 8,0 if it is not already within
this range.
NOTE The optimum water content of the test soil is dependent on the test material. It is usually between
40 % and 60 % of the total water-holding capacity.
It is recommended that the ratio of organic carbon in the test or reference material to nitrogen in
the soil (C:N ratio) be adjusted to at least 40:1, if it is not already at this level, so as to ensure good
biodegradation. This may be done by adding nitrogen as an aqueous solution of ammonium chloride or
by using an aqueous solution containing the salts listed in Table 2.
8.3.5 Handling and storage of the soil
Store the soil in a sealed container at 4 °C ± 2 °C until it is used in the test. Do not handle the soil in any
way that could inhibit the activity of the microorganisms in it.
ISO 10381-6 shall be followed to ensure that the microbial activity of the soil is not affected by sampling.
8.4 Start-up and execution of the test
Prepare the following numbers of flasks:
a) three test flasks for the test material (symbol F );
T
b) three test flasks for the blank control (symbol F );
B
c) three test flasks for checking the soil activity using a reference material (symbol F );
C
and, if required:
d) one flask for checking for possible abiotic degradation or non-biological changes in the test material
(symbol F );
S
e) one flask for checking for any possible inhibiting effect of the test material (symbol F ).
l
Place the soil (see 8.3) at the bottom of each flask and add test material (see 8.1) or reference material
(see 8.2), as indicated in Table 3, to the soil. Record the mass of each flask containing this test mixture.
When two replicates are used, this shall be stated in the test report.
It is important that the test material be homogeneously mixed with the soil, in the case of powder, and as
widely spread as possible in the soil, in the case of film, to improve the contact of the test material with
the microorganisms in the soil. Also, it is recommended that the surface of the test mixture be pressed
with a spatula to improve the contact between the test material and the microorganisms in the soil.
If the abiotic-degradation check is carried out, details of the procedures used to inhibit microbial
activity at the start of the test and maintain aseptic conditions during the test shall be provided in the
test report.
ISO 17556:2019(E)
Place the flasks in a constant-temperature environment (see Clause 5) and allow all the flasks to
reach the desired temperature. Make all necessary connections with the respirometer or CO -free-air
production system and start the incubation.
If measuring the oxygen consumption, take the necessary readings on the manometers (if manual) or
verify that the recorder of oxygen consumption is functioning correctly (automatic respirometer) (see
Annex A).
If measuring the carbon dioxide evolved, measure (at regular intervals depending on the carbon dioxide
evolution rate) the amount of carbon dioxide evolved from each flask, using a suitable and sufficiently
accurate method (see Annexes B and C).
Table 3 — Final distribution of test and reference materials
Reference
Flask Test material Test soil
material
F Test + − +
T
F Test + − +
T
F Test + − +
T
F Blank − − +
B
F Blank − − +
B
F Blank − − +
B
F Soil activity check − + +
C
F Soil activity check − + +
C
F Soil activity check − + +
C
F Abiotic-degradation check (optional) + − −
S
F Inhibition check (optional) + + +
I
+ = present;
− = not present.
If the biodegradation rate is considered to have slowed down because the test soil has dried out
during the test, stop the measurements and remove the flasks from the respirometer or CO -free-air
production system. Weigh the flasks and add a suitable amount of water to the test soil to bring its
water content back to its initial value. Reconnect the flasks to the system and restart measurement
of the oxygen consumed or carbon dioxide evolved. These operations shall be conducted without
inhibiting the activity of the soil microorganisms and without influencing the measurement of oxygen
consumption or carbon dioxide evolution, and the fact that they have been carried out shall be clearly
stated in the test report.
When a constant level of BOD or carbon dioxide evolution is attained (plateau phase reached) and no
further biodegradation is expected, the test is considered to be completed.
The test period should typically not exceed six months. However, if significant biodegradation
is still observed and the plateau phase has not been reached after this length of time, then the test
may be extended, but not to longer than two years. If the test is run for longer than six months, check
periodically for possible leaks. Any extension and any special measures taken, for example to ensure
microbial diversity or to provide sufficient nutrients, shall be detailed in the test report.
At the end of the test, remove the flasks and weigh them to check for any decrease in the water content
of the test soil. Optionally, the residual test material may be extracted from the soil with a suitable
solvent (if this is possible) and weighed.
8 © ISO 2019 – All rights reserved
ISO 17556:2019(E)
9 Calculation and expression of results
9.1 Calculation
9.1.1 Percentage biodegradation from oxygen consumption values
Read the oxygen consumption value for each flask, using the method given by the manufacturer for the
type of respirometer concerned, and determine the oxygen demand per kilogram of test soil. Calculate
the percentage biodegradation of the test material using Formula (1):
BB−
TtBt
D = ×100 (1)
t
T×ρ
T
where
D is the percentage biodegradation for test material at time t;
t
B is the BOD of the flask F containing test material at time t, in milligrams per kilogram of test
Tt T
soil, calculated by dividing the measured oxygen consumption, in milligrams, by the amount
of test soil, in kilograms;
B is the BOD of the blank control flask F at time t, in milligrams per kilogram of test soil;
Bt B
ρ is the concentration of the test material in the reaction mixture of flask F , in grams per kilo-
T T
gram of test soil;
T is the ThOD, in milligrams per gram of test material.
Calculate in the same way the BOD and percentage biodegradation of the reference material F and, if
C
included, the abiotic-degradation check F and the inhibition check F . For calculation of the ThOD, see
S I
Annex D.
9.1.2 Percentage biodegradation from carbon dioxide evolved
9.1.2.1 Theoretical amount of carbon dioxide evolved by test material
The theoretical amount of carbon dioxide evolved by the test material (ThCO ) is given, in milligrams,
by Formula (2):
ThCO =×mw× (2)
2 C
where
m is the mass of test material, in milligrams, introduced into the test system;
w is the carbon content of the test material, determined from the chemical formula or
C
from elemental analysis, expressed as a mass fraction;
44 and 12 are the relative molecular and atomic masses of carbon dioxide and carbon, respectively.
Calculate in the same way the theoretical amount of carbon dioxide evolved by the reference material
and by the mixture of test and reference material in flask F .
I
ISO 17556:2019(E)
9.1.2.2 Percentage biodegradation
Calculate the percentage biodegradation D for each test flask F from the amount of carbon dioxide
t T
evolved during each measurement interval using Formula (3):
ΣΣmm−
TB
D = ×100 (3)
t
ThCO
where
is the amount of carbon dioxide, in milligrams, evolved in the test flask F between the
Σ m T
T
start of the test and time t;
is the amount of carbon dioxide, in milligrams, evolved in the blank control flask F be-
B
Σ m
B
tween the start of the test and time t;
ThCO is the theoretical amount of carbon dioxide, in milligrams, evolved by the test material.
Calculate in the same way the percentage biodegradation of the reference material in the soil activity
check flask F .
C
9.2 Expression and interpretation of results
Compile a table of the BOD values or amounts of carbon dioxide measured and the percentage
biodegradation values for each point in time when measurements were made. For each flask, plot a
...
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