ISO 24304:2026

International
Standard
ISO 24304
First edition
Textiles — Determination of the
2026-10
aerobic biodegradation of textile
materials in seawater
Textiles — Détermination de la biodégradation aérobie dans
l'eau de mer des matériaux textiles
Reference number
© ISO 2026
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ii
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 Apparatus . 4
7 Reagents and materials . 5
8 Test method . 6
8.1 Preparation of natural seawater with or without sediment .6
8.2 Preparation of test material .7
8.2.1 Test material size and shape .7
8.2.2 Test material amount for biochemical oxygen demand (BOD) measurement .7
8.2.3 Test material amount for evolved carbon dioxide measurement .7
8.3 Preparation of reference material . .7
8.4 Preparation of flasks (6.2) .8
8.5 Pre-conditioning .8
8.6 Test procedure .8
8.7 Measurements . .9
8.7.1 Biochemical oxygen demand (BOD) .9
8.7.2 Evolved carbon dioxide .9
8.8 Duration of the test .10
9 Calculation .10
9.1 Total aerobic biodegradation .10
9.1.1 General .10
9.1.2 Calculation of total aerobic biodegradation from biochemical oxygen demand
(BOD) .10
9.1.3 Calculation of total aerobic biodegradation from evolved carbon dioxide .11
9.2 Relative biodegradation .11
10 Expression and interpretation of results .11
11 Validity of results .12
12 Test report .12
Annex A (informative) Example of a system for measuring biochemical oxygen demand (BOD)
and the amount of evolved carbon dioxide (8.7.2) . 14
Annex B (informative) Examples of total and relative aerobic biodegradation for fibre and yarn
test materials in seawater, measured by evolved carbon dioxide (8.7.2) .15
Annex C (informative) Example of determining a plateau phase . 19
Bibliography .21

iii
Foreword
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This document was prepared by Technical Committee ISO/TC 38, Textiles.
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iv
Introduction
This document was developed in response to worldwide demand for evaluation of biodegradability of
textile materials as these products release fibre fragments after washing and thus, contribute to pollution
of oceans. In addition to fibres shed from garments and home textiles, there are fibre fragments found in
marine environments released from textile bodies. In order to address the environmental impact of textile
and fibre fragments in marine environments and to carry out a proper product design, it is important to
know how a textile material biodegrades in a specified environment.
Test methods for measuring the level of marine biodegradation are available for plastic materials, however,
there is no standard test method available for the evaluation of marine biodegradability of textile materials.
This test method fills that knowledge gap and aims to analyse the biodegradation of textile materials based
on oxygen and carbon dioxide contents.
This test method is intended for comparative laboratory studies on textile materials and is not intended to
be used for product claims or labelling.

v
International Standard ISO 24304:2026(en)
Textiles — Determination of the aerobic biodegradation of
textile materials in seawater
1 Scope
This document specifies a laboratory test method for the determination of the aerobic biodegradability of
textile materials in seawater by measuring the biochemical oxygen demand (BOD) or the amount of evolved
carbon dioxide.
This method involves a test under an aerobic condition, which is intended to replicate the sea surface area
conditions. It applies to textile materials, such as staple fibres, tops, yarns and fabrics. This test method is not
intended for evaluating anaerobic biodegradation of textile materials, as simulating deep sea environments
is out of the scope of this document.
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 139, Textiles — Standard atmospheres for conditioning and testing
ISO 3696, Water for analytical laboratory use — Specification and test methods
ISO 5667-3, Water quality — Sampling — Part 3: Preservation and handling of water samples
ISO 8245, Water quality — Guidelines for the determination of total organic carbon (TOC) and dissolved organic
carbon (DOC)
ISO 10523, Water quality — Determination of pH
ISO 11261, Soil quality — Determination of total nitrogen — Modified Kjeldahl method
ISO 20743:2021, Textiles — Determination of antibacterial activity of textile products
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 http:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
3.1
pelagic zone
water body above the seafloor
Note 1 to entry: It is also referred to as the open water or the water column.
Note 2 to entry: The surface of the pelagic zone is moved by wind-driven waves, is in contact with the atmosphere and
exposed to sunlight. With increasing depth pressure increases, temperature decreases, and light and surface wave
energy are attenuated.
[1]
[SOURCE: ISO 22766:2020 , 3.4]
3.2
littoral zone
shallow marginal zone of a body of water where light penetrates to the bottom and is usually colonized by
rooted vegetation
[2]
[SOURCE: ISO 6107:2021 , 3.322]
3.3
biochemical oxygen demand
BOD
mass concentration of the dissolved oxygen consumed under specified conditions by the aerobic biological
oxidation of a chemical compound or organic matter in water
Note 1 to entry: It is expressed as milligrams of oxygen uptake per milligram or gram of test compound.
[3]
[SOURCE: ISO 18830:2016 , 3.1]
3.4
theoretical oxygen demand
ThOD
maximum theoretical amount of oxygen required to oxidise 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]
[SOURCE: ISO 18830:2016 , 3.2]
3.5
theoretical amount of evolved carbon dioxide
ThCO
maximum theoretical amount of evolved carbon dioxide after completely oxidizing a chemical compound,
calculated from the molecular formula
Note 1 to entry: It is calculated from the molecular formula.
Note 2 to entry: It is expressed as milligrams of carbon dioxide evolved per milligram or gram of test compound.
[4]
[SOURCE: ISO 14852:2021 , 3.5]
3.6
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.
[5]
[SOURCE: ISO 17556:2019 , 3.14]
3.7
dissolved inorganic carbon
DIC
part of the inorganic carbon in water which cannot be removed by specified phase separation
−2
Note 1 to entry: Phase separation can be achieved, for example, by centrifugation at 40 000 m⋅s for 15 min or by
membrane filtration using membranes with pores of 0,2 µm to 0,45 µm diameter.
[4]
[SOURCE: ISO 14852:2021 , 3.4]

3.8
lag phase
time 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 (3.11)
Note 1 to entry: It is measured in days.
[4]
[SOURCE: ISO 14852:2021 , 3.8]
3.9
biodegradation phase
time from the end of the lag phase (3.8) of a test until the plateau phase (3.10) has been reached
Note 1 to entry: It is measured in days.
[4]
[SOURCE: ISO 14852:2021 , 3.10]
3.10
plateau phase
time from the end of the biodegradation phase (3.9) until the end of a test
Note 1 to entry: It is measured in days.
[4]
[SOURCE: ISO 14852:2021 , 3.11]
3.11
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
Note 1 to entry: It is measured in percent.
[4]
[SOURCE: ISO 14852:2021 , 3.9]
3.12
total aerobic biodegradation
biodegradation value which is calculated by dividing the theoretical oxygen demand (ThOD) (3.4) with the
ratio of actual oxygen consumption when measuring biochemical oxygen demand (3.3) or by dividing the
theoretical amount of evolved carbon dioxide (ThCO ) (3.5)2) with the ratio of actual evolved carbon dioxide
when measuring evolved carbon dioxide
Note 1 to entry: It is expressed as percentage biodegradation.
3.13
relative aerobic biodegradation
biodegradation value of test material relative to the total aerobic biodegradation (3.12) of the reference
material
Note 1 to entry: It is expressed as percentage biodegradation.
4 Principle
This method primarily applies to untreated or uncoated textile materials; for finished products, results shall
be interpreted with caution.
A textile material (e.g. fibre, yarn, or textile) is used as a test material. The test material is cut and placed
in a flask (6.2) under mesophilic test conditions for up to one year by incubating test materials with either
seawater only (“pelagic seawater test”, also see pelagic zone) or with seawater to which low amount of
sediment has been added (“suspended sediment seawater test”), coming from the same site as that from
which the seawater was taken.
Evaluation of biodegradation can be performed by two methods, biochemical oxygen demand (BOD) and the
amount of evolved carbon dioxide. The test material, which is the sole source of carbon and energy, is mixed
with seawater and/or suspended sediment seawater in a closed flask (6.2) and is allowed to stand over a
period of time. Microorganisms in the vessel consume oxygen and form carbon dioxide which is absorbed in
a suitable absorber in the headspace of the flask (6.2).
The consumption of oxygen biochemical oxygen demand (BOD) is determined, for example, by measuring
the amount of oxygen required to maintain a constant volume of gas in the respirometer flasks (6.2), or by
measuring the change in volume or pressure (or a combination of the two) either automatically or manually.
The level of biodegradation is determined by comparing the biochemical oxygen demand (BOD) with the
theoretical oxygen demand (ThOD) and expressed in percentage.
Measurement of the evolution of carbon dioxide is performed using a suitable, analytical method. The level
of biodegradation is determined by comparing the amount of evolved carbon dioxide with the theoretical
amount of evolved carbon dioxide (ThCO ) and expressed in percentage.
The test result is the maximum level of biodegradation, determined from the plateau phase of the
biodegradation curve.
This method is intended to compare the aerobic biodegradability potential between textile materials under
laboratory conditions. The test conditions described in this document may not always correspond to the
optimum conditions for maximum degree of aerobic biodegradation to occur, nor represent the actual
aerobic seawater environment conditions.
As this document relies on an aerobic principle, this test method is not intended to evaluate the
[6]
biodegradability potential under anaerobic sea environments , for example, in a mud on the sea floor,
which has relatively very low level of dissolved oxygen. Thus, the overall marine biodegradability potential
of a textile material or product cannot be evaluated by this method alone.
5 Test environment
Incubation shall take place in the dark or in diffused light, in an enclosure which is free from vapours
inhibitory to marine microorganisms and which is maintained at a constant mesophilic temperature. During
the test, the incubation temperature should be controlled under (20 ± 2) °C as a standard condition.
Temperature conditions between 15 °C to 25 °C is acceptable, as long as the selected condition is justified
and clearly indicated in the test report. Justification should be stated in consideration of actual marine
environment conditions, bridging the test conditions with other related standards for specific purposes, or
for the purpose of evaluating the effect of temperatures on the degradation process.
6 Apparatus
6.1 Plastic and glass vessels shall be carefully cleaned and, in particular, made free of absorbed toxic and
[7]
biodegradable compounds and shall be protected from contamination. Also see ISO 5815-1 .
6.2 Flask, made of glass with a volume approximately 300 ml. Flasks with higher or lower volumes can
be used, if environmental conditions are not affected. Ensure that all flasks are thoroughly cleaned and, in
particular, free from organic or toxic matter.
6.3 Biochemical oxygen demand (BOD) measurement system. Any closed respirometer with sufficient
accuracy to measure the biochemical oxygen demand (BOD), preferably a respirometer which can measure
and replace automatically and continuously the oxygen consumed so that no oxygen deficiency and no
inhibition of the microbial activity occurs during the degradation process. As carbon dioxide absorbers use
sodium hydroxide pellets or another suitable absorbent.
An example of the apparatus is shown in Annex A.

6.4 Apparatus for measuring nitrate and nitrite concentrations. At the end of the biodegradation
test, a qualitative test (for example test strips or photometric tests for nitrate and nitrite) is recommended
[7]
first to decide if any nitrification (seeISO 5815-1 ) has occurred. If there is evidence of nitrate/nitrite
in the medium, a quantitative determination of the oxygen demand due to nitrification is required (see
[8]
ISO 14851:2019 , Annex B).
6.5 Apparatus for measuring the amount of evolved carbon dioxide, with sufficient accuracy, such as
a carbon dioxide or dissolved inorganic carbon (DIC) analyser or apparatus for titrimetric determination
after complete absorption in a basic solution. Container for the carbon dioxide absorber (CO absorber), (e.g.
glass beaker) to be located in the headspace of a test flask (6.2) and filled with 10 ml of 0,0125 mol/l Ba(OH)
(7.3) or 3 ml of 0,5 mol/l KOH (7.4). As an alternative to Ba(OH) and KOH 5 ml of 1 mol/l NaOH (7.5) can be
used as a CO absorber in the case of 300 ml reaction vessel.
A suitable apparatus is shown in Annex A.
6.6 Analytical balance, which shall have a resolution of at least 0,1 mg.
6.7 pH-meter, which fulfils the requirements for the determination of pH, as specified in ISO 10523.
6.8 Magnetic stirrer and magnetic stirring bar, used for mixing the seawater with the sediment
(“suspended sediment seawater test”). It is recommended that either a PTFE-coated dumbbell shaped
magnetic stirring bar be used or a PTFE-coated magnetic bar equipped with a pivot ring in order to reduce
excessive abrasion of sediment during the test period. Other stirring systems can be used, too.
6.9 Automatic titrator.
6.10 Autoclave, capable of operating at a temperature of (121 ± 2) °C , in accordance with ISO 20743:2021,
5.28.
6.11 Filter, pore size of ≤200 μm.
7 Reagents and materials
All reagents and materials shall have the quality suitable for microbiological tests, i.e. free of toxic substances
for use with microorganisms.
7.1 Sterilized water, which shall be analytical-grade water for microbiological media preparation, which
is ion-exchanged and/or freshly distilled and/or ultra-filtered and/or filtered with reverse osmosis (RO) or
grade 3 water in accordance with ISO 3696. Sterilize by an autoclave (6.10) at a temperature of 121 °C for 15
min before use.
7.2 0,05 mol/l barium hydroxide solution (0,05 mol/l Ba(OH) ), analytical reagents grade (AR).
7.3 0,012 5 mol/l barium hydroxide solution (0,012 5 mol/l Ba(OH) ).
Prepare the solution at the concentration of 0,012 5 mol/l by mixing 100 ml of 0,05 mol/l Ba(OH) (7.2) with
400 ml of sterilized water (7.1).
7.4 0,5 mol/l potassium hydroxide solution (0,5 mol/l KOH), analytical reagents grade (AR).
7.5 1 mol/l sodium hydroxide solution (1 mol/l NaOH), analytical reagents grade (AR).
7.6 1 mol/l hydrochloric acid solution (1 mol/l HCl), analytical reagents grade (AR).

7.7 0,05 mol/l hydrochloric acid solution (0,05 mol/l HCl), analytical reagents grade (AR).
7.8 Phenolphthalein, analytical reagents grade (AR).
7.9 Potassium dihydrogen phosphate (KH PO ), analytical reagents grade (AR).
2 4
7.10 Ammonium chloride (NH Cl), analytical reagents grade (AR).
7.11 Sodium nitrate (NaNO ), analytical reagents grade (AR).
1)
7.12 Microcrystalline cellulose powder, CAS RN® 9004-34-6, fine crystalline powder, purity not less
than 98 %.
8 Test method
8.1 Preparation of natural seawater with or without sediment
The natural seawater shall be collected from a littoral zone.
Sampling, preservation, handling, transport and storage of natural seawater, and, if applicable, sediment
collected from the same site as that from which the seawater is taken, shall be in accordance with ISO 5667-3.
Prior to use, remove coarse particles from the seawater and, if applicable, from the sediment by appropriate
means. The procedure used shall be reported.
Seawater can be filtered using a filter (6.11) in order to remove coarse particles while minimizing the
disturbance to microbial activities. Any kind of material is acceptable as long as the filter (6.11) is not
damaged by seawater. It is recommended to reduce the amount of coarse particles in sediment by means of
at least two washing steps using filtered seawater without coarse particles.
Measure total organic carbon (TOC), pH and total nitrogen content of seawater and, if applicable, of sediment
samples according to ISO 8245, ISO 10523 and ISO 11261, respectively.
If the total organic carbon (TOC) content of the seawater sample is found to be high, the seawater should be
pre-conditioned for about a week prior to use. If, for instance, the background concentration of total organic
carbon (TOC) exceeds about 20 % of the total total organic carbon (TOC) after addition of the test item, then
pre-condition the seawater and, if applicable, the sediment by stirring under aerobic conditions at the test
temperature and in the dark or in diffuse light in order to reduce the content of easily degradable organic
material.
Provide the following information on the seawater, and, if applicable, on the sediment sample itself:
— date of collection;
— site location (name of location);
— depth of collection (m);
— appearance of sample - turbid, clear, etc.;
— temperature at the time of collection (°C);
— salinity (PSU);
— tot
...