National foreword

This British Standard is the UK implementation of ISO 18957:2026.

The UK participation in its preparation was entrusted to Technical Committee PRI/89, Plastics - Environmental Aspects.

A list of organizations represented on this committee can be obtained on request to its committee manager.

Contractual and legal considerations

This publication has been prepared in good faith, however no representation, warranty, assurance or undertaking (express or implied) is or will be made, and no responsibility or liability is or will be accepted by BSI in relation to the adequacy, accuracy, completeness or reasonableness of this publication. All and any such responsibility and liability is expressly disclaimed to the full extent permitted by the law.

This publication is provided as is, and is to be used at the recipient’s own risk.

The recipient is advised to consider seeking professional guidance with respect to its use of this publication.

This publication is not intended to constitute a contract. Users are responsible for its correct application.

Compliance with a British Standard cannot confer immunity from legal obligations.

This British Standard was published under the authority of the Standards Policy and Strategy Committee on 31 October 2026.

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 document 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).

ISO draws attention to the possibility that the implementation of this document may involve the use of (a) patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent rights in respect thereof. As of the date of publication of this document, ISO had not received notice of (a) patent(s) which may be required to implement this document. However, implementers are cautioned that this may not represent the latest information, which may be obtained from the patent database available at www.iso.org/patents. ISO shall not be held responsible for identifying any or all such patent rights.

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.

Introduction

Plastics have been used in various fields because of their highly durable characteristics. Plastics are also used intentionally in the environment or in applications where unintentional loss to the environment is unavoidable. The degree of biodegradation of plastics in natural environment is of interest in order to better characterize the behaviour of plastics in these very particular environments. Thus, the test methods to measure the degree and rate of biodegradation are of major interest to obtain an indication of the potential biodegradability of plastic materials when exposed to different marine habitats.

The biodegradability of plastics is defined in laboratory tests, for example ISO 18830, ISO 19679, ISO 23977‑1 and ISO 23977‑2, but these test methods in a laboratory basically use only seawater and sediment.

Since existing test methods are not intended to shorten the test period, the test period often extends to one year and it is sometimes difficult to assess the degree of biodegradability of the sample in a short period of time.

This document provides an accelerated test method for determining the biodegradation level of plastics exposed to seawater in laboratory in shorter time by increasing the number of microorganisms in seawater and enriching the flora, by adding nutrients, pre-treatment by sediment, and condensation of seawater. The degree of biodegradation is calculated based on measurement of the oxygen (O₂) demand in a closed respirometer or carbon dioxide (CO₂) evolution.

Test material is taken up by microorganisms, metabolized, and the contained carbon finally mineralized to CO₂. Part of the carbon originating from the test material is temporarily converted to biomass. The biomass cannot be detected unless the bacteria die and undergo self-digestion. It takes a longer period of time than the conversion to biomass and it may require a long test period to complete the mineralization of the test material. On the other hand, since biomass components are produced by the microbial activity, the total biodegradation considered by carbon flow can be estimated by the sum of the degree of biodegradation based on O₂ and/or CO₂ analysis and the degree of conversion to biomass. Therefore, for the purpose of promoting the development of biodegradable plastics, this document also provides a method for measuring the biomass components produced by metabolizing the test material before it is completely mineralized to CO₂, that enables to evaluate the potential biodegradability considered by carbon flow in much shorter period of time than full mineralization.

1 Scope

This document describes a laboratory test method to determine the aerobic biodegradation of plastic materials exposed to seawater using accelerated conditions. It describes the general requirements of the apparatus and the procedures for using this test method.

This test method is designed to give an early indication of the potential biodegradability of plastic materials in marine environment.

For the purpose of promoting the development of biodegradable plastics, this document also provides a method for measuring the biomass components produced by metabolizing the test material before it is completely mineralized to CO₂, that enables to evaluate the potential biodegradability considered by carbon flow by the sum of the degree of biodegradation based on O₂ or CO₂ analysis and the degree of conversion to biomass in much shorter period of time than full mineralization.

This method is not suitable to assess the degree of disintegration of plastic materials caused by abiotic factors like heat or UV radiation.

2 Normative references

3 Terms and definitions

4 Principle

5 Test environment

6 Reagents

6.1

6.2 Natural seawater/sediment

7 Apparatus

7.1 Detection system for calculation of biodegradability

7.2 Analytical equipment for measuring nitrate and nitrite concentrations (optional)

7.3 Analytical equipment for measuring remaining test material and degradation products (optional)

8 Procedure

8.1 Test material

8.2 Reference materials

8.3 Test set-up

8.4 Preparation of seawater with high biodegradation capability

8.5 Start of the test

8.6 End of the test

8.7 Chemicals for the test

9 Calculation and expression of results

9.1 General

9.2 Calculation based on BOD

9.3 Calculation based on evolved CO₂

9.4 Calculation of potential of biodegradation considered by carbon flow (optional)

9.5 Visual inspection

9.6 Expression and interpretation of results

10 Validity of results

11 Test report

Bibliography