GB/T 42764-2023: Plastics - Assessment of the intrinsic biodegradability of materials exposed to marine inocula under mesophilic aerobic laboratory conditions - Test methods and requirements

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Scope

This document describes test methods for assessing the inherent biodegradability of
plastic raw materials and polymers in marine environments without any environmental
exposure or pretreatment.
The test methods in this document are carried out under aerobic, mesophilic conditions
and are aimed to obtain the ultimate biodegradability of materials, i.e. conversion into
carbon dioxide, water, and biomass.
This document is only used to evaluate the inherent biodegradability of materials. It is
not used to evaluate the environmental hazards of possible constituents such as heavy
metals and other substances, nor is it used to evaluate its potential ecotoxicity. This
document is suitable for assessing the overall environmental impact of plastics released
intentionally or unintentionally into the marine environment.
This document is not used to evaluate the performance of products processed from
biodegradable plastic raw materials and biodegradable polymers. The lifetime and
biodegradation rate of biodegradable plastic products in the ocean are often affected by
specific environmental conditions as well as the thickness and shape of the product.
The test results of biodegradability obtained under the test conditions specified in this
document cannot be directly extrapolated to the actual marine environment.
This document does not apply to “marine biodegradable” claims for biodegradable
plastic raw materials. If necessary, refer to the relevant product standard.
The test methods specified in this document cannot be used to determine the specific
biodegradation rate (i.e. rate per available surface area) of the test material. If necessary,
refer to the relevant standards about biodegradation rates.
4.3 Negative control material
The negative control material shall be tested in parallel with the test material. The
negative control material is virgin polyethylene.
4.4 Biodegradation test methods
Plastic raw materials, polymers or each organic constituent shall be subjected to marine
biodegradation tests together with reference materials and negative control materials,
respectively. The tests shall be carried out in accordance with any of the following 6
documents: ISO 18830, ISO 19679, ISO 22404, ASTM D6691-17, ISO 23977-1, and
ISO 23977-2.
The test ends when the test reaches a plateau phase. When the average biodegradation
rate of at least 3 test materials is less than 3 % within 2 months, the test can be
considered to have reached a plateau phase. After 1 year of testing, the test conditions
shall be carefully monitored following the corresponding standard test methods to
ensure long-term reliability of the test conditions. The results are only valid if the test
method meets the corresponding standards.
4.5 Requirements
For whole test material or each individual constituent, organic carbon shall mineralize
into carbon dioxide within 2 years for a degree of mineralization of at least 90 %, or for
the extent of the reference material. In this document, this requirement is met if the
mineralization relative to the reference material is ≥90 %. Both the reference material
and the test material shall be tested within the same period, and the results shall be
compared at the same point after both tests have reached a plateau phase.
For organic constituents with a content between 1 % ~ 15 % (dry mass) in the material,
the biodegradability shall be determined separately. It may refer to OECD 301 Methods
A ~ F to determine based on the existing biodegradation test results. This document
recognizes the biodegradability under conditions described in OECD 310.
Alternatively, it may also use an artificial blend of the same material to determine the
biodegradability of an organic constituent. The artificial blend shall contain ≥15 % of
the corresponding organic constituent [by total organic carbon (TOC) content]. The
chemical composition and the structure of the material shall remain the same, but the
content of the organic constituent of concern shall be increased to ≥15 % [by total
organic carbon (TOC) content]. The preparation of the artificial blend shall use the same
process conditions (e.g. extrusion) as used for the raw materials, except that the content
of each constituent in the raw materials may be less than 15 % (by dry mass). If the
artificial blend meets the above requirements, the organic constituent is considered
biodegradable. Therefore, when the content of this constituent in a certain material is
≤15 % (based on dry mass), the above results are also applicable.
NOTE 1: The purpose of testing an artificial blend is to verify a synergistic effect demonstrating
that a constituent, which is suspected of being non-biodegradable when tested alone, may
become biodegradable when combined with another biodegradable constituent of a material.
NOTE 2: The purpose of increasing the content of a certain constituent in the artificial blend to
≥15 % is to avoid false-positive test results, because theoretically a material contains 10 % of a
non-biodegradable constituent may still reach the pass level for biodegradation.
Natural materials and constituents that have not been chemically modified (such as
wood, wood fiber, cotton fiber, starch, paper pulp, bagasse, jute) shall be considered to
be biodegradable in nature without testing.
In principle, the biodegradation test results obtained using any of the test methods in
4.4 can prove whether the material is susceptible to biodegradation by marine
microorganisms. However, some test materials that fail the test may be the consequence
of being affected by the quality or quantity (or both) of the ineffective microbial
population in an inoculum. Thus, when the test is repeated using different inoculum,
the material may show signs of biodegradability.
The above laboratory test methods shall be carried out between 15 °C and 25 °C, but
not exceeding 28 °C.
NOTE 3: When the test temperature is higher than 20 °C ~ 22 °C, the biodegradability of
psychrophilic microbes may be inhibited.

Basic Data

Standard ID	GB/T 42764-2023 (GB/T42764-2023)
Description (Translated English)	Plastics - Assessment of the intrinsic biodegradability of materials exposed to marine inocula under mesophilic aerobic laboratory conditions - Test methods and requirements
Sector / Industry	National Standard (Recommended)
Classification of Chinese Standard	G31
Classification of International Standard	83.080.01
Word Count Estimation	9,913
Date of Issue	2023-05-23
Date of Implementation	2023-12-01
Issuing agency(ies)	State Administration for Market Regulation, China National Standardization Administration