- Email: [email protected]
ISO standard activities in standardization of biodegradability of plastics—development of test methods and definitions
Polymer Degradation and Stability 59 (1998) 365-370 0 1998 Else&r Science Lmited. All rights reserved Printed in Northern Ireland 0141-3910/98/$19.00
PII: s0141-3910(97)00191-2 ELSEVIER
IS0 standard activities in standardization of biodegradability of plastics-development of test methods and definitions Hideo Sawada* Biodegradeable Plastics Society, 3-2534 Sayama. Osaka-Sayama, Osaka 589, Japan
(Accepted 25 June 1997) A new working group (WG22) of subcommittee (SC 5) on biodegradability was created by the International Organization for Standardization (ISO) Technical Committee on Plastics (TC61) in 1993. The following three aerobic test methods have recently advanced to the DIS (Draft of International Standard) stage: (1) evaluation of the ultimate aerobic biodegradability in an aqueous mediummethod by determining the oxygen demand in a closed respirometer; (2) evaluation of the ultimate aerobic biodegradability in an aqueous medium-method by analysis of released carbon dioxide; and (3) evaluation of the ultimate aerobic biodegradability and disintegration of plastics under controlled composting conditions-method by analysis of released carbon dioxide. The definition of biodegradation should be as wide as possible and consistent with the meaning intended. The level of biodegradation should be established in standard test methods. In addition, WG22 plans to develop two test methods for anaerobic biodegradability as well as a test scheme for the final acceptance of the compostability. 0 1998 Elsevier Science Limited. All rights reserved
1 INTRODUCTION
by the IS0 technical committee on plastics (TC 61) in 1993. This paper reviews the development of IS0 standards and other standards-related activities in this area.
With the increasing use of plastics, their disposal has become a major environmental issue. Biodegradable plastics are now emerging as one of the available options to solve such environmental issues. Therefore, it is very important to determine the biodegradability of such plastics. The International Organization for Standardization (ISO) is a worldwide federation of national standards bodies (IS0 member bodies). The work of preparing International Standards is normally carried out through IS0 technical committees (TC). Each member body interested in a subject for which a technical committee has been established has the right to be represented on that committee. At the present time, there are no International Standards available from the IS0 that deal with the biodegradability of plastics. A new working group (WG 22) of the subcommittee (SC 5) on biodegradability was created
2 IS0
PROJECT
APPROACH
Table 1 shows the sequence of project stages through which the technical work is developed, and gives the name of the document associated with each project stage.’ The preparatory stage covers the preparation of a working draft (WD) and this stage ends when a WD is available for circulation to the members of the technical committee (TC) or subcommittee (SC) as a first committee draft (CD). The committee stage is the stage at which comments from national bodies are taken into consideration. National bodies should therefore carefully study the texts of the CD and submit all pertinent comments at this stage. The decision to circulate an enquiry draft should be taken on the basis of the consensus principle. Within the ISO, in
*To whom correspondence should be addressed. Fax: + 81. 723-65-0074; e-mail: [email protected]
the case of doubt concerning consensus, approval 365
366
H. Sawada Table 1. I’@& stages and associated documents
Project stage
Associated document Name
1. Proposal stage 2. Preparatory stage 3. Committee stage 4. Enquiry stage 5. Approval stage 6. Publication stage
Abbreviation
New work item proposal
NP
Working draft
WD
Committee draft
CD
Draft of International Standard Final Draft International Standard International Standard
DIS
International Standard requires approval by at least 75% of the member bodies casting a vote. If the FDIS is approved, it will then proceed to the publication stage.
3 IS0 STANDARDS
FDIS IS0
by a two-thirds majority of the members of TC or SC voting may be deemed to be sufficient for a CD to be accepted for registration as an enquiry draft; however, every attempt shall be made to resolve negative votes. The committee stage ends when all technical issues have been resolved and a CD is accepted for circulation as an enquiry draft. At the enquiry stage, a Draft of International Standard (DIS) is circulated to all national bodies for a five-month vote. An enquiry draft is approved if: 1. a two-thirds majority of the votes cast by members are in favor, and 2. not more than one-quarter of the total number of votes cast are negative. At the approval stage, the Final Draft International Standard (FDIS) is circulated to all national bodies for a two-month vote. Publication as an
DEVELOPMENTS
Since the working group on biodegradability of plastics (WG 22) was created in 1993, rapid advances have been made in this area. The following three aerobic biodegradation test methods have recently advanced to the DIS stage. Their general features are summarized in Tables 2 and 3. 1. ISO/DIS 14851: evaluation of the ultimate aerobic biodegradability in an aqueous medium-method by determining the oxygen demand in a closed respirometer 2. ISO/DIS 14852: evaluation of the ultimate aerobic biodegradability in an aqueous medium-method by analysis of released carbon dioxide 3. ISO/DIS 14855: evaluation of the ultimate aerobic biodegradability and disintegration of plastics under controlled composting conditions-method by analysis of released carbon dioxide Both ISO/DIS 14851 and 14852 are aerobic test methods in an aqueous medium. As far as these two test methods are concerned, for the determination of the biodegradability of plastic material by aerobic microorganisms using an aqueous test system, the test mixture contains an inorganic medium, the organic test material as the sole source of carbon and energy at a concentration
Table 2. Test methods of the ultimate aerobic biodegradability in aqueous conditions
Parameter Inoculum Monitering Duration Temperature Test material Reference
Validity Negative reference
ISO/DIS 14851
ISO/DIS 14852
Activated sludge Soil and/or compost suspensions 02
co2
28 days (max. 3 months) 20-25 f 1°C High temperatures may be appropriate with a compost inoculum Powder, films, pieces, fragments or shaped articles Aniline Well defined biodegradable polymer (microcrystalline cellulose powder, Well defined biodegradable polymer ashless cellulose filters, (microcrystalline cellulose powder, ashless cellulose filters, polyhydroxybutyrate) polyhydroxybutyrate) Reference material has not been degraded at least 60% at the end of the test Polyethylene (optional) In the same form as the test material
367
IS0 standard activities in standardization of biodegradability of plastics Table 3. Tests methods of the ultimate aerobic biodegradability under controlled cornposting conditions __~__. ISO/DIS 14855
Parameter Inoculum Monitering Duration Temperature Test material Reference Validity
Mature MSW compost (the age of the compost should preferably be between 2 and 4months) CO2 45 days 583~2°C In special cases, e.g. when the melting point of test material is low, another temperature may Films, formed articles like dog bones, granules or powder Thin-layer chromatography grade cellulose (particle size of less than 20 wrn) For a valid test, reference material is more than 70% after 45 days
between 100 mg/l test material and about 2000 mg/l organic carbon and as the inoculum activated sludge or a suspension of active soil or compost. ISO/DIS 14851 specifies a method for the determination of oxygen demand in a closed respirometer. Evolved carbon dioxide is absorbed in a suitable absorber in the headspace of the test flasks. The consumption of oxygen (BOD) is determined, for example, by measuring the amount of oxygen in volume or pressure (or a combination of the two) either automatically or manually. The mixture is stirred in the closed flask of a respirometer. The biodegradation is calculated as the ratio of the biological oxygen demand (BOD) to the theoretical oxygen demand (TOD). ISO/DIS 14852 specifies a method for determining released carbon dioxide. The carbon dioxide released during the microbial degradation is determined by an appropriate analytical system that is basically the same as the Strum test. The carbon dioxide produced is trapped in a basic solution [Ba(OH)z or KOH] and its amount is determined by the titration of the remaining base using hydrochloric acid. Released carbon dioxide can be also determined as dissolved inorganic carbon (DIS) using a DOC analyser. The level of biodegradation is determined by comparing the released carbon dioxide with the theoretical amount (ThC02) and expressed as a percentage. Depending on the inoculum used, ISO/DIS 14851 and 14852 simulate biodegradation processes of the natural aquatic environment, if, for example, no pre-exposed inoculum (standard medium) is used. If a mixed or pre-exposed inoculum (optimized medium) is used, it is a method for investigating any potential biodegradability of the test materials. Due to the rather low biodegradation potential of the aquatic laboratory tests compared with the aerobic cornposting tests, the source of the inoculum should not be prescribed and any pre-exposure
be chosen
should be allowed. In addition, a higher amount of inoculum can be used if necessary, but this may cause problems in establishing carbon balances. When a biodegradation process in a natural environment should be simulated or when a carbon balance is carried out, an inoculum concentration of 30 mg/l suspended solid and a 100 mg/l concentration of the test material are recommended. If a test material is used at higher concentrations, the optimized test medium with higher buffering capacity and nutrient concentrations should be used. Polymers having positive results in tests of standard medium will rapidly biodegrade in the natural environment. A negative result does not necessarily mean that the plastics will not degrade under specific conditions. On the other hand, polymers having positive results in tests of optimized medium may not be assumed to be readily biodegradable in natural environments. ISO/DIS 14855 is designed to be an optimized simulation of an intensive aerobic cornposting process in order to determine the ultimate biodegradability and disintegration of a test material under controlled aerobic cornposting conditions. The inoculum consists of a stabilized and mature compost preferably derived from cornposting the organic fraction of municipal solid waste. The test material is mixed with the inoculum and introduced into a static cornposting vessel over a 45-day period at a .constant temperature of 58It 2°C. The percentage of biodegradation is obtained by comparing the carbon dioxide produced from the test material and that which is calculated from its measured total organic carbon (TOC). This ISO/DIS is based on ASTM D 5338 and the European Committee for Standardization (CEN) draft as a draft of the standard test for evaluation of the ultimate aerobic biodegradability and disintegration of packaging materials under controlled cornposting conditions. The only difference
368
H. Sawada
between these two tests is the temperature profile. The ASTM test method recommends a profile incubation temperature to simulate the temperature profile of an intensive aerobic composting process: 1 day at 35°C 4days at 58°C 28 days at 50°C and finally a reduction in temperature to 35°C until 45days. The CEN draft test procedure uses a constant temperature (58°C). For aliphatic polyesters with a low melting point such as poly(caproplactone) (PCL), no degradation could be measured in the CEN draft. For example, PCL is biodegradable, but in this test it produced too much acid and therefore a low pH. PCL was inhibitive to the inoculum due to unfavorable conditions such as low pH (5.0). In conclusion, PCL (m.p. 60°C) was not degraded under thermophilic conditions (58°C) and was leading to acidification and inhibition of the compost inoculum at the tested concentrations.2 An aliphatic polyester with a high melting point such as poly(lactic acid) (PLA) (m.p. 180°C) was easily degraded. On the other hand, according to ASTM D 5338, which follows a temperature profile over 35-58-50-35°C PCL was readily degraded3 but PLA did not easily degrade.2 The reasons why we decided to accept the CEN test procedure using a constant temperature are given below. 1. A constant temperature could improve this laboratory test. The degradation potential is better at higher temperature and when favorable conditions are used from the beginning. For practical reasons of test performance and test duration, it is better to use a constant temperature. 2. In special cases, e.g. when the melting point of the test material is low, other temperatures may be chosen. This temperature should be
constant during the test and kept in a range of +2C. We are now studying the following two anaerobic biodegradation test methods as shown in Table 4. Some harmonization of the global level will be needed. 1. ISO/CD 14853: evaluation of ultimate anaerobic biodegradation of plastic materials in aqueous system-method by analysis of carbon conversion to carbon dioxide and methane 2. ISO/WD: evaluation of the ultimate anaerobic biodegradability and disintegration of plastics under high-solids anaerobic digestion conditions CD 14853 is currently in the CD stage of development and incorporates improvements over ASTM D 5210. This test method is designed to estimate the degree of anaerobic biodegradation by measuring the evolution of carbon dioxide and methane as a function of exposure time to anaerobicdigester sludge. The inoculum consists of sludge from a well-operated anaerobic-sludge digester with a total volatile organic solids level of at least l-2% (w/v). In the case of simulating anaerobic biodegradation behavior in natural environments, inocula stemming from anaerobic lake and river sediments can be used. Another anaerobic biodegradability test method determines the biodegradability in a high-solids, anaerobic digestion process. This is representative of systems used for the anaerobic biogasification of the organic fraction of municipal solid waste. The inoculum is derived from a digester operating under dry (more than 20% of total solids) conditions. The percentage of biodegradation is expressed as the percentage of mineralization based on
Table 4. Test methods of ultimate anaerobic biodegradability
Parameter Outline Inoculum
Test material Duration Temperature Monitering Reference Negative control Validity
ISOjWD
ISOjCD 14853 Anaerobic-digester municipal sewage sludge Anaerobic-digester sludge, total volatile organic solid level at least l-2% (w/v), anaerobic lake and river sediments Powder, films, pieces, fragments, or formed articles Two consecutive weeks (at least 80 days) 3&35 + 1°C Well defined anaerobically biodegradable polymers, e.g. polyhydroxybutyrate Non-biodegradable polymers, e.g. polyethylene Reference substance is more than 70%
High-solid anaerobic digestion conditions Anaerobic-digester sludge, total solid content of at least 20%
Films, formed articles like dog bones, granules of powder 15 days 52+2”c CH4 and CO2 Cellulose for thin-layer chromatography with a particle of less than 20 pm Reference substance is more than 70% after 15 days
/SO standard activities in standardization of biodegradability of plastics
carbon conversion. This test method submitted as a new work item is very similar to ASTM D 55 11. We plan to develop a test scheme for the final acceptance of the compostability and biological treatability of plastics. Various test methods do exist or are now being developed. Therefore, it is necessary to integrate all the various aspects and characteristics into one logical test scheme. ISO/TC207/SC3 deals with the subject of environmental labelling, and has been developing an International Standard related to Environmental Labels and Declarations-Self-Declared Environmental Claims. In this document, ISO/DIS 14851, 14852, 14855 and CD 14853 will be adopted as appropriate test methods.
occurring microorganisms and algae.
369
such as bacteria, fungi
4.2.2 Discussion The level of biodegradability may be indicated as shown in subordinate definitions for biodegradable plastics. We agreed to proceed with the test method development activities. However, we reached a consensus on the following two points, and we will reconsider the definition at a later date. 1. The definition should be as wide as possible for the present statutes such as IS0 472 and ASTM D 883. 2. The level of biodegradation should be established in the standard test methods.
4 DEFINITIONS In 1994 at the 43rd ISO/TC61 meeting, the definition of biodegradability was discussed. The IS0 definition of biodegradation (IS0 472 1993, Plastics-vocabulary, Amendment 3) has recently been published. IS0 472 is similar to ASTM D 883 as shown below. 4.1 IS0 472 Plastics--Vocabulary-l9934 4.1.1 Amendment 3 General terms and terms relating to degradable plastics. 4.1.2 Biodegradable plastic A degradable plastic in which the degradation process rest&s in lower-molecular-weight fragments produced by the action of naturally occurring microorganisms such as bacteria, fungi and algae. 4.1.3 Degradable plastic A plastic designed to undergo a significant change in its chemical structure under specific environmental conditions, resulting in a loss in some properties that may vary as measured by standard test methods appropriate to the plastics and the application in a period of time that determines its classification. 4.2 ASTM D 883 Standard Terminology Relating to Plastics---1991 5 4.2.1 Biodegradable plastic A degradable plastic in which the degradation process results from the action of naturally
ISO/TCl47/SC5 (Water Quality, Biological methods) is going to use new definitions for the level of biodegradation within the IS0 standards. Therefore, the following definition of ultimate aerobic biodegradation was used in DIS 14851, 14852 and 14855. “The breakdown of an organic chemical compound by microorganisms in the presence of oxygen to carbon dioxide, water and mineral salts of any other elements present (mineralization) and new biomass.” It is also important to introduce the definition of cornposting. The definition of composting adopted in ISO/DIS 14855 is as follows: “Composting is an aerobic process to produce compost. Compost is an organic soil conditioner obtained by the biodegradation of a mixture principally consisting of various vegetable residues, occasionally with other organic material and having a limited mineral content.”
5 CONCLUSIONS 1. Three ISO/DIS 14851, 14852 and 14855 are recognized as useful screening tests for estabiishing the aerobic biodegradabmty or compostability of plastics. 2. Two anaerobic biodegradation tests currently under development still need harmonization on a global level.
370
H. Sawada
3. Definitions should be as wide as possible and consistent with the meaning intended. The level of biodegradation should be established in standard test methods. ACKNOWLEDGEMENTS The author would like to thank Professor R. Narayan, Dr U. Pagga, Mr M. Pantke and Mr B. De Wilde for their preparation of related IS0 documents.
REFERENCES ISOjIEC Directives, Part 1 Procedures for the technical work, ISO, Geneva, 1995, p. 17. Sawada, H., Preprint of Biodegradable Plastics Symposium, October 1996, Biodegradable Plastics Society, Tokyo, 1996, p. 17. Pettigrew, C. A., Rece, G. A., Smith, M. C. and King, L. W.. J.M.S.-Pure Appl. Chem., 1995, A32, 811. IS0 472 Plastics-Vocabulary, Amendment 3; General Terms and Terms Relating to Degradable Plastics, ISO, Geneva, 1993. ASTM D 833, Standard Terminology Relating to Plastics, ASTM, PA. 1991.
PII: s0141-3910(97)00191-2 ELSEVIER
IS0 standard activities in standardization of biodegradability of plastics-development of test methods and definitions Hideo Sawada* Biodegradeable Plastics Society, 3-2534 Sayama. Osaka-Sayama, Osaka 589, Japan
(Accepted 25 June 1997) A new working group (WG22) of subcommittee (SC 5) on biodegradability was created by the International Organization for Standardization (ISO) Technical Committee on Plastics (TC61) in 1993. The following three aerobic test methods have recently advanced to the DIS (Draft of International Standard) stage: (1) evaluation of the ultimate aerobic biodegradability in an aqueous mediummethod by determining the oxygen demand in a closed respirometer; (2) evaluation of the ultimate aerobic biodegradability in an aqueous medium-method by analysis of released carbon dioxide; and (3) evaluation of the ultimate aerobic biodegradability and disintegration of plastics under controlled composting conditions-method by analysis of released carbon dioxide. The definition of biodegradation should be as wide as possible and consistent with the meaning intended. The level of biodegradation should be established in standard test methods. In addition, WG22 plans to develop two test methods for anaerobic biodegradability as well as a test scheme for the final acceptance of the compostability. 0 1998 Elsevier Science Limited. All rights reserved
1 INTRODUCTION
by the IS0 technical committee on plastics (TC 61) in 1993. This paper reviews the development of IS0 standards and other standards-related activities in this area.
With the increasing use of plastics, their disposal has become a major environmental issue. Biodegradable plastics are now emerging as one of the available options to solve such environmental issues. Therefore, it is very important to determine the biodegradability of such plastics. The International Organization for Standardization (ISO) is a worldwide federation of national standards bodies (IS0 member bodies). The work of preparing International Standards is normally carried out through IS0 technical committees (TC). Each member body interested in a subject for which a technical committee has been established has the right to be represented on that committee. At the present time, there are no International Standards available from the IS0 that deal with the biodegradability of plastics. A new working group (WG 22) of the subcommittee (SC 5) on biodegradability was created
2 IS0
PROJECT
APPROACH
Table 1 shows the sequence of project stages through which the technical work is developed, and gives the name of the document associated with each project stage.’ The preparatory stage covers the preparation of a working draft (WD) and this stage ends when a WD is available for circulation to the members of the technical committee (TC) or subcommittee (SC) as a first committee draft (CD). The committee stage is the stage at which comments from national bodies are taken into consideration. National bodies should therefore carefully study the texts of the CD and submit all pertinent comments at this stage. The decision to circulate an enquiry draft should be taken on the basis of the consensus principle. Within the ISO, in
*To whom correspondence should be addressed. Fax: + 81. 723-65-0074; e-mail: [email protected]
the case of doubt concerning consensus, approval 365
366
H. Sawada Table 1. I’@& stages and associated documents
Project stage
Associated document Name
1. Proposal stage 2. Preparatory stage 3. Committee stage 4. Enquiry stage 5. Approval stage 6. Publication stage
Abbreviation
New work item proposal
NP
Working draft
WD
Committee draft
CD
Draft of International Standard Final Draft International Standard International Standard
DIS
International Standard requires approval by at least 75% of the member bodies casting a vote. If the FDIS is approved, it will then proceed to the publication stage.
3 IS0 STANDARDS
FDIS IS0
by a two-thirds majority of the members of TC or SC voting may be deemed to be sufficient for a CD to be accepted for registration as an enquiry draft; however, every attempt shall be made to resolve negative votes. The committee stage ends when all technical issues have been resolved and a CD is accepted for circulation as an enquiry draft. At the enquiry stage, a Draft of International Standard (DIS) is circulated to all national bodies for a five-month vote. An enquiry draft is approved if: 1. a two-thirds majority of the votes cast by members are in favor, and 2. not more than one-quarter of the total number of votes cast are negative. At the approval stage, the Final Draft International Standard (FDIS) is circulated to all national bodies for a two-month vote. Publication as an
DEVELOPMENTS
Since the working group on biodegradability of plastics (WG 22) was created in 1993, rapid advances have been made in this area. The following three aerobic biodegradation test methods have recently advanced to the DIS stage. Their general features are summarized in Tables 2 and 3. 1. ISO/DIS 14851: evaluation of the ultimate aerobic biodegradability in an aqueous medium-method by determining the oxygen demand in a closed respirometer 2. ISO/DIS 14852: evaluation of the ultimate aerobic biodegradability in an aqueous medium-method by analysis of released carbon dioxide 3. ISO/DIS 14855: evaluation of the ultimate aerobic biodegradability and disintegration of plastics under controlled composting conditions-method by analysis of released carbon dioxide Both ISO/DIS 14851 and 14852 are aerobic test methods in an aqueous medium. As far as these two test methods are concerned, for the determination of the biodegradability of plastic material by aerobic microorganisms using an aqueous test system, the test mixture contains an inorganic medium, the organic test material as the sole source of carbon and energy at a concentration
Table 2. Test methods of the ultimate aerobic biodegradability in aqueous conditions
Parameter Inoculum Monitering Duration Temperature Test material Reference
Validity Negative reference
ISO/DIS 14851
ISO/DIS 14852
Activated sludge Soil and/or compost suspensions 02
co2
28 days (max. 3 months) 20-25 f 1°C High temperatures may be appropriate with a compost inoculum Powder, films, pieces, fragments or shaped articles Aniline Well defined biodegradable polymer (microcrystalline cellulose powder, Well defined biodegradable polymer ashless cellulose filters, (microcrystalline cellulose powder, ashless cellulose filters, polyhydroxybutyrate) polyhydroxybutyrate) Reference material has not been degraded at least 60% at the end of the test Polyethylene (optional) In the same form as the test material
367
IS0 standard activities in standardization of biodegradability of plastics Table 3. Tests methods of the ultimate aerobic biodegradability under controlled cornposting conditions __~__. ISO/DIS 14855
Parameter Inoculum Monitering Duration Temperature Test material Reference Validity
Mature MSW compost (the age of the compost should preferably be between 2 and 4months) CO2 45 days 583~2°C In special cases, e.g. when the melting point of test material is low, another temperature may Films, formed articles like dog bones, granules or powder Thin-layer chromatography grade cellulose (particle size of less than 20 wrn) For a valid test, reference material is more than 70% after 45 days
between 100 mg/l test material and about 2000 mg/l organic carbon and as the inoculum activated sludge or a suspension of active soil or compost. ISO/DIS 14851 specifies a method for the determination of oxygen demand in a closed respirometer. Evolved carbon dioxide is absorbed in a suitable absorber in the headspace of the test flasks. The consumption of oxygen (BOD) is determined, for example, by measuring the amount of oxygen in volume or pressure (or a combination of the two) either automatically or manually. The mixture is stirred in the closed flask of a respirometer. The biodegradation is calculated as the ratio of the biological oxygen demand (BOD) to the theoretical oxygen demand (TOD). ISO/DIS 14852 specifies a method for determining released carbon dioxide. The carbon dioxide released during the microbial degradation is determined by an appropriate analytical system that is basically the same as the Strum test. The carbon dioxide produced is trapped in a basic solution [Ba(OH)z or KOH] and its amount is determined by the titration of the remaining base using hydrochloric acid. Released carbon dioxide can be also determined as dissolved inorganic carbon (DIS) using a DOC analyser. The level of biodegradation is determined by comparing the released carbon dioxide with the theoretical amount (ThC02) and expressed as a percentage. Depending on the inoculum used, ISO/DIS 14851 and 14852 simulate biodegradation processes of the natural aquatic environment, if, for example, no pre-exposed inoculum (standard medium) is used. If a mixed or pre-exposed inoculum (optimized medium) is used, it is a method for investigating any potential biodegradability of the test materials. Due to the rather low biodegradation potential of the aquatic laboratory tests compared with the aerobic cornposting tests, the source of the inoculum should not be prescribed and any pre-exposure
be chosen
should be allowed. In addition, a higher amount of inoculum can be used if necessary, but this may cause problems in establishing carbon balances. When a biodegradation process in a natural environment should be simulated or when a carbon balance is carried out, an inoculum concentration of 30 mg/l suspended solid and a 100 mg/l concentration of the test material are recommended. If a test material is used at higher concentrations, the optimized test medium with higher buffering capacity and nutrient concentrations should be used. Polymers having positive results in tests of standard medium will rapidly biodegrade in the natural environment. A negative result does not necessarily mean that the plastics will not degrade under specific conditions. On the other hand, polymers having positive results in tests of optimized medium may not be assumed to be readily biodegradable in natural environments. ISO/DIS 14855 is designed to be an optimized simulation of an intensive aerobic cornposting process in order to determine the ultimate biodegradability and disintegration of a test material under controlled aerobic cornposting conditions. The inoculum consists of a stabilized and mature compost preferably derived from cornposting the organic fraction of municipal solid waste. The test material is mixed with the inoculum and introduced into a static cornposting vessel over a 45-day period at a .constant temperature of 58It 2°C. The percentage of biodegradation is obtained by comparing the carbon dioxide produced from the test material and that which is calculated from its measured total organic carbon (TOC). This ISO/DIS is based on ASTM D 5338 and the European Committee for Standardization (CEN) draft as a draft of the standard test for evaluation of the ultimate aerobic biodegradability and disintegration of packaging materials under controlled cornposting conditions. The only difference
368
H. Sawada
between these two tests is the temperature profile. The ASTM test method recommends a profile incubation temperature to simulate the temperature profile of an intensive aerobic composting process: 1 day at 35°C 4days at 58°C 28 days at 50°C and finally a reduction in temperature to 35°C until 45days. The CEN draft test procedure uses a constant temperature (58°C). For aliphatic polyesters with a low melting point such as poly(caproplactone) (PCL), no degradation could be measured in the CEN draft. For example, PCL is biodegradable, but in this test it produced too much acid and therefore a low pH. PCL was inhibitive to the inoculum due to unfavorable conditions such as low pH (5.0). In conclusion, PCL (m.p. 60°C) was not degraded under thermophilic conditions (58°C) and was leading to acidification and inhibition of the compost inoculum at the tested concentrations.2 An aliphatic polyester with a high melting point such as poly(lactic acid) (PLA) (m.p. 180°C) was easily degraded. On the other hand, according to ASTM D 5338, which follows a temperature profile over 35-58-50-35°C PCL was readily degraded3 but PLA did not easily degrade.2 The reasons why we decided to accept the CEN test procedure using a constant temperature are given below. 1. A constant temperature could improve this laboratory test. The degradation potential is better at higher temperature and when favorable conditions are used from the beginning. For practical reasons of test performance and test duration, it is better to use a constant temperature. 2. In special cases, e.g. when the melting point of the test material is low, other temperatures may be chosen. This temperature should be
constant during the test and kept in a range of +2C. We are now studying the following two anaerobic biodegradation test methods as shown in Table 4. Some harmonization of the global level will be needed. 1. ISO/CD 14853: evaluation of ultimate anaerobic biodegradation of plastic materials in aqueous system-method by analysis of carbon conversion to carbon dioxide and methane 2. ISO/WD: evaluation of the ultimate anaerobic biodegradability and disintegration of plastics under high-solids anaerobic digestion conditions CD 14853 is currently in the CD stage of development and incorporates improvements over ASTM D 5210. This test method is designed to estimate the degree of anaerobic biodegradation by measuring the evolution of carbon dioxide and methane as a function of exposure time to anaerobicdigester sludge. The inoculum consists of sludge from a well-operated anaerobic-sludge digester with a total volatile organic solids level of at least l-2% (w/v). In the case of simulating anaerobic biodegradation behavior in natural environments, inocula stemming from anaerobic lake and river sediments can be used. Another anaerobic biodegradability test method determines the biodegradability in a high-solids, anaerobic digestion process. This is representative of systems used for the anaerobic biogasification of the organic fraction of municipal solid waste. The inoculum is derived from a digester operating under dry (more than 20% of total solids) conditions. The percentage of biodegradation is expressed as the percentage of mineralization based on
Table 4. Test methods of ultimate anaerobic biodegradability
Parameter Outline Inoculum
Test material Duration Temperature Monitering Reference Negative control Validity
ISOjWD
ISOjCD 14853 Anaerobic-digester municipal sewage sludge Anaerobic-digester sludge, total volatile organic solid level at least l-2% (w/v), anaerobic lake and river sediments Powder, films, pieces, fragments, or formed articles Two consecutive weeks (at least 80 days) 3&35 + 1°C Well defined anaerobically biodegradable polymers, e.g. polyhydroxybutyrate Non-biodegradable polymers, e.g. polyethylene Reference substance is more than 70%
High-solid anaerobic digestion conditions Anaerobic-digester sludge, total solid content of at least 20%
Films, formed articles like dog bones, granules of powder 15 days 52+2”c CH4 and CO2 Cellulose for thin-layer chromatography with a particle of less than 20 pm Reference substance is more than 70% after 15 days
/SO standard activities in standardization of biodegradability of plastics
carbon conversion. This test method submitted as a new work item is very similar to ASTM D 55 11. We plan to develop a test scheme for the final acceptance of the compostability and biological treatability of plastics. Various test methods do exist or are now being developed. Therefore, it is necessary to integrate all the various aspects and characteristics into one logical test scheme. ISO/TC207/SC3 deals with the subject of environmental labelling, and has been developing an International Standard related to Environmental Labels and Declarations-Self-Declared Environmental Claims. In this document, ISO/DIS 14851, 14852, 14855 and CD 14853 will be adopted as appropriate test methods.
occurring microorganisms and algae.
369
such as bacteria, fungi
4.2.2 Discussion The level of biodegradability may be indicated as shown in subordinate definitions for biodegradable plastics. We agreed to proceed with the test method development activities. However, we reached a consensus on the following two points, and we will reconsider the definition at a later date. 1. The definition should be as wide as possible for the present statutes such as IS0 472 and ASTM D 883. 2. The level of biodegradation should be established in the standard test methods.
4 DEFINITIONS In 1994 at the 43rd ISO/TC61 meeting, the definition of biodegradability was discussed. The IS0 definition of biodegradation (IS0 472 1993, Plastics-vocabulary, Amendment 3) has recently been published. IS0 472 is similar to ASTM D 883 as shown below. 4.1 IS0 472 Plastics--Vocabulary-l9934 4.1.1 Amendment 3 General terms and terms relating to degradable plastics. 4.1.2 Biodegradable plastic A degradable plastic in which the degradation process rest&s in lower-molecular-weight fragments produced by the action of naturally occurring microorganisms such as bacteria, fungi and algae. 4.1.3 Degradable plastic A plastic designed to undergo a significant change in its chemical structure under specific environmental conditions, resulting in a loss in some properties that may vary as measured by standard test methods appropriate to the plastics and the application in a period of time that determines its classification. 4.2 ASTM D 883 Standard Terminology Relating to Plastics---1991 5 4.2.1 Biodegradable plastic A degradable plastic in which the degradation process results from the action of naturally
ISO/TCl47/SC5 (Water Quality, Biological methods) is going to use new definitions for the level of biodegradation within the IS0 standards. Therefore, the following definition of ultimate aerobic biodegradation was used in DIS 14851, 14852 and 14855. “The breakdown of an organic chemical compound by microorganisms in the presence of oxygen to carbon dioxide, water and mineral salts of any other elements present (mineralization) and new biomass.” It is also important to introduce the definition of cornposting. The definition of composting adopted in ISO/DIS 14855 is as follows: “Composting is an aerobic process to produce compost. Compost is an organic soil conditioner obtained by the biodegradation of a mixture principally consisting of various vegetable residues, occasionally with other organic material and having a limited mineral content.”
5 CONCLUSIONS 1. Three ISO/DIS 14851, 14852 and 14855 are recognized as useful screening tests for estabiishing the aerobic biodegradabmty or compostability of plastics. 2. Two anaerobic biodegradation tests currently under development still need harmonization on a global level.
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3. Definitions should be as wide as possible and consistent with the meaning intended. The level of biodegradation should be established in standard test methods. ACKNOWLEDGEMENTS The author would like to thank Professor R. Narayan, Dr U. Pagga, Mr M. Pantke and Mr B. De Wilde for their preparation of related IS0 documents.
REFERENCES ISOjIEC Directives, Part 1 Procedures for the technical work, ISO, Geneva, 1995, p. 17. Sawada, H., Preprint of Biodegradable Plastics Symposium, October 1996, Biodegradable Plastics Society, Tokyo, 1996, p. 17. Pettigrew, C. A., Rece, G. A., Smith, M. C. and King, L. W.. J.M.S.-Pure Appl. Chem., 1995, A32, 811. IS0 472 Plastics-Vocabulary, Amendment 3; General Terms and Terms Relating to Degradable Plastics, ISO, Geneva, 1993. ASTM D 833, Standard Terminology Relating to Plastics, ASTM, PA. 1991.