ASTM D7991-15

Standard Test Method for Determining Aerobic Biodegradation of Plastics Buried in Sandy Marine Sediment under Controlled Laboratory Conditions

SIGNIFICANCE AND USE
5.1 Plastic is sometimes carried by rivers or accidentally discharged by ships into the sea; this plastic can then reach different parts of the marine environment. Tides and waves also frequently deliver plastic marine debris into the sandy tidal zones.  
5.2 This test method simulates the environmental conditions found in the tidal zone. Plastic debris that reaches the sandy tidal zone can settle there and become partially or totally buried by sand and kept wet by waves or tides. It is of interest to assess the biodegradation behavior of plastic materials under these conditions to predict the removal time of this waste in the environment.  
5.3 This test method is applied to determine the extent of biodegradation of a plastic exposed in the laboratory to a sandy sediment kept wet with seawater. Both sediment and seawater are collected from a sandy beach in the tidal zone. If the natural microbial population present in the sediment is able to biodegrade the plastic, there will be an evolution of CO2 as a consequence of the aerobic microbial respiration. The level of biodegradation at any given time is the ratio between the cumulative amount of the evolved net carbon dioxide and the theoretical amount produced in the case of total conversion of the organic carbon present in the plastic into carbon dioxide.  
5.4 This test method does not measure the amount of organic carbon that is converted into biomass, but only the biodegradation that leads to mineralization (that is, the formation of CO2).
SCOPE
1.1 This test method determines the biodegradation level of plastic materials exposed to laboratory conditions that simulate the environment found in the sandy tidal zone.  
1.2 The tidal zone, that is, the part of the coast affected by the tides and movement of the waves, is the borderline between sea and land, frequently a sandy area that is kept constantly damp by the lapping of the waves. Stony and rocky shorelines also exist.  
1.3 Plastic marine debris is frequently washed up in this habitat where it must be removed in order to restore the original landscape.  
1.4 It is of interest to know the biodegradation behavior of plastics when exposed to conditions simulating this habitat, because this information can help in predicting the time needed for the biodegradation of the litter.  
1.5 Biodegradation is determined by measuring the CO2 evolved by the plastic material when exposed to a sediment kept wet with salt-water in a reactor, to simulate the tidal zone.  
1.6 Marine fresh-water habitats (for example, those found in brackish waters and estuaries) are not considered by this standard.  
1.7 Reports shall clearly state the percentage of net CO2 generation for both the test and reference samples at the completion of the test. Furthermore, in the laboratory reports, the results shall not be extrapolated beyond the actual duration of the test.  
Note 1: There is no known ISO equivalent to this standard.  
1.8 Units—The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.  
1.9 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.

General Information

• Status: Historical
• Publication Date: 31-Aug-2015
• ICS: 83.080.01 - Plastics in general
• Technical Committee: D20 - Plastics
• Drafting Committee: D20.96 - Environmentally Degradable Plastics and Biobased Products

Standards Content (Sample)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation: D7991 − 15
Standard Test Method for
Determining Aerobic Biodegradation of Plastics Buried in
Sandy Marine Sediment under Controlled Laboratory
1
Conditions
This standard is issued under the fixed designation D7991; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope responsibility of the user of this standard to establish appro-
priate safety and health practices and determine the applica-
1.1 This test method determines the biodegradation level of
bility of regulatory limitations prior to use.
plastic materials exposed to laboratory conditions that simulate
the environment found in the sandy tidal zone.
2. Referenced Documents
1.2 The tidal zone, that is, the part of the coast affected by
2
2.1 ASTM Standards:
thetidesandmovementofthewaves,istheborderlinebetween
D5988 Test Method for Determining Aerobic Biodegrada-
sea and land, frequently a sandy area that is kept constantly
tion of Plastic Materials in Soil
damp by the lapping of the waves. Stony and rocky shorelines
3
2.2 ISO Standards:
also exist.
ISO 8245 Water quality Guidelines for the determination of
1.3 Plastic marine debris is frequently washed up in this
total organic carbon (TOC) and dissolved organic carbon
habitat where it must be removed in order to restore the
(DOC)
original landscape.
3. Terminology
1.4 It is of interest to know the biodegradation behavior of
plastics when exposed to conditions simulating this habitat,
3.1 Definitions:
becausethisinformationcanhelpinpredictingthetimeneeded
3.1.1 tidal zone, n—the part of the marine environment that
for the biodegradation of the litter.
extends from the high tide line, which is rarely inundated with
water, to the low tide line, which is typically always covered
1.5 Biodegradation is determined by measuring the CO
2
with water.
evolved by the plastic material when exposed to a sediment
3.1.1.1 Discussion—Synonyms are: eulittoral zone, midlit-
kept wet with salt-water in a reactor, to simulate the tidal zone.
toral zone, mediolittoral zone, intertidal zone, foreshore.
1.6 Marinefresh-waterhabitats(forexample,thosefoundin
brackish waters and estuaries) are not considered by this
4. Summary of Test Method
standard.
4.1 This test method consists of the following:
1.7 Reports shall clearly state the percentage of net CO
2
4.1.1 Selection of plastic material for the determination of
generation for both the test and reference samples at the
aerobic biodegradation in a controlled laboratory system.
completion of the test. Furthermore, in the laboratory reports,
4.1.2 Obtaining sediment and seawater from the shoreline.
the results shall not be extrapolated beyond the actual duration
4.1.3 Exposing the plastic material to the wet sediment
of the test.
under controlled conditions.
4.1.4 Measuring CO evolved as a function of time.
NOTE 1—There is no known ISO equivalent to this standard.
2
4.1.5 Assessing the degree of biodegradation by determin-
1.8 Units—The values stated in SI units are to be regarded
ing the percentage of organic carbon in the plastic material that
as standard. No other units of measurement are included in this
is converted to CO during the duration of the test. This
2
standard.
percentagerepresentsthepercentageofmineralizationandwill
1.9 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the
2
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
1
This test method is under the jurisdiction ofASTM Committee D20 on Plastics contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
and is the direct responsibility of Subcommittee D20.96 on Environmentally Standards volume information, refer to the standard’s Document Summary page on
Degradable Plastics and Biobased Products. the ASTM website.
3
Current edition approved Sept. 1, 2015. Published September 2015. DOI: Available fromAmerican National Standards Institute (ANSI), 25 W. 43rd St.,
10.1520/D7991–15. 4th Floor, New York, NY 10036, http://www.ansi.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
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D7991 − 15
notincludetheamountofcarbonconvertedtocellbiomassthat 7. Reagents and Materials
is not in turn metabolized to CO during the course of the test.
2
7.1 Purity of Reagents—Reagent grade chemicals shall be
4.1.6 Estimating the qualitative disintegration of the test
used in all tests. Unless otherwise indicated, it is intended that
material by visual inspection at the end of the test.
...