1、Designation: D7991 15Standard Test Method forDetermining Aerobic Biodegradation of Plastics Buried inSandy Marine Sediment under Controlled LaboratoryConditions1This standard is issued under the fixed designation D7991; the number immediately following the designation indicates the year oforiginal a
2、doption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method determines the biodegradation level ofplastic materi
3、als exposed to laboratory conditions that simulatethe environment found in the sandy tidal zone.1.2 The tidal zone, that is, the part of the coast affected bythe tides and movement of the waves, is the borderline betweensea and land, frequently a sandy area that is kept constantlydamp by the lapping
4、 of the waves. Stony and rocky shorelinesalso exist.1.3 Plastic marine debris is frequently washed up in thishabitat where it must be removed in order to restore theoriginal landscape.1.4 It is of interest to know the biodegradation behavior ofplastics when exposed to conditions simulating this habi
5、tat,because this information can help in predicting the time neededfor the biodegradation of the litter.1.5 Biodegradation is determined by measuring the CO2evolved by the plastic material when exposed to a sedimentkept wet with salt-water in a reactor, to simulate the tidal zone.1.6 Marine fresh-wa
6、ter habitats (for example, those found inbrackish waters and estuaries) are not considered by thisstandard.1.7 Reports shall clearly state the percentage of net CO2generation for both the test and reference samples at thecompletion of the test. Furthermore, in the laboratory reports,the results shal
7、l not be extrapolated beyond the actual durationof the test.NOTE 1There is no known ISO equivalent to this standard.1.8 UnitsThe values stated in SI units are to be regardedas standard. No other units of measurement are included in thisstandard.1.9 This standard does not purport to address all of th
8、esafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D5988 Test Method for Deter
9、mining Aerobic Biodegrada-tion of Plastic Materials in Soil2.2 ISO Standards:3ISO 8245 Water quality Guidelines for the determination oftotal organic carbon (TOC) and dissolved organic carbon(DOC)3. Terminology3.1 Definitions:3.1.1 tidal zone, nthe part of the marine environment thatextends from the
10、 high tide line, which is rarely inundated withwater, to the low tide line, which is typically always coveredwith water.3.1.1.1 DiscussionSynonyms are: eulittoral zone, midlit-toral zone, mediolittoral zone, intertidal zone, foreshore.4. Summary of Test Method4.1 This test method consists of the fol
11、lowing:4.1.1 Selection of plastic material for the determination ofaerobic biodegradation in a controlled laboratory system.4.1.2 Obtaining sediment and seawater from the shoreline.4.1.3 Exposing the plastic material to the wet sedimentunder controlled conditions.4.1.4 Measuring CO2evolved as a func
12、tion of time.4.1.5 Assessing the degree of biodegradation by determin-ing the percentage of organic carbon in the plastic material thatis converted to CO2during the duration of the test. Thispercentage represents the percentage of mineralization and will1This test method is under the jurisdiction of
13、 ASTM Committee D20 on Plasticsand is the direct responsibility of Subcommittee D20.96 on EnvironmentallyDegradable Plastics and Biobased Products.Current edition approved Sept. 1, 2015. Published September 2015. DOI:10.1520/D799115.2For referenced ASTM standards, visit the ASTM website, www.astm.or
14、g, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3Available from American National Standards Institute (ANSI), 25 W. 43rd St.,4th Floor, New York, NY 10036, http:/www.ansi.org.C
15、opyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1not include the amount of carbon converted to cell biomass thatis not in turn metabolized to CO2during the course of the test.4.1.6 Estimating the qualitative disintegration of the testma
16、terial by visual inspection at the end of the test.5. Significance and Use5.1 Plastic is sometimes carried by rivers or accidentallydischarged by ships into the sea; this plastic can then reachdifferent parts of the marine environment. Tides and waves alsofrequently deliver plastic marine debris int
17、o the sandy tidalzones.5.2 This test method simulates the environmental conditionsfound in the tidal zone. Plastic debris that reaches the sandytidal zone can settle there and become partially or totally buriedby sand and kept wet by waves or tides. It is of interest toassess the biodegradation beha
18、vior of plastic materials underthese conditions to predict the removal time of this waste in theenvironment.5.3 This test method is applied to determine the extent ofbiodegradation of a plastic exposed in the laboratory to a sandysediment kept wet with seawater. Both sediment and seawaterare collect
19、ed from a sandy beach in the tidal zone. If the naturalmicrobial population present in the sediment is able to biode-grade the plastic, there will be an evolution of CO2as aconsequence of the aerobic microbial respiration. The level ofbiodegradation at any given time is the ratio between thecumulati
20、ve amount of the evolved net carbon dioxide and thetheoretical amount produced in the case of total conversion ofthe organic carbon present in the plastic into carbon dioxide.5.4 This test method does not measure the amount oforganic carbon that is converted into biomass, but only thebiodegradation
21、that leads to mineralization (that is, the forma-tion of CO2).6. Apparatus6.1 ReactorGlass vessel approximately 2 to 4-L internalvolume that can be sealed air-tight, such as 150-mmdesiccators, with an airtight opening, large enough to allow thehandling of the content. Biometer flasks are also approp
22、riate.Asuitable apparatus is shown in Figure 1 in Test Method D5988.Reactors with higher volumes can be used, if environmentalconditions are not affected.6.2 Container for the CO2AbsorberA glass beaker to belocated in the headspace of the reactor and filled with 100 mlof Ba(OH)20.025 N or with 30 mL
23、 of KOH 0.5 N.6.3 Darkened Chamber or Cabinet, in which the tempera-ture can be maintained at a constant level within a 62C range.NOTE 2Incubator with either built in lights that can be programmed orelse plug in lights that can be operated with a timer power strip can beused to better simulate the e
24、nvironment. The lighting in that case need tobe 12:12 day/night. Details on the lighting regime, light intensity, wavelength, incubator type, etc. shall be provided in the report.6.4 Analytical Balance, to weigh the test specimen.6.5 Technical Balance, to weigh reactors and sediment.6.6 pH Meter.7.
25、Reagents and Materials7.1 Purity of ReagentsReagent grade chemicals shall beused in all tests. Unless otherwise indicated, it is intended thatall reagents conform to the specifications of the Committee onAnalytical Reagents of the American Chemical Society wheresuch specifications are available.4It
26、is acceptable to use othergrades provided it is first ascertained that the reagent is ofsufficiently high purity to permit its use without lessening theaccuracy of the determination.7.2 Barium Hydroxide Solution (0.025 N), prepared bydissolving 4.0 g anhydrous Ba(OH)2/L in distilled water. Filterfre
27、e of solid material and store sealed as a clear solution toprevent absorption of CO2from the air. It is recommended that2 to 4 L be prepared at a time when running a series of tests.Confirm normality by titration with standard acid before use.When using Ba(OH)2, however, care must be taken that a fi
28、lmof BaCO3does not form on the surface of the solution in thebeaker, which would inhibit CO2diffusion into the absorbingmedium. Alternatively, potassium hydroxide solution (KOH,0.5 N) could be used and is prepared by dissolving 28 g ofanhydrous KOH/L in distilled water and proceeding in thesame way
29、as for the Ba(OH)2solution.7.3 Hydrochloric acid, 0.05 N HCl when using 0.025 NBa(OH)2or 0.3 N HCl when using 0.5 N KOH.7.4 SedimentCollect seawater and sediment samples fromthe shoreline of a sandy beach, where the sediment is sub-merged in the shallow water. Collect top sediment (the layerfrom sur
30、face till about 20 cm depth). It is important to obtainsediment from multiple samples from the same location (atleast 3). Collect the seawater with a bucket and then collectsediment samples with a shovel in separate containers overlainwith water, then transfer all samples to a watertight containeran
31、d quickly deliver it to the laboratory. Remove any obviousplant material, shells, pieces of driftwood, petroleum tar, andother large material. Store the sediment and seawater atapproximately 4C until use. Allow air exchange at time toavoid anaerobiosis. Use preferably within four weeks ofsampling. R
32、eport the storage times. Before use, performgravity filtration on the sediment in a funnel with a coarse filterpaper to remove excess water. Sediment is ready for testingwhen seawater is no longer recovered from the filtration.Nitrogen sources (such as NH4Cl or NaNO3) can be added tothe sediment if
33、this is considered as a factor limiting biodeg-radation. These additions shall be reported in the test report.NOTE 3No data are available at this stage indicating that a specificnitrogen level is beneficial for the biodegradation process.7.5 Plastic MaterialDetermine the total organic carbonboth of
34、the test material and the reference material using ISO8245 and report it, preferably, as grams of total organic carbonper gram of total dry solids. Alternatively, provided thematerials do not contain inorganic carbon, it is possible to4Reagent Chemicals, American Chemical Society Specifications, Ame
35、ricanChemical Society, Washington, DC. For suggestions on the testing of reagents notlisted by the American Chemical Society, see Analar Standards for LaboratoryChemicals, BDH Ltd., Poole, Dorset, U.K., and the United States Pharmacopeia andNational Formulary, U.S. Pharmacopeial Convention, Inc. (US
36、PC), Rockville, MD.D7991 152determine the carbon content by elemental analysis. The testmaterial shall have sufficient organic carbon to yield CO2in anamount suitable for the determination.7.6 Reference MaterialA cellulose filter paper5for labo-ratory purposes. Determine the carbon content as descri
37、bed in7.5.7.7 Negative Control Material (optional)A polyethylenefilm. Determine the carbon content as described in 7.5.7.8 Test SamplesIt is preferable that the plastic material isin the form of film or plate. Cut out square-shaped sampleswith a dimension of approximately 5 cm. Likewise preparesquar
38、e-shaped samples of reference material and negativecontrol material. Record the mass of each sample.NOTE 4It is acceptable that the test material be introduced as powder.Mix the powder homogeneously with the sediment. Refer to ISO 10210for preparation of powder from plastic materials. Furthermore, r
39、eport datashowing that milling has not changed the chemical structure of the testmaterial.NOTE 5It is acceptable that the test material be introduced as aperforated film or plate in order to facilitate gas exchange.8. Hazards8.1 This standard does not purport to address all of thesafety concerns, if
40、 any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applicabil-ity of regulatory limitations prior to use.9. Procedure9.1 Test Set-upPrepare at least the following number ofreactors (6.1): a) thre
41、e reactors for the test material; b) threereactors for the reference material; c) three reactors fornegative control (optional); d) three reactor for the technicalcontrol (optional); and (e) three reactors for the blank.NOTE 6Two replicates are sufficient for screening purposes.NOTE 7The technical c
42、ontrols contain only the absorbing solution andno sediment. The ambient air which fills the headspace of all the vesselsintroduces CO2into the system. The technical controls allow accountingfor and subtracting this introduced CO2. Additionally, the technicalcontrols indicate the air-tightness of the
43、 vessel system by showingpossible infiltration of CO2into the sealed vessel.9.2 Preliminary Phase:9.2.1 Place an equal volume (between 200 and 600 g) of wetsediment (see 7.4) in the bottom of each reactor. In a typicalcase, weigh out 400 g of wet sediment and place it into thebottom of the reactor t
44、o form a homogenous layer. Do not pressor compact the sediment. Introduce a container (6.2) with theCO2trapping solution (7.2) to each reactor. Close the reactorsand locate them in a room or chamber preferably at atemperature from 15 to 25C, but not exceeding 28C. Monitorthe CO2production (9.4).9.2.
45、2 This phase is carried out in order to: (i) verify thevitality of the sediment, as shown by the respiration level; (ii)verify that the different reactors have similar backgroundrespiration; and (iii) obtain a preliminary oxidation of excessorganic matter, so as to start the test with a lower level
46、ofendogenous respiration.9.2.3 This phase is generally carried out for one week. In thecase that the CO2evolution of a given reactor is significantlydifferent from its replicates, reject the diverging reactor, or inthe case of multiple anomalies, restart using new sediment.Report CO2evolution and de
47、tails of this phase on the testreport.9.3 Start of the TestOpen the vessels and remove about100 g of sediment from the layer in the bottom of the reactor.Transfer it in a clean container. Smooth the surface of theresidual sediment with a spatula but do not apply pressure.Place 100 mg of plastic mate
48、rial (7.5) or of reference material(7.6) onto the surface of the sediment. The blank reactor willnot include any sample. Cover the plastic or reference materialwith the withdrawn sediment , forming a homogenous layer.Close the vessels tightly. Select a temperature preferablybetween 15 to 25C, but no
49、t exceeding 28C, and maintain theselected temperature at 62C.NOTE 8If the test material is introduced as a powder, mix ithomogenously with the sediment9.4 CO2Analysis:9.4.1 The CO2produced in each reactor will react withBa(OH)2and precipitate as barium carbonate (BaCO3). Theamount of CO2produced is determined by titrating the remain-ing Ba(OH)2with 0.05 N hydrochloric acid to a phenolphtha-lein end-point or by using an automatic titrator. Because of thestatic incubation, the (BaCO3) builds up on the surface of theliquid and must be broken up periodically
