ISO 19679:2016 download

05-21-2021 comment

ISO 19679:2016 download.Plastics Determination of aerobic biodegradation of non floating plastic materials in a seawater/sediment interface Method by analysis of evolved carbon dioxide.
Products made with biodegradable plastics are designed to be recovered by means of organic recycling in composting plants or in anaerobic digesters. The uncontrolled dispersion of biodegradable plastics in natural environments is not desirable. The biodegradability of products cannot be considered as an excuse to spread wastes that should be recovered and recycled. However, test methods to measure rate and level of biodegradation in natural environments (such as soil or the marine environment) are of interest in order to better characterize the behaviour of plastics in these very particular environments. As a matter of fact, some plastics are used in products that are applied in the sea (e.g. fishing gear) and sometimes they can get lost or put willingly in marine environment. The characterization of biodegradable plastic materials can be enlarged by applying specific test methods that enable the quantitative assessment of biodegradation of plastics exposed to marine sediment and seawater. Plastic products are directly littered or arrive with fresh waters in the pelagic zone (free water). From there, and depending on density, tides, currents, and marine fouling plastics may sink to the sublittoral, and reach the seafloor surface. Many biodegradable plastics have a density higher than 1 and therefore tend to sink. The sediment passes from aerobic to anoxic and finally anaerobic conditions going from the surface (the interface with seawater) into deeper layers, displaying a very steep oxygen gradient.
I Scope
ISO 19679 specifies a test method to determine the degree and rate of aerobic biodegradation of plastic materials when settled on marine sandy sediment at the interface between seawater and the seafloor, by measuring the evolved carbon dioxide.
This test method Is a simulation under laboratory conditions of the habitat found in different seawater/sediment-areas in the sea, e.g. In a benthic zone where sunlight reaches the ocean floor (photk zone) that. In marine science, is called sublittoral zone
The determination of biodegradation of plastic materials buried In marine sediment is outside the scope of this International Standard.
Measurement of aerobic biodegradation can also he obtained by monitoring the oxygen consumption. as described in ISO 18830.
The conditions described in this International Standard may not always correspond to the optimum conditions for the maximum degree of biodegradation to occur.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and are indispensable for its application. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 14852:1999, Determination of the ultimate aerobic biodegradability of plastk materials in an aqueous medium — Method by analysis of evolved carbon dioxide
ISO 8245. Water quality — Guidelines for the determination of total organic carbon (TOC) and dissolved organic carbon (DOC)
3 Terms and definitions
For the purposes of ISO 19679 the following terms and definitions apply.
theoretical amount of evolved carbon dioxide ThCO
maximum theoretical amount of carbon dioxide evolved after completely oxidising a chemical compound, calculated from the molecular formula or from determination of total organic carbon (TOC)
Note Ito entry: It is expressed as milligrams of carbon dioside evolved per melligram or gram or test compound.
total organic carbon
amount or carbon bound In an organic compound
Note 1 to entry: Total organic carbon is expressed as milligrams of carbon per 100 mg of the compound.
dissolved organic carbon
that part of the organic carbon in water which cannot be removed by specified phase separation methods. (or example by centrltugation at 40 000 ms-2 for 15 mm or by membranes with pores of 0.2 im 100,45 itm diameter
pre-conditloning phase
pre-incubation of .rn inoculum under the conditions of the subsequent test in the absence of test material, with the aim to consume potential organic matter present in excess that could disturb biodegradation measurement and to improve the acclimatization of the microorganisms to the test conditions
4 PrincIple
This test method is based on the determination of evolved carbon dioxide and derives from ISO 14852. The testing medium is based on a solid phase and a liquid phasc The solid phase Is a sandy marine sediment laid in the bottom of a closed flask; the liquid phase Is a column of natural or artificial sea water, poured on the sediment. The test material is preferably in the form of a film to be laid down on top of the sediment, at the interface between the solid phase and the liquid phase. This Is a simulation of an object that has sunk and finally reached the sea floor. The system is contained in a dosed fbsk.
The carbon dioxide evolved during the microbial degradation is determined by a suitable analytical method. The level of biodegradation Is determined by comparing the amount of carbon dioxide evolved with the theoretical amount (ThCO2) and expressed in percentage. The test result is the maximum level of biodegradation, determined from the plateau phase of the biodegradation curve. The principle of a system for measuring evolved carbon dioxide is given in ISO 14852:199g. Annex A.
The details of interlaboratory testing based on the test method specified in this International Standard are available in Reference [5).
5 Test environment
Incubation shall take place in the dark or in diffuse light in an enclosure which is Free from vapours
Inhibitory to microorganisms and which is maintained at a constant temperature, preferably between
15 °C to 25 °C, but not exceeding 28 °C. to an accuracy of ±2 DC. Any change In temperature shall be
justified and clearly indicated In the test report.
NOTE Test results are obtained for temperature that may be different from real conditions In marine environment.
6 Reagents
6.1 DistIlled or deionized water, free of toxic substances (copper In particular) and containing less
than 2 mg/I of DOC.
6.2 ArtIficial seawater
Sodium chloride (NaCI) 22 g
Magnesium chloride hexahydrate (MgCl2 . 6 H20) 9,7 g
Sodium sulfate (Na2SO4) 3,7 g
Use a test material concentration of at least 100 mg/I of seawater plus sediment. This mass of the sample should correspond to TOC of about 60 mg/I. The maximum mass of sample per flask Is limited by the oxygen supply to the gbss flask. The use 01150 mg to 300 mg oltest material per litre seawater plus sediment Is recommended.
Calculate the TOC from the chemical formula or determine it by a suitable analytical technique (eg. elemental analysis or measurement in accordance with ISO 8245) and calculate the ThCO2.
The form and shape of the test material may influence its biodegradability. Similar shapes and thicknesses should preferably be used if different kinds of plastic materials are to he compared.
NOTE I The lest material may also be Introduced as powder. If owever. this can be critical, as practical experience hss shown that tt Is difficult to keep a powder settled at the sediment/seawater interlace without special measures. Refer to ISO 10210 for preparation of powder from plastic materials.
NOTE 2 When the tt material In form of film Is laid down on the surface of the sediment, it could limit the gas exchange between the water body and the sediment, promoting thc formation of anaerobic zones under the lest material. In order to reduce this rffect. It Is possible to perforate tb film sample homogeneously over the entire surface,
8.2 Reference material
Use ashless cellulose filters as a reference material’). If possible, the TOC. form, and size should be comparable to that of the test material. As a negative control, a non-biodegradable polymer (e.g. polyethylene) In the same form as the test material can optionally be used.
8.3 Preparation of the sediment
Filter the sediment in a funnel with a coarse filter paper to eliminate excess seawater. Sediment Is ready for testing when dripping of sea water Is ended. Sediment after filtering Is named wet sedlment hereafter.
8.4 Test setup
Provide several flasks, so that the test indudes at least the following:
a) three flasks for the test material (symbol FT):
b) three flasks for the blank (symbol FR);
c) three flasks for reference material (symbol Fe).
In addition, it is possible to add three more flasks for negative control (symbol FN). if required. NOTE Two flasks for test material, blank, reference material, and negative control may be used Instead of three for screeni rig purposes.
8.5 Pre.condltlonlng phase
In a typical case, use a test flask with a volume of 250 ml. Lay down 30 g of the wet sediment on the bottom of the fLask. Carefully pour 70 ml of natural or artificial seawater. The test should be performed with a water/sediment volume ratio between 3:1 and 5:1 and a sediment layer of about 0.3 cm to 0.5 cm, depending on the granulometry of the sediment.
NOTE When using very coarse-grained sediment, the layer may be increased up to 1,5cm.
residual test material may be extracted from the sediment with an appropriate method and quantified (optional).
NOTE The evolved CO2 can be quantitatively measured also using other suitable methods such as those based on infrared CO2analysers or those based on TOC analysers equipped with an infrared photometer or on gravimetric analysis.
8.8 End of the test
When a constant level of CO2 evolution is attained (plateau phase reached) and no further biodegradation is expected, the test is considered to be completed. The maximum test period is 24 months. In the case of long test durations, special attention shall be paid to the technical system (e.g. tightness of the test vessels and connections). Any special measures taken e.g. to ensure microbial diversity or to provide sufficient nutrients shall be detailed in the test report. On the last day of the test, measure the p11, acidify all the bottles with 1 ml of concentrated hydrochloric acid in order to decompose the carbonates and bicarbonates, continue the test for 24 h and finally measure the amount of carbon dioxide evolved in each of the series of flasks.
9 Calculation and expression of results
9.1 Calculation
9.1.1 Amount of CO2 produced
The first step in calculating the amount of CO2 produced is to correct the test material reactors for endogenous CO2 production. The control reactor serves as a blank to correct for CO2 which may be produced through endogenous respiration of the microorganisms. The amount of CO2 produced by a test material is determined by the difference (in ml of titrant) between the experimental and blank containers. The next step is to convert millilitres of 1-ICI titrated into milligrams of CO2 produced.

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