ISO 19679:2020 pdf download Plastics — Determination of aerobic biodegradation of non-floating plastic materials in a seawater/sediment interface — Method by analysis of evolved carbon dioxide
Use a test material concentration of at least 100 mg/l of seawater plus sediment. This mass of the sample should correspond to a TOC of about 60 mg/l. The maximum mass of sample per flask is limited by the oxygen supply to the glass flask. A test material concentration of 150 mg/l to 300 mg/l of seawater plus sediment is recommended. Calculate the TOC from the chemical formula or determine it by a suitable analytical technique (e.g. elemental analysis or measurement in accordance with ISO 8245) and calculate the ThCO 2 .
The form and shape of the test material may influence its biodegradation. Similar shapes and thicknesses should preferably be used if different kinds of plastic materials are to be compared. NOTE When the test material in form of film is laid down on the surface of the sediment, it can limit the gas exchange between the water body and the sediment, promoting the formation of anaerobic zones under the test material. In order to reduce this effect, it is possible to perforate the film sample homogeneously over the entire surface.
8.2 Reference material Use ashless cellulose filters as a reference material 1) . If possible, the TOC, form, and size should be comparable to that of the test material. As a negative control, a non-biodegradable polymer (such as polyethylene) in the same form as the test material shall 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 sediment” hereafter. 8.4 Test setup Provide several flasks, so that the test includes at least the following:
a) three flasks for the test material (symbol F T ); b) three flasks for the blank (symbol F B );
c) three flasks for reference material (symbol F C );
d) three flasks for negative control (symbol F N ). Two flasks for test material, blank, reference material, and negative control may be used instead of three for screening purposes. 8.5 Pre-conditioning phase In a typical case, use a test flask with a volume of 250 ml. Put 30 g of the wet sediment on the bottom of the flask. Carefully pour 70 ml of natural or artificial seawater. Reactors with higher volumes can be used, if test conditions are not affected. 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.
When using very coarse-grained sediment, the layer can be increased up to 1,5 cm. Add CO 2 absorber to the absorber compartments of the test flask in a typical case 3 ml of KOH 0,5 mol/l or 10 ml of Ba(OH) 2 0,0125 mol/l. Place the flasks in a constant-temperature environment and allow all vessels to reach the desired temperature. Take the necessary readings and monitor the CO 2 evolution.
This phase is carried out in order to verify that the endogenous respiration is similar in the different vessels and also to obtain a preliminary oxidation of excess organic matter, in order to start the test with a lower endogenous respiration. The inoculum can be gently stirred in order to accelerate the biodegradation of excess organic matter. This phase is generally protracted for a week but is possible to extend this time if a high amount of CO 2 evolved is measured. In case the CO 2 evolution of a vessel is different, reject the diverging vessel or in case of multiple anomalies, start again using new sediment.
8.6 Start of the test Dunk the plastic film sample, cut as described in 8.1, on the sediment of each vessel. Mass of samples (test and reference material) should be about 20 mg each when using a flask with a volume of 250 ml corresponding to an initial test item concentration specified in 8.1. In order to ensure a homogeneous contact between sample and sediment, it is recommended to cover the sample with a suitable cover slip. The cover slips shall also be introduced in blank vessels, for assuring similar conditions.
NOTE A suitable cover slip can be made using a common non-biodegradable vinyl-coated fibreglass mosquito net with a fibre diameter of about 280 µm and a 1,8 mm × 1,6 mm mesh. For an example, see Annex A. Repeat the procedure for the reference material and the material for the negative control to the respective flasks. Record the mass of the sediment, the sample and the volume of seawater introduced in each vessel. Nutrients may be supplemented as needed to support microbial diversity and to maintain the capacity to biodegrade the test material. The need and timing of additional nutrients or other appropriate measures may be judged by observation of the temporal course of the biodegradation of the reference substance cellulose. Any addition and the applied method shall be reported in the test report.ISO 19679-2020