ISO 18830:2016 download free.Plastics Determination of aerobic biodegradation of non floating plastic materials in a seawater/ sandy sediment interface Method by measuring the oxygen demand in closed respirometer.
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 foiling may sink to the sublittoral, and reach the seafloor surface. Many biodegradable plastics have a density higher than I 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.
1 Scope
ISO 18830 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 oxygen demand in a closed respirorneter.
Measurement of aerobic biodegradation can also be obtained by monitoring the carbon dioxide evolution. This is not in the scope of ISO 18830 but of ISO 19679.
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 (photic 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.
The conditions described in ISO 18830 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 14851:1999, Determination of the ultimate aerobic biodegradability of plastic materials in an aqueous medium — Method by measuring the oxygen demand in a closed respirometer
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 this document, the following terms and definitions apply.
3.2
theoretical oxygen demand
TI1OD
theoretical maximum amount of oxygen required to oxidize a chemical compound completely, calculated from the molecular formula
Note Ito entry: It is expressed as milligrams of oxygen uptake per milligram or gram of test compound.
3.3
total organic carbon
TOC
all the carbon present In organic matter which is dissolved or suspended in water
3.4
pre-conditloning phase
pre-incubation ofan inoculum under the conditions of the subsequent test in the absence oftest 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 biological oxygen demand (BOO) and derives from ISO 14851. The testing medium is based on a solid phase and a liquid phase. The solid phase is 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 interlace 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 closed flask, in a respirometer. The carbon dioxide evolved Is absorbed In a suitable absorber in the headspace of the flasks. The consumption of oxygen (BOO) is determined, for example, by measuring the amount of oxygen required to maintain a constant volume of gas in the respirorneter flasks, or by measuring the change in volume or pressure (or a combination of the two) either automatically or manually.
6.3 Natural seawater/sediment
Take a sample of a sandy sediment and seawater with a shovel beneath the low-water line into a bucket. Transfer the wet sediment together with seawater into sealed containers for transport and fast deliver it to the laboratory. After delivery, conserve the sediment at low temperature (approximately 4°C) until use. The seawater/sediment sample should be preferably used within 4 weeks after sampling. Record storage time and conditions.
NOTE Seawater and sediment can also be sampled from large, well-running public marine aquaria.
Measure the TOC, pH and nitrogen content of the sediment and of the natural seawater if used instead of artificial seawater. The carbon content of sediment should be in the range of 0,1 % to 2 %.
A preliminary oxidation can be applied to the sediment in order to decrease the organic matter content
and the background respiration. Sediment and seawater are fluxed with air and gently stirred (max.
20 r/min to 30 r/min) in a large container for the desired period of time. Report this pre-treatment
procedure in the test report.
7 Apparatus
7.1 Closed respirometer, including test vessels (glass flasks) and all other necessary equipment. shall be located In a constant-temperature room or in a thermostat apparatus (e.g. water-bath). For an example, see Annex A or ISO 14851:1999, Annex C. Stirring can be applied on seawater on condition that it does not disturb the sediment/seawater interface. An example of a stirred apparatus is given in OECD TG 308, Annex 4.131
NOTE Any respirometer able to determine with sufficient accuracy the biochemical oxygen demand is suitable, preferably an apparatus which measures and replaces automatically and continuously the oxygen consumed so that no oxygen deficiency and no inhibition of the microbial activity occurs during the degradation process. Analytical equipment to measure total organic carbon (TOC) and dissolved organic carbon (DOC) is given in ISO 8245.
10 Validity of results
The test is considered valid, if
a) the degree of biodegradation of the reference material (Fe) is >60 % after 180 days,
b) the 1301) of the blank F11 at the end of the test does not exceed an upper limiting value,
NOTE This value depends on the amount of Enoculum; in a typical case, reported in 8.5. the value is 300 mg/I after 6 months, as shown in the interlaboratory test IlL
c) the BOD values of the three blanks FB are within 20 % of the mean at the plateau phase or at the end of the test,
d) the difference between the percentage biodegradation of the reference material in the different vessels is less than 20 % of the mean at the end of the test.
If flask FN (negative control) was included, no significant amount of BOD shall be observed.
If these criteria are not fulfilled, repeat the test using another sediment.