Aquatic, Aerobic Biodegradation Tests

This test is also known under its more popular name of Sturm test after the scientist who developed this test and wrote the first publication on it [6]. The test later became standardised at the OECD level (OECD 301B) [7] and ISO level (ISO 9439) [8]. Yet, these two test procedures were written for low-molecular-weight compounds to be tested at low concentrations and were less suitable for biodegradable polymers with a high molecular weight. 

For this latter field of biodegradable materials such as bioplastics or packaging, the test procedure was slightly modified and officialised under the form of ISO 14852 [9]. This norm was developed by the working group on biodegradable plastics ISO TC 61/SC 5/WG 22 and published in 1999. 

The two similar but older norms, OECD 301B [7] first published in 1981 and ISO 9439 [8] first published in 1990 are different because for several aspects less flexibility is permitted. Temperature for example must be ambient (20-25 °C) inoculum must be activated sewage sludge pretreated according to a strict procedure or surface water. Also the possibility for biomass determination is not mentioned and the concentration of test item is lower. 

Another norm, which is very similar, is ASTM D5209 [10] originally published in 1992 and comparable to ISO 9439. The ASTM norm is now being modified to be in line with ISO 14852. Two European norms are identical to the ISO norms EN 29439 [11] to ISO 9439 and EN 14047 [12] to ISO 14852. The latter European norm however has expanded the field of application to packaging whereas ISO is limited in principle, to plastics only. In Japan the ISO 14852 method was transposed by the Japanese Institute for Standards (JIS) without changes into the JIS K 6951 [13]. 

Besides the Sturm test another frequently cited aquatic, aerobic biodegradation test is the ISO 14851 [14], in parallel developed by the same working group ISO TC 61/SC 5/WG 22 and also published in 1999. 

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Handbook of Biodegradable Polymers, 2nd Edition 5.3.2 Aquatic, Aerobic Biodegradation Tests 5.3.2.1 Based on Carbon Conversion ( Sturm Test)... 

Besides the Sturm test another much used aquatic, aerobic biodegradation test is ISO 14851 - Determination of the ultimate aerobic biodegradability of plastic materials in an aqueous medium - Method by measuring the oxygen demand in a closed respirometer. 

Some other norms for aquatic, aerobic biodegradation tests have also been published, but are not suitable for biodegradable polymers. They have been developed for pure chemical substances and monitor parameters such as dissolved organic carbon, which cannot be used for polymers. Examples are ISO 7827, ISO 10708, ISO 10707, ISO 9888 and ASTM D5864-00. 

Several other norms for aquatic, aerobic biodegradation tests have been published as well but are not frequently used for biodegradable polymers. Mostly the conditions of incubation (mineral medium, inoculum, temperature, concentration, etc.), are identical or at least similar to the Sturm and MITI methods. The differences lie in the parameters that are being measured and the method for calculating the biodegradation. The following different tests can be used ... 

Readily biodegradable substances achieve rapid degradation in ultimate biodegradability tests, which are so stringent that it can be assumed that the substances will rapidly and completely biodegrade in the natural, aerobic, aquatic environment. 

Pagga U, Schefer A, Muller RJ, Pantke VM. Determination of the aerobic biodegradability of polymeric material in aquatic batch tests. Chemosphere 2001 42 319-331. 

Another, more drastic approach to improve the precision of CO2 measurement and ascertain that CO2 derived from a test material is effectively determined, involves the use of radiolabelled test material. An aerobic, aquatic composting test procedure in which the production of C02 is measured by absorption and liquid scintillation counting has been published as ASTM D6340-98(2007) - Standard test methods for determining aerobic biodegradation of radiolabelled plastic materials in an aqueous or compost environment. 

ASTM 5209 Aquatic aerobic test, can be used to simulate the biodegradability under real life conditions... 

Tests have show n that isosorbide esters are fully biodegradable under aquatic aerobic conditions. Although they are readily biodegradable under aquatic conditions, there are no indications that PVC plasticised with isosorbide based plasticisers is more vulnerable to microbial attack than PVC plasticised by phthalates. 

In the first years of the existence of biodegradable plastics, it became clear that the aerobic, aquatic biodegradation tests were not appropriate to evaluate the biodegradation of these polymers in composting. The environmental conditions are of course very different high temperatures up to 60-65 °C in composting as opposed to ambient temperature in water, different moisture content, etc. An important difference is also the activity... 

Sediment estimated first-order t,/2 = 23-69.3 d from biodegradation rate constant k = 0.01-0.03 d 1 at 9-21°C by river die-away test in slurry sediment of aquatic systems (Lee Ryan 1979 quoted, Scow 1982) t,/2 = 27 d for sediment-water microcosm under aerobic conditions (quoted, Muir 1991). 

ASTM D5864-00, Standard Test Method for Determining Aerobic Aquatic Biodegradation of Lubricants or Their Components, 2000. 

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