Aerobic biodegradability test development

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. 

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. 

Anaerobic conditions often develop in hydrocarbon-contaminated subsurface sites due to rapid aerobic biodegradation rates and limited supply of oxygen. In the absence of O, oxidized forms or natural organic materials, such as humic substances, are used by microorganisms as electron acceptors. Because many sites polluted by petroleum hydrocarbons are depleted of oxygen, alternative degradation pathways under anaerobic conditions tend to develop. Cervantes et al. (2001) tested the possibility of microbially mediated mineralization of toluene by quinones and humus as terminal electron acceptors. Anaerobic microbial oxidation of toluene to CO, coupled to humus respiration, was demonstrated by use of enriched anaerobic sediments (e.g., from the Amsterdam petroleum harbor). Natural humic acids and... 

Another test method has been developed to assess the rate and degree of aerobic biodegradation of plastics exposed to marine microorganisms (93). Aerobic biodegradation is determined by measuring the amount of biogas produced in the course such an exposure. It has been stated that there is no similar or equivalent ISO standard. 

ISO/CD 18830 Plastics - Test method for determining aerobic biodegradation of plastic materials sunk at the sea water/sandy sediment interface Under Development... 

Another, more drastic approach to improve the precision of the measurement of CO2 production and biodegradation and ascertain that effectively the CO2 derived from a test material is determined, is by the use of radiolabelled test material. An aerobic aquatic test procedure as well as an aerobic, composting test procedure using such material in which the production of 002 is measured by absorption and liquid scintillation counting has been developed in the ASTM subcommittee D20.96 on degradable plastics and has been published as ASTM D6340-98 [47]. 

Another ASTM method, ASTM D6691-01 [71] is determining the aerobic biodegradation of plastic materials in the marine environment by a defined microbial consortium. The latest development at ASTM is the inclusion of a marine variant in a new revision of the Sturm test, ASTM D5209 [10]. Yet, this project is still in development. As it looks now, it would be the first norm that determines the biodegradation of plastics under marine conditions by measuring directly the mineralisation and not a secondary parameter. 

Because of the central role that estimates of biodegradability play in environmental impact assessments, a great deal of effort has been devoted to developing standardized test procedures (Gerike and Fischer 1981). In spite of this, conventional tests for biodegradability under aerobic conditions retain some questionable, or even undesirable, features from an environmental point of view. Attention is therefore drawn to two valuable critiques of widely used procedures (Howard and Banerjee 1984 Battersby 1990). Some of the important issues in the design of such tests are therefore only briefly summarized here. 

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