Temperature biodegradability tests

The initial species present, their relative concentrations, the induction of their enzymes, and their ability to acclimate once exposed to a chemical are likely to vary considerably, depending upon such environmental parameters as temperature, salinity, pH, oxygen concentration (aerobic or anaerobic), redox potential, concentration and nature of various substrates and nutrients, concentration of heavy metals (toxicity), and effects (synergistic and antagonistic) of associated microflora (Howard and Banerjee, 1984). Many of the parameters affect the biodegradation of chemicals in the environment as well as in biodegradation test systems used to simulate the environment. 

Marine biodegradation is measured according to ASTM D6691 test methods with measurement of CO2 evolution from the plastic samples. As per ASTM standards of using actual marine water rather than synthesized one, ocean water was retrieved from beaches in Half Moon Bay, California, with a surface temperature of approximately 20°C. Water was maintained at room temperature until testing began. The marine water was not characterized for sea microorganisms. 

Soil is a highly variable entity in terms of its composition and biological activity, both varying with location, season, pretreatment, and storage. To date it is impossible to standardize soil as a biodegradation test medium. Most test protocols use these soils with different texture characteristics namely sandy, loam and clay textured soil, and under near optimal conditions of moisture, aeration, temperature and pH [115]. 

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 ... 

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... 

Although very good rates of biodegradation have been claimed in composting tests it is stated that biodegradation will only occur where there is sufficient moisture and concentration of soil bacteria and fungi and somewhat elevated temperatures. 

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