Testing of Solid Samples

Complex samples, such as compost and soil could either inhibit or enhance the growth or reproduction rate of the test organisms compared with a synthetic control. The reasons for inhibition could be some physical properties, such as water-holding capacity or particle size, or even pH value or salinity. The reasons for increased metabolic activity could be organic (earthworm) or mineral (plants and algae) nutrients. In such cases it is very difficult to detect any chemical inhibition apart from the beneficial effects of nutrients if real samples, which have degraded polymers, are compared with synthetic controls. 

It is therefore essential to use controls of exactly the same composition as the samples this could be achieved if a bigger amount of a natural matrix (compost, soil or sediment), than needed for the biodegradation experiments, is collected. One part 

Some examples (taken from [67]) may demonstrate the necessity for separate matrix blind tests  

In summary, the inclusion of a control which is identical to the sample or at least representative in its chemical composition and in its physical properties is strongly recommended for all investigations involving degradation intermediates and residues. 

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