Test No. 304A: Inherent Biodegradability in Soil

The method described in this Test Guideline is designed for the evaluation of the mineralisation rate of a 14C-labelled compound in soil. The method is applicable to volatile or non-volatile, soluble or insoluble compounds which are not inhibitory to micro-organisms.

The basic test consists on the treatment of a small sample of soil (50g) with the 14C-labelled test chemical (100µl) in a biometer flask apparatus. The soil and the radioactive test solution are mixed. In addition, an equivalent volume of test solution is placed in a 100 ml volumetric flask for direct determination of the added radioactivity. The biometer flask is closed with a stopper through which an Ascarite filter is inserted. The unit is charged by injecting 10 ml of alkali solution into the side tube. Experiment duration times of 1, 2, 4, 8, 16, 32 and - if necessary - 64 days should be chosen for measurement. The test requires parallel determinations. The method can included optional experiments: for chemicals of a vapour pressure higher than 0.0133 Pa and for relatively persistent chemicals. Release of 14CO2 from the test chemical is measured by means of alkali absorption and liquid scintillation counting. The 14CO2 radioactivity recovered is plotted versus time. Incubation time is sufficient when a total of 50 per cent CO2 expressed as 14C originally applied can be measured. Incubation should be stopped after reaching 64 days, whether or not this value is obtained.

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