The aim of ready biodegradability testing is to obtain a basic statement about whether a substance is rapidly and finally biodegraded in the environment. Due to the strict test conditions, negative results are not considered as evidence of persistence. Instead, there exist the option to investigate inhibitory or poorly water-soluble substances or materials under modified test conditions. Compounds with a water solubility of <100 mg/L are usually referred to as poorly water-soluble. In this case, the surface / volume ratio can be so low that the hydrolysis or degradation rates are significantly reduced Further on, substances with a low specific weight can also float up and thereby decouple from the inoculum.
The updated standard EN ISO 10634 (August 2020) describes various methods for the "preparation and treatment of organic compounds that are sparingly soluble in water for the subsequent determination of their biodegradability in an aqueous medium":
Similar methods are used e.g. also for testing poorly water-soluble lubricants according to DIN EN 17181 (May 2019) "Determination of the aerobic biological degradation of formulated lubricants in aqueous solution - test method using CO2 production" (solution in hexane via transfer to glass fibre filter).
All described addition methods have their advantages and disadvantages, which depend on the properties of the test substances. Since the addition of auxiliaries can influence the test result, control vessels with the auxiliaries must always be run in parallel. Hydrotox GmbH has many years of experience with the use of the various forms of addition of substances that are difficult to dissolve in water.