By Little Pro on 2016-03-23 Views: Update:2018-02-09
Degradation is the process by which a chemical substance is broken down to smaller molecules by biotic means (biodegradability) or abiotic means (hydrolysis, photolysis or oxidisation). Half-lives (DT50) are used as measures of the stability and persistence of a chemical substance in the environment. Half-life (DT50) is defined as the time it takes for an amount of a compound to be reduced by half through degradation. It is a very important value for PBT assessment.
Biodegradation is the process by which organic substances are broken down by living organisms such as bacteria and fungi. Biodegradation can happen in surface water, sediment and soil.
The pass levels for ready biodegradability are 70% removal of DOC and 60% of ThOD or ThCO2 production for respirometric methods (OECD 301). The pass values have to be reached in a 10-d window within the 28-d period of the test.
If a substance is not readily biodegradable, an inherent biodegradability test may be conducted to assess whether the chemical substance has any potential for biodegradation under aerobic conditions.
Simulation tests aim at assessing the rate and extent of biodegradation in a laboratory system designed to represent either the aerobic treatment stage of STP or environmental compartments, such as fresh or marine surface water.
It mainly includes hydrolysis and photolysis. Hydrolysis in water is often dependent on pH. It half-life value will help to estimate how long a chemical substance will persist in an aqueous environment.
Under EU REACH regulation (Annex XIII), a substance fulfils the persistence criterion (P-) when:
US EPA uses the following persistence criterion (link):
All testing guidelines above can be accessed here.
You have learned the definition of degradation (biodegradation and abiotic), simulated tests, testing guidelines, dose descriptors (half-lives), and persistence criteria. .