The pass level of 60% (O2
demand or CO2
evolution) may seems to be a low value, but it demonstrates complete mineralisation, as the remaining carbon of the test substance is assumed to be built into the growing biomass. Theoretical curve and the 10-day window For pure substances, the theoretical biodegradation curve starts with a lag phase, which is the period from inoculation until degradation has increased to about 10%. The lag phase is followed by the degradation phase, which is the time from the end of the lag period to the point at which 90% of the maximum level of degradation has been reached (the plateau).
The 10-d window is the 10 days immediately following the 10% of biodegradation, i.e., from the end of the lag phase.
is reached, resulting in the production of carbon dioxide, water, mineral salts and new biomass; a positive result (pass level) assumes that the chemical will undergo rapid and ultimate biodegradation in the environment.
UVCBs, lubricants or greases are specific matrices for which the best method is based on CO2
the best mode of introduction is adsorption on inert support.
Many factors influence biodegradability, and even if test conditions in a laboratory test try to reduce these, the uncertainty remains high. The best way to limit test variation and to compare some compounds is to carry out the biodegradation tests in the same laboratory, using the same inoculum.
The 60% pass level may seem like a low value but it demonstrates large mineralisation because a part of the carbon from the test substance is used for biomass growth.
The general requirement for all ready biodegradability tests is that the pass level is achieved within the 10-day window. Nevertheless, the 10-day window criteria may be waived for complex (UVCBs), multi-component substances and the pass level is raised to 28 days. It is anticipated that sequential biodegradation of the individual structures is taking place, leading to a curve without an inflexion point, making the 10-day window unsuitable.
A case-by-case evaluation should, however, take place as to whether a biodegradability test on such a substance will give valuable information regarding its biodegradability or whether an investigation into the degradability of carefully selected individual components of the complex, multi-component substance is required instead.
Conclusion
Biodegradation is a key parameter for estimating the risk of long-term adverse effects on the environment.
The term ultimate, ready or mineralisation must be used only when the final stage of degradation
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The biodegradation curve for UVCBs, lubricants and greases are usually not similar to the theoretical curve with the lag phase, the degradation phase and the plateau; this is due to the sequential biodegradation of the individual structures, leading to a curve without an inflexion point, which is why the 10-day window should not be applied.
References [1] OECD Harmonised Integrated Classification System for Human Health and Environmental Hazards of Chemical Substances and Mixtures. OECD Series on Testing and Assessment. No. 33.
[2] OECD Guidelines for the Testing of Chemicals, Section 3 Degradation and Accumulation, Ready Biodegradability, 301Adopted: 17.07.92.
[3] OECD Guidelines for the testing of chemicals, Section 3 Part 1: Principles and strategies related to the testing degradation, of organic chemicals, Adopted 23 March 2006.
[4] United Nations Economic Commission for Europe – annex 9 “Guidance on hazard to the aquatic environment”. 2017.
evolution and
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