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EC number: 423-460-8 | CAS number: 3508-98-3 SALICYNALVA
Biodegradation in water and sediment: simulation tests
Administrative data
Link to relevant study record(s)
Description of key information
In view of the similar removal between the reference substance, sodium benzoate, and the test substance it can be expected that a significant level of ultimate biodegradation/removal was obtained but no final conclusion on ultimate biodegradation can be made based on this study.
Key value for chemical safety assessment
Additional information
The biodegradation and/or removal within sewage treatment processes was investigated using the OECD Test Guideline 303A with appropriate modifications to ensure compliance with EPA "Public Draft" Guideline OPPTS 835.3220. Salicynalva (purity > 99%) fresh test solutions were prepared daily at a nominal concentration of 31 mg/L (26 mg/L as carbon; from the empirical formula supplied by the Sponsor, Salicynalva was calculated to consist of 83% carbon).The activated sludge is retained in a porous polythene cylinder into which the test substance is dosed together with a mixture of domestic and synthetic sewage(predominantly domestic sewage; adaptation not specified but assumed to be non-adapted).Treated effluent percolates through the porous liner (pore size 50-70 um) and overflows to a collection vessel. The use of a porous reactor wall eliminates the need for a sludge settlement chamber. The methods of analysis used to determine biodegradability and removal of the test substance were Dissolved Non-Purgeable Organic Carbon (DNPOC) analysis and specific test substance analysis using gas chromatography.
The test substance attained a level of primary biodegradation/removal in this study of 88% and 89%, as shown by the parent compound analytical data. These high levels of test substance removal were already attained on day 4 of the equilibrium period and remained as such during the whole test. The level of ultimate biodegradation/removal achieved, provided by an assessment of the level of dissolved organic carbon removed, was 87%(attained already on day 9 of the equilibrium period and remained as such during the whole test). Whilst this figure was shown to be statistically different to the levels of DOC removal observed in the control and reference substance pots, the statistical analyses also showed significant differences between duplicate control and reference substance pots. Therefore including the small data-set, undue emphasis should not be placed on the statistical results obtained. The overall difference, in terms of percentage carbon removal, between the test pots and the control and reference substance pots, during the definitive period, was only 3%. Although there was apparent adsorption of the test substance to the test solution feed lines, there was no notable amount of adsorption to either the sludge solids or the porous pot apparatus. A final reasoning considering primary degradation and ultimate degradation is therefore not possible.
A substantial amount of nitrification was observed within all of the porous pots as shown by the analytical data for NH₄-N and total oxidised nitrogen. The test substance appeared to cause no detrimental effect to this important and sensitive environmental process.
Thus, in view of the similar removal between the reference substance, sodium benzoate, and the test substance it can be expected that a significant level of ultimate biodegradation/removal was obtained but no final conclusion on ultimate biodegradation can be made based on this study
Simulation study: Conclusion
It is stated in the OECD 303A Guideline that, if a high initial removal has taken place, the simulation test cannot differentiate between biological and abiotic elimination processes. In such cases, the ready biodegradation screening test is more appropriate to evaluate biological processes. Furthermore, according to Annex II, section II.2.3.5 of the Guidance on the Application of the CLP Criteria (version 4.0, November 2013), results from tests simulating the conditions in a sewage treatment plant (STP) e.g. the OECD Test Guideline 303 cannot be used for assessing the degradation in the aquatic environment. The main reasons for this are that the microbial biomass in a STP is significantly different from the biomass in the environment, that there is a considerably different composition of substrates, and that the presence of rapidly mineralized organic matter in waste water may facilitate degradation of the test substance by co-metabolism.
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