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Environmental fate & pathways

Biodegradation in water and sediment: simulation tests

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Description of key information

The partitioning of AKD in soil, sediment and sludge was calculated with EUSES using the maximum Koc value of 1*10E6 L/kg 

Key value for chemical safety assessment

Additional information

Experimental data on the biodegradation in water and sediment of Alkyl Ketene Dimer are not available. Therefore, for the degradation rate the default value according to the TGD is estimated, assuming that no degradation takes place in the bound phase. As no tests under anaerobic conditions are available, it is assumed that the substance is not degraded in the anoxic sediment layer.


            


When the Koc of AKD was calculated using EPIWIN (v2.00) it was found to be 3.8E08 L/kg. Based on the maximum validated values in the EUSES program, the Koc is set to the maximum value of 1 * 106L/kg. This means that for risk assessment purposes, all partitioning coefficients for soil, sediment, suspended sediment and sludge are based on this maximum Koc value using the predominantly hydrophobics QSAR (EUSES).


Overview of the partitioning coefficients:


Kp soil = 2.104L/kg


Kp sed = 5.104L/kg


Kp susp = 1.105L/kg


 


The suggested half-life for a readily degradable substance with a Kpsed in the range>10000-≤ 100000 l/kg is 30000 days for the aerobic sediment layer and 300000 days for the bulk sediment.


Chemical hydrolysis of AKD is not influenced by adsorption onto solids nor by the absence of oxygen and therefore the half life in the aerobic sediment layer and in the anaerobic bulk sediment should be based on the hydrolysis rate in the aqueous phase (Macalady and Wolfe, 1984; Burkhard and Guth, 1981). The hydrolysis half live in the aqueous phase at pH 8 and 25 °C ranges between 35 to 210 hours.