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Studies on the adsorption/desorption behaviour of naphthenic acids, zinc salts, basic are not available. Thus, read-across to the assessment entities zinc cations and naphthenate anions is applied since the ions of the substance naphthenic acids, zinc salts, basic determine its fate in the environment.

Several partition coefficients for zinc are available for relevant fractions of environmental compartments, i.e. partition coefficients for solid particulate matter and water (110000 L/kg), water-sediment partitioning (73,000 L/kg), solids-water in soil (158.5 L/kg) and marine Zn partitioning (6010 L/kg).

Regarding naphthenate, based on the analysis of a number of representative naphthenic acid samples, a log Koc range of 2.02-6.59 was estimated. In addition, a supporting study is available yielding partition coefficients (solids-water in soil) ranging from 1.3 to 17.8 L/kg, corresponding to calculated values of Log Koc of 1.85 to 2.82. Thus, modelled values indicate a minor to strong adsorption for naphthenic acids to soil, whereas experimental values indicated a low degree of adsorption. A LogKoc of 4.7 is applied in the CSA.

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