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Environmental fate & pathways

Adsorption / desorption

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Description of key information

Goodwin PA et al (1989):
The soil adsorption/desorption properties of the substance were studied on four surface soils (Caitlin silt loam, Appling Coarse sandy loam, Hoytville clay, and Webster loam) with varying textures and organic carbon contents. The adsorption study was equilibrated at four initial solution concentrations of approximately 0.1, 0.6, 1.2, and 3.5 ppm, while a desorption study used the same soils with similar quantities of the substance, but with a 24 -hour incubation time prior to desorption. An additional aged-soil desorption study consisted of soils incubated with 0.20 ppm of the substance at 25 degrees C and 75% of 1/3 bar moisture for periods of approximately 0,7,14,28, or 34 and 56 or 59 days. The adsorption Koc value average was 15 ml/g for the four soils tested, while the 24 hour and aged-soil desorption Koc's averaged 27 and 49 mL/g respectively. These Koc values indicate that the substance may be relatively mobile in soil.
Study by Lehmann et al (1989):
Although the four soils in the Goodwin PA et al. (1989) study represent a variety of organic carbon contents, pH values, and textures and additional study was performed to examine the degradation and sorption of Flumetsulam in a larger population of soils and to consider a broader base of information the degradation of the substance was studied in 24 soils from the U. S. soybean market. The first order half-life was strongly related to adsorption Kd in that the substance degraded more quickly in soils which adsorbed it less strongly. Adsorption, in turn, decreased on higher pH soils, but increased with higher organic carbon content. The Koc values vary from 5 to 74 mL/g. The median Koc value from this study is 24 at 25°C and this is the value that has been used for risk assessment purposes.
Results showed that Flumetsulam should be relatively mobile in these soils, with some indication that mobility would be decreased at lower soil pHs and at higher organic carbon contents.

Key value for chemical safety assessment

Additional information

Koc values are in the range >= 5 — <= 74 mL/g at 25°C.

Both studies are considered to be of good quality and have been assigned Klimisch 1 ratings. The study by Lehmann et al (conducted using 24 soils) is an extended study and supplementary to the study by Goodwin et al (conducted using 4 soils). The resulting Koc values are in the same range (between 5 and 74) and so are broadly comparable.

The study by Lehmann et al has been assigned as the key study because it is based on more soils and provides a broader background of information, including influence of ph and half life as well as providing information on metabolites.

The median Koc value from this study is 24 at 25°C and this is the value that has been used for risk assessment purposes.