Aniline

Adsorption / desorption

Description of key information

Adsorption to solid soil phase is possible. The empirically determined Koc-value of 410 l/kg (log Koc of 2.6) is used, describing the adsorption potential of aniline.

Additional information

First, it should be considered, that in soil, two competitive reactions occur: biodegradation and formation of covalent bounds onto the organic matter. The latter pathway leads to aniline-humic acid adducts which are immobile and only slowly degraded. Thus accumulation of the reaction product with humic substances occurs. The fate in sediments is considered to be similar than in soils. The formation of covalent bonds with humic matter is a general property of aniline and its derivatives.

Adsorption measurements on soil and sewage sludge revealed moderate adsorption properties of aniline. Using the batch equilibrium method according to OECD guideline 106, log Kocs ranging from 1.279 (loam) to 2.384 (clay) were measured in soil (Gawlik et al. 2000). Similar adsorption properties were determined in four different sewage sludges with log Kocs ranging from 1.41 to 1.92, using the same method (Koerdel et al. 1997). Using a HPLC-screening method, equivalent to OECD guideline 121, an average log Koc of 1.53 was determined for four sewage sludges (Koerdel et al. 1997).

In a distribution experiment with radiolabelled aniline (6 concentrations, 0.0317-10 ppm), the radioactivity was measured in the supernatant water phase and the Freundlich adsorption

constants were determined. Equilibrium was reached in nonsterile soils within 60 h, but was not attained in sterile soils by 120 h. With 2 nonsterile soils Koc values of 310 resp. 910 l/kg were calculated, while the values decreased to 130 resp.410 l/kg when the same soils were autoclaved before the experiment. Aniline is degraded partially before adsorption, and the distribution constants for the degradation products (azobenzene, azoxybenzene, phenazine) are much higher;therefore the constants determined in nonsterile soils seem to be overestimated. A minor effect is that the surface is slightly reduced leading to few lower constants (Pillai et al., 1982).