Sorption of phenylarsenicals including 4-hydroxy-3-nitrophenylarsonic acid (roxarsone), an animal feed additive widely used for growth stimulation, on soils was investigated in batch systems. Phenylarsonic acid, o-arsanilic acid and roxarsone were retained differently by unpolluted, non-sterilized soils. Sorption isotherms were analyzed by the Henry, Toth and Langmuir-Freundlich equations. The saturation capacity of the Acrisol soil was 3.4 for o-arsanilic acid, 10.9 for phenylarsonic acid and 1.9 g(As) kg(soil)(-1) (dry mass) for roxarsone. The iron content in the soil was not the only factor determining retention of the studied phenylarsenicals. The order of retention on the three soils after 24 h was: roxarsone > o-arsanilic acid > phenylarsonic acid. Besides arsenite and arsenate, new arsenic-containing compounds were detected. (C) 2010 Elsevier B.V. All rights reserved.