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Arsenic (As) concentrations in soils and waste material in two areas of former As mining and processing: Złoty Stok (Złote Mts.) and Żeleźniak (Kaczawskie Mts.), SW Poland, were measured to assess levels and environmental risk associated with possible increases in arsenic mobility under changing pH and redox conditions. Twenty six soil samples were collected from 12 sites, and represented a broad spectrum of soil properties and parent material origin, including natural soils, mine spoils, slags and tailings. Arsenic species were examined using a sequential extraction technique. The changes in As solubility were determined from extraction test solutions adjusted to solution pH values varying from 2 to 8. The effects of reducing conditions on As mobility were examined in incubation tests. Most of soils demonstrated extremely high concentrations of As, both of natural and anthropogenic origin. Total As concentrations in all samples were in the range 100–43,500 mg/kg. Sequential extraction techniques suggested that the main species of As in all soils were those bound to iron (Fe) oxides, in particular amorphous ones, whereas the contributions of mobile and specifically sorbed As forms were relatively low. In tailings and tailings-affected alluvial soils, As occurred mainly in residual forms, however these soils also had considerable amounts of mobile As. In all other soils, mobile As forms were very low. Arsenic mobilization could be possible at extremely low or high pH conditions (pH<2 or pH>8), and this may be of particular practical importance in the case of tailings, which are highly alkaline. High pH promotes solubilization of As forms in reducing conditions, whereas in neutral and acidic soils the risk of As release under reducing conditions is limited. [Copyright &y& Elsevier]