Eroded soil material may be an important transporting agent for pesticides that are strongly sorbed to soil. The abilityof the fungicide propiconazole to interact with colloidal andparticulate materials has been studied by means of sorptionand desorption experiments. Size separation of silty clay soilfrom Mørdre, Norway and subsequent characterization showedthat different size fractions of soil possessed different physical and chemical properties and, therefore, different capacity to associate with propiconazole. A large part of the soil organic carbon was associated with coarser material (2–0.02 mm), which also showed higher affinity towards propiconazole than for smaller size fractions (<20 and <2 μm). Similar K ₒc values (2306 and 2244) for the size fractions <2 and <20 μm indicate that organic carbon played a dominant role in the sorption of propiconazole. Furthermore, organic carbon associated with these size fractions seemed to have similar properties withrespect to binding of propiconazole. Although, poor in organiccarbon (0.4%), the smallest size fraction (<2 μm) had higher sorption capacity for propiconazole compared to the medium size fraction (<20 μm). Higher sorption for the smallest size fraction (<2 μm) is probably due to higherspecific surface area, cation exchange capacity and content of Fe/Al oxides (free, organically bound and amorphous oxides) than the other size fractions. Results from the desorption experiments indicate that a part of propiconazole associates with sites in the soil material that resist desorption. Fluvialsediments originating from propiconazole treated fields may, therefore, represent potential reservoirs of propiconazole.Treatment with H₂O₂ modified the sorption/desorptioncharacteristics of the soil beyond that which could be expectedsimply by the removal of organic material. The pH values for all the size fractions decreased, and the specific surface areaof the medium sized fraction (<20 μm) increased from 14 to 19 m² g⁻¹ after the treatment with H₂O₂,probably due to disruption of the aggregate structure. Carrying out fractionation and separation procedures, it is important to be aware of physical and chemical changes that areintroduced during the different steps. An effort should be made to develop fractionation methods that keep the original characteristics of the soil material as intact as possible.

Migration and chemical availability of ¹³⁷Cs and⁹⁰Sr in the long-term was studied on a36-yr-old deposition experiment on pastureconsisting of a sandy soil and a clay soil,contaminated in 1961 with radionuclides in aqueoussolution. Comparisons were made with a study of thesame soils in 1967. Soil samples to 55 cm depth wereanalysed for ¹³⁷Cs and ⁹⁰Sr to establish thevertical distribution. Chemical availability wasstudied using sequential extractions with H₂O,NH₄Ac, NH₂OH·HCl, H₂O₂ andHNO₃. Both ¹³⁷Cs and ⁹⁰Sr were found atall depths in both soil types. Cs-137 waspredominantly retained within the upper 10 cm (70%)in both soils. For ⁹⁰Sr, the soils differedsignificantly, retention within the upper 10 cm was27% in sandy soil and 47% in clay soil. Migrationsince 1967 was faster in the sandy soil for bothnuclides. More than 95% of ¹³⁷Cs was bound inthe acid-digestible and residual fractions in bothsoils. The residual fraction was larger in clay soil.⁹⁰Sr was highly available in both soils. Noresidual fraction was found, and the easilyexchangeable fraction was 63–75%.