Thin-layers of soil are treated with the test substance and irradiated by simulated sunlight (Xenon lamp) under controlled laboratory conditions. Simultaneously, not-irradiated dark controls are kept under identical conditions to distinguish between photochemical and other reactions. After appropriate time intervals, the soil thin-layers are extracted and analysed for the parent test substance and/or for major phototransformation products. Volatile products are collected by appropriate absorption devices and are also analysed for at time intervals. Using l4C-labelled material, phototransformation products can be identiﬁed and a mass balance, including the formation of soil bound (non-extractable) residues, can be established.