Since only transformation products (TPs) were found, ratios were calculated between TPs of DDT to distinguish between direct and erosive input (DDD/DDE) as well as to assess the purity of the used product (4,4'-DDD/2,4'-DDD). In this study, DDD was used as indicator for direct input of DDT formulation into the lake, followed by transformation to DDD in the mostly anaerobic sediment. In contrast, DDE was deemed indicative for erosive transport into the sediment following transformation in aerobic conditions in the topsoils outside the lake body. DDD:DDE ratios were calculated of 4,4' congeners only, as these were found in higher concentrations and thus more consistently throughout the length of the profiles. For the same reason, 4,4':2,4' ratios were calculated only for DDD. The technical mixture of DDT contains about 63-80 % 4,4'-and 15-21 % 2,4'-DDT, resulting in ratios between 3 and 5.1 (Braun et al. 1999), while in higher quality mixtures, the 4,4'-DDT proportion is higher.