Distribution of pesticides in the sediment of the small Teufelsweiher pond (southern Germany)

Within the scope of the joint research project “Research Network on Agroecosystems Munich (FAM)” in Scheyern, Upper Bavaria, Germany, the concentration and distribution of pesticides were studied in sediment samples in order to elucidate their fate in the aquatic environment. Of seven recently applied pesticides, only atrazine, bifenox and their metabolites were measured both in the solid sediment and the proewater isolated from the Teufelsweiher pond (area 3155 m2, depth 0.3–1.3 m) near Scheyern from 1992 to 1994. The mean total concentrations ranged from 33–76 ng litre−1 in the porewater and 1.3–4.9 μg kg−1 in the solid sediment for atrazine and 9.5–23 ng litre−1 and 4.1–18.3 μg kg−1 for bifenox, respectively. They exhibited a small spatial but obviously no temporal variation. This variation depends on the sediment particle-size distribution, because the highest pesticide concentrations were found in both the smallest ( < 6.3 μm) and the largest fraction (63–200 μm). The organic matter content of the sediment contributes mainly to this concentration distribution. In addition, comparing the in situ measured Koc with the Koc determined in the laboratory, the generally lower Koc values indicate that dissolved organic carbon (DOC) adsorbs pesticides, resulting in a higher total concentration in the porewater than in the absence of DOC. This “solubilization effect” may increase pesticide remobilization and availability in the aquatic environment. Atrazine and bifenox were mainly transported by runoff from the inclined areas nearby into the Teufelsweiher, but their transport pattern and metabolism schemes show some differences according to the different physiochemical properties.