Epsilon Archive for Student Projects

Abstract

In April 2000, bed sediment cores were collected at three locations in the Vemmenhog area, an intensively farmed catchment in southern Sweden. Additional samples of surface and mobile sediments were collected from April to September at one of the locations. The sediment samples were analysed for 20 pesticides, including 9 herbicides, 3 fungicides and 8 insecticides. The aim of the investigation was to study 1) the occurrence and distribution of mostly currently used pesticides in bed sediment and 2) their temporal variation in surface and mobile sediment during the cropping season. This to examine if these sediments could be used as a 'fingerprint' of historical use as well as reflect current use of pesticides in the area. In addition to this the results were compared with the results of an investigation performed in 1990/91 at the same locations.
Altogether 10 pesticides, including 4 herbicides ( diflufenican, diuron, isoproturon and methabenzthiazuron), 2 fungicides (fenpropimorph and propiconazole) and 4 insecticides
(DDT, esfenvalerate, permethrin and pirimicarb) were detected. The results show that streambed and pond sediments act as sinks for hydrophobic pesticides in the Vemmenhog area. Six out of twelve pesticides in this investigation having log Kow-values above 3.5 were detected. Of the remaining six pesticides, having log Kow-values above 3.5, five were pesticides which had very limited use in the area during the last decade.
Most of the detected pesticides showed distribution trends in concentration with depth. The results imply that bed sediments in the area has the potential for being used as a historical
'fingerprint' of inputs of pesticides to the freshwater sediment ecosystem. With few exceptions the distribution of pesticide concentrations down through the sediment cores indicate that the input of pesticides to the sediments in the Vemmenhog area are decreasing. To get a more accurate picture, methods of dating relatively young alluvial deposits are needed. Further, it would be valuable to investigate the temporal and spatial variation in sedimentation patterns at the collection sites more thoroughly.
Concentrations of most pesticides detected in surface and mobile sediment showed little temporal variation during the collection period. No elevated amounts of pesticides were found in periods following pesticide application or rain as is common for pesticides detected in surface water in the area. The lack of any trends for most of the detected pesticides is likely an effect of their strong sorption and slow movement in soil in addition with a small or insignificant contribution of pesticides from spills, spray drift and surface runoff, during the investigation period.