ATRAZINE AND ITS PRIMARY METABOLITES IN SWISS LAKES - INPUT CHARACTERISTICS AND LONG-TERM BEHAVIOR IN THE WATER COLUMN

In order to assess the impact of herbicides on aquatic ecosystems, det ailed information on the factors that govern the input and the behavio r of such chemicals in rivers, lakes, and coastal seawater is required . In this context, we studied the input characteristics (seasonal vari ation) as well as the distribution and residence time of the herbicide s atrazine, simazine, and terbutylazine and of the primary atrazine me tabolites hydroxyatrazine, desethylatrazine, and deisopropylatrazine i n three Swiss lakes exhibiting quite different catchment areas and/or hydraulic properties. The results obtained from numerous field measure ments (period of 5 years, 1990-1994) combined with computer simulation s indicate that all compounds investigated showed a conservative behav ior in the water column of the lakes (i.e., no elimination other than by flushing), except for a short period in the summer, where some mino r elimination occurred in the epilimnion. The major input of both the parent triazine herbicides and the metabolites occurred in the epilimn ion during or right after the application period. For atrazine, the mo st abundant of the three herbicides investigated, it is shown that the total annual input depended strongly on the rainfall during the appli cation period. For a given lake, the annual input varied between 0.5% (dry weather) and 2% (very wet weather) of the total amount applied in the catchment area. For different lakes receiving similar amounts of rainfall, very similar input fractions were found despite the signific antly different catchment areas. Among the metabolites, desethylatrazi ne occurred at levels similar to those for atrazine, while hydroxyatra zine and deisopropylatrazine were present at 2-4 times lower levels. N ote that this study provides the first quantitative data on the transp ort of hydroxyatrazine from soils to surface waters. The results of th is study form an important base for assessing or predicting past, pres ent, and future inputs of triazines to lakes for which only limited da ta are available. Finally, this study demonstrates that small lakes ex hibiting a well-characterized catchment area represent excellent exper imental field systems for evaluating quantitatively the transport char acteristics of herbicides and their metabolites from soils to surface waters and for assessing the persistence of such compounds in surface waters.