Using the Sorbicell Passive Sampler in Contaminant Monitoring As Compared to Grab Sampling.

The extensive use of pesticides in agriculture results in more and more groundwater wells and, via tile drains, freshwater streams being contaminated with either the parent compound or metabolites thereof. In Denmark, >99% of the municipal water supply is extracted from groundwater reservoirs and legislation allows only very limited pre-treatment of the water before it reaches the consumer. It is therefore important to assess the leaching risk of a given compound in order to reduce the risk of future drinking water contaminations.

In order to assess the leaching risk of agro-chemicals the Danish Pesticide Leaching Assessment Program (PLAP) was initiated in 2000. The program includes 5 fields representative of the dominant soil types and climate conditions in Denmark. The fields are cultivated conventionally, and agro-chemicals are used in maximum permitted doses, and in accordance with current regulations. The fields are intensively monitored using automatic flow proportional sampling in drains and grab-sampling in monitoring wells. The samples are analyzed for a suite of pesticides and their metabolites. The grab-sampling program is expensive in man-power and there is a risk of “missing” contaminants associated with sudden larger flow events e.g. following rain storms.

The SorbiCell is a passive sampling device for in situ sampling of mobile dissolved compounds. It is a flow-through cartridge containing a sorbent which absorbs the contaminant and a tracer salt that leaches proportionally with the water passing through the cartridge. Installing groundwater samplers equipped with SorbiCells in monitoring wells and drains will decrease the sampling frequency to e.g. once every month freeing up funds for more installations to be monitored.

The aim of this study is to compare the concentrations of a selected group of pesticides found by flow proportional as well as grab-sampling as compared to the passive SorbiCell samplers at the PLAP field in Silstrup, Denmark. The contaminants chosen are bentazone, bifenox-acid, CyPM, and TFMP. These contaminants are all found regularly in tile-drains and groundwater at the Silstrup site.