Chemical watchdogs monitor streams 

Storstrøm County has been using two types of chemical "watchdogs" to identify the pesticides found in three of the county’s watercourses. This followed suspicions that the discharge of pesticides could be behind the changes in fauna observed in the three watercourses.

This is the first time that two watchdogs have been combined in this way. One consists of a flat, closed plastic tube (disc) filled with a fatty substance. The tube is placed on the surface of the water for a month at a time, where it traps lipid-soluble pesticides and environmentally hazardous substances.

The other is similarly constructed, but the filling is designed to trap organic, environmentally detrimental substances such as modern pesticides, which are relatively water-soluble. Using this method, COWI - in carrying out the project for the county – has identified 30 out of 60 selected pesticides during the spraying season. In addition, COWI has pinpointed possible causes for the changes in fauna that have been observed.

A good picture

Storstrøm County biologist Finn Gunnar Hansen comments: "In contrast to traditional water sampling, which only gives a point-in-time picture, this method gives a good picture of concentrations of environmentally hazardous substances and pesticides over a longer period of time. The technology is also well suited to identifying environmentally hazardous substances in situations where there is a risk of accidents where, for instance, pesticide sprays are released into the watercourse for a short period of time."

Technology known from USA

While relatively new in Denmark, the technology has been in use in the US for about ten years. COWI has previously used chemical watchdogs to measure environmentally hazardous substances in waste water and discharges. It is also suitable for monitoring pesticides in drinking water and groundwater reservoirs.

Adds Finn Gunnar Hansen: "The technology is not yet widespread and to date there has been a lack of documented results for modern pesticides. Also, the user has to develop his own float on which to mount the watchdog. There is as yet no comprehensive solution on the market."

By: Christina Tækker, cht@cowi.com
Published: 25.05.2004