Dahllöf, I., Mogensen, B.B., Bossi, R. & Jensen, I. 2008. National Environmental Research Institute, University of Aarhus. 21 pp. – Research note from NERI no. 244.

 

Summary

 

Herbicides originating from farming activities were detected in Nissum Fjord during the autumn 2007 by the use of passive samplers. Altogether 20 herbicides were detected, including atrazine and isoproturon that can no longer be used in Denmark.

 

Sampling took place during two three-week periods in October-December, at two sites in Nissum Fjord: Felsted Kog at the inner part of the fjord, and at Mellem Fjord, a bit further out.

 

Felsted Kog had the highest levels of herbicides during both periods, which indicates that there is transport of herbicides via Storå. There were also higher levels during the first period, compared to the second, at both sites, indicating either a larger use of herbicides and/or a higher run-off due to precipitation.

 

The combination of herbicides differed between the two localities, suggesting either other transport pathways, and/or that there is degradation or sedimentation along the way.

 

Average concentrations for diuron and isoproturon were calculated based on uptake rates under freshwater conditions. True average concentrations can only be calculated when calibration under marine conditions has been performed. However, the preliminary average concentration of diuron was of the same magnitude as those where growth effects on eelgrass have been experimentally shown.

 

Since it has now been shown that herbicides also reach coastal areas, we conclude that there is a need for extended studies where the results from passive samplers are calibrated to marine conditions, and that further toxicity tests of eelgrass is conducted in order to facilitate a more conclusive risk assessment of herbicides in the marine environment.

 

 

 

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