Miljøprojekt, 1158 – Risikovurdering af pesticidpunktkilder

Risikovurdering af pesticidpunktkilder

Summary and conclusions

The topic of this project is pesticide pollution from farm yards, and mainly from machine pools. A review of the data from the national survey systems: GRUMO and LOOP, and articles concerning investigations of pesticide point sources shows that pesticide point sources are a major concern for Danish drinking water resources. The review of data makes it clear that there probably exists a large number of pesticide point sources in Denmark. At the same time, it is clear that a large number of these point sources are insignificant in terms of a direct threat to drinking water resources.

In this project, the mass flow and the handling of pesticides on farms were estimated, and detailed investigations on 5 different sites (farm yards) polluted with pesticides were carried out. This has resulted in a better understanding of which mechanisms are important for the creation of a pesticide point source. Furthermore, we have gained a more precise knowledge of how big a threat pesticide point sources pose to the groundwater resources.

The most important factor is the amount of pesticides spilled. The amount of pesticides spilled is, to a great extent, dependent on the handling of the residual pesticides leftover in the sprayer, and whether the residual pesticides are diluted before disposal. The construction of the machine pool is also an important factor considering the potential risk of creating a pesticide point source, which presents an actual risk to the ground water resource. Up to 80 % of the machine pools in Denmark are without storage tanks, and here the spilled pesticides will leak into the ground water or other nearby recipients.

Despite that the investigated sites are - in Danish terms - heavily polluted with pesticides, the actual amounts of pesticides observed in the groundwater are between 1 - 300 grams active pesticides. At the same time, we have observed a large reduction in the concentration of pesticides at down stream hot spots, at approx. 20 – 70 m distance. This indicates that pesticide point sources will only pose a threat if situated close to a pumping well.

The conclusion of the project is that future investigations of pesticide point sources should focus on potential point sources with a true history of extensive handling of pesticides and on sites situated close to drinking water wells.

The obtained knowledge of the spreading and the character of pesticide point sources is synthesized in a paradigm for investigations of sites potentially polluted with pesticides.