Report from the Sub-comittee on the environment and health

The studies of
watercourses are
representative of Denmark
4.2.1 Conclusions
32 different pesticides have been detected in Danish watercourses,
corresponding to about 30% of <strong>the</strong> substances tested for, toge<strong>the</strong>r with 4
metabolites. The frequency of finds is greatest in <strong>the</strong> spraying periods
and in connection with precipitation events with increased run-off. The
highest value of 10 microgrammes per litre was found for bentazon. 12 of
<strong>the</strong> pesticides were found in concentrations above 1 microgramme per
litre and 31 substances were found in concentrations above 0.1
microgramme per litre. Glyphosate was tested for in 6 samples and found
in all of <strong>the</strong>m in concentrations <strong>from</strong> 0.02 to 0.21 microgramme per litre
(Funen County 1997, Kronvang 1998; Spliid, Mogensen 1995). The
pesticides occur in all types of watercourse, but mostly in clayey
agricultural catchment areas. Pesticides can be transported to lakes and
watercourses with surface run-off. That applies both to water-soluble
substances and to substances that bind to particles of soil and that are
only transported with heavy run-off, which causes soil erosion.
Therefore, both substances that are banned because of <strong>the</strong>ir mobility in
soil (e.g. atrazine, dichlorprop and hexazinone) and substances that, as
far as is known today, are only transported to <strong>the</strong> groundwater with
leaching rainwater under extreme conditions (e.g. glyphosate,
esfenvalerate and pirimicarb) have been detected. Also detected is
DNOC, which can come <strong>from</strong> transboundary atmospheric transport and
be syn<strong>the</strong>sised <strong>from</strong> car emissions through atmospheric, chemical
processes (see section 4.5).
The first study was carried out in <strong>the</strong> period 1989-91, and <strong>the</strong> o<strong>the</strong>rs in
<strong>the</strong> period 1994-97. There are big differences in <strong>the</strong> sampling intensity
and strategy in <strong>the</strong> various analyses. In some cases, sampling was done
on predesignated dates; in some, it was concentrated in <strong>the</strong> spraying
season, and in some, sampling extended over <strong>the</strong> whole year. Some
sampling was done in connection with increased water flow in <strong>the</strong>
watercourse. The analyses did not include samples taken because of
suspected pollution <strong>from</strong>, for example, point sources. The watercourses
analysed cover a number of counties and different types of catchment
area and types of soil, and must generally be regarded as representative
of Denmark. There are not as yet any long time series of measurements
of pesticides in watercourses, but monitoring programmes in progress in
<strong>the</strong> counties and countrywide studies will in time result in <strong>the</strong> necessary
database for determining <strong>the</strong> development.
The following specific conclusions can be drawn:
• 32 pesticides have been detected in watercourses, corresponding to
30% of <strong>the</strong> substances tested for.
• In many watercourses, several pesticides have been detected at <strong>the</strong>
same time.
• Detection of pesticides in springs indicates that pesticides can be
carried to watercourses via groundwater.
• The frequency of detection is highest in spraying periods and in
connection with heavy precipitation, but pesticides have also been
detected in watercourses outside <strong>the</strong> spraying periods.
33