Report from the Sub-comittee on the environment and health

34
• The frequency of detection is highest in agricultural catchment areas
with clayey soils.
• There are not many different pesticides in forest watercourses, but
pesticides that are or have been used in forests occur frequently
(atrazine, hexazinone and dimethoate).
• There are many different pesticides in urban watercourses.
• The distance requirements made in connection with authorisation of
pesticides are expected to reduce <strong>the</strong> frequency of detection in <strong>the</strong>
future.
4.3 Pesticides in lakes and ponds
Pesticides enter lakes, coastal waters and ponds via watercourses, surface
run-off <strong>from</strong> adjacent land, groundwater and atmospheric deposition,
including spray drift. The effects of pesticides in stagnant water are
described in section 5.3. There are as yet no systematic data on <strong>the</strong>
occurrence of pesticides in Danish lakes and coastal waters. Data <strong>from</strong>
<strong>the</strong>se compartments are <strong>the</strong>refore not included in <strong>the</strong> report. In
connection with Aquatic Environment Plan II, a measuring programme is
being initiated, but results for lakes cannot be expected in <strong>the</strong> coming
year.
The studies <strong>from</strong> stagnant water cover results <strong>from</strong> two projects. One
includes samples <strong>from</strong> four ponds in <strong>the</strong> Køge district (Spliid, Mogensen
1995), while <strong>the</strong> o<strong>the</strong>r includes a number of ponds in South Funen and
Avernakø (Briggs in press). In both districts, <strong>the</strong> ponds are in fields with
clayey soil. Many field ponds have nei<strong>the</strong>r inflow nor outflow. It must
<strong>the</strong>refore be expected that pesticides remain in <strong>the</strong>m longer than in
watercourses and that <strong>the</strong> risk to <strong>the</strong> aquatic organisms in <strong>the</strong>m is greater.
The results of <strong>the</strong>se studies are given in table 4.12.
The concentration interval in <strong>the</strong> table indicates <strong>the</strong> lowest and highest
concentration in <strong>the</strong> samples in which <strong>the</strong> pesticide in question was
detected. Column 3 shows <strong>the</strong> number of samples analysed for <strong>the</strong>
pesticide in question and <strong>the</strong> number of samples in which <strong>the</strong> substance
was detected. All <strong>the</strong> substances for which <strong>the</strong> samples were analysed
were detected, with <strong>the</strong> exception of bromoxynil and simazine. The
highest concentration for an individual substance was 11 microgrammes
per litre.
Table 4.12
Pesticides detected in ponds in Danish farmland in studies carried out by
DMU in 1989-1991 and by Amphiconsult in 1994-1995 (Mogensen,
Spliid 1997)