Report from the Sub-comittee on the environment and health

56
Example 1: IPU dosage 1000 g
active ingredient per ha:
- 10 l remaining spray liquid
- 100 times diluted
Example 2: Express dosage 7.5 g
active ingredient per ha:
- 10 l remaining spray liquid
- 100 times diluted
IPU = isoproturon.
µg/L = microgramme per litre
67 g
0.7 g
0.5 g
5 mg
670,000 m 3
6,700 m 3
5,000 m 3
50 m 3
A model calculation by GEUS of <strong>the</strong> potential importance of point
sources to groundwater pollution shows that only a minimal proportion
of pesticide detections comes <strong>from</strong> point sources (GEUS 1996). The
calculations are based on various assumptions – for example, that <strong>the</strong>
size of <strong>the</strong> point source is only 0.3 x 0.3 m. Since washing sites and
sprayed farmyard areas are usually much larger than that, <strong>the</strong> leaching
could be much greater than calculated.
In an ongoing project in which DIAS, GEUS and DMU are participating,
<strong>the</strong> extent of a pesticide plume <strong>from</strong> a washing and filling site is being
studied. This will provide supplementary knowledge about <strong>the</strong>
importance of point sources.
4.6.10 Conclusions
• The use of pesticides and cleaning of tractors and sprayers near wells
and <strong>the</strong> use of herbicides on farmyard areas and similar can lead to
pollution of water supplies.
• Filling and washing sites are serious but limited, potential sources of
pollution because <strong>the</strong> concentration and area load are high.
• Serious pollution can occur if a sprayer is filled directly <strong>from</strong> <strong>the</strong>
water supply and <strong>the</strong> tube is left in <strong>the</strong> spray tank, since water can
pollute <strong>the</strong> well by back-siphoning into <strong>the</strong> pipe.
• It is assumed that point sources with pesticides pollute groundwater
and surface water. In directions <strong>from</strong> 1966, farmers were advised to
bury small remnants of pesticides, but despite later warnings and
extensive information, pesticides are still sometimes detected in
groundwater or watercourses in such high concentrations that <strong>the</strong>
source is unlikely to be field application. It has not been proven that
such point-source pollution is <strong>the</strong> cause of <strong>the</strong> cases found in which
limit values are exceeded in groundwater and wells.
• There is as yet no complete evaluation of filling and washing sites as
sources of pollution.
4.7 The sub-committee’s conclusions and recommendations
1. There are studies of pesticides in <strong>the</strong> different compartments –
groundwater, watercourses, drain water, soil water and rainwater.
There are only a few measurements of pesticides in ponds and lakes.
Only in <strong>the</strong> case of groundwater are <strong>the</strong>re time series, but <strong>the</strong>