Report from the Sub-comittee on the environment and health

Soil
Residues in <strong>the</strong> soil
Drain water
The atmosphere
190
Scenarier = Scenarios
Plus-plus = ++scenario
Plus = +scenario
Nul-plus = 0+scenario
Nul = 0-scenario
Nudrift = present production
Anvendt pesticidmængde i tons = Quantity of pesticide used, in tonnes)
10.2.2 Pesticides in soil, surface water and <strong>the</strong> atmosphere
After spraying, pesticides are broken down and absorbed by <strong>the</strong> soil and
plants. Normally, only substances with a half-life of max. 3 months in
soil at 10°C and at 20°C are authorised. In <strong>the</strong> case of substances with
shorter half-lives, <strong>the</strong> residual quantity is much smaller. However, in
field conditions, where <strong>the</strong> conditions for degradation are not optimal,
degradation can take longer. The temperature and humidity are important
factors in this connection, as described in section 4.6.4. In <strong>the</strong> winter
months, <strong>the</strong> degradation process in <strong>the</strong> topsoil thus comes to a standstill
at low temperatures, and in <strong>the</strong> summer months, drying out of <strong>the</strong> soil
halts <strong>the</strong> degradation process. If use of <strong>the</strong> currently authorised pesticides
ends in a given area, <strong>the</strong> residues in <strong>the</strong> soil will normally be degraded
and thus not accessible to plants or animals, or leach to <strong>the</strong> groundwater,
after a cultivation season.
Degradation of <strong>the</strong> residues of all pesticides is prevented by <strong>the</strong> fact that
<strong>the</strong> molecules diffuse into microscopic pores in <strong>the</strong> soil particles, where
<strong>the</strong>y can no longer be reached by microorganisms. These residues can be
detected with special analytical methods with effective extraction and
sensitive apparatus and are of <strong>the</strong> same order of magnitude as <strong>the</strong>
concentrations supplied to <strong>the</strong> cultivation systems through atmospheric
deposition of pesticides transported over long distances. Lastly, it should
be mentioned that it is possible to detect formerly authorised persistent
pesticides, such as DDT and lindane, in relatively high concentrations in
<strong>the</strong> soil in areas in which <strong>the</strong>y were used more than 15 years ago. That
applies particularly to orchards. It can thus be concluded that old,
persistent pesticides that are no longer authorised are still being detected
in soil, whereas most of <strong>the</strong> authorised pesticides will be degraded one to
two years after use of <strong>the</strong>m ceases.
The supply of pesticides to drain water depends on <strong>the</strong> dosage, <strong>the</strong>
degradation and adsorption in <strong>the</strong> topsoil and evaporation. If pesticides
were totally phased out, <strong>the</strong> amount that could be transported down in <strong>the</strong>
soil would disappear. However, leaching of <strong>the</strong> residues in <strong>the</strong> soil could
continue for some years, depending on precipitation events and <strong>the</strong> soil
conditions, which determine <strong>the</strong> adsorption and degradation of <strong>the</strong>
substances.
If pesticides were no longer used <strong>the</strong> problem of evaporation and spray
drift <strong>from</strong> <strong>the</strong> areas in question would disappear. However, <strong>the</strong>re would
still be a supply of pesticides through long-range transboundary
atmospheric transport. Pesticides would thus continue to be supplied with
precipitation, although less frequently and in considerably smaller
concentrations than described in section 4.5. It should be noted here that
<strong>the</strong> finds described cover only some of <strong>the</strong> pesticides that could be
transported to <strong>the</strong> atmosphere through spray drift and evaporation here in