Berg R van den ,
Linden AMA van der ,
Mulschlegel JHC ,
Beek CGEM van ,
Jobsen JA ,
Leistra M ,
Hoeks J
152 p
in Dutch
1990
Toon Nederlands
English Abstract With reference tot the Memorandum Environmental
Criteria for the Protection of Soil and Water against Chemical Pollutants,
the objective of this study was to indicate whether dilution and degradation
in the ground water had to be accounted for in case of Approval of
Pesticides. In this report the possible occurrence of pesticides in the
upper (1 m) layer of the ground water and the deep, extracted ground water
has been evaluated based on the actual use of soil and pesticides in a
number of vulnerable agricultural areas in the Netherlands. Dilution,
defined as the physical process of mixing of water streams in the extraction
well, is determined by two factors: the actual use of a pesticide and the
acreage fractions of the crops to which a pesticide may be applied. In case
of public drinking water supplies the dilution factor, defined as the ratio
of the pesticide concentration in the upper (1 m) layer of the ground water
and that in the deep, extracted ground water, has a minimum value of 3.7
for pesticides which leaks into the ground water with resulting
concentrations higher than 0.1 mg.m -3. This dilution factor can be much
higher for the various combinations of pesticide and crops. This dilution
cannot prevent that the EC standard (for all pesticides together) of 0.5
mg.m -3 in the extracted ground water is exceeded (by factors of 10 to
1000) and that for 13 of the 130 pesticides evaluated the individual EC
standard of 0.1 mg.m -3 is exceeded. For private water extraction wells
the situation may be somewhere between two extremes: no dilution (in case of
very shallow extractions) or dilutions comparable to those of a public
drinking water supply. It was concluded that degradation of the pesticides
in the saturated zone may have a substantial effect on the concentrations in
the extracted groundwater. The extent is determined by the relation between
the residence time in this zone and the degradation rate of the pesticide in
this zone. Only very limited information is available on the transformation
of pesticides in the water satured zone and a reasonable certainty about the
formation of harmless metabolites does not exist. Therefore the influence
of transformation in the subsoil on the levels of pesticides in deep ground
water has not been evaluated. In the discussion attention has been given to
the uncertainties of the model (parameters) and the overground processes
which determine the fraction of the dosage reaching the
soil.