Report from the Sub-comittee on the environment and health

Fuzzy Expert model
Expert assessment
Deterministic models: <strong>the</strong>
MACRO model
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concentration of pesticides in <strong>the</strong> uppermost groundwater by means of
<strong>the</strong> deterministic model PESTLA, using data for degradation and
adsorption to soil. The Yardstick operates with sandy soil, which is
typical for <strong>the</strong> Ne<strong>the</strong>rlands. The results are given for five classes of soil
and spring and autumn spraying, where <strong>the</strong> temperature and precipitation
vary. Since <strong>the</strong> method is based on <strong>the</strong> same simple indexing methods or
on <strong>the</strong> deterministic model PESTLA, it does not produce results
fundamentally different <strong>from</strong> <strong>the</strong>se. Like <strong>the</strong> Dutch point system, <strong>the</strong>
method is based on risk thinking and <strong>the</strong>refore cannot be used directly for
ranking pesticides because it depends partly on local environmental
conditions and partly on <strong>the</strong> actual cultivation practice.
This method was developed in <strong>the</strong> Ne<strong>the</strong>rlands (van der Werf, Zimmer
1998). The risk of groundwater pollution is assessed partly on <strong>the</strong> basis
of a GUS index and partly on <strong>the</strong> basis of a “leaching risk” parameter.
This parameter requires supplementary considerations or model analyses.
A high level of expert knowledge is needed to use <strong>the</strong> method, making it
difficult to work with. The method can <strong>the</strong>refore not be used under
Danish conditions without considerable input <strong>from</strong> a variety of experts.
For this reason, <strong>the</strong> model has not been used here to assess leaching.
However, <strong>the</strong> method also covers o<strong>the</strong>r environmental aspects than
groundwater so its use could be considered in continuing work on
environmental indices.
In an expert assessment, one or more experienced experts designate
substances on <strong>the</strong> basis of existing data and an integrated assessment. An
expert assessment thus includes a systematic review of data and
assessment elements that can be classified and ranked in <strong>the</strong> normal way,
but must at <strong>the</strong> same time be combined with an experience-based
assessment of lacking data and unclassifiable elements. A large number
of factors are considered in <strong>the</strong> assessment of <strong>the</strong> risk of leaching to <strong>the</strong>
groundwater within <strong>the</strong> framework of <strong>the</strong> authorisation scheme for
pesticides. They include <strong>the</strong> inherent properties of <strong>the</strong> substances and
<strong>the</strong>ir metabolites and degradation products, combined with <strong>the</strong> dosage,
<strong>the</strong> time of application and any finds in groundwater. On <strong>the</strong> basis of
experience, some substances are judged to lie closer to <strong>the</strong> critical limit
for leaching to groundwater than o<strong>the</strong>rs. This assessment determines
whe<strong>the</strong>r a product can be authorised or not. Precise designation of <strong>the</strong>
most problematical substances requires a thorough examination of <strong>the</strong>
documentation and assessment of monitoring results, and possibly
calculations with a leaching model, e.g. MACRO (see below). This form
of assessment has been used in <strong>the</strong> assessment of many of <strong>the</strong> pesticides
that have been placed on <strong>the</strong> blacklist.
A number of actual transport models that describe <strong>the</strong> transport of
pesticides down through <strong>the</strong> root zone have been developed (e.g.
LEACHM, PELMO, PESTLA and MACRO). These are so-called
deterministic models in which it is assumed that <strong>the</strong> outcome under given
assumptions will always be <strong>the</strong> same. The so-called stochastic (or
probabilistic) models, on <strong>the</strong> o<strong>the</strong>r hand, take account of variations in <strong>the</strong>
system and thus only talk about <strong>the</strong> probability of a given outcome. There
are as yet no suitable stochastic models for ranking pesticides’ potential
leaching to <strong>the</strong> groundwater. Unlike <strong>the</strong> simple index methods, both