Íslenskar landbúnaðarrannsóknir - 01.09.1982, Side 16

14 ÍSLENZKAR LANDBÚNAÐARRANNSÓKNIR
the investigation did not take into account
any possible effects of linuron residue on
yield or on quality of the potatoes.
The level of linuron measured in the
potato samples is twenty times lower than
the maximum tolerance level calculated by
Maier - Bode and Hártel (1981) which
they based on FAO/WHO consumption
data and on an acceptable daily intake for
linuron taken from Deutsche
Forschungsgemeinschaft. Several coun-
tries have established linuron tolerance
levels for foods and those recorded for
potatoes are shown in table 7 (Maier —
Bode and Hártel 1981).
All the potato samples in the present
investigation would not exceed even the
most stringent of these tolerances.
A visual assessment of the crop at each
samplingsitein August 1981 didnotreveal
any noticeable degree of typical linuron
damage (i.e veinal chlorosis leading to
necrosis of the leaf tissue). In some potato
fields in the Eyjafjördur area where loamy
soils predominate, it has been noted in
TABLE 7.
Tolerance levels for linuron in potatoes as estab-
lished by some countries (Maier - Bode and
Hártel 1981).
7. TAFLA.
Hámarksgildi fyrir linuron í kartóflum, sem nokkur lónd
hafa komið á (Maier - Bode and Hartel 1981).
Country Tolerance limit (ppm)
Land Hámarksgildi (ppm)
USA.............. 1.0
Argentina........ 1.0
Brazil .......... 1.0
Belgium ......... 0.2
Switzerland ..... 0.2
W. Germany ...... 0.15
USSR............. 0.1
Netherlands...... 0.05
recent years that there have been a few
cases of linuron damage mostly veinal
chlorosis (plate 1). These are usually due to
accidental overdoses on the outskirts of the
fields where spraying has been started
before the tractor moves or where the
tractor has become stuck and spraying has
not been stopped immediately. A good
example of the latter type of overdose is
shown in plate 2 where nothing has grown
since it received an overdose in 1978. Soil
samples taken from this bare patch con-
tained about 12 ppm linuron in the dry
matter. This is more than double the
highest content found elsewhere in this
study.
The summer of this investigation (1981)
was not unusual in that there was the
occasional case of linuron damage in the
loam soils of Eyjafjördur but no wide-
spread effect was noted. It could therefore
be concluded for the year of this investiga-
tion that the residue levels measured,
althought relatively high in the loamy soils,
did not have any exceptional effect on the
appearance ofthe potato plants and did not
leave high levels of residue in the tubers
themselves.
In the summer of 1982, one year after the
investigation, symptoms of linuron toxic-
ity were apparently more pronounced than
usual in the loamy soils of Eyjafjördur.
Veinal chlorosis was more pronounced
and necrosis was becoming evident. One
field was particularly badly affected and
most of the crop there showed toxicity
symptoms. Such extensive damage has
previously not been known. The winter of
1981 —82 was unusually long and cold in the
Eyjafjördur area. The first snow fell
around October lst, even before all the
potatoes had been harvested. This long