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Subject: A case of rape (1/7)
From: (Torsten Brinch)
Date: May 20 1995
Newsgroups: sci.agriculture

                                        13th of June 1991

* Possible connection between wildlife losses and seed
  dressing agents for rape seed.*

  M.Ph. Torsten Brinch, Independent Agrochemical Observer
  Risb√łge 55, 6640 Lunderskov, Denmark.

*Abstract: *
   The use of seed dressing agents, applied to rape seed
before sowing, has great potential for intoxication of birds
and other wildlife, due to extreme toxicity of active
ingredients and rate of application.
Possibly, acute deaths of hares ,the European Brown Hare
Syndrome (EBHS), have been directly caused by the chemical
compound *isofenphos*, which is widely used in the EEC for
seed dressing in oilseed rape. Other cholinesterase inhibitors
may have contributed as well. *Gamma-HCH* may have
contributed to the chronic poisoning of wildlife.


   Cultivation of winter oilseed rape 00, which has been done in
Denmark since growth season 1983/84, was early linked to
acute deaths of hares observed since autumn 1983. Several
places in Europe similar incidents have been observed since
1986, where cultivation af oilseed rape 00 was initiated.

  The current official view: that the deaths are caused by a
viral infection, leads to considerable difficulties in
explaining the known facts. In particular:
the concentration of deaths in a short period spring and autumn,
the sudden appearance in areas widely separated,
healthy hare populations in close proximity to heavily affected,
the seemingly close connection to  winter oilseed rape 00, and
the observed CNS-symptoms by affected animals.
Roe deer and wood pigeons have been affected, too.

When numbers of dead hares are found in or close to cultivated
fields, one should immediately suspect the possibility of
agrochemical poisoning. Strange as it seems, no attempt
has been done to exclude this possibility.

*Conditions for growing of oilseed rape in Denmark.*

Depth of sowing should be less than 4 cm and the soil
well prepared to ensure germination and good root
The sowing of winter oilseed rape is done in the week
following the 15th of August. If the sowing is done much
later it leads to reduced yield. Local climate, the weather
in the autumn and the ability to be ready in time with the
soil well-prepared after harvesting the former crop may
affect the precise date for sowing.
Germination is usually complete in the beginning of September,
when the cotyledons appear on the surface .
During September the first leaves  develops from the

Spring rape is sown in the beginning of April - apart from
that, its development is similar to winter rape.

The aim is 40-80 flowering plants pr. m2, the largest
number for spring rape. For sowing usually 4 kg of seed is
used pr ha, which is the equivalent of 80-100 seeds pr m2.
Normally the seed is sown in furrows 10 or more cm apart.

Cultivation of spring and winter oilseed rape crops is
quite common in the Eastern part of Denmark, while in the
Western and Northern parts their share of the fields is
much less. This is mainly caused by the soil demands of the
plant. The risk for frost damage in winter oilseed rape is
taken into account, too.

The area with oilseed rape has increased for some years.
From the autumn 1988 there has been a change in proportions
between the area with spring vs. winter oilseed rape.
The growth season 1990/91 brought for the first time
a greater area sown with winter than with spring oilseed rape.
The total rape seed area in 1991 is approximately 10 % of the
total area in crop rotation.

*Seed dressing agents for rape seed.*

In  Denmark  3 seed dressing products have been approved :
*Oftanol-T*, *Vitavax RS* og *Loptox*.

In 1990 most of the seeds ( 65 %) were dressed with
*Oftanol-T*, the remaining part with *Vitavax RS*.
Both treatments were done by seed companies,who supplemented
with different encrusting agents, resp. Sacrust and Sepiret.

The treatment leaves the seeds with a glossy dustless surface.
The dust has formerly given problems during treatment and
handling of the product.

*Loptox* has minor use by farmers, who for some reason wants
to dress their own seeds.

A new product (Promet) is under testing and approval for
oilseed rape. This product will not be in use the first
couple of years. Due to high toxicity of the active
ingredient furathiocarb, there is considerable difficulties
in enclosing the seed dressing process, for the protection
of workers.

Oftanol-T has been withdrawn from the market by the end of
1990 . Stocks are empty and the machinery for
Oftanol-application has been taken down. A new formulation
of the same main ingredient, Oftanol-E, is expected to be
marketed in time, but not for this or the next growth season.

Until 1990 seed dressing with *Oftanol-T* has dominated the
market. From spring 1991 the main part of rape seeds sown is
dressed with  *Vitavax RS*

Part of the seeds for sowing is imported and may be dressed
with other products or at application rates not approved in
Denmark, see page 6 for further information.

Common to all seed dressing products for rape seeds is their
high content of insecticides. Usually a smaller amount of
thirame is added, partly as a wildlife-deterrant, partly as a
fungicide. Other fungicides may be added as well.


Active ingredients in approved seed dressing products  for
Denmark 1990, and approved application rates.

Oftanol-T            Isofenphos   40%
20 g/kg seed         Thirame      10%

Vitavax RS           gamma-HCH   675 g/l
20 ml/kg seed        Thirame      90 g/l
                     Carboxin     45 g/l

Loptox               gamma-HCH    75 %
45 g/kg seed         Thirame      10 %

(gamma-HCH is another name for lindane)

No knowledge is available on the ingredients of the
encrusting agents, which is a matter of continued R&D effort.

The risk of acute intoxication from the seed dressing agents
originates from the use of the chemical compounds *isofenphos*
and *gamma-HCH*.

Isofenphos has been approved for the use on seed from
Cruciferae, radish is excluded, however. The acute toxicity
of the compound taken into consideration, the approved rate
is remarkably high. The approved rate for gamma-HCH is
remarkably high in comparison with seed dressing with
gamma-HCH for other crops (10-20 times higher).

*High content of isofenphos and gamma-HCH in seed*
*and young oilseed rape plants after seed dressing*


                         seed         plant           plant
                                     stage 1         stage 2.2

ppm Isofenphos           8000        400-40         80-8
ppm gamma-HCH (Vitavax) 13500        675-67.5      135-13.5
ppm gamma-HCH (Loptox)  34000       1800-180       340-34

For comparison
NOEL for rat , feeding over 2 years:
 1 ppm in diet for isofenphos
25 ppm in diet for gamma-HCH

Calculations have been done from weight of plant 100 mg  at
stage 1  and 500 mg at stage 2.2 (2 leaves from the epicotyl).
Weight of seed 5 mg, which is typical for winter oilseed rape.
The spring varieties usually produce seeds with weight 4 mg,
which will lead to concentrations in plant 20 % lower.

The concentrations in plants are given as an interval. The
upper limit (not realistic) is for a 100 % transfer to the
young plant, the lower limit for only 10 %  transferred.

It is evident, that a transfer from the seed coat to the
plant is happening to a certain degree. The aim with
the seed dressing is to protect the young plant from attack
by insects.
The part, which is not transferred, may be lost to the soil
surrounding the seed or may be bound to the thin seed coat.
Shortly after appearance the seed coat is often carried
overground on the still not fully separated cotyledons.
At this stage (early stage 1) the seed coat is easily eaten
with the leaves.

Isofenphos is systemic, which means, that it may be taken up
by the root after transfer to the soil. The compound has
considerable water solubility, and is readily soluble in

Gamma-HCH is easily soluble in lipids. The seed contains
40 % lipids.

Until more data is available, an estimate could be that 10 %
is transferred. This estimate might be far to low.

Even the low estimate points to the possibility, that winter
oilseed rape for the entire autumn and winter period could
contain unacceptably high concentrations of insecticides.

*The possibility of acute deaths among hares. *

It has been shown that hares may eat complete young oilseed
rape plants, that they prefer eating germinating or young
parts and that some hares in a single feeding cycle may
feed almost entirely on rape.
This could probably be the situation in early autumn if the
hares find it difficult to find more palatable food,
because of plowing etc. or glyphosate-treatment of stubble
field. The daily intake can be as high as 1000 g fresh
plant material.

For an evaluation of the possibility of acute deaths, a daily
consumption of 500 g young plants is supposed.
Daily   by         consumption   consumption
                   at stage 1    at stage 2.2      LD50-dosis
mg Isofenphos         200-20         40-4             60
mg Lindan (Vitavax)   340-34         70-7            150
mg Lindan (Loptox)    940-94        170-17           150
LD50-values (20 mg/kg for isofenphos og 50 mg/kg for
lindan) are values for rabbit and weight of hare 3 kg.

Isofenphos is an irreversible cholinesterase inhibitor, and
repeated intake of subletal/subtoxic amounts may lead to
death/intoxication, because of the extremely slow regeneration
of cholinesterase.
Gamma-HCH is distributed to fatty tissue and slowly
metabolized and eliminated.

It seems clear that a possibility for acute deaths and
serious intoxication exists for hares, who for a short period
feeds on young oilseed rape plants, if these plants are
grown from seeds, which have been dressed according to

*What can be done?:*

1. Data on the concentration of isofenphos, the metabolite
   isofenphos-O and HCHs in seeds and young plants
   after seed dressing are *urgently needed*.

2. If ethical (according to data mentioned in 1.) feeding
   experiments may be conducted, to elucidate if the symptoms
   of European Brown Hare Syndrome can be reproduced.

3. Data on supplier of seeds for sowing *must be* collected
   when (if) wildlife losses is observed in connection with
   oilseed rape cultivation, to be able to trace the seed
   dressing agents used.

4. *Great caution* should be used when approving new seed
   dressing agents. An assessment of the resulting toxic load on
   wildlife should be indispensable. In particular renewed
   approval of seed dressing with isophenphos should be

 *Seed dressing with insecticides in some European countries.*

Isofenphos and gamma-HCH have been used.
The use of isofenphos stopped  1st of October 1990.


Isofenphos and gamma-HCH have been used.
The use of isofenphos temporarily stopped from the end of 1990.


Isofenphos is not used.
Gamma-HCH has been used at rates 12-45 g /kg seed. (Gammalex)


Isofenphos commonly used, but at double the rate common in
Denmark, i.e. 16 g isofenphos/kg seed.
The carbamate Methiocarb is commonly used, at the rate 25 g
methiocarb/kg seed. Gamma-HCH has minor use.


Isofenphos commonly used, but at double the rate common in
Denmark, i.e. 16 g isofenphos/kg seed.
Methiocarb and  gamma-HCH is also used in Germany.

Other potential ingredients:

The carbamates carbosulfan, carbofuran and furathiocarb may
be present in seed dressing agents.

; Torsten Brinch               If you understand nothing but chemistry, ;
;          you do not really understand chemistry.  ;
; 6640, Ferup, Denmark                   G.C. Lichtenberg  (1742-1799)  ;

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