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The issues
Eleven years of information from WIIS
WIIS incidents involving chemicals used to control vertebrate pests
Incidents by cause
Low-level rodenticide residues in UK Wildlife
The issues
Research over many years has highlighted two main areas
of concern with regard to the use of rodenticides and wildlife
in the UK. Occasionally, bodies of individuals of some
wildlife species are found to have died as a result of the
use of pesticides. The scope of this is monitored and
reported annually through the Wildlife Incident Investigation
Scheme (WIIS) run by the Pesticides Safety Directorate (PSD)
of the Department for Environment, Food and Rural Affairs
(DEFRA).
Another concern is that several species of
wildlife in the UK carry low-level residues of some of the
commonly-used rodenticides in their bodies. There is
no evidence that these have any adverse effects, either on
the individual animals that carry them or on wildlife populations.
However, those who use rodenticides should do so in ways that
seek to reduce, to a minimum, any exposure of wildlife.
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Eleven years of information from WIIS
The Wildlife Incident Investigation Scheme (WIIS) is Europe’s
most extensive post-registration surveillance scheme monitoring
the effects of pesticides on wildlife.
Information on individual incidents was provided
for the first time in 1993. This
has allowed a detailed examination of WIIS data and, with eleven years' data
now available, it permits an in-depth look at WIIS and the conclusions that
can be drawn from it.
WIIS relies mainly on reports from the public
of incidents involving wildlife casualties. Further investigations
normally involve post mortem analysis of carcases, chemical analysis of
tissues for pesticide residues and on-site investigations to determine,
if possible, the circumstances of the incident. Mortality is attributed
to a pesticide if a residue is found that is above a level considered to
represent lethal exposure.
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WIIS incidents involving chemicals used to control vertebrate pests
The results of WIIS are presented to the Environmental Panel of the Advisory
Committee on Pesticides and published in an annual report (www.pesticides.gov.uk).
Since 1993, these reports have included a table giving information of individual
incidents, allowing detailed analysis of WIIS incidents to be carried out
(Figure 1).
The cause of each incident is attributed as:
abuse of a pesticide,
in the form of deliberate, illegal attempts to poison animals;
misuse of
a product, by careless, accidental or wilful failure to follow correct
practice;
approved use of a product, according to the specified conditions
of use; and
unspecified use, where the cause could not be assigned to one
of the above categories.
An analysis of all 756 WIIS incidents involving
chemicals used to control vertebrate pests has been carried for the years
1993 to 2003. In terms
of the numbers of active ingredients, the products involved are mainly anticoagulant
rodenticides (Figure 2) but there are also non-anticoagulant rodenticides,
e.g. alphachloralose and products such as strychnine, which is only legally
used for mole control.
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Incidents by cause
Abuse - 422 (55.8%) were
cases of 'abuse', where vertebrate control agents were used
in deliberate attempts to harm wildlife and companion animals.
This abuse often takes the form of poisoned meat baits, put
out mainly for rooks, crows, magpies and foxes for the protection
of game birds. These baits are indiscriminate and are
also taken by other mammals, including dogs and a wide range
of birds of prey. Many of these incidents involve criminal
investigations and may result in enforcement action, including
prosecution.
The Campaign Against Illegal Poisoning is also
run by the Pesticides Safety Directorate and draws attention
to this issue by publicising prosecutions (www.pesticides.gov.uk).
The campaign appeared to be having some effect in the late
1990s,
with incidents steadily declining. However, increases
have been seen more recently (Figure
1).
The geographical
distribution of these incidents shows a high degree of association
with moorland used for shooting, with relatively large numbers
of abuse incidents in Tayside, Co. Down, Antrim, Highland,
Tyrone, North Yorkshire, Grampian, Strathclyde and Londonderry.
Misuse
- 89 (11.8%) were incidents involving 'misuse' when
the products were used in an inappropriate manner, either
deliberate or accidental, in contravention of the approval
and instructions on the label.
Approved - Only 35 (4.6%)
incidents over the eleven-year period could be attributed with
certainty to the use of products in an ‘approved’ manner
and this provides confidence that, when they are properly
used, vertebrate control agents do not present a significant
risk to wildlife and companion animals.
The numbers
of incidents involving the approved use of vertebrate pesticides
is extremely small and this reassures those users who follow
good practice that labelling and use patterns are largely
correct.
Recent WIIS reports have included information on
incidents involving vertebrate control agents where the compounds
were not considered to be the primary causes of death. Thirteen
such incidents were recorded in the 2002 and 2003 WIIS reports.
Unspecified
- 197 (26.1%) were ‘unspecified’ incidents,
where investigations did not permit a specific cause to be
attributed. Anticoagulant rodenticides are the products
that predominate in these incidents.
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Low-level rodenticide residues in UK Wildlife
During the 1980s, barn owls in the UK were found carrying
residues of some of the most commonly-used anticoagulant
rodenticides. Most of the birds were otherwise healthy
and there was no evidence that the residues, present only
in trace amounts, were causing them harm.
Nevertheless,
as methods of analysis grew more sophisticated and the
frequency of carcase collection was stepped up, it was
found during the 1990s that up to 40% of barn owls carried
traces of rodenticides. This indicated that
at some time during their lives the birds had taken one
or more rodents that had been treated with rodenticides.
Although
owls may occasionally take rats and mice for food, analysis
of the food of barn owls shows that they feed mainly on
wild small mammals, such as field mice and voles. It
is difficult to explain the extent of exposure of owls
to rodenticides by their consumption of contaminated target
rodents. It may be that they are indirectly exposed when
non-target rodents take rodenticide baits during application
of rodenticides in the countryside.
This information on
rodenticide residues in owls must be seen in the context
of the fact that the most common documented cause of death
in barn owls is collision with road traffic. Indeed,
it may be that as many as 3,700 owls are killed every year
on our roads.
Recognition of the level of exposure of barn
owls to anticoagulants resulted in the search for residues
in other wildlife species. It
has been shown that populations of several other species,
including red kites, kestrels, polecats, stoats and weasels,
also contain residues of anticoagulants.
Once again, there
is no evidence that populations of these species are in
any immediate danger as a result of this. Indeed
some species, such as stoats and weasels, are actively
controlled by gamekeepers to protect game birds.
Others,
such as red kites and polecats, are showing dramatic increases
in their populations in the UK thanks to re-introduction
programmes and other beneficial changes in the countryside.
A recent survey has shown that polecat numbers have increased
by 420% during the past ten years and the red kite re-introduction
programme is a significant success.
However, the widespread
distribution of these low-level residues of anticoagulants
in wildlife is of concern. |
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| Images courtesy of www.brianphipps.net |
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