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| RODENTICIDES AND WILDLIFE |
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The issues
Fifteen 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 though the Wildlife Incident Investigation Scheme
(WIIS) run by the Chemicals Regulation Directorate (CRD).
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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Fifteen years of information from WIIS
The Wildlife Incident Investigation Scheme (WIIS) is Europe’s most extensive postregistration 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 fifteen years data now available, it
permits an in-depth look at WIIS and the conclusions that can be drawn from it.
WIIS mainly relies 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 - 492 (44.0%) 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
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
- 123 (11.0%) were incidents involving 'misus' 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 38 (3.4%) incidents, over the fifteen 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.
Unspecified
- 375 (33.6%) were ‘unspecified’ incidents, where investigations did not
permit a specific cause to be attributed.
Other - 89 (8.0%) were incidents in which causes other than the pesticides detected on
analysis were the primary cause of death. This includes several different categories
including starvation, trauma and injury. Such causes of death have only been recorded
in WIIS reports since 2002 (Figure
1).
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Low-level rodenticide residues in UK Wildlife
During the 1980’s 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
Nevertheless, as methods of analysis grew more sophisticated and the frequency of
carcase collection was stepped up, it was found during the 1990’s 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 nontarget
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 also contain residues of anticoagulants, including red kites, kestrels, polecats,
stoats and weasels (Figure
3).
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, including buzzards, 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% over 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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Campaign for Responsible Rodenticide Use is a company limited by guarantee,
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