Document ID: EPA-HQ-OPP-2006-0955-0008
Agency: epa
Document Type: Supporting & Related Material
Title: 
Posted Date: 2007-01-17T05:00Z

UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

WASHINGTON D.C., 20460

November 15, 2006

Memorandum

Subject:	Rodenticide Incidents Update

To:

	Susan Lewis, Chief

Kelly Sherman

SRRD

From:

	Bill Erickson, Biologist

ERB 2/EFED

Through:

	Tom Bailey, Chief

ERB 2/EFED

OPP/EFED’s ecological assessment of Potential Risks of Nine
Rodenticides to Birds and Nontarget Mammals:  a Comparative Approach,
dated July 2004, presented the rodenticide incidents with birds and
nontarget mammals known at that time.  The incidents are discussed in
the assessment, and individual incidents and residue levels are listed
in an attachment (Attachment D).  Other incidents have occurred since
then, and additional reports prior to that time have become available. 
These incidents are contained in OPP/EFED’s Ecological Incidence
Information System (EIIS).  The current report summarizes the available
incident information as of November 2006.

Most of the incident reports for the anticoagulant rodenticides were
submitted from the New York State Department of Environmental
Conservation (Wildlife Pathology Unit) or the California Department of
Fish and Game (Pesticides Investigation Unit).  Anticoagulant incidents
are based on detection of residue or residues in liver tissue and
corroborating evidence from carcass necropsy.  Such analyses are
expensive, and lack of sufficient funding limits the extent of analyses
and incident reporting.  As discussed in the ecological risk assessment,
most incidents are not reported due to a variety of reasons.  For
example, most animal carcasses are never found by humans, scavengers
quickly remove and consume carcasses, carcasses or ill animals
discovered by humans are not reported to proper authorities for a
variety of reasons, carcasses discovered and reported are not typically
analyzed for rodenticides, and various other reasons.

Incident reports are only one of several lines-of-evidence used to
evaluate risk.  Other lines include acute toxicity, persistence of
compounds in body tissues of primary consumers (i.e., bait eaters),
information from laboratory and pen studies in which poisoned prey are
fed to predators or scavengers in various amounts for one or more days,
and data from field trials and operational control programs.  In many
incident reports, the consequence of rodenticide exposure is not known,
although in many cases the examining toxicologist determined that a
rodenticide likely caused or contributed to the mortality. 
Anticoagulants typically do not cause death until 4 to 10 days or more
after a lethal dose is ingested.  However, exposed individuals become
progressively weaker and lethargic due to blood loss, and that added
stress may contribute to the proximate cause of death.  Even if a
cause-effect relationship has not been determined for many incidents,
the findings of exposure of such a wide variety of nontarget wildlife,
both birds and mammals, is a concern.  As discussed below, several
monitoring programs have found that a major portion of some animal
populations are being exposed to second-generation anticoagulant
rodenticides.

Anticoagulant Rodenticides

The second-generation anticoagulant rodenticides (SGARs) consist of
brodifacoum, bromadiolone, and difethialone.  First-generation
anticoagulant rodenticides (FGARs) include diphacinone, chlorophacinone,
and warfarin.  Both SGARs and FGARs are registered for use in and around
buildings, transport vehicles, and inside sewers; however, difethialone
and bromadiolone are labeled only for indoor use in “non-urban”
areas.  Diphacinone and chlorophacinone also have field uses (e.g.,
orchards, rangelands), including hand- or mechanical-broadcast
applications for pests such as voles and ground squirrels.  These uses
are described in more detail in the ecological risk assessment.

Avian incidents

Residues of anticoagulants have been detected in 27 species of wild
birds (and 14 spp. of captive birds in zoo incidents), including owls,
diurnal raptors and vultures, corvids, and others (Table 1).  Other dead
or ill birds were reported in some incidents, but the tabulated data
include only those birds analyzed for residues.  Of the 290 individuals
in which anticoagulants were detected, SGARs were detected in 97% and
FGARs in 4% (3 birds contained both SGARs and FGARs).  Brodifacoum was
detected in 87% of the 290 birds and bromadiolone in 13% (brodifacoum
and bromadiolone were both detected in several great horned owls).

Table 1.  Detection of Anticoagulant Rodenticides in Birds 

  

   Species	No. detections	SGARs	FGARs

Owls

   Great-horned owl (  SEQ CHAPTER \h \r 1 Bubo virginianus)	71	71	2

   Eastern screech-owl (  SEQ CHAPTER \h \r 1 Otus asio)	18	18

	   Barn owl (  SEQ CHAPTER \h \r 1 Tyto alba)	8	  8

	 *Northern spotted owl (  SEQ CHAPTER \h \r 1 Strix occidentalis)	2	  2

	   Long-eared owl (  SEQ CHAPTER \h \r 1 Asio otus)	2	  2

	   Barred owl (  SEQ CHAPTER \h \r 1 Strix varia)	2	  1	1

   Snowy owl (  SEQ CHAPTER \h \r 1 Nyctea scandiaca)	1

1

   Northern saw-whet owl (  SEQ CHAPTER \h \r 1 Aegolius acadicus)	1	  1

	Diurnal raptors

   Red-tailed hawk (  SEQ CHAPTER \h \r 1 Buteo jamaicensis)	87	85	2

   Cooper’s hawk (  SEQ CHAPTER \h \r 1 Accipiter cooperii)	24	24	2

   Golden eagle (  SEQ CHAPTER \h \r 1 Aquila chrysactos)	13	13

	 *Bald eagle (  SEQ CHAPTER \h \r 1 Haliaeetus leucocephalus)	3	  2	1

   Red-shouldered hawk (  SEQ CHAPTER \h \r 1 Buteo lineatus)	3	  3

	   Sharp-shinned hawk (  SEQ CHAPTER \h \r 1 Accipiter striatus)	2	  2

	   Broad-winged hawk (Buteo platypterus)	1	  1

	   American kestrel (  SEQ CHAPTER \h \r 1 Falco sparverius)	2	  2

	   Peregrine falcon (  SEQ CHAPTER \h \r 1 Falco peregrinus)	1

1

   Unidentified hawk	1	  1

	   Turkey vulture (  SEQ CHAPTER \h \r 1 Cathartes aura)	2	  1	1

   Black vulture (  SEQ CHAPTER \h \r 1 Coragyps atratus)	1	  1

	Others

   Corvids (Corvus spp.  SEQ CHAPTER \h \r 1   SEQ CHAPTER \h \r 1 ), 3
spp.	20	20

	   Turkey (  SEQ CHAPTER \h \r 1 Meleagris gallopavo), wild   SEQ
CHAPTER \h \r 1 	5	  	5

   Captive birds (3 zoos), 14 spp.	15	15

	   Others, 4 spp.  SEQ CHAPTER \h \r 1 	5	5	1

Total birds:	290	278

(97%)	17

(6%)

* listed (endangered or threatened) species

	Mammalian incidents

Anticoagulant residues have been detected in 218 mammals comprising 17
species, including the endangered San Joaquin kit fox (Table 2).  SGARs
were detected in 92% of the individuals and FGARs in 18% (both SGARs and
FGARs were detected in some individuals).  By rodenticide, brodifacoum
was detected in 83% of the 218 mammals, bromadiolone in 32%, diphacinone
in 13%, chlorophacinone in 6%, difethialone in 5%, and warfarin in 2%. 
Brodifacoum and bromadiolone were detected together in some individuals,
especially bobcats and mountain lions but also several coyotes and kit
foxes.

Table 2.  Detection of Anticoagulant Rodenticides in Mammals

   Species	No. detections	SGARs	FGARs

Canids (wild)

  *San Joaquin kit fox (  SEQ CHAPTER \h \r 1 Vulpes macrotis mutica)	32
27	6

   Coyote (  SEQ CHAPTER \h \r 1 Canis latrans)	25	23	5

   Red fox (  SEQ CHAPTER \h \r 1 Vulpes vulpes)	5	5

	   Gray fox (  SEQ CHAPTER \h \r 1 Urocyon cinereoargenteus)	3	3

	Felids (wild)

   Bobcat (  SEQ CHAPTER \h \r 1 Lynx rufus)	37	35	7

   Mountain lion (  SEQ CHAPTER \h \r 1 Felis concolor)	30	28	5

Other carnivores

   Raccoon (  SEQ CHAPTER \h \r 1 Procyon lotor)	10	9	2

   Striped skunk (  SEQ CHAPTER \h \r 1 Mephitis mephitis)

5

	   Badger (  SEQ CHAPTER \h \r 1 Meles meles)	1

1

   Long-tailed weasel (  SEQ CHAPTER \h \r 1 Mustela frenata)	1	1

	Others

   Opossum (  SEQ CHAPTER \h \r 1 Didelphis virginiana)	5	5

	   White-tailed deer (  SEQ CHAPTER \h \r 1 Odocoileus virginianus)	7	5
2

   Gray squirrel (  SEQ CHAPTER \h \r 1 Sciurus carolinensis)	57	51	9

   Others, 4 spp.	5	4	1

Total mammals:	218	201

(92%)	39

(18%)

* listed (endangered or threatened) species

Extent of SGAR Exposure in Wildlife Populations

The extent of exposure to SGARS has been reported for several species in
the U.S., Canada, and the UK (Table 3).  The data from New York also
include detections of FGARs, but they comprised only 5% of all
detections.  In both New York and Ontario, SGARs were detected in more
than 80% of all great horned owls analyzed and in more than 50% of the
red-tailed hawks.  Other owls and raptors in which SGARs are frequently
detected include Eastern screech-owls, Cooper’s hawks, kestrels, and
kites.  SGARs also have been detected in 71 to 84% of the kit foxes,
bobcats, and mountain lions analyzed in California.  Clearly, more
information is urgently needed on the potential impacts such exposure
may be having on populations of wild canids, wild felids, and raptors.

Table 3.  Widespread Detection of SGARs in Nontarget Birds and Mammals
in the U. S. and Elsewhere

Location/

  Species	no. analyzed

for liver residue	%

positive

New York:a

All (15 species)	265	48*

   Great horned owl 	53	81

   Red-tailed hawk 	78	58

   Eastern screech-owl 	22	45

   Cooper’s hawk 	50	36

California:b

   San Joaquin kit fox 	32	84

   Bobcat 	39	79

   Mountain lion 	35	71

Ontario:c

   Great horned owl	24	87

   Red-tailed hawk	30	57

United Kingdom:d

   Red kite (Milvus milvus)	20	70

   Kestrel (Falco tinnunculus)	36	67

   Polecat (Mustela putorius)	100	31

  Least weasel (Mustela nivalis)	10	30

  Stoat (Mustela erminea)	40	23

* 6 (5%) positives were first-generation anticoagulants:  3 diphacinone,
2 warfarin, 

1 chlorophacinone; 122 (95%) positives were second-generation
anticoagulants:  108 (84%) brodifacoum and 28 (22%) bromadiolone (note: 
brodifacoum and bromadiolone were both detected in 15 birds)

a Stone et al. (2003). Bull. Environ. Contam. Toxicol. 70:34-40

b California Department of Fish and Game, Pesticides Investigation Unit;
 

   U. S. National Park Service

c National Wildlife Research Centre, Canadian Wildlife Service 

d Shore et al. (2003). Environ. Poll. 122:183-193  

  Burn et al. (2002). Aspects Appl. Biol. 67:203-212

  McDonald et al. (1998). Environ. Pollution 103:17-23

Non-anticoagulant Rodenticides

Considerably less incident information is available on the
non-anticoagulant rodenticides.  Some incident information is available
for zinc phosphide (ZP; Table 4) but none for bromethalin or
cholecalciferol.  Most ZP incidents are for waterfowl and wild turkeys. 
Based on the species and numbers impacted, most ZP incidents likely were
due to field applications rather than homeowner use.  

Table 4.  Zinc Phosphide Incidents

   Species	No. incidents	No. individuals

Birds

   Turkey (  SEQ CHAPTER \h \r 1 Meleagris gallopavo), wild	17	71

   Canada goose (Branta canadensis)	8	157

   Snow goose (Chen caerulescens) and/or

  White-fronted goose (Anser albifrons)	2	~390

   Mallard (Anas platyrhynchos)	1	29

Mammals

   Red fox (  SEQ CHAPTER \h \r 1 Vulpes vulpes)  	1	2

   Gray squirrel (  SEQ CHAPTER \h \r 1 Sciurus carolinensis) 	2	20

   Eastern cottontail (Sylvilagus floridanus)  	1	1

Total:	32	670

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