Pesticide Profile - Brodifacoum

Quick Facts

• Chemical name: 3-[3-(4'-bromobiphenyl-4-yl)-1,2,3,4-tetrahydro-1-naphthyl]-=4- hydroxycoumarin

• Trade names: Talon, Havoc, D-Con mice and rat traps

• Pesticide type: rodenticide

• Formulation: meal bait, paraffinized pellets, rat and mouse bait ready-to-use place packs, and paraffin blocks.  All end-use products contain 0.005 percent active ingredient.

• Mechanism of Action: second-generation anticoagulant. Absorbed through the gut and inhibits the vitamin K-dependent steps in the synthesis of multiple clotting factors. Death usually occurs through gastric hemorrhage.

• Persistence: brodifacoum is persistent in soils with a half-life of 157 days. It is relatively immobile in soil and the potential for groundwater and surface water contamination is low. It is stable to hydrolysis at pH 5, 7, and 9.

• Metabolism: brodifacoum is retained in the tissues at high rates, sometimes remaining in organ systems during the entire lifetime of an exposed animal. In a study that measured the retention of radioactive brodifacoum in the livers of single-dosed rats, 34% of the single dose is found in the liver after 13 weeks, and 11% of the dose remained in the liver for 104 weeks, approaching the normal lifespan of a rat (U.S. EPA MRID 42007502).

• Toxicity:Very highly toxic to aquatic organisms. Due to its extremely low solubility and usage patterns however, it is assumed that not enough brodifacoum would dissolve in water to create a hazard to non-target animals. Products used in sewers are water-resistant paraffinized blocks and are not expected to dissolve in water.

• Very highly toxic to mammals and birds. Brodifacoum is extremely dangerous to birds through secondary exposure, especially raptors feeding on poisoned rats and mice. Hundreds of avian and other wildlife mortalities have been reported across North America.

• Avian LD50: 0.26 mg/kg (Mallard)

Background

Brodifacoum was first registered in 1979.  Currently, it is registered for the control of rats and mice in and around farm structures, households, and domestic dwellings, inside transport vehicles, commercial transportation facilities, industrial areas, sewage systems, aircraft, ships, boats, railway cars, and food processing, handling and storage areas. Products containing brodifacoum are available to the general public and application may be made as often as necessary. Brodifacoum is formulated as meal bait, paraffinized pellets, rat and mouse bait ready-to-use place packs, and paraffin blocks. All end-use products contain 0.005 percent active ingredient.

Brodifacoum is absorbed through the gut and works by preventing the normal clotting of blood, leading to fatal hemorrhage. It is highly effective at small doses - usually a rodent ingests a fatal dose after a single feeding and will die within 4-5 days. The greatest risk to wildlife from brodifacoum is secondary poisoning. Rodents continue to eat poisoned bait so at the time of death the amount of brodifacoum present in their bodies is many times the amount required to kill them. Non-target wildlife such as predators and scavengers may then consume rodents that have ingested large doses of brodifacoum. It can take as little as one poisoned rodent, or a predator may accumulate enough brodifacoum after consuming several poisoned prey items, to induce life-threatening or fatal effects. A single dose of brodifacoum can depress blood clotting for months in some animals, including birds. Stress or slight wounds incurred in the field, such as small scratches that normally occur when a raptorial bird captures its prey, are often sufficient to cause a fatal hemorrhage.

Field studies have shown that mortality of non-target wildlife will occur when they have access to domestic and agricultural rodents poisoned by brodifacoum. A field trial in 1988 (Hegdal and Colvin), demonstrated the secondary exposure effects of brodifacoum on non-target wildlife. Thirty-two eastern screech owls were radio-tracked after the application of 0.001% active ingredient (one-fifth the concentration used today) bait to orchards for vole control during the fall and winter of 1981 - 1982. A minimum documented mortality of 58% was calculated for owls having more than 20% of their home range in treated orchards. In 1983, ICI Americas, Inc. reported mortality of screech owls and other animals collected during field trials with 0.005% active ingredient bait in orchards. Residue was detected in the liver of ten of twenty owls (nineteen screech owls, one long-eared owl) examined. A 1995 study conducted in New Zealand found that beetles that ate brodifacoum baits did not die and retained residues of the poison in their bodies, indicating that insects may provide a route of exposure to insectivorous non-target organisms.

Incidents

Numerous cases of brodifacoum poisoning of wildlife have been reported.  Brodifacoum incidents recorded in the EPA's EIIS database for the 5-year period of 1994-98 were surpassed in number only by diazinon (Mastrota, unpublished account, 1999). Affected bird species include Great Horned Owls, Barn Owls, Eastern Screech-owls, Golden Eagles, Red-tailed Hawks, Cooper's Hawks, and Crows.  The EPA also has on record incidents involving other wildlife such as coyotes, deer, squirrels, chipmunks, a mountain lion, a bobcat and foxes including the endangered San Joaquin Kit Fox.

Listed below are confirmed brodifacoum cases as reported by the Wildlife Pathology Unit of the New York State Division of Fish, Wildlife, and Marine Resources.

• Nassau County, New York, 1999. A female great horned owl was observed lifeless on the nest. The dead owl, three eggs and four rats, one partially consumed, were collected. The cause of death was reported as hemorrhage induced by the anticoagulant brodifacoum, which was detected in most of the tissues analyzed.

• Saratoga County, New York, 1999. A male red-tailed hawk was found debilitated and died the next day at a wildlife resources center. Brodifacoum was found in the liver sample and the cause of death was determined to be blood loss induced by brodifacoum.

• Washington County, New York, 1997.A moribund golden eagle was found in December and received by a local veterinarian. The bird died nine days later lead and brodifacoum were detected in sampled tissues. The cause of death was diagnosed as lead intoxication exacerbated by brodifacoum-induced hemorrhage.

Patterns of avian mortality due to brodifacoum poisoning are different from other pesticides, namely, organophosphates. Birds are usually found singly, and most of the affected species are raptors: hawks, owls, and eagles. Signs of an anticoagulant-induced death are usually quite obvious; the birds' organ systems and muscles are pale due to lack of blood, pooled blood is sometimes observed in the abdominal cavity, and blood is commonly found in the mouth. Superficial wounds are often found somewhere on the body of the bird, usually on the feet and legs. When residue tests are performed, brodifacoum is detected at much higher rates than any other anticoagulant.

Raptor species maintain hunting territories that may include areas near agricultural or other industrial and urban buildings where rodent control is ongoing. Local avian predators may consume rodents living in and around these structures. However, the death of such a predator will most likely occur some distance away from treated sites, making it difficult to observe patterns of mortality attributable to any one cause. Furthermore, birds that have been exposed to lethal levels of brodifacoum may be more likely to die from other causes such as accidents or predation. Most mortality undoubtedly goes undiscovered. For these reasons, the true impact on birds of many pesticides, including brodifacoum, is obscured.

Is it Ever OK to Use Brodifacoum?

ABC is opposed to the use of brodifacoum by the public and in indoor and outdoor pest control situations where less toxic approaches are effective or where the bait cannot be controlled. ABC feels strongly that brodifacoum should not be available to non-licensed applicators and, further, has serious questions about outdoor uses of any kind.  However, situations may arise in which the use of brodifacoum can be critical to protecting endangered and/or migratory bird species, e.g., in island situations to protect birds imperiled by rodent predation. ABC is willing to work with the U.S. Fish and Wildlife Service and the EPA to preserve the option of such uses when integrated pest management strategies are in place and careful monitoring accompanies use.