What are rodenticides?

“For, after all, how do we know that two and two make four? Or that the force of gravity works? Or that the past is unchangeable? If both the past and the external world exist only in the mind, and if the mind itself is controllable – what then?” ― George Orwell, 1984. Baltimore Polytechnic Institute. File Type PDF Macbeth Major Works Data Sheet Answers language processing, the field that supports a variety of language technologies, from predictive text and email. The year is 1984. Aomame is riding in a taxi on the expressway, in a hurry to carry out an assignment.

Rodenticides are pesticides that kill rodents. Rodents include not only rats and mice, but also squirrels, woodchucks, chipmunks, porcupines, nutria, and beavers. Although rodents play important roles in nature, they may sometimes require control. They can damage crops, violate housing codes, transmit disease, and in some cases cause ecological damage.¹

Rodents, humans, dogs and cats are all mammals, so our bodies work in very similar ways. Rodenticides have the same effect when eaten by any mammal. They can also affect birds. Rodenticides are usually formulated as baits, which are designed to attract animals. Flavorings may include fish oil, molasses or peanut butter. Baits used in agriculture and natural areas may contain ground meat, vegetables, grains, or fruits.² These may be attractive to children and pets, so they should never be used or stored within their reach. Tamper-resistant bait stations make it even more difficult for accidents to happen. For ways to prevent exposures to children, pets, and wildlife, see the information below about what you can do to reduce risks.

How many kinds of rodenticides are there?

There are many different active ingredients registered as rodenticides in the United States. They can be grouped together according to how they work. Many rodenticides stop normal blood clotting; these are called anticoagulants. Bromadiolone, chlorophacinone, difethialone, brodifacoum, and warfarin are all anticoagulants. There are a number of rodenticides that are not anticoagulants, and these work in different ways. This fact sheet will discuss zinc phosphide, bromethalin, cholecalciferol, and strychnine.

How toxic are rodenticides?

All rodenticides can be toxic when eaten.^3,4,5,6 Most rodenticides are also toxic when inhaled and when they come into contact with skin. The exceptions include warfarin, which is low in toxicity when inhaled or if skin contact occurs.⁶ Strychnine, cholecalciferol, and zinc phosphide are relatively low in toxicity upon skin contact.^3,5,7 Bromethalin is moderately toxic for dermal exposure.⁴ See Table 1.

How do anticoagulants work?

Our livers make a special enzyme that allows our bodies to recycle Vitamin K. Our bodies need Vitamin K to make the blood clotting agents that protect us from bleeding too much. Anticoagulants stop this enzyme from doing its job. Our bodies store an extra supply, but if we are exposed to enough anticoagulant, the supply will run out and internal bleeding may begin.⁸

Table 1. ACUTE TOXICITY CLASSIFICATION - RODENTICIDES
Oral	Inhalation	Dermal	Primary Eye Irritation	Primary Skin Irritation
Warfarin^3,6	Moderate - High toxicity	Not significant	Not significant	No data	No data
Chlorphacinone⁴	High toxicity	High toxicity	High toxicity	Non-irritating	Non-irritating
Diphacinone⁴	High toxicity	High toxicity	High toxicity	Moderate irritation	Slight irritation
Bromadiolone⁴	High toxicity	High toxicity	High toxicity	Low irritation	Minimally irritating
Difethialone³	High toxicity	High toxicity	High toxicity	Mild irritant	Non-irritating
Brodifacoum⁴	High toxicity	High toxicity	High toxicity	Minor irritation	Mild irritant
Bromethalin⁴	High toxicity	High toxicity	Moderate toxicity	Slight irritation	Non-irritating
Cholecalciferol³	High toxicity	Very low toxicity	Low toxicity	No data	No data
Zinc phosphide⁵	High toxicity	High toxicity	Low toxicity	Slight irritation	Non-irritating
Strychnine⁷	High toxicity	High toxicity	Low toxicity	Highly irritating	Non-irritating
Classification categories were modeled after the U.S. Environmental Protection Agency, Office of Pesticide Programs, Label Review Manual, Chapter 7: Precautionary Labeling. http://www.epa.gov/oppfead1/labeling/lrm/chap-07.pdf

Warfarin was the first anticoagulant rodenticide.¹ It was registered for use in 1950.⁴ Warfarin was discovered in moldy sweet clover that had made a herd of cattle sick. Researchers found that a fungus had converted a chemical that occurs naturally in the clover to a more toxic chemical.⁹ Warfarin was widely used until many rodents began to become resistant to it. This led to the development of new rodenticides.⁹

Which anticoagulants require more feedings to work?

Warfarin, chlorophacinone, and diphacinone generally require that an animal eat multiple doses of the bait over several days. These are known as multiple-dose anticoagulants. Single-dose anticoagulants, such as brodifacoum, bromadiolone, and difethialone are more toxic. One day's feeding can deliver a toxic dose.⁴

Table 2. Summary of common rodenticides
Rodenticide	Type	Chemical Class	Days of feeding needed
Warfarin	Anticoagulant	Hydroxycoumarin	multiple
Chlorophacinone	Anticoagulant	Indandione	multiple
Diphacinone	Anticoagulant	Indandione	multiple
Bromadiolone	Anticoagulant	Hydroxycoumarin	single
Difethialone	Anticoagulant	Hydroxycoumarin	single
Brodifacoum	Anticoagulant	Hydroxycoumarin	single
Bromethalin	Non-anticoagulant	other	single
Cholecalciferol	Non-anticoagulant	Vitamin D3	multiple
Zinc phosphide	Non-anticoagulant	other	single
Strychnine	Non-anticoagulant	other	single

Single-dose anticoagulants are more toxic because they bind more tightly to the enzyme that makes bloodclotting agents. They can also interfere with other steps in Vitamin K recycling. Second-generation, or single-dose anticoagulants, are not easily excreted from the body, and they can be stored in the liver.¹⁰ Most of the single-dose rodenticides are not allowed to be marketed to non-licensed applicators.¹¹ Instead of classifying anticoagulants into 'first generation' or 'second generation', many sources refer to them as single-dose or multiple-dose rodenticides because this is less confusing.

What are some of the other rodenticides?

There are a number of rodenticides that work differently than anticoagulants. These are currently used within the United States: bromethalin, cholecalciferol, zinc phosphide, and strychnine. Each of these pesticides works in a different way.

Bromethalin was first registered by the U.S. Environmental Protection Agency (EPA) in 1984.⁴ It stops the cells in the central nervous system from producing energy. The nerve cells swell, this puts pressure on the brain, and paralysis and death soon follow.¹² The major breakdown product of bromethalin is more toxic than bromethalin itself. The varying ability of different species to break down bromethalin may explain why it is more toxic to some animals than others.¹² Bromethalin is considered a single-dose rodenticide. ⁴

Cholecalciferol was first registered as a rodenticide in the United States in 1984.⁴ Cholecalciferol is vitamin D3.¹³ Vitamin D helps the body maintain calcium balance by enhancing absorption of calcium from the

Major Works Data Sheet 1984