cat with rat

Secondary Poisoning

Secondary Poisoning

Rats and mice can pose a serious health risk to humans, and they can also be incredibly destructive. Unfortunately, they can grow in numbers rapidly and a few rodents can quickly become a full-blown infestation. It’s no surprise people want to get rid of them as quickly as possible and turn to rodenticides as a solution.  Sadly, rodenticides can often kill more than just rats and mice by causing secondary poisoning.

Secondary poisoning occurs when an animal containing traces of poison is consumed by another. The primary poisoned animal transfers the poison to the consuming animal — most commonly through the liver. This is often exemplified when a wild or domestic animal eats a rat or mouse that has died from rat poison (rodenticides).

Common rodenticides include:

  • ACR (Anticoagulant Rodenticides)
  • Cholecalciferol (Vitamin D3)
  • Bromethalin
  • Phosphides


secondary poisoning

 Secondary poisoning can have adverse effects on ecological systems. While the immediate threat to your common cat or dog is obvious, we have seen an increase in deaths in wild animals over recent years. With urban sprawl increasing the displacement of rodents, the use of rodenticides has become a more common method to dispose of pests.

Birds of prey such as owls, hawks, eagles and other raptors are often casualties of rodenticides. A study in 2018 looked at two owl species in California. It showed 70% of northern spotted owls and 40% of barred owls were exposed to anticoagulant rodenticides. The northern spotted owl is currently listed on the Endangered Species Act. These rodenticides can kill all rodents, including some that may not be targeted — such as chipmunks and all species of squirrels.

Another study has shown hawks prefer prairie dogs poisoned by rodenticides because the poisoned animals are slower and less alert — making them easier to catch. When the livers of fishers were tested, an astonishing 85% were shown to have rodenticide exposure.

Larger animals like mountain lions, bears, bobcats, raccoons, coyotes and foxes have even higher exposure. Testing from 2015-2016 by WildCare shows rodenticide exposure in these animals is as high as 86%. Snakes and other reptiles can also be affected when feeding on rodents. There are also known cases of tertiary poisoning. Tertiary poisoning can happen when a larger animal like a mountain lion eats a coyote or other mammal that has fed on a poisoned rodent. 

California Department of Fish & Wildlife states, “The best way to control rodents and protect wildlife and pets is to use non-chemical means of rodent control.” In California alone, rodenticides have injured or killed, “hundreds or thousands of wild animals and pets.” 


In 2018, legislation to ban some rodenticides passed the Assembly Environmental Safety and Toxic Materials Committee. The bill would ban first and second generation anticoagulant rodenticides (FGARs and SGARs). In September of 2020, the bill was passed by Gov. Newsom making California the first state to ban second generation rodenticide use. 

These types of anticoagulant rodenticides prevent the rodent’s blood from clotting by blocking the enzyme in the liver that creates vitamin K. The second-generation rodenticides are more likely to stay in the rodent’s tissue for a longer period of time because of their higher concentration, increasing the risk of poisoning to other animals feeding on them.

Some examples of second-generation anticoagulant rodenticides are brodifacoum, flocoumafen and difenacoum. These rodenticides caused 12 of d-Con’s products to be cancelled as of 2005 because, “8 of the 12 products contain second-generation anticoagulants pesticides that pose unacceptable risks to non-target wildlife.”

There are also non-anticoagulant toxins such as Bromethalin. Bromethalin is a neurotoxin causing brain swelling and destruction of the nervous system. Other non-anticoagulants rodenticides include cholecalciferol and zinc phosphide.  These toxins all work in different ways, but are all harmful to wildlife.

All of the rodenticides mentioned above cause a slow, painful death for the rodent, and possible deadly consequences for any animal feeding on them. All too often, animals are found suffering and there is nothing that can be done to save them. The numbers of dead owls and raptors are increasing as people continue to use rodenticides to battle rodents.  

It is a typical reaction to want to eliminate a rat or mouse infestation with the use of rat poisons, but the use of rodenticides reminds us that we are all linked to a larger ecosystem — that can be impacted beyond your immediate scope. Think about the impact on animals, domesticated pets, and overall what it means to introduce foreign toxins into your community.

The avoidance of toxins is a fundamental pillar of the Goodnature philosophy. Our trap is designed as an alternative to conventional rodenticides that can pose a threat to pets, children, and other wildlife.

If you are concerned that your dog, cat, or even a child has been exposed to rat poison, don’t hesitate to call the American Association of Poison Control Centers at 1-800-222-1222 or text poison to 797979. They offer free, confidential advice that can help you act quickly in a crisis.