Secondary poisoning
Secondary poisoning, or relay toxicity, is the poisoning that results when one organism comes into contact with or ingests another organism that has poison in its system. It typically occurs when a predator eats an animal, such as a mouse, rat, or insect, that has previously been poisoned by a commercial pesticide. If the level of toxicity in the prey animal is sufficiently high, it will harm the predator.
Mammals susceptible to secondary poisoning include humans, with infants and small children being the most susceptible. Pets such as cats and dogs, as well as wild birds, also face significant risk of secondary poisoning.
Pesticides
Various pesticides such as rodenticides may cause secondary poisoning. Some pesticides require multiple feedings spanning several days; this increases the time a target organism continues to move after ingestion, raising the risk of secondary poisoning of a predator.| Pesticide | Type | Classification | Target | Oral Toxicity | Feedings | Secondary Risk to Mammals | Secondary Risk to Birds |
| Warfarin | Anticoagulant | Hydroxycoumarin | Rodenticide | Moderate | Multiple | Low | Minimal |
| Bromadiolone | Anticoagulant | Hydroxycoumarin | Rodenticide | High | Single | Moderate | Moderate |
| Difethialone | Anticoagulant | Hydroxycoumarin | Rodenticide | High | Single | Moderate | Highest |
| Brodifacoum | Anticoagulant | Hydroxycoumarin | Rodenticide | Highest | Single | Highest | Highest |
| Chlorophacinone | Anticoagulant | Indandione | Rodenticide | High | Multiple | Highest | Minimal |
| Diphacinone | Anticoagulant | Indandione | Rodenticide | High | Multiple | Highest | Moderate |
| Bromethalin | CNS | other | Rodenticide | High | Single | Low | Low |
| Fluoroacetate | Metabolism | other | Rodenticide | Highest | Single | High | Highest |
| Zinc phosphide | other | other | Rodenticide | High | Single | Minimal | Low |