This article originally appeared in the Winter 2015 issue of Cummings Veterinary Medicine.
Because more than 10,000 children end up in the ER every year after coming into contact with household rodent poisons, the U.S. Environmental Protection Agency has tightened the restrictions for their use.
“While the words ‘safe’ and ‘poison’ inherently do not go together,” says wildlife veterinarian Maureen Murray, V03, the goal of the new EPA regulations is to replace highly potent rodenticides with products that pose less risk to humans and other species that may be exposed to the poison. Research done at the school on the risk these products pose for wildlife was also instrumental in the EPA’s decision to crack down on the powerful poisons.
The new regulations limit the use of anticoagulant rodenticides—which work by causing animals to bleed to death—in favor of products that require higher doses over many days for dangerous blood thinning to occur. The regulations also prohibit certain forms of poison baits, including loose pellets, and require that all poisons be enclosed in tamper-resistant packaging.
So-called “second-generation” anticoagulant rodenticides, or SGARs, became popular because even a single feeding easily kills mice or rats. However, because it takes several days for the poisoned rodents to bleed out, they can continue to feed on the poison. When they do die, their carcasses can contain residues that are lethal for hawks, owls, and other animals that often make a meal of rodents, living and dead.
SGARs also can accumulate in liver tissue, so an animal that repeatedly feeds on prey containing nonlethal amounts can store up a deadly dose over time. Murray has been studying rodenticide poisoning in birds of prey for years and published research in 2011 that the EPA has cited frequently. That study, published in the Journal of Zoo and Wildlife Medicine, found anticoagulant rodenticide residues in 86 percent of 161 birds that were tested over five years at Tufts Wildlife Clinic. Murray examined four species of birds—red-tailed hawks, barred owls, Eastern screech owls, and great horned owls—and found that of those that tested positive, 99 percent had residues of the SGAR brodifacoum, one of the most widely used rodent poisons in the world.
If you have a rodent problem, Murray offers the following recommendations to minimize harm to children, pets, and wildlife:
Rodent-proof your home. Before using a poison, remove or securely contain any potential food sources for rodents. Also repair any exterior areas of your home that rodents can use to come inside.
Consider alternatives to poison, such as snap traps. People often believe poisons are more humane than snap traps, but an animal bleeding to death is neither quick nor especially humane.
Check the active ingredients before you buy any poison. Opt for products that comply with the new EPA regulations and contain bromethalin, chlorophacinone or diphacinone.
Purchase poisons only in bait stations. Avoid any in pellet form.
If you hire a pest control company, have it explain any claims that its products are “safe for wildlife.” Despite the EPA ban on the household use of SGARs, pest-control professionals may still legally use these poisons in homes. Request that the company not use products containing brodifacoum, bromadiolone, difenacoum, or difethialone. Look for an “integrated pest management” company, one that uses multiple approaches to pest control instead of relying solely on poisons.
Know that less risk is not the same thing as no risk. Although the EPA deems the poison bromethalin “safer” than SGARs, little research has been done on its potential to poison the nervous system in wildlife. Remember, any poison used or stored improperly can harm children, pets, and wildlife.