By Lega Medcalf

Walk into any grocery, hardware, or building supply store and you will come across a large display of rodenticides, a/k/a rodent-killing poisons. Walk around the exterior of many local businesses and even family neighborhoods and you are likely to see innocuous black boxes that contain poisonous bait. "Rodenticide" implies that only rodents are killed, but this word is a misnomer because all animals, including humans, can die from ingesting or inhaling the poison as the body systems of all species work in similar ways.

Most brands are touted as “mouse killer” and “resistant to weather and to tampering by children and dogs.” Sounds like a perfect solution to a mouse/rat/mole problem but look at the back side of the containers and the fine print states that the “product is extremely toxic to fish, birds, and other wildlife. Dogs, cats, and other predatory and scavenging mammals and birds might be poisoned if they feed upon animals that have eaten this bait.”

Different brands have different formulas of poison. A Google search of bromethalin, an active ingredient found in a widely-marketed product, describes the bait as a nerve poison that is fatal if inhaled or swallowed and has no antidote.” Bromethalin is a single-dose killer, which means that if an animal eats the bait directly it will be killed but secondary poisoning can also occur when another animal eats the poisoned mouse, rat, chipmunk, or squirrel. The only barrier to direct contamination is the plastic box in which the poison is housed, which is certainly no deterrent — especially to one of our dogs, who loves to chew on anything with corners.

Another common bait poison by a different manufacturer is cholecalciferol. This one causes kidney failure within two to three days, has no antidote, and is also poisonous to wildlife and pets that eat a sick or dead rodent that has ingested the poison.

Zinc phosphide is a bait that when mixed with fluids in an animal’s stomach turns into phosphine, a very toxic gas. People have been sickened after inhaling the gas when dogs were induced to vomit after eating the bait.

Bromadiolone is an anticoagulant rodenticide that can only be applied by a licensed operator. Animals that eat it bleed to death internally. Residues of anticoagulants can remain in the liver for many weeks, so predators, including dogs and cats, foxes, hawks, and owls are at risk of death if they eat poisoned rodents. It is no surprise that veterinarians and wildlife rehabilitation shelters are all too familiar with the sickness and death caused by these poisons.

The warnings associated with rodenticides are alarming — the following is a typical statement found on a manufacturer’s website “CAUTION: ENVIRONMENTAL HAZARDS: This product is extremely toxic to mammals and birds. Children, dogs, cats and other predatory and scavenging mammals and birds might be poisoned if they feed upon animals that have eaten this bait. Do not contaminate water when disposing of equipment wash water. Harmful if swallowed or absorbed through the skin. Keep away from children. All handlers must wear long pants, shoes, socks, and waterproof gloves. Wear waterproof gloves when retrieving carcasses or unused bait. Keep and wash clothing separately from other laundry. Wash hands thoroughly after applying bait and before eating, drinking, chewing gum.”

Why on earth are these products so readily available and so casually-used? It is particularly irksome that all these poisons can be purchased and applied by a homeowner or pest-control operator outdoors without notification of neighbors. Our neighbor has bromadiolone bait boxes around the exterior of her house. We thought it odd that our dogs were suddenly able to catch sick and dead squirrels, mice, and chipmunks because our chain link fence had been in existence for five years and our dogs had never caught any animal. A chance conversation with the neighbor’s relative identified why sickly mice were entering the enclosure and now we have to be very vigilant when the dogs are let outdoors.

Again, rodenticides don’t just kill rodents, they are also very toxic to aquatic life including fish and amphibians. They can sicken or kill other species such as eagles, owls, bobcats, coyotes, and foxes that consume sick or dead rodents that have been poisoned. Since, these predators are also nature’s rodent control, it is even more imperative that we do not use poison so they can do their part to keep rodent populations in check.

So, what is the homeowner to do if mice move in? First, prevention is the best cure because it is also humane. Blocking entry points and removing food and water sources is a start. To find entry points around foundations, shine a light along the sill and have an assistant on the other side look for light that shines through. The next best method is the old-fashioned snap trap which is environmentally safe, cheap, and relatively humane. An indoor cat is a good mouse exterminator and has a positive influence on health and well-being. Toxologist Pam Bryer, with the Maine Board of Pesticides Control, has found that electrocution mouse traps work very well in her house. Catch and release traps are effective. I evacuated over seven mice from our garage with mouse Havahart traps, and while many friends and my husband joked that I was repeatedly catching the same mouse, that was not the case, because our garage has been mouse-free for many years.

Who knows the long-term effects of these very prevalent rodenticides on human health since 85 percent of human and mouse genes are identical. There is also the long-term contamination of soil and groundwater to consider. One has to wonder how the EPA sees fit to allow these products to be sold. It would be one thing if these products were tightly-controlled but they are produced in huge quantities and mass-marketed irresponsibly.

As a side note, I noticed that website for the rodenticide Tomcat (tomcatbrand.com) had reviews that were all very positive so I decided to send in a comment noting that, in fact, this poison is nonselective and is indeed toxic to children, pets, and wildlife, not just rodents. I received this terse response: “Our staff has read your review and values your contribution even though it did not meet all our website guidelines. Thanks for sharing, and we hope to publish next time.”