[Vertebrate Pests] Bravo to EPA

As you are probably aware, there are thousands of children (and pets) accidentally exposed to rodenticide baits each year. The great majority of these exposures are from consumer use of off-the-shelf rodent baits from their local supermarkets or big box stores. Fortunately, only a small number of exposed children experience medical symptoms or suffer adverse health effects as a result of their exposure. In fact, it could be argued that the greatest hazard in the overwhelming majority of rodent bait exposure cases is the incident itself and the resultant fretting, phone calls and subsequent hospital visits made by a frantic parent or pet owner.

Nevertheless, to minimize children’s exposure to rodenticide products used in homes, EPA released its long-awaited Risk Mitigation Decision (RMD) regarding consumer and professional uses of 10 rodenticides in May. It is not the point of this month’s column to review each of the specifics of the RMD here. (See “EPA Issues Rodenticide Ruling,” June 2008 PCT.)

Still it needs to be stated that there are several benefits the RMD provides to the public and to the environment. For example, EPA is requiring that all rodenticide bait products available for sale to consumers be sold only in bait stations. A range of different types of bait stations will meet the new requirements, providing flexibility in cost. None of the second-generation anticoagulants (e.g., bromadiolone, brodifacoum, difethialone) are permitted for sale as consumer products. And loose bait such as pellets will be prohibited as a bait form.

THE SALIENT DECISION. In my opinion, the most salient decision, and one that those pest management professionals experienced in indoor rodent baiting procedures will be applauding, is the restriction of pellet formulations in consumer products, as well as the restriction on the PCO that pellets will not be allowed for use in areas where children, pets or non-target wildlife may be exposed. Whew! A long time coming.

Why do I say this? Why is this such an important milestone? The answer lies more with the biological and behavioral aspects of rodents and rodent control than with rodenticide toxicities and application hazards. Let me explain.

HOARDING AND CACHES. As early as your childhood animal storybooks you learned that rodents (squirrels, mice, rats, gerbils, etc.), often carry off and then store some of the foods they encounter during their foraging. This is called hoarding. The hoarded food stored in a nest, burrow or some ground shallow is called a cache. If you’ve ever had a hamster, gerbil or a rat for a pet and cleaned their cages, you quickly learn all about “secret caches.”

In the wild, rodents don’t hoard all the food items they encounter — they can’t. It is mostly those items that are easy for the rodent to carry and/or store in their mouths and cheek spaces. Some food items that are commonly hoarded include seeds, nuts, bugs and berries that are wind-blown or that drop off a tree or some other plant. Because the rodent never knows when “food-finds” are likely to happen again, it pays for them to have a strategy of hoarding food.

And hoarding itself may vary among different mammals. For example, some squirrels, deer and white footed mice and Norway rats sometimes “scatter hoard.” That is, they deposit found foods in several locations within their home ranges that they regularly travel over. All of us are familiar with similar behavior from tree squirrels burying acorns all over the yard.

Hoarded foods may be eaten soon after transport, or sometimes not for days, weeks or months later. Or, the foods may never be consumed at all. They may be forgotten and then spoil.

THE INHERENT FLAW. So how does this hoarding discussion tie into EPA’s RMD on rodenticides? Well, consider the four primary formulations in which rodent baits are made: meal, blocks, pellets, liquids. For consumer products, pellets are the primary bait form.

Well, for pet rabbits, fish, gerbils, lab rodents, hamsters and horses, grain pellets are a convenient food form. But based on the natural hoarding behavior of mice and rats discussed above, pellets — poisonous pellets for free-ranging rodent pests inside occupied buildings — is, and has always been, an inherently flawed match of pest to pesticide.

Most experienced pest professionals have at one time or another, witnessed pellet bait translocation indoors (either as loose bait or in entire packets). Over the years, I have found rodent bait pellets moved from totally inaccessible areas to accessible areas multiple times. This includes finding pellet baits in couches, chairs, inside shoes in a closet, a silverware drawer, in a child’s clothes dresser, and even inside the bottom of a box containing granola bars.

So, it doesn’t matter if a pellet bait is originally installed with forethought and care into areas inaccessible to people and pets. Or even if it the pellets are installed inside an iron-clad, tamper-resistant bait station. With loose pellets, it is the rodents — not the applicator — that will ultimately dictate what will be “accessible” to children, adults and pets.

But can we guarantee zero bait translocation potential even when consumer baits are switched to block baits installed into tamper-resistant containers? Technically, it is conceivable that small crumbs of block baits may still break or fall off and migrate out of tamper-resistant stations. But unless the bait station is placed out in areas that are highly accessible to children under age 6 (hard to imagine), a child-bait exposure event is likely to be very, very remote. (Moreover, it is not likely the block baits will be carried out, because mice are not usually successful in carrying large and cumbersome pieces out from tight spaces.)

Nevertheless, as with most things and chemicals in today’s world, we can’t guarantee zero hazards even with the new EPA decision. We know this. We also know that the goal is to measure the risks for items and chemicals and to then minimize those risks as much as possible. Relative to the use of rodenticides, eliminating pellets from interior uses where children or pets may be exposed is a very significant step in achieving this.

So congratulations to EPA. And thanks for all the hard work on this complicated and controversial (at least to some) ruling. This decision, as the EPA states in its summary RMD document, “will help reduce rodenticide exposures to children and wildlife, while still allowing residential users, livestock producers, and professional applicators access to a variety of effective and affordable rodent control products.”

Bravo.

The author is president of RMC Consulting, Richmond, Ind.