[Vertebrate Pests] Protecting children from rodent baits, part I

There is some interest by the Environmental Protection Agency and other agencies in further evaluating and minimizing the hazards associated with the use of rodent baits (rodenticides) in urban environments. The primary interest is to further protect children from being harmed by these pesticides.
One thought is to perhaps mandate that all rodenticide baits contain a bittering agent such as denatonium benzoate (e.g., Bitrex®). The thought is that should a child (or any other person) encounter a rodent bait and attempt to eat the bait, the bittering agent causes an unpleasant taste sensation and he or she will cease eating, and may even spit the bait out before consuming a more harmful quantity.
When considered casually this seems to make sense. Why not, assuming it doesn’t affect bait acceptance by the rodents, proceed with a regulation that all rodenticide baits contain a bittering agent (or possibly some other material that achieves the same goal)?
Why not?  Because this is a much more complex issue than it may seem.  The domestic rodent pests associating with humans are complex mammals that can adapt relatively quickly in their co-existence with us. We can’t underestimate the significance of this.Because, while the concept of protecting children and other non-targets from pesticide poisoning is easy to grasp, the feeding parameters of rodents in the multitude of real world urban environments is not.
It certainly is no surprise to any of us practicing rodent pest management for many years, of the periodical baiting failures that occur with both rats and mice. The majority of these seem to occur in commercial environments. And typically, it is those facilities where there is a history of long-term infestations, or long-term presence of rodents in the general area. Most times, we do the best we can with on-the-job analyses of what may be responsible for the bait failures. But, like you, I have encountered baiting failures where it was hard to explain why the rodents ignored fresh bait that was placed directly into their high-activity runways, even when there was not a readily accessible supply of human foods nearby.  
What caused the rejection of the baits?  Was it the bait brand? Or the particular active ingredient? Or was the brand formulation a mismatch for the specific colony of rodents that had an affinity for pellets over meal, or seeds over pellets, etc.? Or perhaps, as is often suspected, the bait was competing against an easily attainable source of human food, or an abundance of their natural foods?
ADDITIONAL FACTORS.There are even more factors. Maybe the rodents had “squirreled” enough food away in their nests before we began our baiting program?  Or, perhaps the rats were exhibiting a new object reaction to the new baits and bait stations? Or, did somehow the bait become contaminated with insecticide odors in the truck or in the shop? Or, is it possible the manufacturer made a “bad batch” of bait? Or, could the rodents in this particular colony be sensitive to the bittering agent in this brand bait. Or, or, or...
And to all of this, we must, of course, consider the complexity of the feeding behavior of the commensal rodents and, of course,  here there are so many questions. The anecdotal evidence and field observations by pest professionals on the feeding behavior of the commensal rodent is plentiful. But formal research addressing this science is actually scarce. But interestingly, some research published just recently demonstrated that rats have a strikingly similar taste/selection process as we humans. In other words, like us, they too gravitate towards foods that are both nutritious and taste good. 
So what happens then, when we add bittering agents to the food-grade rodent baits? We humans certainly find these agents repulsive to our tongues and taste. Perhaps with some rodents and in some field environments, or in laboratory animals, they can’t detect denatonium benzoate at 10 ppm in their foods or, if they do, at this concentration this chemical along with the active ingredient of the bait at 50 ppm, it is not repulsive to them as it is to humans.
Or maybe, with these animals that are behaviorally “hard–wired” as opportunistic foragers (i.e., it is to these animal’s advantage to consume most edible items upon encountering them), the taste of chemicals (e.g., a poison) at parts per million are “not worth” rejecting, since it is an uncertainty if and when their next feeding opportunity will present itself, nor with what quality of food.

PROS & CONS OF ADDING BITREX. In some areas of the U.S., some rodent control personnel have asserted that baits containing bittering agents do not achieve the same level of control as the same bait prior to the addition of the bittering agent. And until we know more we can’t rule out that, in some areas, bittering agents may impact certain rodent colonies, or possibly the local genetics of some colonies.
But there is some strong evidence and research indicating that Bitrex added at low concentrations in baits may not affect bait palatability. And if it does, it may not be a on a universal scale. An excellent 1992 research paper titled “Evaluations of aversive agents to increase the selectivity of rodenticides with emphasis on denatonium benzoate (Bitrex®) bittering agent,” by Dale Kaukeinen and Alan P. Buckle published in the 15th Proceedings of the California Vertebrate Pest Proceedings sheds important light on this theory.
Their research demonstrated that Bitrex at concentrations of 10 ppm when added to Talon bait (the anticoagulant brodifacoum at 50 ppm), did not affect the bait’s palatability to laboratory rodents and to the rodents in three farms tested (two in the United Kingdom, and a pig farm in North Carolina). In these tests, the Bitrex baits performed equally, or actually exceeded the non-Bitrex baits in some cases.
Add to this the fact that Bitrex-containing baits have been on the marketplace for close to 10 years now, and while there have been some areas of question, we do not seem to have any universal baiting failures that we can associate with the addition of Bitrex.

NOT SO FAST. So, why not then, just proceed with requiring that a bittering agent be added to all baits for the extra baiting safety benefit.
Well, because of the sheer scope of this issue,  I think we need to step very carefully.Because it is those pesky callbacks and baiting failures in the commercial sector from all over the country during the past few decades I worry about. Areas where  rodents are used to having a wide selection of foods: in the alleyway of the meat and seafood restaurant; or the storage room of a grocery store where the community purchases their foods; or the mice in the clean office building break room, and so forth...times one thousand.  This is a very large inference space, and we do not have enough data to come to any conclusions yet.  A study with laboratory rodents and three farms is not a complete representation of the thousands of urban rodent scenarios.
And, what if a new inert food carrier is discovered in a few years that  tremendously improves grain bait palatability over what is now used?  Except we find this new food material is not compatible with a bittering agent, and causes a repellent taste to rodents?  If we should have regulated that all baits must contain a bittering agent, we would lose the option of employing this new advancement.
 Or, suppose over time, the rodents learn to associate the taste of bittering agents and rodent bait-associated lethargy or illness?  Remember, research has shown the rat is capable of detecting chemicals in its food down to parts per billion. The Bitrex in baits are currently mixed in to the baits at parts per million).
Ten (or two) years from now if we begin to observe an increase in baiting failures, we are going to need to figure it out quickly (as was so impressively done with the cockroach baits). If all rodent baits are required to contain a bittering agent, this factor will need to be considered. If, on the other hand, alternative non Bitrex baits are available or can be quickly manufactured, evaluating whether or not the bittering agent is responsible or not can be rapidly facilitated by the manufacturers, researchers and by practicing professionals on the job.
So, considering the complexity of urban rodents and the multitudes of feeding scenarios in cities around the country, I think it prudent at least for commercial applications to have the option of Bitrex-treated baits and non-Bitrex baits.
For all residential applications, however, it makes sense to always use Bitrex baits.And so maybe all over-the-counter products  and all professional level products to be used in residential settings or other areas where children might be present (e.g., all child care facilities) should be labeled to contain a bittering agent (at concentrations that do not cause taste aversions in rodents).

MORE MEASURES NEEDED. But I don’t think we stop with the mere addition of a bittering agent. Because even though Bitrex (or some other bittering agent) may help in protecting children once they have begun tasting a rodent bait, we certainly should not be rely on this chemical as the primary measure of safety in this regard.
The primary measure should be to take the steps necessary to truly minimize the chances that children do not encounter the baits in the first place. And for both professional applications, and especially for most homeowner applications (where the great majority of children-rodenticide bait encounters occur), much more could be done within the entire model of residential applications of rodenticides. All the way from packaging to formulations, to the specific applications by the users. These will be discussed in Part II.

The author is president of RMC Consulting, Richmond, Ind., and can be contacted at rcorrigan@gie.net.