Rodenticide Changes

Changes Needed With Rodenticides
Pest Management Professional
By Hanif Gulmahamad
Aug 21, 2006

Second-generation anticoagulant rodenticides (SGARs) — brodifacoum, bromadiolone, difethialone (United States), and floucomafen and defenacoum (international) — have been implicated in secondary poisoning of non-target animals and wildlife from diverse geographic areas of the world.

Secondary poisoning basically is the ingestion by a predator or scavenger of the original animal poisoned and dying as a result. In the United States, California and New York have reported the most significant non-target losses from SGARs including endangered and threatened birds and mammals (Golden eagles and San Joaquin kit foxes).

Since 1994, the California Department of Fish and Game (DFG) investigated 58 cases of possible wildlife exposure to anticoagulant rodenticides. Residues of these toxicants were detected in 38 birds and mammals, and brodifacoum was found in 31 birds and mammals, accounting for 82 percent of the anticoagulant exposures. Clinical signs of anticoagulant poisoning were observed in 10 to 20 percent of the 31 animals with brodifacoum residues. Eleven of the animals also contained residues of at least one other anticoagulant.

It is speculated that since wildlife in the final stages of anticoagulant poisoning generally retreat to burrows, dens, concealed nests, and other inaccessible areas, exposure of non-target wildlife to anticoagulant rodenticides may be more extensive than what is currently known. Most of the mammals and birds that contained brodifacoum residues were recovered from areas adjacent to urban developments in Santa Clara, Los Angeles, Ventura, Orange, San Benito, Alameda, and Contra Costa counties.

On Dec. 30, 1999, the California Department of Pesticide Regulation (DPR) placed rodenticides containing brodifacoum into re-evaluation. This was done as a result of concerns expressed by DFG regarding non-target wildlife incidents resulting from products containing brodifacoum. Five of the animals involved were San Joaquin kit foxes, Vulpes marotis mutica, a federally listed endangered species. Based on available information, DPR determined there is a need for mitigation measures to prevent further sublethal effects and/or deaths of non-target wildlife from continued use of SGARs.

Some fear that restrictions placed on the use of brodifacoum will result in increased use of difethialone and bromadiolone, both of which have secondary poisoning hazards. Thus, some have suggested placing restrictions on the use of all SGARs in California.

Examination of Available Data

The following statement is contained in a document circulated by DPR: "Currently, rodenticides containing difethialone and bromadiolone are used far less than rodenticides containing brodifacoum." (Pesticide Registration and Evaluation Committee Meeting, Nov. 18, 2005, Brodifacoum and Wildlife Losses: History, Wildlife Impacts and Regulatory Options). This statement does not appear to be correct, especially as it relates to the 2004 data. The most-recent data readily available to the public for pesticide use in California is the 2004 Annual Statewide Pesticide Use Report — Indexed by Chemical.

The study reveals two significant pieces of information: By far, bromadiolone is the most commonly used second generation anticoagulant rodenticide in California in 2004; and the greatest use of second-generation anticoagulant rodenticides in California is by the structural pest control industry.

Second-generation anticoagulant rodenticides are basically single-dose toxicants. A commensal rodent can obtain a lethal dose of these materials from one feeding. Some of these rodenticides have been referred to as "super warfarins" because of their toxicity and quick mortality.

Real-world experiences have shown that generally first mortality from SGARs can occur in about three days after ingestion of a lethal dose, depending on how much was consumed, animal size, etc. What this means is that a poisoned rodent can continue to feed on the bait, resulting in the animal receiving multiple lethal doses. At the time of death, the rodent may have a significant "body burden" of these toxicants. Residues of these materials are commonly found in the liver, muscle, and gastro-intestinal tract of poisoned rodents.

The three SGARs available for use in the United States are toxic materials. The study shows some basic comparative toxicity data for these materials.

It is interesting to note that based on oral lethal dose (LD) 50 numbers, all of the second-generation anticoagulant rodenticides are more toxic than the three listed non-anticoagulant toxicants. It is reported that as little as one feeding of 2 grams of pellet bait will kill a Norway rat and less than 1 gram is effective against mice. These dosages generally amount to a couple of pellets of bait or small portions of a bait block.

Review of Current Proposals

Some suggest we restrict the SGARs to "indoor structural use only," and prohibit the use of these rodenticides outside homes, industrial, commercial, agricultural, public buildings, and around transport vehicles (ships, trains, aircrafts) and related port and terminal buildings. For the protection of children, pets, companion animals, they say rodenticides should be limited to indoor use in tamper-resistant bait stations. But this proposal in not relevant or realistic because the structural pest control industry has been gradually moving away from indoor use of rodenticides because of risks and liabilities involved and the chance of rodents dying in inaccessible areas and creating odor and fly problems. With the exception of a handful of situations, professional pest management companies do not use rodenticides indoors for rodent control.

Another suggestion is to designate the SGARs as "Restricted Materials." In California, this means that users of these products would have to obtain a permit from the County Agricultural Commissioner before they can purchase and use these rodenticides. This appears to be a good solution in that it would restrict the use of these materials to professional pest control operators who are better qualified to use these materials sparingly and judiciously and only where and when necessary and in such a manner to mitigate risks to non-target animals and wildlife. Also, all of the SGARs are considered "general use materials" and they are available for purchase by the general public at numerous retail and wholesale stores. This would help take these materials out of the hands of homeowners and put them within the exclusive domain of pest management professionals (PMPs).

Conculsions

What is not clear at this time is who or what uses of SGARs are responsible for these undesirable non-target wildlife losses. What is obvious is that the structural pest control industry uses the lion share of SGARs in California.

My opinion is that much of the wildlife losses are due to misuse, misapplication and over-application of these materials by untrained, un- or ill-informed and inexperienced technicians as well as the general public at large.

Use of these materials inconsistent with label directions, such as fence line baiting far removed from structures at certain sensitive accounts such as food and pharmaceutical facilities, are occurring in the industry. The structural pest control industry needs to become better informed and more aware of secondary poisoning hazards that rodenticides pose to endangered, threatened, and species of special concern, and non-target wildlife in general as well as to pets and companion animals.

Here's my take on the situation:

There exist available cost effective alternatives to SGARs;
Using alternative rodenticides and methodologies would not put an unnecessary burden on the structural pest control industry.
Given the data that exist, the industry should embark on more prudent and judicious use of SGARs.
The industry should make more efficient use of monitoring blocks, and deploy rodenticides only when there is evidence of rodent activity.

I am flabbergasted by the industry's general response to the various proposals by DPR regarding the SGARs. At a recent meeting of the Structural Pest Control Board, industry representatives vigorously and strenuously defended the status quo. They offered no propositions to ameliorate the documented wildlife losses but they vehemently opposed any and all proposals put forth by DPR.

Outrageous statements were made by some industry representatives, including: rats will take over California; we will be visited by plague (Black death) if any restrictions are placed on SGARs; homeowners will get a substandard service if limitations are placed on SGARs.

In listening to the above assertions, I wondered what happened to such pronunciations by the industry as: We are protectors and conservators of the environment; we are guardians of the environment; we are the true environmentalists. These proclamations cannot be reconciled with the xenophobic position the industry took on this issue.

This situation presented the structural pest control industry in California with a golden opportunity to show that it is a true environmentalist and a responsible environmental citizen, but the industry squandered the opportunity.

I leave you with a few questions to ponder:

• Because of the persistence and toxicity of SGARs, do we really need these toxicants in areas where there are no resistance to first-generation anticoagulants?
• Does the technology exist for executing profitable and cost effective commensal rodent management without SGARs or only occasional, judicious use of these materials?
• Should our first line of defense against commensal rodents be non-chemical techniques that will provide long term control?
• Given the heightened environmental awareness of the public, should rodenticides be a last resort for rodent control?
• Does the industry needs SGARs in maintenance baiting?
• Should the industry advocate and practice more responsible and judicious use of SGARs and rodenticides in general?
• Should the industry make better and more effective use of non-toxic monitoring blocks?
• Should the industry make better and more effective use of trap stations?
• Is it prudent for the industry to always take an integrated rodent management approach to commensal rodent control?

Editor's note: The views and opinions expressed in this paper are those of the author, and they do not reflect the official policy or position on any other entity.

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