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Parrafinized Rodenticides are Here to Stay
1 Mar, 2009 By: Dale E. Kaukeinen Pest Management ProfessionalThe continued availability of wax block rodenticides for commensal rodent control has been assured by the May 2008 decision of the Environmental Protection Agency (EPA) to recommend the use of block baits in bait stations for homeowner use (PMP July 2008, pg. 90).
While PMPs have discretion as to whether to use pellets, placepacks, blocks or some other rodenticide presentation according to the needs of the situation, wax blocks securely held in bait stations have long been the standard for much of the baiting done by professionals, particularly around commercial accounts. Rodenticide product labels require baits secured in stations for any application accessible to children, pets, domestic animals or wildlife.
Paraffinized Commensal Rodenticide Bait Block Products
Many block baits are sold with a central hole that allows them to be mounted on bait station rods or otherwise fastened down. This is seen as an important benefit over pellets and other loose bait, in that rodenticide containment has become an important issue with regard to safety in use.
A Lasting Development
Ordinary baits made of cereal ingredients or other perishable contents do not last well when placed out in many environments inhabitated by rodents. Paraffin-type solid baits have an interesting history and, once marketed, they received immediate acceptance by pest management professionals (PMPs). They were developed principally to improve rat control by preventing or reducing the problems of mold and mildew in cereal baits when used in damp or wet environments, helping ensure continued bait availability over the several days needed to achieve control with first-generation anticoagulant ingredients.
The use of paraffin, animal fats and various oils of plant origin to coat rodent baits for weather-proofing goes back to the early 1900s, but cereal-based baits suspended in a solid matrix of paraffin, although explored experimentally by some researchers and practitioners, did not come into use in the United States and elsewhere until the late 1950s and early 60s.
The late Lloyd Plesse of San Jose, Calif. is credited with first making up solid block-type paraffinized rodent baits for use in the U.S. Plesse was assistant agricultural commissioner for the Santa Clara County Agricultural Commissioner's Office. Among his duties was supervising the manufacture of rodent baits, which were sold by that office to farmers and the general public. The idea is said to have come to him when a friend commented that rats had gotten into a box of candles and chewed them up.
These semi-permanent baits were made by blending roughly equal parts of melted paraffin with cereal-based rodent bait. This thick, flowable mixture was then poured into appropriate molds and allowed to solidify.
The article Semipermanent Anticoagulant Bait (Pest Control Magazine, Aug. 1961) expounding on the benefits and versatility of paraffinized baits, was co-authored by Rex Marsh and Plesse and published in the California Department of Agriculture Bulletin. This article caught the attention of several commercial rodent bait formulators, as well as a number of PMPs and other entities that formulated their own rodent baits — a relatively common practice in those days.
The marketplace could quickly change in those days before the EPA and Federal product registration requirements. Within a few months, the J.T. Eaton Company had produced and marketed solid paraffinized rat baits and was promoting them for a variety of applications. Also, the American Chemical Company made the paraffinized "Rodent Cake," which was advertised and marketed by the Bug X Company of Davenport, Iowa.
These were the beginnings of commercially-prepared paraffinized rodent baits, which, after nearly five decades, we now take so much for granted. Following California's lead, health departments across the country also began making paraffinized baits, principally for sewer rat control.
Early on, the forward thinking president of J. T. Eaton and Co. did secure "Bait Blocks" as a registered trademark. This is one reason that subsequent manufacturers named their paraffinized rodenticide bait products as bloks, blox or similar descriptors.
As the paraffinized baits gained in popularity, other articles began to appear in Pest Control touting the effectiveness of such baits — especially for use in sewers.
As more and more firms began to add paraffinized rodent baits to their line of rodent products, competition increased. Baits were soon marketed in a variety of aromas and flavors.
New methods of anchoring baits were devised and scored baits were produced that could be easily broken into individual segments.
EPA Elevates Bait Block Efficacy
The creation of the Environmental Protection Agency in 1970 led to the adoption of regulations summarized in the Federal Insecticide, Fungicide and Rodenticide Act (FIFRA). Rodenticide bait products had to pass numerous tests in the registration process, and wax blocks were no exception.
To be considered "weatherable," they had to be placed in 100% humidity and high temperature and then (when usually covered with mold) tested against rats and mice to ensure they were efficacious.
Feeding protocols were devised for the three commensal species and paraffinized baits were tested opposite a desirable challenge diet known as EPA meal, which contained corn meal, ground oats, corn oil and sugar. A minimum level of palatability and kill was required before products could receive registration. These new requirements were tough to meet for wax blocks, because many of these early wax block products were not highly palatable. The EPA initially lowered minimum acceptance levels for paraffinized baits from 33-percent to 25-percent, and sometimes allowed reduced kill levels of test groups as well.
Because of palatability requirements for registration, and the increasingly competitive marketplace, many manufacturers began to explore ways in which paraffinized bait formulations could be improved to increase rodent acceptance.
Casting Limits
In the 1970s and 1980s, many rodenticide manufacturers began to realize the basic manufacturing process of mixing ingredients into molten wax and pouring into molds created many limitations and drawbacks. Cast blocks needed extended cooling time before mechanical release from molds. The wax content could separate from other ingredients, creating less than palatable layers within the block product. The cooling wax could shrink, leaving a crater in the center rather than a uniform surface or shape. Only simple shapes and rounded edges could be produced so that blocks could be removed from the molds.
One of the last innovative cast blocks on the professional market was the ICI (later Syngenta) early WeatherBlok formulation, which was poured into disposable 420 gram circular molds with break-apart channels, and the molds were sealed with a cardboard label lid. These blocks could be packed while the wax was warm, to save time. Some users appreciated that individual blocks were sealed from contamination or exposure until the lid was removed and the block slipped from the mold container. And until opened, these blocks did not deform in heat, nor stick together.
Eventually, the costs of conventional casting and hand labor, combined with the rise in the cost of paraffin — a component of oil — led to the development of a new process to lower costs while producing new shapes and paraffinized products. This new process was to be subsequently adopted by nearly all wax block manufacturers.
Extrusion Pushes out the Old Ways
Extrusion is the process of forcing a molten product through an opening or die, and had long been used to make small feed and bait pellets. An early U.S. inventor of extruded wax pelletized baits, particularly those containing zinc phosphide, was Howard Arbaugh of ArChem in Ohio. Arbaugh received a patent on this process in 1971, but remained one of the few using the technology until Bell Laboratories improved the process to make extruded block-like rodenticides. Their patent filed in 1989 expanded upon the block baits they had been making since the mid-1970s, and led to distinctive extruded bait shapes featuring gnawing edges.
The extrusion process allows for a reduction in wax and temperatures from the cast process, shortening the cooling time. Extrusion allows for a more homogeneous and uniform block that can be automatically cut to a desired length. For manufacturers, these advantages came with reduced costs associated with a high volume of production with less hand labor.
The modern paraffinized block bait was born and soon nearly all manufacturers followed suit. The advent of the single-feed second-generation anticoagulants led to block downsizing — smaller, 20-gram to 1-ounce blocks were developed and became popular, allowing for single placements for mouse control.
Today, a number of highly palatatable and proven paraffinized rodenticide bait products are available from the major rodenticide manufacturers and formulators. These represent not only the various first- and second-generation anticoagulant rodenticides, but also the non-anticoagulant products as well.
Extensive research and development have resulted in excellent rodent palatability such that most of these paraffinized products are the equal (or nearly so) of pelletized baits containing no paraffin. Yet these wax block products, not only weatherable, offer advantages of especial relevance in today's climate of concerns for containment, safety liability and reduction of contamination.
Placed on a wire in a sewer, or on a rod in a tamper-resistant bait station, these products reflect a lineage of more than 50 years of development and change to provide users peace of mind and customers successful resolution of their rodent problems.
Rodenticide manufacturers are looking at yet other binding materials to replace wax, to perhaps offer cheaper, weatherable and palatable solid bait alternatives. For now, though, nothing has replaced paraffin's central role in making block rodenticide products.
Clearly, these durable products continue to offer advantages that have withstood the test of time and changes in the pest management industry.
You can reach Kaukeinen, frequent PMP contributor and industry veteran, at dkaukein@comcast.net. You can reach Marsh, Emeritus Specialist in Vertebrate Ecology at the University of California's Department of Wildlife, Fish and Conservation Biology at Davis CA at marsh-r@sbcglobal.net.
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