Derek Gammon

• Doctor of Philosophy
• FMC Corporation

BACKGROUND Pyrethroids generally have relatively low oral toxicity but variable inhalation toxicity. The pharmacokinetics of bifenthrin in the rat after oral, inhalation and intravenous administration is described. Pyrethroid acute toxicity via oral and inhalation routes is also presented.RESULTSGroups of male rats were dosed by oral gavage at 3.1...

Carbofuran is a carbamate insecticide that inhibits AChE. Although toxic by ingestion in mammals, it has low dermal toxicity, with relatively few confirmed worker illnesses. This risk assessment describes its time of onset, time to peak effect and time to recovery in rats using brain AChE inhibition in acute and 21 day dermal studies; in vitro rat/...

Insects are more similar in structure and physiology to mammals than plants or fungi. Consequently, insecticides are often of greater toxicity to mammals than herbicides. This is particularly the case with neurotoxins. However, some insecticides are targeted at structures or hormonal systems specific to insects (insect growth regulators/chitin synt...

A Scientific Advisory Panel (SAP) in June 2009 concluded that a common mode of action existed for pyrethroids, with two subgroups. The purpose of this SAP was to advise the U.S. Environmental Protection Agency on the validity of regulation of pyrethroids as a single class under the Food Quality Protection Act of 1996. Two types of pyrethroid action...

This chapter outlines usage, environmental fate, and effects of sulfur. Elemental sulfur is the most heavily used crop protection chemical; it is generally applied to crops as a dust to combat fungal disease, at rates of approximately 10 to 30 lbs. The range of fungal diseases controlled by sulfur includes brown rot, scab, mildew, powdery mildew, a...

Endosulfan has been used for over 50 years. Although most analogs have been discontinued, endosulfan has less environmental persistence. Nevertheless, pressure groups are lobbying for a worldwide ban. The reasons are: possible rodent male reproductive toxicity, other endocrine effects and cancer; human epidemiology, and exposure studies; residues a...

A symposium in honor of Dr Gerry Brooks winning the International Award for Research in Agrochemicals was organized by me, D Gammon, with help from RD Wauchope. The award is the highest given by the AGRO Division (formerly Agrochemicals Division) of the ACS. The symposium lasted a full day and consisted of an introduction, a lecture by Gerry and ni...

Some sublethal effects of tetrodotoxin (TTX) on the cockroach were investigated using chronically implanted extracellular electrodes. Prostration and subsequent paralysis were correlated with blockage of peripheral nerves, the CNS being apparently unaffected at the dose employed. Over several days following treatment many cockroaches showed a rever...

Derek W Gammon and Gerald T Brooks (awardee), summarise the award and related symposium presentations given at the 233rd National Meeting of the American Chemical Society on March 27th 2007, in honour of the awardee. Dr Gammon organised the symposium for this award, which is the highest one given by the ACS Agrochemical Division.The symposium laste...

West Nile virus is becoming increasingly prevalent in the USA, causing fever, encephalitis, meningitis and many fatalities. Spread of the disease is reduced by controlling the mosquito vectors by a variety of means, including the use of pyrethroid insecticides, which are currently under scrutiny for potential carcinogenic effects in humans. Pyrethr...

An outbreak of human illnesses associated with West Nile Virus (WNV) occurred in New York City in 1999. Since then, it has gradually spread westwards, reaching northern California for the first time in 2005. WNV is transmitted by several mosquito species and birds serve as the main reservoir. Several control measures have been used, targeting both...

A risk assessment of the triazine herbicide atrazine has been conducted by first analyzing the toxicity database and subsequently estimating exposure. Margins of safety (MOS) were then calculated. Toxicity was assessed in animal studies and exposure was estimated from occupational and dietary sources. In acute toxicity studies, atrazine caused deve...

Insects constitute an immense drain on food resources worldwide, as well as being serious disease vectors. Insecticide applications are made directly to raw agricultural commodities to protect plants and animals from insect attacks. Official national and international bodies regulate pesticide use and set permitted maximum residue levels or MRLs/to...

Insect pheromones are classified as “semiochemicals” and affect the behavior of other insects. Semiochemicals include pheromones, kairomones, feeding stimulants, synthetic attractants, and so on, and they are useful components of pest management systems. Sex attractant pheromones released by female Lepidoptera to attract the male for mating purpose...

Agrochemicals are regulated very thoroughly at both the national and international levels. Toxicology tests generally include lifetime rodent studies to determine whether or not the the compound is capable of causing cancer. In addition, a battery of shorter duration tests designed to evaluate an agent's genotoxic potential are conducted. These stu...

Insects constitute an immense drain on food resources worldwide, as well as being serious disease vectors. Insecticide applications are made directly to raw agricultural commodities to protect plants and animals from insect attacks. Official national and international bodies regulate pesticide use and set permitted maximum residue levels or MRLs/to...

Few chlorinated organic insecticides remain in use in North America and Europe. Several have been classified as Persistent Organic Pollutants and proscribed globally. However, their considerable benefits to humanity in the past should not be overlooked nor should the lessons that were learned during the period when they were applied to control dise...

Glufosinate-ammonium is a nonselective contract herbicide. Glufosinate was introduced as a herbicide in 1981 and is used for controlling a wide range of annual and perennial broad-leaved weeds in fruit orchards, vineyards, rubber and palm oil plantations, ornamental trees and brushes, noncropland, and pre-emergence in vegetables. It is also used as...

This chapter describes chronic risk assessment for trianize herbicide cyanazine in detail to provide an example of the process for regulating carcinogens in practice. The risks of long-term exposure to cyanazine are estimated by first reviewing the studies defining the toxicity of the chemical, usually conducted on laboratory animals, and determini...

A lunchtime Panel Discussion addressed issues related to human data collection for pesticides. The distinguished panelists described their own perspectives on the subject and then time allowed for a few comments from the audience.

The contribution of maternal toxicity to the teratogenic effects of the herbicide cyanazine has been assessed to determine whether it may be a hazard to development. Eye defects such as anophthalmia and microphthalmia were observed in rat fetuses and pups. Maternal toxicity was determined from body weight data and clinical signs. Two approaches wer...

Substitution of silicon for carbon was explored in etofenprox and MTI-800, primarily to establish the suitability of silicon for pesticide construction and to probe steric effects. It was shown that silicon is an effective building block for insecticides with subtle qualitative and quantitative differences relative to the carbon analogs. The silane...

A. E. Lund: I want to provide a context for our discussion on the role of biochemical, physiological, and neurochemical research in this process. Figure 1 shows a schematic view of insecticide discovery that highlights some key steps taken by most agricultural chemical companies. Probably no company fully integrates all the functions shown here, an...

Classical neuropharmacological procedures have been used to elucidate insecticide mode of action in vitro. A good deal has thus been learned about pyrethroids but novel techniques have been necessary to explain the toxicology and symptomology. The free-walking, electrode-implanted cockroach technique, which was developed for this purpose, is descri...

Since the classic studies on pyrethroid mode of action using cockroach giant axons, a diverse array of preparations and techniques have been used to study pyrethroid action. These have ranged from attempts to correlate the in vitro effects of pyrethroids on nerve with those recorded in insects in vivo to attempts at displacing radioligands from Tor...

3-Phenoxybenzyl (1R-)-cis-3-(1,2-dibromo-2, 2-dichloroethyl)-2, 2-dimethylcyclopropanecarboxylate [dibromo-(1R)-cis-permethrin] was >100 times less active than (1R)-cis-permethrin in causing repetitive firing in a cockroach cereal sensory nerve in vitro, although its toxicity, symptomology and nerve effects in vivo were comparable to the parent com...

Conversion of chrysanthemates to their cyclopropane, episulfide, and epoxide derivatives by addition of methylene, sulfur, or oxygen, respectively, to the 2-methyl-1-propenyl double bond yields products generally of reduced toxicity but enhanced neurophysiological activity and photostability. The reduced toxicity is established with cis-cyphenothri...

Deltamethrin and three insecticidal cyano analogs causing the Type II pyrethroid syndrome increased the input resistance of crayfish claw opener muscle fibers bathed in gamma-aminobutyric acid (GABA). In contrast, two non-toxic stereoisomers and three insecticidal pyrethroids causing the Type I syndrome were inactive. Known GABA antagonists includi...

The potent insecticide 4-chlorophenyl cyclopropyl ketoxime (3-phenoxy)benzyl 0-ether (1) is more resistant to photodegradation at 300 nm in hexane than the corresponding ester and current commercial pyrethroids. The predominant photochemical process is isomerization (ΦE→Z = 0.26) resulting in photoactivation of the non-insecticidal (Z)-1 to (JE)-1....

The analog of cis-tetramethrin with a 2,2-dimethyl-cyclopropyl replacement for the 2-methyl-1-propenyl group, i.e., "methanotetramethrin", is one of the most neuroactive compounds ever described. It is 10(3)- to greater then 10(5)-fold more potent than tetramethrin in inducing repetitive firing following stimulation in a cockroach cercal sensory ne...

Diazepam delayed the onset of action of deltamethrin and fenvalerate (pyrethroids producing the Type II syndrome) but not of permethrin and allethrin (pyrethroids producing the Type I syndrome) in both the mouse and cockroach. Phenobarbital was less potent as an anticonvulsant and also less selective since it delayed the onset of signs for both del...

Pyrethroids are divided into two classes (Types I and II) based on their effects on the cercal sensory nerves recorded in vivo and in vitro and on the symptomology they produce in dosed cockroaches, Periplaneta americana. Type I compounds include pyrethrins, S-bioallethrin, [1R,cis]resmethrin, kadethrin, the 1R,trans and 1R,cis isomers of tetrameth...

The effects of permethrin and cypermethrin on the isolated abdominal nerve cord of insecticide-resistant [R] and -susceptible [S] strains of Spodoptera littoralis larvae have been studied. Above ca. 19°C, permethrin at 10−7M caused a prolonged spike train to follow electrical stimulation of the nerve cord. The time of onset of this repetitive firin...

Pyrethroid insecticides have long been known to act on insect nerve (Wigglesworth, 1941; Lowenstein, 1942) and the mode of action of allethrin, the first synthetic pyrethroid, has been studied extensively using a variety of invertebrate nerve preparations (Narahashi, 1971a). One of the distinctive features of pyrethroids is their greater toxicity t...

Some effects of DDT on the cockroach nervous system have been correlated with poisoning symptoms, using free-walking cockroaches with implanted electrodes. Experiments at 16.5°C and 32°C used LD95 doses and at 25°C, an estimated LD95. DDT had excitant actions on each nerve studied; cercal afferent and efferent neurones, and abdominal interneurones....

The action of allethrin has been studied in the free-walking cockroach, Periplaneta americana (L) using implanted electrodes, at 15 and 32°C, following topical application of an LD95 dose (that at 32°C being approximately ten times the LD95 at 15°C). At both temperatures there was marked hyperexcitation of the peripheral nervous system. At 32°C the...

This paper describes a technique enabling the mode of action of insecticides to be followed using a free-walking cockroach. The nervous effects can be followed over a period of days, using the same individual insect. Information can be obtained concerning the central nervous system, a sensory nerve, and the synapses between them.