Dermal carbaryl

Carbamates are also used as insecticides and again, their trade names are probably familiar if you have done any serious gardening and pest control. The use of these compounds is restricted to certain parts of the growing cycle and specific non-food produce. Notice their low degree of dermal toxicity. Carbaryl, for example, is used topcially in some countries to get rid of head lice. It was the misuse of Temik several years ago on watermelons in California which... 

Carbaryl [65-25-2], 1-naphthyl ZV-methylcarbamate (111) (mp 142°C, d 1.232 g/cm3, vp 0.67 Pa at 20°C), is ca 95% pure as the technical grade and is soluble in water to 120 mg/L. Carbaryl has a rat oral LD5Q of 540 mg/kg and a dermal LD50 of >2000 mg/kg. It is a broad-spectrum insecticide registered on more than 100 crops. Carbaryl is rapidly detoxified and eliminated in animal urine and is neither concentrated in fat nor secreted in the butterfat of milk, thus it is favored for application to food crops. 

Table 1 shows the number and types of workers and the various situations in which these workers were monitored for dermal exposure to carbaryl. Formulations of carbaryl that were evaluated included 80S, a wettable powder containing 80% active carbaryl 50W, a wettable powder containing 50% active carbaryl Sevimol 4, a liquid suspension of carbaryl in molasses containing 40% active ingredient and XLR, a water based flowable containing 4 lbs active carbaryl per gallon. 

Table I.—Operations in which workers were monitored for dermal exposure to carbaryl.

Pesticidal organic derivatives of carbamic acid, for which the formula is shown in Figure 15.8, are known collectively as carbamates. Some carbamate insecticides such as carbaryl, carbofuran, and pirimicarb have been in use for many years others, including Dunet, are relatively recent. Carbamate pesticides have been widely used because some are more biodegradable than the formerly popular organochlorine insecticides and have lower dermal toxicides than most common organophosphate pesticides. 

Carbamates also include pesticides such as Sevin, aldicarb, and carbaryl. They are more degradable than organophosphates and have lower dermal toxicides. Their toxicity is also due to inhibition of acetylcholinesterase but they do not penetrate the central nervous system, so most effects are respiratory in nature. An acetylcholinesterase, which has been carbamylated can undergo spontaneous hydrolysis in vivo, which reactivates the enzyme leading to less severe symptoms or a shorter duration of symptoms. Carbaryl has a low toxicity for mammals however, Perimicarb is highly toxic to mammals, but not readily absorbed through the skin. 

Inhalation, ingestion, dermal Acetylcholinesterase degradation Weakness, headache, dizziness, shaking, nausea, stomach cramps, diarrhea, loss of appetite, perspiration Insecticides, acaricides Aldicarb, propoxur, carbaryl, benomyl, pyridostigmide bromide... 

In another dermal penetration study, it was shown that the absorption of the insecticide carbaryl was enhanced by the solvent acetone and the surfactant sodium lauryl sulfate. The synergist PO significantly increased the absorption of carbaryl when added to the acetone-carbaryl rnixJ31 This study points out both the enhanced absorption of pesticide by individual inert additives as well as the further enhanced mixture effect. 

Baynes RE, Riviere JE. Influence of inert ingredients in pesticide formulations on dermal absorption of carbaryl. AmJ Vet Res 1998 59(2) 168—75. 

Baynes at al. (1997) Rodent, pig stin DEET. permethrin, carbaryl DEET does not enhance dermal absorption of permethrin... 

Tos-Luty, S., Tokarska-Rodak, M., Latuszynski, J., and Prczcbiruwska, D. (2001). Dermal absorption and distribution of C-carbaryl in Wistar rats. Arm. Agric. Environ. Med. 8( 1), 47-50. 

Ladies, G- S.. Smith. C., Heap.s, K., and Lovetc.ss. S. E. (1994). Evaluation of the humoral immune response of CD rats following a 2-week exposure to the pesticide carbaryl by the oral, dermal, or inhalation routes. J. Toxicol. Environ. Health 42,143-156. 

Zweig, G-, Gao, R., and Witt, J. M. (1984). Dermal exposure to carbaryl by strawberry harvc.sters, J, Agric. Food Chem. 32, 1232-1236. 

Rgure 9.2 Inhibiting effects of DEET on the dermal absorption of (a) carbaryl and (b) permethrin. 

Dermal dose-ChE response and percutaneous absorption studies were conducted with parathion, carbaryl, and thiodicarb in the rat. Parathion and thiodicarb inhibited 50% of the red cell cholinesterase activity at dose levels of 3.2 and 33 mg/kg of bw. Carbaryl at the highest dose level tested (417 mg/kg of bw) produced no detectable red cell cholinesterase Inhibition. 

Dermal Dose-Response Studies. The dermal dose red cell ChE-response curves for parathion and thiodicarb are given in Figure 2. Para-thion, the most toxic pesticide used, inhibited 50Z of the red cell ChE activity at a dose level ot 31 t%/cm (3.2 mg/kg) of treated skin in 72 hr, tdiile 322 ug/cm of thiodicarb (33.3 mg/kg) gave 50 ChE inhibition in 24 hr. Carbaryl at dose levels up to 4,000 ng/cn of treated skin (417 sig/kg) did not produce detectable ChE inhibition 24 hr after application of the dose. Thiodicarb was dermally more toxic than carbaryl, but substantially less toxic (1/10) than parathion. 2... 

Figure 3. Time-course recovery of dermally applied [ C] labeled paraChion, carbaryl, and thiodicarb equivalents in percentage of dose in feces, urine, carcasses, and skin (surface and penetrated residues) after application. (Reproduced with permission from Ref. 9. Copyright 1984, Academic Press.)...

Thlodicarb is a new insecticide being marketed by Union Carbide as Larvin for the control of insects on cotton. Thiodicarb is metabolized in the rat to acetamide, acetonitrile, CO, methomyl, and methomyl metabolites. No illnesses have been reported among applicators or field workers coming in contact with this carbamate insecticide. Thiodicarb is somewhat more persistent on crops than methomyl and is less toxic dermally in rabbit studies. The dermal dose-CliE response study showed that a dose of 33 mg/kg produced 50% ChE inhibition 24 hr. after the application of the dose, while a dose of 87 mg/kg of thiodicarb did not produce more inhibition than a dose of 44 mg/kg. The poor solubility of this carbamate in water/lipid most likely prevented the absorption of additional quantities of thiodicarb, thereby reducing its toxicity. Thiodicarb was found in lower concentrations in skin than either parathion or carbaryl during the percutaneous absorption studies. The concentrations in plasma. 

Dermal exposure to captan and benomyl by strawberry harvesters has been the subject of several previous studies (1.2.3). This field study was designed to test a number of hypotheses and the reproducibility of dermal exposure rate measurements taken under field conditions. Most of our past studies have not been designed for a particular pesticide but were modified to accommodate the pesticide chosen by the grower to control a certain pest. In this case, the pesticide was carbaryl (1-naphthyl N-methylcarbamate) an insecticide used to control the spittlebug and leafroller. Our results could then he compared with those obtained by Maitlen and co-workers (A) who studied workers exposed to carbaryl in an apple orchard. Furthermore, attempts will be made to test possible positive correlations between age and dermal dose rate versus productivity and dermal dose rate versus age of harvesters. Difference of dermal exposure due to age or... 

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