Absorption of paraquat

Several studies indicate the special nature of the dodecyl chain in interactions with a variety of biomembranes Zaslavsky s (7 ) data on the haemolysis caused by alkyl ethers, our own data (10 ) on the absorption of paraquat by gastric mucosa,... 

Gorsline, J. Okerholm, R.A. Rolf, C.N. Moos, C.D. Hwang, S.S. Comparison of plasma nicotine concentrations after application of nicoderm (nicotine transdermal system) to different skin sites. J. Clin. Pharmacol. 1992,32, 576-581. Wester, R.C. Maibach, H.I. Bucks, D.A.W. In vivo percutaneous absorption of paraquat from hand, leg and forearm of humans. J. Toxicol. Environ. Health 1984, 14, 759-762. Taskovich, L. Shaw, J.E. Regional differences in the morphology of human skin correlation with variations in drug permeability. J. Invest. Dermatol. 1978, 70, 111. Roberts, M.S. Eavretto, W.A. Meyer, A. Reckmann, M. Wongseelashote, T. Topical bioavailability of methyl sahcy-late. Aust. N.Z. J. Med. 1982, 12, 303-305. 

Srikrishna, V., Riviere, J, E.. and Monieiro-Riviere, N. A. (1992). Cutancoms toxicity and absorption of paraquat in porcine skin. Toxicol. Appl. Pharmacol. 115, 89-97. 

Wester, R.C., Maibach, H.I., and Bucks, D.A.W. (1984). In vivo percutaneous absorption of paraquat from hand, leg, and forearm of humans, J. Toxicol. Environ. Health, 14, 759-762. 

A case of periungual eczematous dermatitis with striking nail lesions due to paraquat was reported by Botella et al. [87]. Patch-testing to paraquat 0.001% and 0.1% in water was negative. A necrotic ulcer of the scrotum following direct contact with paraquat solution was reported by Sharvill [88]. Deaths arising from percutaneous absorption of paraquat have also been reported [89]. 

Vilaplana, Azon A, Romaguera C, Lecha M (1993) Phototoxic contact dermatitis with toxic hepatitis due to the percutaneous absorption of paraquat. Contact Dermatitis 29 163-164... 

Diquat and paraquat are quaternary ammonium compounds largely used as contact herbicides and crop desiccants. When systemic absorption occurs, paraquat and diquat are rapidly distributed into the body. Paraquat primarily accumulates in the lungs and kidneys, while the highest diquat concentrations have been found in the gastrointestinal tract, liver, and kidneys (WHO, 1984). Urine is the principal route of excretion for both diquat and paraquat, which are primarily eliminated as unmodified compounds. Occupationally exposed workers can be monitored by measuring paraquat and diquat concentrations in urine samples (Table 6). Blood concentrations are useful to monitor acute poisoning cases. 

Holmstedt (1959) and Brown and Muir (1971) have reviewed perocular absorption of pesticides. More recently, Sinow and Wei (1973) have shown that the quartemary herbicide paraquat can be lethal to rabbits if applied directly to the surface of the eyes. Parathion, in particular, is exceedingly toxic when administered via the eye, a concern that must be kept in mind for the protection of pesticide applicators. 

PARAQUAT AND DIQUAT Granular preparations usually contain 2.5% of paraquat md 2.5% of diquafi liquid preparations may contain 20% wA of p aquat only. Treatment consists of reducing p aquat absorption by administering copious noimts of file adsorbents Fuller s Earth or bentonite, with cathartics. Active elimination techniques (forced diuresis, haemodialysis, charcoal haemoperfusion) may also be applied. 

This list may be lengthened when the effects of adsorption are considered, because a molecule bound on a surface may be activated for photodegradation even if the reaction is not favorable for the same molecule dissolved in solution. For example, paraquat apparently photodecomposes more rapidly when adsorbed on layer silicate minerals than when in solution (Helling et al., 1971). This phenomenon may be related to the fact that adsorption on clay shifts the UV absorption band of paraquat to longer wavelength (256 - 275 nm) and closer to the atmospheric window for UV light (see Figure 10.20). In other words, adsorption on clay increases the probability that paraquat will absorb UV radiation and thereby decompose. 

Despite a 3-fold range in follicle area in the marmoset, no differences in absorption rates of paraquat, mannitol, water, and ethanol were observed between different body sites (Scoll et al., 1991). However, among the different species examined in this study, there was an 80-fold range in follicle area, which correlated with observed differences in the rate of mannitol and paraquat absorption. The authors concluded that this correlation was only possible with relatively slowly ab.sorbed le.st penetrants, such as paraquat and mannitol. Further work is needed to determine to what extent unique anatomical features at different body sites play a role in absorption and penetration of both lipophilic and hydrophilic pesticides. 

An ideal pharmacokinetic model of the percutaneous absorption process should be capable of describing not only the time course of penetration through skin and Into blood (or receptor fluid In a diffusion cell), but also the time course of disappearance from the skin surface and accumulation (reservoir effect) of penetrant within the skin membrane. Neither Pick s Plrst Law of Diffusion nor a simple kinetic model considering skin as a rate limiting membrane only Is satisfactory, since neither can account for an accumulation of penetrant within skin. To resolve this dilemma, we have analyzed the In vitro time course of absorption of radiolabeled benzoic acid (a rapid penetrant) and paraquat (a poor penetrant) through hairless mouse skin using a linear three compartment kinetic model (Figure 5). The three compartments correspond to the skin surface (where the Initial dose Is deposited), the skin Itself (considered as a separate compartment), and the receptor fluid In the diffusion cell. The Initial amount deposited on the skin surface Is symbolized by XIO, and K12 and K23 are first order rate constants. 

Gamier et al. [90] reported two cases of paraquat poisoning resulted from skin absorption. One patient died from respiratory failure 26 days after applying paraquat onto his whole body as a treatment for scabies. The other with a previous history of psoriasis developed extensive generalized pustular erythroderma and a moderate, transitory renal and respiratory impairment 13 days after exposure. 

In terrestrial plants, paraquat s action is at the point of local absorption (Anonymous 1963). Characteristic damage signs to susceptible species include wilting and general collapse in herbaceous plants. Regrowth may occur in some perennial plants, but in resistant species temporary scorch may be the most marked effect (Anonymous 1963). In sugarcane (Saccharum officinarum), paraquat... 

Tanaka, R., S. Fujisawa, and K. Nakai. 1981. Study on the absorption and protein binding of carbaryl, dieldrin and paraquat in rats fed on protein diet. Jour. Toxicol. Sci. 6 1-11. 

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