Absorption of herbicides

Herbicides, or weed killers, may be classified as pesticide chemicals. They can kill plants on contact, or they can be translocated (i.e absorbed by one part of the plant and carried to other parts where they exert their primary toxic effect). Most commonly used herbicides have a low toxicity and have caused few adverse effects in users. Some herbicides pose more serious problems to the central nervous system (CNS) and can cause depression. The skin absorption of herbicides also may cause skin irritation, dermatitis, and photosensitization in addition to peripheral motor neuropathies. 

Charnel A. Foliar absorption of herbicides study of the cuticular penetration using isolated cuticles. Physiol Veg 1986 24 491-508. 

Features Patented allows for rapid spreading and absorption of herbicide sprays info plant leaves and stems, and is esp. effective with water-based herbicides may be used with other pesticide and/or fertilizer prods. 

Chester, G., Loftus, N.J., Woollen, B.H., and Anema, B.P. (1990b) The effectiveness of protective clothing in reducing dermal exposure to, and absorption of, the herbicide fluazifop-P-butyl by mixer-loader-applicators using tractor sprayers, in Book of Abstracts, Seventh International Congress of Pesticide Chemistry, Vol. Ill, Freshe, H. and Kesseler-Smith, E., Eds., Conway, Hamburg. 

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. 

T (1) workers compared to 2,4-D or 2,4,5-T ingestion studies (2, 4, 5,6) probably reflects the slower rate of plasma absorption of the herbicides, compared to ingestion. The data suggests the workers did a poor job of skin protection and subsequent washing. 

The principles of successful weed control in orchards include herbicide placement, movement, adsorption, absorption, translocation of herbicides, and their inherent biological activity. The residual characteristics of the herbicides are also important, as is the response of the trees and weeds. 

The quantum yield (9) is a measure of the efficiency of the photochemical excitation process, which may result in herbicide degradation and indicates the number of herbicide molecules degraded per photon absorbed. A value of 0 indicates that no chemical reaction occurred, while a value of 1 indicates that all molecules excited due to photon absorption were converted to products. Chain reactions, which can lead to quantum values greater than unity, are unlikely at the very low concentrations found in the aquatic environment. 

Penetration of herbicide solutions through cuticle in the absence of stomata is also common, and under field conditions it may be the dominant portion of the penetration of herbicides. The existence of both polar (hydrophilic) and apolar (lipophilic) absorption pathways through plant cuticle seems certain from several laboratory and greenhouse studies (10). 

Through the further combined use of radiolabeled herbicides and additives in tracer and metabolic studies, it may be possible to develop new concepts regarding formulation of herbicides for differential absorption, translocation, and selective action, while at the same time minimizing chemical residues. 

Sun, Y. and Pignatello, J.J. (1993) Photochemical reactions involved in the total mineralization of 2,4-D by iron(3+)/hydrogen peroxide/UV. Environ. Sci. Technol. 27, 304-310 Toepfer, B., Gora, A. and Li Puma, G. (2006) Photocatalytic oxidation of multicomponent solutions of herbicides Reaction kinetics analysis with explicit photon absorption effects. Appl. Catal. B Environ. 68,171-180... 

The transformation of the herbicide bromoxynil (3,5-dibromo-4-hydroxy-benzonitrile) was studied upon direct photolysis in water and in the presence of added nitrite. The addition of nitrite reduces the transformation rate of the substrate, most likely due to competition for absorption of radiation, but induces the formation of nitro derivatives (3-bromo-4-hydroxy-5-nitrobenzonitrile, 4-hydroxy-3-nitrobenzonitrile) [140]. 

The lowest concentration of herbicide detectable in the atmosphere depends on the sample volume and the collection time. For an absorption sample volume of 5.0 ml. n-decane and a collection time of 24 hours, the lowest detectable atmospheric concentration is 1.0 /xgram/cu. meter for methyl MCP, 0.14 /xgram/cu. meter for the 2,4-D esters, and 0.03 /xgram/cu. meter for methyl 2,4,5-T. 

This group of herbicides consists of clopyralid, fluroxypr, picloram, and triclopyr. These compounds have both soil absorption and foliar activity. 

Chlorophenoxy compounds are moderately irritating to skin. In case of dermal or eye exposure, the contaminated area should be bathed or flushed with copious amounts of water for 15 min and if irritation persists a physician should be contacted. Ingestion of substantial amounts of these chemicals results in spontaneous emesis. If the patient is fully alert and there are no apparent signs of emesis, emesis is induced with syrup of ipecac (adults, 30 ml children <12 years, 15 ml), followed by one to two glasses of water. In order to limit the absorption of the herbicide in the gut, 30-50 g of activated charcoal is administered in 6-8 ounces of water. Severe intoxication with chlorophenoxy compounds may result in renal failure. To avoid... 

Feldman RJ, Maibach HI. Percutaneous absorption of some pesticides and herbicides. Tox Appl Pharmacol 1974 28 126-32. 

Abiotic. With absorption maxima in the range 280 to 290 nM ( 6) phenoxyalkanoic acids are able to absorb radiation found in sunlight and undergo photochemical decomposition. Their breakdown in irradiated aqueous solutions is well studied ( 5). However, photochemical breakdown of phenoxyalkanoic acids by sunlight at the soil surface is not considered to be a major source of herbicidal loss (5), since the chemicals are applied as post-emergence applications to growing crops, and residues reaching the soil will thus be protected from the sun s radiation by the crop canopy. 

Owing to their different steric configuration, the absorption of acylureas by plants is different from that of the other urea herbicides, which may partly explain their different selectivity. Presumably, these compounds exert their action after hydrolysis of the acid group. 

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