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Chapter 27 - Biological Monitoring

Phenoxy herbicides are scarcely biotransformed in mammals. In humans, more than 95% of a 2,4-dichlorophenoxyacetic acid (2,4-D) dose is excreted unchanged in urine within five days, and 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) and 4-chloro-2-methylphenoxyacetic acid (MCPA) are also excreted mostly unchanged via urine within a few days after oral absorption. The measurement of unchanged compounds in urine has been applied in monitoring occupational exposure to these herbicides. In field studies, urinary levels of exposed workers have been found to range from 0.10 to 8 µg/l for 2,4-D, from 0.05 to 4.5 µg/l for 2,4,5-T and from below 0.1 µg/l to 15 µg/l for MCPA. A 24-hour period of urine collection starting at the end of exposure is recommended for the determination of unchanged compounds. Analytical methods for the measurements of phenoxy herbicides in urine have been reported by Draper (1982).

Synthetic pyrethroids are insecticides similar to natural pyrethrins. Urinary metabolites suitable for application in biological monitoring of exposure have been identified through studies with human volunteers. The acidic metabolite 3-(2,2’-dichloro-vinyl)-2,2’-dimethyl-cyclopropane carboxylic acid (Cl2CA) is excreted both by subjects orally dosed with permethrin and cypermethrin and the bromo-analogue (Br2CA) by subjects treated with deltamethrin. In the volunteers treated with cypermethrin, a phenoxy metabolite, 4-hydroxy-phenoxy benzoic acid (4-HPBA), has also been identified. These tests, however, have not often been applied in monitoring occupational exposures because of the complex analytical techniques required (Eadsforth, Bragt and van Sittert 1988; Kolmodin-Hedman, Swensson and Akerblom 1982). In applicators exposed to cypermethrin, urinary levels of Cl2CA have been found to range from 0.05 to 0.18 mg/l, while in formulators exposed to α-cypermethrin, urinary levels of 4-HPBA have been found to be lower than 0.02 mg/l.

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Chapter 27 - Biological Monitoring GENERAL PRINCIPLES

reaction, the synthesis of 2-Methylphenoxyacetic Acid follows an SN2 reaction mechanism

Convenient and efficient procedures have been developed for the synthesis of tris(2-hydroxyethyl)-ammonium 4-halo-2-methylphenoxyacetates (halocresacins). 4-Chloro-2-methylphenoxyacetic acid necessary for the preparation of chlorocresacin has been obtained by chlorination of 2-methylphenoxyacetic acid with sulfuryl chloride in the presence of aluminum powder. Bromocresacin has been synthesized by reaction of triethanolamine with 4-bromo-2-methylphenoxyacetic acid prepared by bromination of 2-methylphenoxyacetic acid with molecular bromine. Fluoro- and iodocresacins have been synthesized by exchange reaction of chlorocresacin with potassium fluoride and sodium iodide, respectively.

A microorganism capable of degrading 4-chloro-2-methylphenoxyacetic acid (MCPA) was isolated from soil and identified as Flavobacterium peregrinum. All of the chlorine of MCPA was released as chloride, and the carboxyl-carbon was converted to volatile products by growing cultures of the bacterium, but a phenol accumulated in the medium. The phenol was identified as 4-chloro-2-methylphenol on the basis of its gas chromatographic and infrared characteristics. Extracts of cells of F. peregrinum and of a phenoxyacetate-metabolizing Arthrobacter sp. dehalogenated MCPA and several catechols but not 4-chloro-2-methylanisole. The Arthrobacter sp. cell extract was fractionated, and an enzyme preparation was obtained which catalyzed the conversion of MCPA to 4-chloro-2-methylphenol. The latter compound was not metabolized unless reduced nicotinamide adenine dinucleotide phosphate was added to the fractionated extract. The phenol in turn was apparently oxidized to a catechol by components of the enzyme preparation.

Vito Foà and Lorenzo Alessio

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