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A hypothesis that low molecular weight aromatic compounds, which occur naturally in the soil, may act as alternative substrates or inducers for the 2,4-dichlorophenoxyacetate (2,4-D) degrading enzyme system of an Arthrobacter sp. and maintain this enzyme system in the absence of 2,4-D, was examined experimentally. In a nonmanometric resting cell experiment, the 2,4-D adapted Arthrobacter sp. rapidly degraded 6 of the 12 aromatic compounds tested, and these 6 compounds were tested further with 2 additional aromatic compounds in manometric experiments with 2,4-D grown and citrate-grown cells. Homogentisic acid and catechol were oxidized more rapidly by 2,4-D grown cells than by cells grown on citrate medium. Thus, these two compounds could serve as alternative substrates for the 2,4-D degrading enzyme system of the Arthrobacter sp. In further manometric experiments, the 2,4-D degrading enzyme system in cells adapted to 2,4-dichlorophenol, catechol, or sodium benzoate was not induced.

Six auxin-type herbicides in air, rain and dew samples were extracted and derivatised t o the volatile 2,3,4,5,6-pentafluorobenzyl derivatives, followed by confirmation and quantification using gas chromatography with ion trap detection. The extraction recovery of 2,4-dichlorophenoxyethanoic acid and its dimethylamine salt from fortified tubes (air samples), distilled water (rain samples) and filter-paper (dew samples) was acceptable. The powerful selectivity of the gas chromatograph with ion trap detection allowed quantification of the herbicides irrespective of extraneous peaks present at the same retention time. In addition, automatic confirmation was accomplished without using a mass spectrometer. For 2,4-dichlorophenoxyethanoic acid, the method has a limit of detection of 0.72 ng m-3 in air, 8.39 ng 1-1 in rain water and 5.21 ng per 491 cm2 of exposed filter-paper (dew sample).