Analysis of crops and soils for residues of 2,6=dichlorobenzonitrile (dichlobenil) and 2,6=dichlorothiobenzamide (chlorthiamid). II.—Results

Abstract

Crops and soils from a large number of field trials have been analysed for residues of 2,6dichlorothiobenzamide (chlorthiamid) and for residues of 2,6‐dichlorobenzonitrile (dichlobenil). The thiobenzamide is converted to the benzonitrile after application to the soil and only a small percentage of the material applied initially remains unchanged after 4 weeks. However, both the benzonitrile and the thiobenzamide are of similar low mammalian toxicity. The initial half‐life of the ‘total nitrile’ residues (the thiobenzarnide + the benzonitrile) is, on average, near 4 weeks but varies from 1 to 12 weeks depending on the locality, soil type, climate, dosage level and formulation. The penetration of the herbicide into soils of different types is considered and it is shown that in sand, loam, and clay, residues in the 4–12 in. layer are less than 10% of the residue at the same time in the 0–4 in. layer. Residues of the thiobenzamide and the benzonitrile could not be detected in a very wide range of crops (other than rice) harvested at 2–6 months after soil applications of the thiobenzamide at 1–16 lb/acre. In rice grains, where the plants can be in intimate contact with the herbicide, the ‘total nitrile’ residues did not exceed 0·05 ppm.

Herbicide Residue Determinations and Taint Tests on Fruit From Gooseberries Treated With Chlorthiamid and Dichlobenil

“…Beynon & Wright (1968b) showed that the fruit of apple trees grown in the glasshouse, in soil treated with 1 -68 kg/ha of ^^C-chlorthiamid had no detectable residues (<0-004 ppm) although total ^'C residues in the leaves were equivalent to 2-4 ppm of parent chlorthiamid. Beynon, Davies & Elgar (1966) found less than 0-02 ppm total nitrile residue in fruit from gooseberries treated with 2-24 kg/ha. The work reported here was undertaken to ascertain whether high application rates of chlorthiamid or dichlobenil give rise to appreciable residues of 2,6-dichlorobenzonitrile and its metabolites in the fruit.…”

Metabolism of Dichlobenil in Sandy Soil

“…Dichlobenil and 2,6-dichlorobenzamide were found as the main breakdown products, together with traces of two unidentified conversion products, component A (probably identical with our metabolite 2) and compound C, which could be the same as our metabolite 4. It has been shown that chlorthiamid decomposes in the soil to form dichlobenil (Beynon, Davies & Elgar, 1966). In sterilized and unsterilized Boekesteyn soil treated with 1-10 ppm chlorthiamid, this catalytic conversion goes very fast (50% converted in 3 days; Verloop & Nimmo, unpublished results), so that the analogous results are quite understandable.…”

The effect of herbicide dichlobenil to some Streptomyces

“…The toxicity of chlorthiamid to the tested Srreptomyces strains is possibly caused by the transformation of chlorthiamid to dichlobenil (Beynon et al, 1966a).…”