Radiotracer study of the fate of herbicides and herbicide metabolites in the soil-plant system

When (14C-ureido) or (14C-methyl) monolinuron was added to different soils at 1 ppm, 40-50% of the radioactivity was recovered as CO2 in 16 weeks, whereas only 25% was recovered from the ring-labelled herbicide. Not more than 10% of the 14C was recovered as CO2 from atrazine or chloroanilines. Upon a repeated application of 14C-labelled 4-chloroaniline, 16% of the radioactivity was recovered as CO2. Uptake of the herbicide residues by crop plants revealed dependence on the soil absorptive capacity. The accumulation of monolinuron was greater in shoots than in roots, whereas 4- and 3,4-dichloroaniline accumulated more in the roots. The holocellulose fraction contained about 80% of radioactivity in 4-chloroaniline-treated tomato leaves and roots. The leaves and roots mixed with soil releases 6 and 4% respectively of the bound radioactivity as carbon dioxide in 16 weeks. (author)