Fate of sodium 2,4-Dichloro-phenoxy-ethyl-sulphate in the Soil

Abstract

THE possibility that phytotoxicity generated when sodium 2,4-dichloro-phenoxy-ethyl-sulphate is perfused through soil might be due to hydrolysis to a toxic 2,4-dichloro-phenoxy-ethanol has been seriously considered; but I have so far been unable to obtain any evidence that this compound accumulates in the perfusate. The toxicity seems to be due entirely to 2,4-D. Four independent reasons for this conclusion are given in the original paper¹. The most convincing evidence comes from assays using paper chromatography to separate the toxic compounds in any possible mixture². Only one compound has, as yet, been found in this very sensitive assay, which will detect 10^-4 γ equivalents of 2,4-D, and this has an R_F value (0.7) identical with that of 2,4-D. A graph showing toxicity changes due to this compound in the perfusate is reproduced herewith. It is extremely unlikely that the ethanol has the same R_F value (solvent: butanol–ammonia) as the 2,4-D, but it has not been possible as yet to check this experimentally. The most rational explanation of the results to date is that the hydrolysis of sulphate to ethanol is the limiting reaction in the soil and that the shape of the toxicity–time curve is a direct reflexion of the activity of the hydrolysing organism. The further conversion to acid, probably by a different organism, takes place so rapidly that the ethanol intermediate can never accumulate in amounts detectable even by the sensitive assay employed.