Movement of Herbicides through Soil to Soybean Roots
1973
Don Scott, H. | Phillips, Ronald E.
Absorption of pesticides is one of the primary means by which pesticide residues enter the food chains of humans, domestic animals, and wildlife. Thus, a comparison was made between the theoretical and observed uptake of isopropyl m-chlorocarbanilate (chlorpropham) and 2-chloro-4-(ethylamino)-6- (isopropylamino)-s-triazine (atrazine) from soil by soybean roots (Giycine max (L.)). The rate of absorption of both ¹⁴C-herbicides as determined by liquid scintillation techniques was rapid initially and decreased as plant growth increased. These rate curves were approximately parallel throughout the growth range with the rate of absorption of atrazine being always greater than that of chlorpropham. The theoretical movement of the two herbicides to the root surface was calculated assuming certain boundary conditions for the system. Assuming the roots to be “perfect sinks,” the diffusion process accounted for the total quantity of herbicide absorbed except during the early hours following germination. As root growth increased, the roots became less of a sink for these two herbicides, and diffusion to a “perfect sink” could theoretically supply more than the amount absorbed. Assuming the rate of uptake to be proportional to the concentration at the root surface, a curvilinear rate constant was observed during the uptake period. The data indicated that the plant controlled the amount of herbicide accumulated as well as its principal transport mechanism to the root, probably through its influence on the permeability of the root or root saturation.
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