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United States Department of Agriculture

Agricultural Research Service


item Hayes, Thomas
item Hayes, Michael
item Vaidyanathan, L V
item Clapp, Charles

Submitted to: Humic Substances and Organic Matter in Soil and Water Environments; Charact
Publication Type: Book / Chapter
Publication Acceptance Date: 7/21/1996
Publication Date: N/A
Citation: N/A

Interpretive Summary: The increasing application of pesticides in agriculture can cause concern for surface and ground water quality. A study was carried out to measure the effects of natural soil organic fractions on two herbicides or 'weed-killers,' atrazine and trifluralin, and on an insecticide, DDT. The main organic fractions called humic and fulvic acids are found in the drainage waters of most agricultural soils. It has been suggested that these naturally-occurring organic materials are responsible for carrying the pesticides into water supplies. This study looked at the effects of levels of both natural and applied chemicals, as well as water acidity and salt contents. No evidence was found to show that the natural organics brought more of the applied chemicals into solution, in the presence or absence of salts, at the low application levels. The results of this research give us information about the occurrence and movement of applied chemicals into the ground water of soil in intensely farmed areas of the country.

Technical Abstract: The concentrations in aqueous solutions of the xenobiotic substances, atrazine, DDT, and trifluralin in the presence of dissolved humic acid (HA), fulvic acid (FA), and XAD-4 acids, isolated from soil drainage waters, were studied. The concentrations of atrazine in solution were not increased or decreased by the presence in solution of HA, FA, or XAD-4 acids in concentrations ranging from 20 to 100mg L**-1, or by the pH of th environment (4 or 6), or by the presence or absence of salt. There was no evidence to indicate that the solubilities of DDT or of trifluralin were enhanced by the presence of the humic fractions, but evidence indicated that their concentrations in solution can be lowered by the presence of humic fractions. Background electrolyte was applied at concentrations characteristic of the soil solution. Our data show that the concentrations in solution of DDT and of trifluralin can be lowered in the presence of electrolyte concentration equivalent to 0.01M. This effect might be considered as 'salting out.' When DDT or trifluralin were bound to the sorbents, protection was provided against such 'salting out.' However, no convincing evidence was obtained to indicate that the humic substances were dissolved by water in the absence of the HS. This study highlights the need to investigate the ways in which salts in the soil solution will influence the concentrations in solution of anthropogenic chemicals with solubilities in water of less than 1 mg L**-1.

Last Modified: 06/26/2017
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