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Project ID: 2002WA1B

Title: Facilitated Transport of Pesticides by Organic Colloids

Project Type: Research

Focus Categories: Non Point Pollution, Solute Transport, Groundwater

Keywords: Groundwater Quality, Solute Transport, Colloids, Pesticides

Start Date: 03/01/2002

End Date: 02/28/2003

Federal Funds: $15,000

Non-Federal Matching Funds: $31,247

Congressional District: Washington Fifth

Principal Investigators:
Markus Flury
Washington State University

Claudio Stockle
Washington State University

Richelle Allen-King
Washington State University


Pesticide contamination of groundwater resources is of major concern in many areas of the United States, and in particular in the Palouse and Columbia Basin of Washington State. Pesticides have been found to move faster than anticipated through soil profiles. For example, our lab has recently documented movement of a hydrophobic pesticide to > 1 m depth in Palouse soil during the first few months following pesticide application. We hypothesize that one important reason for this accelerated movement is facilitated transport via carbonaceous (non-carbonate, carbon-containing) colloidal particles, such as humic acids and combustion/pyrolysis residues. While previous research has shown that dissolved organic matter can enhance the transport of pesticides, it is not clear which fractions of carbonaceous colloids are mainly responsible for colloid-facilitated transport. The objective of the proposed research is to elucidate the role of carbonaceous colloids in facilitated transport of pesticides through porous media, with special emphasis given to the physical and chemical properties of the colloidal material. Specifically, we address the following objectives: (1) Fractionate and characterize carbonaceous colloids in terms of composition and colloidal properties. (2) Elucidate the mechanisms of mobilization and transport of carbonaceous colloids as affected by the physical and chemical characteristics of the colloids. (3) Study sorption of a model pesticide (atrazine) to carbonaceous colloids that vary in structure and composition. (4) Investigate the transport of atrazine as facilitated by the various well-characterized carbonaceous colloids. (5) Develop a conceptual model for colloid-facilitated pesticide transport with data from well-controlled experiments.

The study is of experimental nature and consists of laboratory batch and column experiments. First, carbonaceous colloids (standard humic acids, powdered charcoal, and native soil-extracted) will be size-fractionated and characterized. Individual size fractions will then be analyzed in terms of their transport behavior in saturated column systems under different solution compositions. Sorption isotherms of atrazine to the colloids will be constructed from batch experiments. Colloid-facilitated transport of atrazine will be investigated in column experiments. The results of this project provide a better fundamental understanding of an important aspect of pesticide transport through the subsurface. We will provide, on a mechanistic level, information on when colloid-facilitated transport of pesticides can occur and which fractions of carbonaceous materials are mainly responsible for it. This knowledge will help to assess vulnerability of certain areas for pesticide leaching as well as to improve management strategies to minimize groundwater pollution.

Progress/Completion Report PDF

U.S. Department of the Interior, U.S. Geological Survey
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