Annual Accomplishments Report on Southern Region Projects and Activities
• Project or Activity Designation and Number: S-280
• Project or Activity Title: Mineralogical Controls on Colloidal Dispersion and Solid-Phase Speciation of Soil Contaminants
• Period Covered: January 1 to December 31, 1999
• Annual Meeting Dates: June 9-11, 1999
• Participants:
J. Shaw (Alabama), W. G. Harris (Florida), P. M. Bertsch and J. C. Seaman (Georgia), R. L. Barnhisel and A. D. Karathanasis (Kentucky), W. L. Kingery (Mississippi), E. Young (Adm. Adv., NCSU), D. Hesterberg and W. P. Robarge (North Carolina), W. C. Lynn and M. Wilson (NRCS-USDA), B. J. Carter (Oklahoma), N. Cavallaro (Puerto Rico), B. R. Smith (South Carolina), M. Essington (Tennessee), J. B. Dixon and G. N. White (Texas), L. W. Zelazny (Virginia), H. Markewitz (USGS)
• Project or Activity Leadership:
Chair: D. Hesterberg (dean_hesterberg@ncsu.edu)
Chair-elect: J. C. Seaman (seaman@srel.edu)
Secretary: J. Shaw (jnshaw@acesag.auburn.edu)
• Brief summary of minutes of annual meeting:
A business meeting was held on the campus of Virginia Tech. The S-280 Administrative Advisor (Eric Young) summarized developments within USDA-CSREES, including FY 1999 and FY 2000 budgets and changes in the new Farm Bill. An action plan for publishing and publicizing the final publication from the previous (S-207) regional project was developed, and the publication of a mineralogy map for the southern US was discussed. The remainder of the meeting focused on the technical project with discussion of accomplishments and future action on each of the two project activities.
• Accomplishments and Impacts:
The S-280 Multistate project involves two research objectives:
1. To develop a predictive model for describing soil colloidal dispersion as a function of mineralogy and commonly measured soil properties. Data from a the previous regional project that produced a large number of soil-property measurements were evaluated for their utility in developing a more general predictive model. The number of soil samples analyzed (about 30) was limited for such a model applied to regional soils. Therefore, data for a larger number of soils available through the USDA-NRCS National Cooperative Soil Survey database were also evaluated by John Seaman, Warren Lynn, and Mark Walthall for their suitability in developing the model. These data more broadly represented soil properties for the southern United States. John Seaman has recruited a statistician to assist in developing a statistically-based model for this large soils database. The accuracy of the model will be evaluated on the original 30 soil samples. Such a model would be a powerful predictive tool to determine how susceptible a soil would be to dispersion (affects soil erosion and colloid mediated transport of soil contaminants) based on properties that are typically measured and available.
2. To determine the nature of contaminant-mineral associations in selected soils in relation to properties and processes and water-dispersible colloids. This objective involves fractionating the soil by different techniques (particle size, density, magnetic susceptibility) to concentrate certain mineralogical components within the various fractions. Dean Hesterberg submitted samples of a surface soil from a heavy-metal contaminated site in North Carolina to develop the project protocols and to determine how much soil is needed to obtain sufficient amounts of each fraction for further analyses. This initial sample was selected from samples taken at different soil depths because it contained a greater amount of water-dispersible clay (27 g WDC/kg soil), and hence a greater amount of particles that are potentially mobile in the soil. The WDC fraction was enriched in copper and lead relative to the whole soil, indicating that transport of these potentially-toxic metals may be enhanced by any mobile colloids in this soil. Zinc was depleted in the WDC fraction.
Samples of the surface soil were fractionated by Bill Smith and Joey Shaw using only sonic dispersion in deionized water (no chemical treatments so as to avoid changes in the speciation of the metals). Bill Smith also showed that the particle-size distribution obtained from the sample sonicated in water was consistent with the distribution obtained using a standard particle fractionation procedure with chemical dispersants, which indicates that our fractionation technique is sound. Concentrations of heavy metals in the different particle-size fractions of the soil sample typically decreased in the order: fine clay > silt > sand. For example, lead, copper, and zinc were all enriched 2-fold in the fine clay compared with the whole soil. This trend is consistent with higher surface areas (e.g., for metal adsorption) with decreasing particle size. The finer particles should be more easily transported through soil if mobilized (dispersed), so an enrichment of metals in this fraction indicates the possibility of an enhanced metal transport mechanism (colloid-mediated transport).
For the coming year, we plan to fractionate additional contaminated soil samples, and continue with mineralogical and chemical characterization of different fractions, including density separates and magnetic separates.
Publications: No publications
Submitted by: Dean Hesterberg, Associate Professor of Soil Science, NC State University
Date Submitted: September 12, 2000