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Selenium (Se) is a potential soil contaminant in many parts of the world where it can pose a health risk to livestock and wildlife. Phosphate ore mining in Southeast Idaho has resulted in numerous waste rock dumps revegetated with forages to stabilize the dumps and support grazing. Alfalfa (Medicago sativa L.), smooth brome (Bromus inermis Leyss.), and western wheat grass [Pascopyrum smithii (Rydb.) A. Love] are the dominant forage species on these lands. To demonstrate the feasibility of using sulfur (S) as a soil amendment to restrict plant Se uptake, 3 kg pots containing 50:50 w/w soil and waste shale were uniformly mixed with 0, 0.5, 1.0, or 2.0 Mg ha(-1) S as either elemental S or gypsum. Pots were seeded with alfalfa or western wheat grass. Dry mass and tissue Se were monitored over several clippings. Soils were sampled at the conclusion of the study and analyzed for water-soluble, oxalate-extractable, and total Se. Sulfur amendments as either elemental S or gypsum at 1.0 Mg ha(-1) or greater equally suppressed Se uptake over 60% in both forage species. Alfalfa accumulated more Se than western wheat grass. Plant removal via successive clippings resulted in lower tissue Se accumulation over time than the use of S soil amendments alone. Alfalfa-planted soils contained lower water-soluble and oxalate-extractable Se than did the non-planted controls while western wheat grass-planted soils contained lower water-soluble Se. Applying S to these shale-based soils may be an economically viable option for treating Se-impacted, revegetated lands.

A nonlinear multireaction model was used to describe kinetic data for HgCl₂ retention by five soils. A three-parameter version of the model consisting of a reversible nonlinear (nth order, n < 1) reaction and an irreversible first-order reaction was capable of describing HgCl₂ retention data for Cecil (clayey, kaolinitic, thermic Typic Kanhapludult) and Windsor (mixed, mesic Typic Udipsamment) soils at all initial solution Hg concentrations, and data for Norwood, [fine-silty, mixed (calcareous), thermic, Typic Udifluvent], Olivier (fine-silty, mixed, thermic Aquic Fragiudalt), and Sharkey (very-fine, montmorillonitic, nonacid, thermic Vertic Haplaquept) soils at initial solution Hg concentrations below 5 mg/L. A five-parameter version of the model, with an added reversible nonlinear reaction, provided a more accurate description of the retention data for the Norwood, Olivier, and Sharkey soils at initial solution Hg concentrations above 5 mg/L. The second reaction needed to describe the data at higher Hg concentrations suggests the presence of a second type of sorption sites, or a precipitation or coprecipitation reaction not encountered at lower Hg concentrations. Release of Hg from the soils was induced by serial dilution of the soil solution, but not all the soil Hg was reversibly retained. This was also indicated by the model. Release of soil Hg depended on the concentration of retained Hg with significant Hg release occurring only at high concentrations of retained Hg. A multireaction model is needed to describe Hg retention in soils because of the many solid phases that can remove Hg from solution. Joint contribution from the USDA Forest Serv. Intermountain Res. Stn.; Hatch Project 2469, Louisiana Agric. Exp. Stn. as Manuscript no. 89-09-3338; and U.S. Army CRREL.

As part of a series of geoenvironmental studies on the mobilization and fate of selenium (Se) and other potentially toxic trace elements in southeast Idaho phosphate mining areas, trace element concentrations (mg kg 1 dry mass) in plant samples collected along transects at the Wooley Valley Unit 1,3, and 4 waste-rock dumps were compared with samples collected from undisturbed sites at Dairy Syncline, Deer Creek, Dry Valley, Maybe Canyon, and Rasmussen Ridge. Additionally, trace-element concentrations in veg- etation samples collected from wetlands associated with mine waste-rock piles were compared with samples collected from a single reference wetland. In undisturbed areas, Se in vegetation growing in soils overlying and derived from Phosphoria Formation phosphatic rocks tended to be higher than vegetation in undisturbed Wells Limestone or Rex Chert soils. Vegetation growing in highly disturbed soils, such as those comprising waste-rock dumps, had the highest tissue Se. Vegetation in a wetland at the base of Wooley Valley Unit 4 waste-rock dump accumulated decreasing concentrations of Se with increasing distance away from the waste-rock dump along the wetland flow path. Iron oxides were observed coating wetland sediment surfaces and helped control Se bioavailability. Plant uptake, as well as coprecipitation and sorption of Se by iron oxides, were key processes in the natural attenuation of Se in this wetland. Legumes at the rock dumps contained higher Se (mean = 80 mg kg -1 ) than trees (mean = 52 mgkg 1 ), grasses (mean = 18 mgkg 1 ), shrubs (mean = 6 mgkg 1 ), and forbs (mean = 3 mg kg -1 ). However, grasses were among the highest Se accumulators among plant lifeforms in contaminated wetlands, with a mean value of 53 mg kg 1 Se. In most places, uptake of Cd, Cr, Cu, Mn, Mo, Ni, and Zn was below critical high levels for plants. However, Se, Cd, Cr, and Zn uptake by some plants may have been large enough to affect their growth. Several plant lifeforms had Se concentrations that surpassed the acute and chronic toxicity thresholds for grazing livestock and wildlife, posing a lethal risk to these animals. Forages, particularly legumes, sampled from waste-rock dumps had increased Mo concentrations, resulting in Cu/Mo ratios below 1. High Mo (above 10 mg kg 1 ) and Cu/Mo ratios below 2 may cause molybdenosis in ruminants. There were instances where tree Zn content exceeded upper chronic intake for livestock/wildlife. This may pose some concern for browsing animals feeding upon trees, particularly in winter months. Based on the vegetation survey, possible remediation strategies via physical, chemical, and biologi- cal manipulations of the contaminated sites include removal of the most contaminated soils, capping contaminated soils and revegetating capping materials, application of selec- tive herbicides to remove legumes from reclaimed waste-rock dumps, and fencing some contaminated areas to better manage grazing.

Several kinetic models, including irreversible and reversible 1st, 2nd, and nth order models, and several equilibrium models, including the linear, Langmuir, two-surface Langmuir, and Freundlich models, were evaluated for their ability to describe the retention/release of Cr, Cd, and Hg by various soils. The retention/release data were obtained using a batch reaction method. In general, no single-reaction kinetic model fit the data over the entire time and concentration ranges studied for any of the metals or soils. The relationship between the amount of metal retained by the soil and the concentration of metal in solution was described by either the two-surface Langmuir or Freundlich models. A significiant fraction of the metals retained by the soil was not released to solution and was not exchangeable, indicating that some irreversible retention of the metals occurred. The results suggest that a multi-reaction model consisting of irreversible and reversible kinetic models is needed to fit all the data.

The objective of this presentation is to relate the abundance and mobility of Cd in components of terrestrial ecosystems with implications for land utilization of sewage sludge. The uptake of Cd by crop plants is a function of the quantity of the element in the soil plus other soil factors affecting the Cd ion activity or electrochemical potential at the plant root surface. The natural abundance of Cd in soils has been reported as 0.5 mug/g which is higher than the background level of 0.2 mug/g found in soils studied in Pennsylvania. Experimental results indicate that the plant availability of Cd increases with each soil addition. While the plant availability of Cd is decreased by liming to increase soil pH, it has not been possible to add Cd salts or sewage sludge Cd without significantly increasing plant uptake. Field studies have shown that land application of sewage sludge can be expected to increase the Cd concentration of corn leaves from a range of 0.05-0.1 mug/g to 1-3 mug/g. Two years after the last application of sludge which added up to 10 ppm Cd to the surface soil, corn grain, sorghum grain, wheat grain, and potatoes showed a 10- to 15-fold increase in Cd over background levels. Studies were conducted with chicks, laying hens, and meadow voles (Microtus Pennsylvanias) to assess the impact of this increase in plant Cd upon the food chain. Corn and sorghum plants were grown on soils with either inorganic or sludge fertilizer for the purpose of producing herbage for use in feeding trials with meadow voles. Eight diets and a synthetic control diet were formulated to study the effect of source (plant vs. inorganic) of Cd on tissue accumulation. Significant accumulation of Cd occurred in kidney and liver, but not muscle, of voles fed diets containing sludge fertilized corn (1.09 mug/g) or sludge fertilized sorghum (2.76 mug/g). The source of Cd had little influence on tissue accumulation. In studies with broiler chicks and laying hens, natural diets containing 0.2 ppm Cd were supplemented with 3 ppm of this element. As with the meadow voles, Cd readily accumulated in liver and kidney. Although the results were not statistically significant, 3 ppm dietary Cd doubled muscle Cd content. There was no transfer of Cd to egg in a long term (12 month) experiment with laying hens. Soil management programs have been developed to maintain animal dietary levels of Cd at less than 1.0 mug/g from the use of sewage sludge on land in Pennsylvania. However, it is concluded that this level over time may cause a significant accumulation of Cd in animal tissues. Interpretation of these results in relation to those for human intake of Cd and the long range health effects of Cd is required for the proper monitoring of sewage sludge applications on land used for production of crops which enter the food chain.

Dichromate‐oxidizable and total organic carbon in soils from the major mineral soil areas in Louisiana were measured. The objective was to determine if it is possible to use one correction factor for calculating total from dichromate‐oxidizable carbon for all mineral soil areas in the state or if separate correction factors are needed for each soil area. The recovery of total organic carbon from 179 soil samples from all mineral soil areas using the dichromate oxidation with no external heating (Walkley‐Black) method ranged from 46 to 87 % with a mean of 71 % and a c.v. of 9.8%. An average correction factor of 1.41 for calculating total from dichromate‐oxidizable organic carbon can be used for all mineral soil areas in Louisiana. However, this correction factor will be inaccurate for many individual soils. Although small but significant differences among the recoveries of total organic carbon from some of the different soil areas were observed, the differences are not large enough to warrant usin...

We present a second-order kinetic approach for the description of solute retention during transport in soils. The basis for this approach is that it accounts for the sites on the soil matrix which are accessible for retention of the reactive solutes in solution. This approach was incorporated with the fully kinetic two-site model where the difference between the characteristics of the two types of sites is based on the rate of kinetic retention reactions. We also assume that the retention mechanisms are site-specific, e.g., the sorbed phase on type 1 sites may be characteristically different in their energy of reaction and/or the solute species from that on type 2 sites. The second-order two-site (SOTS) model was capable of describing the kinetic retention behavior of Cr(VI) batch data for Olivier, Windsor, and Cecil soils. Using independently measured parameters, the SOTS model was successful in predicting experimental Cr breakthrough curves (BTC's). The proposed second-order approach was also extended to the diffusion controlled mobile-immobile or two-region (SOMIM) model. The use of estimated parameters (e.g., the mobile water fraction and mass transfer coefficients) for the SOMIM model did not provide improved predictions of Cr BTC's in comparison to the SOTS model. The failure of the mobile-immobile model was attributed to the lack of nonequilibrium conditions for the two regions in these soils.

Although particulate movement through wind and water erosion is the most important mechanism of dispersion of Pu at the Nevada Test Site, dispersion of water-soluble species may also be occurring. However, because Pu is toxic, usually insoluble, not uniformly distributed in the soil, and can exist in four oxidation states in the environment, it is very difficult to study. Therefore, Cr reactions in soil were investigated as a possible general model for Pu reactions in soil, since it was postulated that the redox chemistries of the two elements should be similar. Chemical fractionation methods were used to determine the redox states of Pu in a Nevada Test Site soil and the amounts of Pu associated with various soil components in order to deduce possible reactions between the various Pu species and soil components so that weathering and dispersion by chemical mechanisms can be predicted. Chemical fractionation and kinetics experiments were performed to study reactions of Cr with soil, manganese oxides, and fulvic acids in order to provide information to eventually develop a qualitative, predictive model for Pu behavior in soil.