Terry J. Logan

Lead Immobilization from Aqueous Solutions and Contaminated Soils Using Phosphate Rocks

This research investigated the effectiveness of phosphate rocks in immobilizing Pb from aqueous solutions and contaminated soils. Different amounts of phosphate rocks were reacted with aqueous solutions containing Pb or with Pb-contaminated soils. The results show that phosphate rocks were effective in immobilizing Pb from aqueous solutions with a minimum Pb removal of 38.8-100%. The reaction time had less effect on Pb immobilization than the quantity of phosphate rocks used. Selected phosphate rocks reduced water-soluble Pb from a contaminated soil by 56.8-100%. The primary mechanism of Pb immobilization was via dissolution of phosphate rocks and precipitation of a fluoropyromorphite-like mineral. Different methods of mixing phosphate rocks and soil and incubation time had little effect on Pb immobilization. Our results strongly demonstrate that phosphate rocks may provide a cost-effective way to remediate Pb-contaminated water, soils, and wastes.

Effects of Aqueous Al, Cd, Cu, Fe(II), Ni, and Zn on Pb Immobilization by Hydroxyapatite

The effects of aqueous Al, Cd, Cu, Fe(II), Ni, or Zn on Pb immobilization by hydroxyapatite [Ca 10 (PO 4 ) 6 (OH) 2 ] were studied. Lead was removed mainly via hydroxyapatite dissolution and hydroxypyromorphite [Pb 10 (PO 4 ) 6 (OH) 2 ] precipitation in the presence of these metals with a Pb removal efficiency of 37-100%. These metals inhibited Pb immobilization by hydroxyapatite in the order. Al>Cu>Fe(II)>Cd>Zn>Ni and Cu>Fe(II)>Cd>Zn>Al>Ni at high and low initial Pb concentrations, respectively. The inhibition was probably through the precipitation of amorphous to poorly crystalline metal phosphates, decreasingthe amountofdissolved P available for precipitation with dissolved Pb ions

Experimental and theoretical vibrational spectroscopic evaluation of arsenate coordination in aqueous solutions, solids, and at mineral-water interfaces

Arsenate (AsO43−) is a common species in oxidizing aquatic systems and hydrothermal fluids, and its solubility and partitioning into different mineral phases are determined by the nature of AsO43− coordination, solution pH, type of soluble cations, and H2O structure at the mineral-fluid interfaces. While the vibrational spectroscopy has been widely used in examining the AsO43− coordination chemistry, insufficient knowledge on the correlation of AsO43− molecular structure and its vibrational spectra impeded the complete spectral interpretation. In this paper, we evaluated the vibrational spectroscopy of AsO43− in solutions, crystals, and sorbed on mineral surfaces using theoretical (semiempirical, for aqueous species) and experimental studies, with emphasis on the protonation, hydration, and metal complexation influence on the As-O symmetric stretching vibrations. Theoretical predictions are in excellent agreement with the experimental studies and helped in the evaluation of vibrational modes of several arsenate-complexes and in the interpretation of experimental spectra. These vibrational spectroscopic studies (IR, Raman) suggest that the symmetry of AsO43− polyhedron is strongly distorted, and its As-O vibrations are affected by protonation and the relative influence on AsO43− structure decreases in the order: H+ ≫ cation ≥ H2O. For all AsO43− complexes, the As-OX symmetric stretching (X = metal, H+, H2O; ≤820 cm−1) shifted to lower wavenumbers when compared to that of uncomplexed AsO43−. In addition, the As-OH symmetric stretching of protonated arsenates in aqueous solutions shift to higher energies with increasing protonation (<720, <770, <790 cm−1 for HAsO42−, H2AsO4−, and H3AsO40, respectively). The protonated arsenates in crystalline solids show the same trend with little variation in As-OH symmetric stretching vibrations. Since metal complexation of protonated AsO43− does not influence the As-OH vibrations significantly, deducing symmetry information from their vibrational spectra is difficult. However, for metal unprotonated-AsO43− complexes, the shifts in As-OM (M = metal) vibrations are influenced only by the nature of complexing cation and the type of coordination, and hence the AsO43− coordination environment can be interpreted directly from the splitting of As-O degenerate vibrations and relative shifts in the As-OM modes. This information is critical in evaluating the structure of AsO43− sorption complexes at the solid-water interfaces. The vibrational spectra of other tetrahedral oxoanions are expected to be along similar lines.

VIBRATIONAL SPECTROSCOPY OF FUNCTIONAL GROUP CHEMISTRY AND ARSENATE COORDINATION IN ETTRINGITE

The functional group chemistry and coordination of AsO43−-sorption complexes in ettringite [Ca6Al2(SO4)3(OH)12·26H2O] were evaluated as a function of sorption type (adsorption, coprecipitation) and pH using Raman and Fourier Transform infrared (FTIR) spectroscopies. The reactive functional groups of ettringite, ≡Al-OH, ≡Ca-OH2, and ≡Ca2-OH exhibit broad overlapping OH bands in the range 3600–3200 cm−1, prohibiting separation of component vibrational bands. The SO42− polyhedra of the channels are present in three crystallographically different sites and exhibit weakly split S-O asymmetric stretch at 1136 cm−1 (with several components) and symmetric stretch at 1016, 1008, and 989 cm−1. During AsO43− adsorption, the vibrational spectra of SO42− were least affected, and the OH stretching intensities around 3600 cm−1 decreased with an increase in AsO43− sorption. In contrast, the S-O symmetric stretch at 1016 and 1008 cm−1 were almost completely removed, and the OH vibrations were relatively unaffected during AsO43−-coprecipitation. The As-O asymmetric stretch of sorbed AsO43− are split and occur as overlapping peaks around 870 cm−1. The As-Ocomplexed stretching vibrations are at ∼800 cm−1. The low pH samples (pH = 10.3–11.0) exhibit distinct As-OH stretching vibrations at 748 cm−1, indicating that some of the sorbed AsO43− ions are protonated. These spectral features demonstrate that AsO43− directly interacts with ettringite surface sites during adsorption and substitute inside the channels during coprecipitation (preferentially for two of the three sites). The energy position of the As-O symmetric stretch vibrations suggest that the AsO43− polyhedra interacts predominantly with ≡Ca-OH2 and ≡Ca2-OH sites rather than with ≡Al-OH sites. Sorption of more than one type of As species was evident in low pH (<11.0) samples.

Effects of NO3-, Cl-, F-, SO42-, and CO32- on Pb2+ Immobilization by Hydroxyapatite.

Remediation of Pb-contaminated wastes has received considerable attention recently. We have previously shown that hydroxyapatite [Ca 5 (PO 4 ) 3 OH] can reduce Pb 2+ concentrations below the EPA action level (72.4 nmol L -1 ) and, thus, has the potential for in situ Pb 2+ immobilization against leaching. This research investigated the effects of NO 3 - , Cl - , F - , SO 4 2- , and CO 3 2- on hydroxyapatite-Pb 2+ interactions. Solutions containing initial Pb 2+ concentrations of 24.1-482 μmol L -1 were reduced to below 72.4 nmol L -1 after reaction with hydroxyapatite, except in the presence of high levels of CO 3 2- and Pb 2+

Agricultural best management practices for water pollution control: current issues

From the first awareness of agricultural sources of water pollution in the US in the 1960s, we finally see in the 1990s a commitment at the national level for agricultural non-point source (NPS) pollution control. This has been occasioned by a growing awareness that, with point sources of some pollutants largely controlled by waste-water treatment, greater attention must be paid to NPS pollution control, a large percentage of which is agricultural. The 1985 Farm Security Act mandated several national erosion control programs that will have some impact on water quality, and there is opportunity to supplement these programs with best management practices (BMPs) specifically designed to address agricultural water pollutants, primarily nitrate, phosphorus and modern pesticides. This paper discusses fundamental processes affecting transport of agricultural pollutants in surface and ground water and suggests how knowledge of these processes can be used to evaluate existing agricultural NPS BMPs and to develop supplemental practices.

Phosphate Characteristics and Bioavailability of Suspended Sediments from Streams Draining into Lake Erie

Abstract Suspended sediments from major U.S. tributaries draining into Lake Erie were analyzed for phosphorus. Analyses included: sediment concentration, reactive and total filtered P, and total P on water samples. Recovered sediment total P was determined by perchloric and persulfate extraction. Sediment was fractionated for NaOH-P citrate-dithionite-bicarbonate (CDB)-P, HCl-P, and organic P. New York streams had the highest suspended solids and the lowest content of most sediment fractions except HCl-P. NaOH-P and CDB-P were highest in sediments from Ohio tributaries; these fractions are considered to be bioavailable with NaOH-P more available than CDB-P. Digestion with perchloric acid consistently removed more P than the persulfate method. The difference in the two methods was negatively correlated with HCl-P.

Relative nitrogen mineralization and nitrification in soils of two contrasting hardwood forests: Effects of site microclimate and initial soil chemistry

Abstract This study determined the relative rates of soil nitrogen mineralization and nitrification in neighbouring mixed oak and mixed mesophytic forest stands on sandstone-derived soils in Neotoma Valley, south central Ohio, U.S.A. The soils of the northeast-facing mesophytic stand had higher pH, moisture, and extractable nutrient levels while those of the southwest-facing oak stand were deeper and had a higher C: N ratio. To evaluate the relative importance of initial soil chemical status and microclimate in controlling nitrogen transformation rates, the polyethylene buried-bag method was modified to include reciprocal transplants of bags between sites. Nitrogen mineralization was greater at the mesophytic site most of the year, though the rates were not different between sites during a very dry September. Total annual N mineralization per gram of soil and per m 2 of forest floor were 208 μg N g −1 dry soil and 5604 mg N m −2 , respectively. The comparable rates for the mixed oak site were 125 μg N g −1 and 2209 mg N m −2 . Approximately 67% of monthly mineralized N was nitrified at the mesophytic site while less than 10% was nitrified at the mixed oak site. Differences in both mineralization and net nitrification rates between sites correlated positively with ammonium pool size and moisture, and negatively with nitrate pool size, while percent nitrification was positively correlated with pH and negatively with C: N ratio. In contrast, seasonal patterns of N transformation within a site were strongly correlated with soil temperature and moisture, and relatively unaffected by soil chemical factors. The rate of N mineralization and relative nitrification in transplanted bags did not differ from those of bags incubated at their native site. Thus, within this watershed, spatial variations in nitrogen dynamics were more closely related to differences in soil chemistry than to microclimate, while seasonal patterns showed just the reverse.

Diffuse (Non-Point) Source Loading of Chemicals to Lake Erie

Abstract Studies of chemical loadings to Lake Erie over the last two decades show that the lake, because of its small volume to drainage area ratio, and the intensive agricultural, industrial, and urban land uses of its watersheds, has been a receptor of a myriad of natural and anthropogenic chemicals. Of these, phosphorus, trace metals, PCBs and other organics and pesticides have received the most attention. Phosphorus reduction plans already in place have produced dramatic decreases in point-source P loadings and observable improvements in lake water quality. Target P loads for complete lake restoration will not be met, however, until substantial reductions of agricultural non-point sources are obtained, and gains in this area are likely to be much slower and more difficult to attain. Source reductions of trace metals and the older chlorinated insecticides have produced some decreases in diffuse loadings of these chemicals although their biomagnification in lake biota means that their impact on the lake will continue for many years. Today, the emphasis has shifted to a broader range of anthropogenic organic chemicals including highly mobile herbicides which have been shown to contaminate Lake Erie basin drinking water supplies, and to easily biomagnified toxics which, with relatively small loadings, can have a major impact on higher species.

Humid tropical leguminous tree and pasture grass responsiveness to vesicular-arbuscular mycorrhizal infection

Phosphorus is the major nutrient limiting plant growth in a Costa Rican silvopastoral system located on an acid, high P-retaining, volcanic soil. We investigated plant responsiveness to vesicular-arbuscular mycorrhizal (VAM) inoculation using the leguminous tree species Erythrina berteroana Urban, and the two dominant grass species Paspalum conjugatum Berg and Homolepsis aturensis Chase of this silvopastoral system. We grew grass seedlings in the greenhouse for 15 weeks in a methyl bromide-sterilized study soil to which either mixed-species VAM inoculum (Theobroma cacao feeder roots) or autoclave-sterilized cacao roots (non-inoculated control) were added. E. berteroana was grown from both seedlings and vegetative stakes (40 cm long) for 30 and 19 weeks, respectively. Upon harvest, we measured above and below ground biomass, N and P content, root∶shoot ratio, legume nodulation, and VAM infection levels. The total above-ground and root biomass of mycorrhizae-inoculated P. conjugatum seedlings were 2.5 and 2.8 times greater than those of noninoculated seedlings. In contrast, VAM-inoculated seedlings of H. aturensis produced 8.4 and 5.9 times more total above-ground and root mass than noninoculated seedlings. Mycorrhizae-inoculated E. berteroana seedlings produced 10.6 times greater shoot biomass for inoculated versus noninoculated seedlings, while E. berteroana vegetative stakes exhibited a negative growth response to VAM inoculation (an approximately 16% decrease in shoot biomass for VAM-inoculated cuttings). The difference in responsiveness between Erythrina growth forms is hypothesized to reflect the cost-benefit relationship between plant host and fungal symbiont for energy and nutrient reserves.