Alan W. Elzerman

Desorption kinetics for selected PCB congeners from river sediments

Abstract Desorption of PCBs from sediment can significantly affect the ultimate fate and effects of PCBs in aquatic systems. Using a gas purging technique to strip soluble and sorbed polychlorinated biphenyls (PCBs) from solutions and sediment suspensions, Henrys law constants, approach to equilibrium, and desorption rate constants for four PCB congeners were measured. Henrys law constants were on the order of 10 −4 m 3 atm mole −1 . Desorption rate constants measured for a predominantly kaolinitic, low-organic carbon sediment were on the order of 0.03–0.1 days −1 . In contrast, desorption rate constants measured for a sediment composed of montmorillonite with a 3% organic carbon content were on the order of 0.009–0.04 days −1 . Desorption data suggest that equilibration times for PCBs with low chlorine content are on the order of six weeks, and months to years for PCBs with a significantly higher chlorine content.

Aqueous solubility and Henry's law constant data for PCB congeners for evaluation of quantitative structure-property relationships (QSPRs)

Abstract Aqueous solubilities and Henrys Law Constants (HLCs) were measured for selected PCB congeners for evaluation of quantitative structure-property relationships (QSPRs) relating chlorine substitution pattern to the chemical parameter. Experimental results were consistent with previously published values. Aqueous solubilities (as solids at 25°C, column generation technique) determined for 26 congeners ranged from 1.08×10 −5 to 9.69×10 −10 mol/L and generally decreased with molecular weight. Values converted to subcooled liquids are also reported. HLCs (25°C, gas purge technique) determined for 20 congeners ranged from 0.3×10 −4 to 8.97×10 −4 atm·m 3 /mol. Measured HLCs were not correlated with molecular weight, but increased with degree of orthochlorine substitution within a molecular weight class. Vapor pressures calculated from the product of solubility (mol/m 3 ) and HLC (atm·m 3 /mol) data, generally decreased with molecular weight and increased with increasing degree of ortho- chlorine substitution. Currently available QSPRs were found to be ineffective for predicting solubilities, HLCs and vapor pressures when compared to experimentally determined results. An empirical data fitting approach based on coefficients related to chlorine substitution patterns appears promising.

Nickel Adsorption to Hydrous Ferric Oxide in the Presence of EDTA: Effects of Component Addition Sequence.

Nickel, EDTA, and hydrous ferric oxide were combined in different sequences to study the effect on equilibration. In this system, the fraction of nickel adsorbed to the hydrous ferric oxide depended on the component addition sequence, but the fraction of EDTA adsorbed did not. In one sequence, nickel and EDTA were combined to preform a NiEDTA[sup 2[minus]] complex. The complex had adsorption characteristics similar to EDTA with high adsorption at pH 7. Equilibrium adsorption of the complex could be modeled using the diffuse layer model. When nickel or EDTA was individually equilibrated with HFO prior to the addition of EDTA or nickel, respectively, the system did not attain equilibrium. Rapid EDTA adsorption at pH 7, nickel adsorption was faster than the formation of the NiEDTA[sup 2[minus]] complex, but once adsorbed, nickel was slowly desorbed through the formation of solution NiEDTA[sup 2[minus]]. 40 refs., 6 figs., 2 tabs.

Nuclide migration and the environmental radiochemistry of Florida phosphogypsum

Phosphogypsum, a waste by-product derived from the wet process production of phosphoric acid, represents one of the most serious problems facing the phosphate industry in Florida today. This by-product gypsum precipitates during the reaction of sulfuric acid with phosphate rock and is stored at a rate of about 40 million tons per year on several stacks in central and northern Florida. The main problem associated with this material concerns the relatively high levels of natural uranium-series radionuclides and other impurities which could have an impact on the environment and prevent its commercial use. We have studied the potential release of radionuclides from phosphogypsum by: (i) analysis of stack fluids, groundwaters, and soils associated with gypsum stacks; and (ii) geochemical modeling. Stack fluids were observed to be very high in dissolved uranium and 210Pb with only moderate concentrations of 226Ra. Underlying soils tend to be enriched in U and 210Pb indicating precipitation when acidic stack fluids enter a buffered environment. Modeling results showed significant increases in radionuclide complexes with sulfate and phosphate, resulting in relatively mobile uncharged or negatively charged solution species within the stacks with likely precipitation of multicomponent solids with increasing pH below the stack. Our evidence thus suggests that, while phosphogypsum stacks do contain significant quantities of dissolved radionuclides, removal mechanisms appear to prevent large-scale migration of radionuclides to the underlying aquifer.

Facilitated transport of selected metals in aquifer material packed columns

Abstract Several factors may enhance the mobility of metals in an aquifer. Metals in such systems may associate with inorganic or organic ligands that affect retardation or with mobile colloids which may provide a faster transport mechanism. Complexation and/or sorption of a fraction of the metal may result in mobility in excess of that predicted using a single equilibrium based distribution coefficient which was derived from a more simple system. Failure to predict enhanced contaminant mobility may result in false predictions of arrival times and concentrations, and underestimation of human exposure to a contaminant. In this paper the results of a series of laboratory column studies designed to investigate factors influencing enhanced mobility of metals (Cd, Cu, Cr and Pb) in an aquifer are presented. The first of two peaks in effluent metal concentration resulting from a pulse input of metal waste to an aquifer material packed column was observed to coincide with a peak in effluent turbidity. SEM/EDX analysis showed metals to be sorbed to the surface of the turbidity causing colloids. These observations indicated association with mobile colloids may facilitate the transport of metals through soil packed columns. The mobilization and/or transport of colloids was apparently influenced by alterations in eluent chemistry, such as pH and ionic strength. The results also indicated complexation can enhance Pb mobility. Greater sensitivity of mobility to alterations in groundwater chemistry was observed for Pb and Cr than for Cd and Cu.

The influence of pH on the binding capacity and conditional stability constants of aluminum and naturally-occurring organic matter☆

Abstract The binding of Al by Aldrich® humic acid and a natural water system of the southeastern U.S.A. was investigated with special emphasis on the influence of pH. Differentiation of “bound” Al and “free” Al was performed using cation-exchange resins. A thermodynamic equilibrium model, GEOCHEM, was used to correct the “bound” Al data for uncharged hydrolysis products. Two methods of data analysis, i.e. Scatchard and Langmuir regressions, were used to estimate conditional stability constants of Al—humic acid complexes. Overall stability constants (log 10 K ) for aluminum humate were ∼ 6.8 with little variation over the pH range 3–5. Al binding capacities were higher in natural waters (0.99–2.86 μmol Al per mg DOC) relative to Aldrich® humic acids (0.33–0.86 μmol Al per mg DOC). Both the natural waters and humic acid samples showed significant increases in Al binding capacity when pH was increased from 3 to 4 (0.99–1.84 μmol Al per mg DOC and 0.33–0.79 μmol Al per mg DOC, respectively). The humic acid showed a much smaller increase in binding capacity when the pH was increased from 4 to 5 (0.79–0.86 μmol Al per mg DOC). Arguments are presented to show that Al is bound to humic acid through a single type of binding site, most probably a carboxylic functionality.

Characterization of the mobilities of selected actinides and fission/activation products in laboratory columns containing subsurface material from the Snake River Plain

Abstract Laboratory column tests were performed to characterize the mobilities of 60Co, 90Sr, 137Cs, 233U, 239Pu, and 241Am in a basalt sample and a composite of sedimentary interbed from the Snake River Plain at the Idaho National Engineering and Environmental Laboratory. The radionuclides were spiked into a synthetic groundwater (pH 8, ionic strength = 0.004 M) and introduced into the columns (D = 2.6 cm, L = 15.2 cm) as finite steps with a width of 1 pore volume followed by unspiked synthetic groundwater. The effluent concentrations were measured continuously for up to 200 pore volumes. Hydrogen-3 was used as a nonreactive tracer in all of the experiments to monitor for channeling. In the basalt sample, the behavior of 90Sr, 137Cs, and 233U was quite different from that of 60Co, 239Pu, and 241Am. The column effluent curves for the former were characterized by single peaks containing, within the limits of experimental uncertainty, all of the activity in the spike. The mobilities were ordered as follows: 233U ([overbar]R = 5.6) > 90Sr ([overbar]R = 29) > 137Cs ([overbar]R = 79). The curves for the other radionuclides were characterized by two or three fractions, each having a distinctly different mobility. Cobalt-60 had high- ([overbar]R = < 3), intermediate- ([overbar]R = 34), and low- (R > 200) mobility fractions. Although a majority of the 239Pu and 241Am had low mobility (R > 200), there were high-mobility (R < 3) fractions of each (17 to 29% for 239Pu and 7 to 12% for 241Am). In sedimentary interbed, mobilities were generally much lower than in basalt. Uranium-233 was the only radionuclide with 100% recovery within 200 displaced pore volumes, and it had a retardation factor of 30. However, high-mobility fractions were observed for 60Co (1 to 4%) and 239Pu (1.1 to 2.4%). These results could have important implications with respect to transport modeling. If the multiple-mobility fractions observed here are also present in the field, transport predictions based on classical modeling approaches that incorporate mobilities from batch sorption experiments are likely to be in error.

Acidification of southern Appalachian lakes.

Measurements of the dissolved (<0.4 ..mu..m) major element water chemistry of 10 lakes and reservoirs situated in the southern Appalachian Mountain and Carolina Piedmont regions are used to examine effects of acidic atmospheric deposition inputs on water chemistry. In the mountain region, lakes with low alkalinity and small watershed/lake area ratio appear to be most susceptible to, and may be undergoing, pH reduction. In the Piedmont region, watershed soils, especially those exposed by mans activities, appear to be effectively neutralizing acid inputs. Weathering of rocks and soils accelerated beyond that expected from carbonic acid alone is probably occurring in the mountain and Piedmont systems. Our analysis suggests that reduction of lake water pH, mobilization of soil chemical constituents, and subsequent changes in the chemical composition of aquatic systems may be a more widespread and potentially serious environmental problem in this area than previous analyses have suggested.

Gas-Liquid Chromatographic Determination of Some Chloro- and Nitrophenols ny Direct Acetylation in Aqueous Solution

Abstract A gas chromatographic method for the determination of trace amounts of some chloro- and nitrophenols is reported. Direct acetylation of chloro- and nitrophenols is carried out by adding acetic anhydride to large volumes of an alkaline aqueous solution of phenols. The stable acetate esters formed improve chromatographic characteristics and also provide for near quantitative extraction using small volumes of methylene chloride. Relative retention times of nine acetates of phenols on 1% SP-1240 A are reported and seven derivatives have been separated. The increased extraction efficiency, short extraction time and small volume of organic solvent used are some of the attractive features of this method in comparison to currently used methods.

Methods for the determination of PAH desorption kinetics in coal fines and coal contaminated sediments

Abstract Conventional batch, modified batch, conventional column, and time-resolved leaching techniques were examined utilizing various miscible organic solvent/water mixtures to determine the desorption kinetics of selected PAHs in coal fines and coal contaminated sediments.