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At least 307 records · Page 17Linked to original sources
USGS2002

Sorption of chlorobenzenes to cape cod aquifer sediments

Sorption of tetra- and pentachlorobenzene by sediment from a glacial outwash aquifer on Cape Cod, MA, was evaluated. Particle size and mineralogical fractions (separated based on paramagnetic susceptibility) were characterized with respect to sediment organic carbon (SOC), mineralogy, surface area, metal oxide coatings, and spatial variability. SOC increases by a factor of 10 as particle size decreases from 500-1000 to <63 um. Magnetic mineral abundance is a function of particle size and increases from 5 % in the 500-1000-xm fraction to > 25 % in the <63-um fraction, and SOC is preferentially associated with the magnetic minerals. Sorption increases with decreasing particle size (increasing SOC, magnetic minerals, surface area, and metal oxyhydroxides), and the magnetic mineral fraction has greater sorption than the bulk or nonmagnetic fractions. Removal of SOC decreases sorption proportional to the decrease in SOC and results in a nonlinear isotherm.

Environmental Science & Technology↗
USGS2002

Transport of sludge-derived organic pollutants to deep-sea sediments at deep water dump site 106

Linear alkylbenzenes (LABs), coprostanol and epi-coprostanol, were detected in sediment trap and bottom sediment samples at the Deep Water Dump Site 106 located 185 km off the coast of New Jersey, in water depths from 2400 to 2900 m. These findings clearly indicate that organic pollutants derived from dumped sludge are transported through the water column and have accumulated on the deep-sea floor. No significant difference in LABs isomeric composition was observed among sludge and samples, indicating little environmental biodegradation of these compounds. LABs and coprostanol have penetrated down to a depth of 6 cm in sediment, indicating the mixing of these compounds by biological and physical processes. Also, in artificially resuspended surface sediments, high concentrations of LABs and coprostanols were detected, implying that sewage-derived organic pollutants initially deposited on the deep-sea floor can be further dispersed by resuspension and transport processes. Small but significant amounts of coprostanol were detected in the sediment from a control site at which no LABs were detected. The coprostanol is probably derived from feces of marine mammals and sea birds and/or from microbial or geochemical transformations of cholesterol. Polcyclic aromatic hydrocarbons (PAHs) in sediment trap samples from the dump site were largely from the sewage sludge and had a mixed petroleum and pyrogenic composition. In contrast, PAHs in sediments in the dump site were mainly pyrogenic; contributed either from sewage sludge or from atmospheric transport to the overlying waters. & 1994 American Chemical Society.

Environmental Science & Technology↗
USGS2002

Behavior of pollutant-degrading microorganisms in aquifers: Predictions for genetically engineered organisms

Bioremediation via environmental introductions of degradative microorganisms requires that the microbes survive in substantial numbers and effect an increase in the rate and extent of pollutant removal. Combined field and microcosm studies were used to assess these abilities for laboratory-grown bacteria. Following introduction into a contaminated aquifer, viable cells of Pseudomonas sp. B13 were present in the contaminant plume for 447 days; die-off was rapid in pristine areas. In aquifer microcosms, survival of B13 and FR120, a genetically engineered derivative of B13 having enhanced catabolic capabilities for substituted aromatics, was comparable to B13 field results; both bacteria degraded target pollutants in microcosms made with aquifer samples from the aerobic zone of the pollutant plume. Results suggest that field studies with nonrecombinant microorganisms may be coupled to laboratory studies with derivative strains to estimate their bioremediative efficacy. Furthermore, laboratory strains of bacteria can survive for extended periods of time in nature and thus may have important bioremediative applications.

Environmental Science & Technology↗
USGS2002

Effects of polar and nonpolar groups on the solubility of organic compounds in soil organic matter

Vapor sorption capacities on a high-organic-content peat, a model for soil organic matter (SOM), were determined at room temperature for the following liquids: n-hexane, 1,4-dioxane, nitroethane, acetone, acetonitrile, 1-propanol, ethanol, and methanol. The linear organic vapor sorption is in keeping with the dominance of vapor partition in peat SOM. These data and similar results of carbon tetrachloride (CT), trichloroethylene (TCE), benzene, ethylene glycol monoethyl ether (EGME), and water on the same peat from earlier studies are used to evaluate the effect of polarity on the vapor partition in SOM. The extrapolated liquid solubility from the vapor isotherm increases sharply from 3-6 wt % for low-polarity liquids (hexane, CT, and benzene) to 62 wt % for polar methanol and correlates positively with the liquid's component solubility parameters for polar interaction and hydrogen bonding. The same polarity effect may be expected to influence the relative solubilities of a variety of contaminants in SOM and, therefore, the relative deviations between the SOM-water partition coefficients (Kom) and corresponding octanol-water partition coefficients (Kow) for different classes of compounds. The large solubility disparity in SOM between polar and nonpolar solutes suggests that the accurate prediction of Kom from Kow or Sw (solute water solubility) would be limited to compounds of similar polarity.

Environmental Science & Technology↗
USGS2002

Molecular weight, polydispersity, and spectroscopic properties of aquatic humic substances

The number- and weight-averaged molecular weights of a number of aquatic fulvic acids, a commercial humic acid, and unfractionated organic matter from four natural water samples were measured by high-pressure size exclusion chromatography (HPSEC). Molecular weights determined in this manner compared favorably with those values reported in the literature. Both recent literature values and our data indicate that these substances are smaller and less polydisperse than previously believed. Moreover, the molecular weights of the organic matter from three of the four natural water samples compared favorably to the fulvic acid samples extracted from similar environments. Bulk spectroscopic properties of the fulvic substances such as molar absorptivity at 280 nm and the E4/E6 ratio were also measured. A strong correlation was observed between molar absorptivity, total aromaticity, and the weight average molecular weights of all the humic substances. This observation suggests that bulk spectroscopic properties can be used to quickly estimate the size of humic substances and their aromatic contents. Both parameters are important with respect to understanding humic substance mobility and their propensity to react with both organic and inorganic pollutants.

Environmental Science & Technology↗
USGS2002

Coupling of hydrologic transport and chemical reactions in a stream affected by acid mine drainage

Experiments in St. Kevin Gulch, an acid mine drainage stream, examined the coupling of hydrologic transport to chemical reactions affecting metal concentrations. Injection of LiCl as a conservative tracer was used to determine discharge and residence time along a 1497-m reach. Transport of metals downstream from inflows of acidic, metal-rich water was evaluated based on synoptic samples of metal concentrations and the hydrologic characteristics of the stream. Transport of SO 4 and Mn was generally conservative, but in the subreaches most affected by acidic inflows, transport was reactive. Both 0.1-um filtered and particulate Fe were reactive over most of the stream reach. Filtered Al partitioned to the particulate phase in response to high instream concentrations. Simulations that accounted for the removal of SO 4 , Mn, Fe, and Al with first-order reactions reproduced the steady-state profiles. The calculated rate constants for net removal used in the simulations embody several processes that occur on a stream-reach scale. The comparison between rates of hydrologie transport and chemical reactions indicates that reactions are only important over short distances in the stream near the acidic inflows, where reactions occur on a comparable time scale with hydrologic transport and thus affect metal concentrations.

Environmental Science & Technology↗
USGS2002

Herbicide interchange between a stream and the adjacent alluvial aquifer

Herbicide interchange between a stream and the adjacent alluvial aquifer and quantification of herbicide bank storage during high streamflow were investigated at a research site on the Cedar River flood plain, 10 km southeast of Cedar Rapids, Iowa. During high streamflow in March 1990, alachlor, atrazine, and metolachlor were detected at concentrations above background in water from wells as distant as 20, 50, and 10 m from the river's edge, respectively. During high streamflow in May 1990, alachlor, atrazine, cyanazine, and metolachlor were detected at concentrations above background as distant as 20, 50, 10, and 20 m from the river's edge, respectively. Herbicide bank storage took place during high streamflow when hydraulic gradients were from the river to the alluvial aquifer and the laterally infiltrating river water contained herbicide concentrations larger than background concentrations in the aquifer. The herbicide bank storage can be quantified by multiplying herbicide concentration by the "effective area" that a well represented and an assumed porosity of 0.25. During March 1990, herbicide bank storage values were calculated to be 1.7,79, and 4.0 mg/m for alachlor, atrazine, and metolachlor, respectively. During May 1990, values were 7.1, 54, 11, and 19 mg/m for alachlor, atrazine, cyanazine, and metolachlor, respectively.

Iowa↗
USGS2002

Reductive dehalogenation of hexachloroethane, carbon tetrachloride, and bromoform by anthrahydroquinone disulfonate and humic acid

The reductive dehalogenation of hexachloroethane (C2Cl6), carbon tetrachloride (CCl4), and bromoform (CHBr3) was examined at 50??C in aqueous solutions containing either (1) 500 ??M of 2,6-anthrahydroquinone disulfonate (AHQDS), (2) 250 ??M Fe2+, or (3) 250 ??M HS-. The pH ranged from 4.5 to 11.5 for AHQDS solutions and was 7.2 in the Fe2+ solutions and 7.8 in the HS- solutions. The observed disappearance of C2Cl6 in the presence of AHQDS was pseudo-first-order and fit k??ccl4 = k0[A(OH)2] + k1[A(OH)O-] + k2[A(O)22-] where A(OH)2, A(OH)O-, and A(O)22- represent the concentrations of the three forms of the AHQDS in solution. The values of k0, k1, and k2 were ???0,0.031, and 0.24 M-1 s-1, respectively. The addition of 25 mg of C/L of humic acid or organic matter extracted from Borden aquifer solids to aqueous solutions containing 250 ??M HS- or Fe2+ increased the reduction rate by factors of up to 10. The logarithms of the rate constants for the disappearance of C2Cl6 and CCl4 in seven different experimental systems were significantly correlated; log k???ccl4 = 0-64 log k??? c2cl6 - 0.83 with r2 = 0.80. The observed trend in reaction rates of C2Cl6 > CCl4 > CHBr3 is consistent with a decreasing trend in one-electron reduction potentials. ?? 1994 American Chemical Society.

Environmental Science & Technology↗
USGS2002

Effect of soil moisture on the sorption of trichloroethene vapor to vadose-zone soil at picatinny arsenal, New Jersey

This report presents data on the sorption of trichloroethene (TCE) vapor to vadose-zone soil above a contaminated water-table aquifer at Picatinny Arsenal in Morris County, NJ. To assess the impact of moisture on TCE sorption, batch experiments on the sorption of TCE vapor by the field soil were carried out as a function of relative humidity. The TCE sorption decreases as soil moisture content increases from zero to saturation soil moisture content (the soil moisture content in equilibrium with 100% relative humidity). The moisture content of soil samples collected from the vadose zone was found to be greater than the saturation soil-moisture content, suggesting that adsorption of TCE by the mineral fraction of the vadose-zone soil should be minimal relative to the partition uptake by soil organic matter. Analyses of soil and soil-gas samples collected from the field indicate that the ratio of the concentration of TCE on the vadose-zone soil to its concentration in the soil gas is 1-3 orders of magnitude greater than the ratio predicted by using an assumption of equilibrium conditions. This apparent disequilibrium presumably results from the slow desorption of TCE from the organic matter of the vadose-zone soil relative to the dissipation of TCE vapor from the soil gas.

New Jersey↗
USGS2002

Differences between nipher and slter shielded rain gages at two Colorado deposition monitoring sites

In the last decade the United States and Canada have made significant progress in establishing spatial ad temporal estimates of atmospheric deposition throughout North America. Fundamental to the wet-deposition portion of these estimates is the accurate and precise measurement of precipitation amount. Goodison and others (I-3) have reported on a new type of shielded snow gage known as the Canadian MSC Nipher shielded snow gage. Because this shielded snow gage has been shown to be superior to other precipitation gages for the estimation of snowfall amount, its design was adapted to the Universal Belfort precipitation gage (4), the dominant precipitation gage used at deposition monitoring sites in the United States. Favorable results taken from monitoring sites using this modified Nipher shielded snow gage (3-6) have prompted the U.S. Environmental Protection Agency and the Electric Power Research Institute to adopt the Nipher shielded Belfort gage as a standard piece of equipment in the Acid MODES and Operational Evaluation Network (OEN) monitoring programs and to propose that is be included as a standard snow gage in other North American deposition monitoring programs. This communication details preliminary results from two of nine NADP/NTN deposition monitoring sites selected by the Environmental Protection Agency to compare Nipher shielded Belfort precipitation gage volumes to volumes obtained from the standard Belfort gage used in the NADP/NTN monitoring program.

Environmental Science & Technology↗
USGS2002

Measurement of in situ rates of selenate removal by dissimilatory bacterial reduction in sediments

A radioisotope method for measurement of bacteria respiratory reduction of selenate to elemental selenium in aquatic sediments was devised. Sediments were labeled with [75Se]selenate, incubated, and washed, and 75Se0(s) was determined as counts remaining in the sediments. Core profiles of selenate reduction, sulfate reduction, and denitrification were made simultaneously in the sediments of an agricultural wastewater evaporation pond. Most of the in situ selenate reduction (85%) and all the denitrificatation activities were confined to the upper 4-8 cm of the profile, whereas sulfate reduction was greatest below 8 cm (89% of total). The integrated areal rate of selenate reduction was 301 mol m-2 day-1, which results in a turnover of water column selenate in 82.4 days.

Environmental Science & Technology↗