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At least 271 records · Page 15Linked to original sources
USGS2002

Reduction of nonpoint source contamination of surface water and groundwater by starch encapsulation of herbicides

The loss of the preemergent herbicide atrazine in surface runoff from experimental field plots growing corn (Zea mays L.) was significantly reduced using a starchencapsulated formulation versus a conventional powdered formulation. Field edge losses of starch-encapsulated atrazine were described as following a Rayleigh distribution totaling 1.8% of applied herbicide compared to exponential powdered atrazine losses of 2.9% applied - a 40% decrease. This has important implications for the reduction of nonpoint source contamination of surface water by agricultural chemicals. Unsaturated zone release of starchencapsulated atrazine was gradual, but comparable weed control was maintained. Deethylatrazine was a major dealkylated metabolite from each formulation, and deisopropylatrazine was a minor metabolite. The determination of soil partition coefficients for deethylatrazine and deisopropylatrazine (0.4 and 0.3, respectively), aqueous solubilities (3200 and 670 mg/L, respectively), and melting points (133 and 177 C, respectively) confirmed that the dealkylated metabolites should move more rapidly through the soil profile to groundwater than atrazine.

Environmental Science & Technology↗
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

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

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

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↗
USGS2002

The surface area of soil organic matter

The previously reported surface area for soil organic matter (SOM) of 560-800 m2/g as determined by the ethylene glycol (EG) retention method was reexamined by the standard BET method based on nitrogen adsorption at liquid nitrogen temperature. Test samples consisted of two high organic content soils, a freeze-dried soil humic acid, and an oven-dried soil humic acid. The measured BET areas for these samples were less than 1 m2/g, except for the freeze-dried humic acid. The results suggest that surface adsorption of nonionic organic compounds by SOM is practically insignificant in comparison to uptake by partition. The discrepancy between the surface areas of SOM obtained by BET and EG methods was explained in terms of the 'free surface area' and the 'apparent surface area' associated with these measurements.The previously reported surface area for soil organic matter (SOM) of 560-800 m2/g as determined by the ethylene glycol (EG) retention method was reexamined by the standard BET method based on nitrogen adsorption at liquid nitrogen temperature. Test samples consisted of two high organic content soils, a freeze-dried soil humic acid, and an oven-dried soil humic acid. The measured BET areas for these samples were less than 1 m2/g, except for the freeze-dried humic acid. The results suggest that surface adsorption of nonionic organic compounds by SOM is practically insignificant in comparison to uptake by partition. The discrepancy between the surface areas of SOM obtained by BET and EG methods was explained in terms of the 'free surface area' and the 'apparent surface area' associated with these measurements.

Environmental Science & Technology↗
USGS2002

Effect of ten quaternary ammonium cations on tetrachloromethane sorption to clay from water

The mineral surface of Wyoming bentonite (clay) was modified by replacing inorganic ions by each of 10 quaternary ammonium compounds, and tetrachloromethane sorption to the modified sorbents from water was studied. Tetrachloromethane sorption from solution to clay modified with tetramethyl-, tetraethyl-, benzyltrimethyl-, or benzyltriethylammonium cations generally is characterized by relatively high solute uptake, isotherm nonlinearity, and competitive sorption (with trichloroethene as the competing sorbate). For these sorbents, the ethyl functional groups yield reduced sorptive capacity relative to methyl groups, whereas the benzyl group appears to have a similar effect on sorbent capacity as the methyl group. Sorption of tetrachloromethane to clay modified with dodecyldimethyl(2-phenoxyethyl)-, dodecyltrimethyl-, tetradecyltrimethyl-, hexadecyltrimethyl-, or benzyldimethylhexadecylammonium bromide is characterized by relatively low solute uptake, isotherm linearity, and noncompetitive sorption. For these sorbents, an increase in the size of the nonpolar functional group(s) causes an increase in the organic carbon normalized sorption coefficient (Koc). No measurable uptake of tetrachloromethane sorption by the unmodified clay or clay modified by ammonium bromide was observed.

Environmental Science & Technology↗