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At least 289 records · Page 16Linked to original sources
USGS2002

Chloride interference in the analysis of dissolved organic carbon by the wet oxidation method

The presence of Cl- in concentrations greater than 0.02 M is shown to interfere with the analysis of aqueous DOC concentrations by the wet oxidation method of analysis when a reaction time of 5 min is employed. Chloride competes with DOC for S2O82-, lowering the overall oxidation efficiency. The resulting HOCl from the oxidation of Cl- reacts with DOC, producing significant amounts of chlorinated intermediate compounds in addition to CO2. These compounds were found in the waste effluent from the reaction chamber and in the gas stream transporting CO2 to the detector. While a possible Cl- effect has been noted for DOC measurements in the past, it has not previously been demonstrated to be a source of error at the concentrations reported in this paper. The interference can be overcome either by increasing the digestion time or by diluting samples to contain less than 0.02 M Cl-.

Environmental Science & Technology↗
USGS2002

A reconnaissance study of herbicides and their metabolites in surface water of the midwestern united states using immunoassay and gas chromatography/mass spectrometry

Preemergent herbicides and their metabolites, particularly atrazine, deethylatrazine, and metolachlor, persisted from 1989 to 1990 in the majority of rivers and streams in the midwestern United States. In spring, after the application of herbicides, the concentrations of atrazine, alachlor, and simazine were frequently 3-10 times greater than the U.S. Environmental Protection Agency maximum contaminant level (MCL). The concentration of herbicides exceeded the MCLs both singly and in combination. Two major degradation products of atrazine (deisopropylatrazine and deethylatrazine) also were found in many of the streams. The order of persistence of the herbicides and their metabolites in surface water was atrazine > deethylatrazine > metolachlor > alachlor > deisopropylatrazine > cyanazine. Storm runoff collected at several sites exceeded the MCL multiple times during the summer months as a function of stream discharge, with increased concentrations during times of increased streamflow. It is proposed that metabolites of atrazine may be used as indicators of surface-water movement into adjacent alluvial aquifers.

Environmental Science & Technology↗
USGS2002

Atrazine degradation in a small stream in Iowa

A study was conducted during 1990 through an 11.2-km reach of Roberts Creek in northeastern Iowa to determine the fate of atrazine in a surface water environment Water samples were collected at ~1-month intervals from April through November during stable low to medium flow conditions and analyzed for atrazine and two of its initial biotic degradation products, desethylatrazine and deisopropylatrazine. Samples were collected on the basis of a Lagrangian model of streamflow in order to sample the same parcel of water as it moved downstream. Atrazine concentrations substantially decreased (roughly 25-60%) between water entering and exiting the study reach during four of the seven sampling periods. During these same four sampling periods, the concentrations of the two biotic atrazine degradation products were constant or decreasing downstream, suggesting an abiotic degradation process.

Iowa↗
USGS2002

Application of headspace analysis to the study of sorption of hydrophobic organic chemicals to α-Al 2 O 3

The sorption of hydrophobic organic chemicals (HOCs) to ??-Al2O3 was investigated with a headspace analysis method. The semiautomated headspace analyzer gave rapid, precise, and accurate results for a homologous series alkylbenzenes even at low percentages of solute mass sorbed (3-50%). Sorption experiments carried out with benzene alone indicated weak interactions with well-characterized aluminum oxide, and a solids concentration effect was observed. When the sorption coefficients for benzene alone obtained by headspace analysis were extrapolated up to the solids concentrations typically used in batch sorption experiments, the measured sorption coefficients agreed with reported sorption coefficients for HOCs and sediments of low fractional organic carbon content. Sorbed concentrations increased exponentially with aqueous concentration in isotherms with mixtures of alkylbenzenes, indicating solute-solute interactions at the mineral surface. Sorption was, however, greater than predicted for partitioning of a solute between its pure liquid phase and water, indicating additional influences of the surface and/or the structured liquid near the mineral surface. ?? 1993 American Chemical Society.

Environmental Science & Technology↗
USGS2002

Nonpoint source contamination of the Mississippi river and its tributaries by herbicides

A study of the Mississippi River and its tributaries during July-August 1991, October-November 1991, and April-May 1992 has indicated that the entire navigable reach of the river is contaminated with a complex mixture of agrochemicals and their transformation products derived from nonpoint sources. Twenty-three compounds were identified, including triazine, chloroacetanilide, thiocarbamate, phenylurea, pyridazine, and organophosphorus pesticides. The upper and middle Mississippi River Basin farm lands are major sources of herbicides applied to corn, soybeans, and sorghum. Farm lands in the lower Mississippi River Basin are a major source of rice and cotton herbicides. Inputs of the five major herbicides atrazine, cyanazine, metolachlor, alachlor, and simazine to the Mississippi River are mainly from the Minnesota, Des Moines, Missouri, and Ohio Rivers. Ratios of desethylatrazine/atrazine potentially are useful indicators of groundwater and surface water interactions in the Mississippi River. These ratios suggested that during baseflow conditions, there is a significant groundwater contribution to the river. The Mississippi River thus serves as a drainage channel for pesticide-contaminated surface and groundwater from the midwestern United States. Conservative estimates of annual mass transport indicated that about 160 t of atrazine, 71 t of cyanazine, 56 t of metolachlor, and 18 t of alachlor were discharged into the Gulf of Mexico in 1991.

Environmental Science & Technology↗
USGS2002

Sorption of N2 and EGME vapors on some soils, clays, and mineral oxides and determination of sample surface areas by use of sorption data

Vapor sorption isotherms of ethylene glycol monoethyl ether (EGME) at room temperature and isotherms of N2 gas at liquid nitrogen temperature were determined for various soils and minerals. The N2 monolayer capacities [Qm (N2)] were calculated from the BET equation and used to determine the surface areas. To examine whether EGME is an appropriate adsorbate for determination of surface areas, the apparent EGME monolayer capacities [Qm (EGME)ap] were also obtained by use of the BET equation. For sand, aluminum oxide, kaolinite, hematite, and synthetic hydrous iron oxide, which are relatively free of organic impurity and expanding/solvating minerals, the Qm (EGME)ap values are in good conformity with the corresponding Qm (N2) values and would give surface areas consistent with BET (N2) values. For other samples (Woodburn soil, a natural hydrous iron oxide, illite, and montmorillonite), the Qm (EGME)ap values overestimate the Qm (N2) values from a moderate to a large extent, depending on the sample. A high-organic-content peat shows a very small BET (N2) surface area; the EGME/ peat isotherm is linear and does not yield a calculation of the surface area. Large discrepancies between results of the two methods for some samples are attributed to the high solubility of polar EGME in soil organic matter and/ or to the cation solvation of EGME with solvating clays. The agreement for other samples is illustrative of the consistency of the BET method when different adsorbates are used, so long as they do not exhibit bulk penetration and/or cation solvation.

Environmental Science & Technology↗
USGS2002

Determination of dissolved-phase pesticides in surface water from the Yakima River basin, Washington, using the Goulden large-sample extractor and gas chromatography/mass spectrometer

Concentrations of pesticides in the dissolved phase of surface water samples from the Yakima River basin, WA, were determined using preconcentration in the Goulden large-sample extractor (GLSE) and gas chromatography/mass spectrometry (GC/MS) analysis. Sample volumes ranging from 10 to 120 L were processed with the GLSE, and the results from the large-sample analyses were compared to those derived from 1-L continuous liquid-liquid extractions Few of the 40 target pesticides were detected in 1-L samples, whereas large-sample preconcentration in the GLSE provided detectable levels for many of the target pesticides. The number of pesticides detected in GLSE processed samples was usually directly proportional to sample volume, although the measured concentrations of the pesticides were generally lower at the larger sample volumes for the same water source. The GLSE can be used to provide lower detection levels relative to conventional liquid-liquid extraction in GC/MS analysis of pesticides in samples of surface water.

Washington↗
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

Batch experiments characterizing the reduction of chromium(VI) using suboxic material from a mildly reducing sand and gravel aquifer

Batch experiments were conducted with sand collected from a shallow sand and gravel aquifer to identify the principal chemical reactions influencing the reduction of Cr(VI), so that field-observed Cr(V1) reduction could be described. The reduction appeared to be heterogeneous and occurred primarily on Fe(I1)-bearing minerals. At only 1 wt % , the fine fraction (<64 μ m diameter) of the sediments dominated the amount of aqueous Cr(V1) reduction because of its greater reactivity and surface area. Although reduction of Cr(V1) increased with decreasing pH, small variations in the abundance of fine fraction among the replicate samples obscured pH trends in the batch experiments. Consistent results could only be obtained by separating the fine material from the sand and running parallel experiments on each fraction. As pH decreased (6.4 to 4.5), Cr(V1) reduction increased from 30 to 50 nmol/m 2 for the sand fraction (64-1000 μ m) and from 130 to 200 nmol/m 2 for the fine fraction. The amount of Cr(V1) reduced in both the sand-sized and fine material increased from 35 to 80 and from 130 to 1000 nmol/m 2 , respectively, for a 10-fold increase in Cr(VI) initial . A consistent description of the rate data was achieved by assuming that intraparticle diffusion limited the observed rate of reduction.

Environmental Science & Technology↗
USGS2002

Preferential dealkylation reactions of s-triazine herbicides in the unsaturated zone

The preferential dealkylation pathways of the s-triazine herbicides, atrazine (2-chloro-4-ethylamino-6-isopropylamino-s-triazine), propazine [2-chloro-4,6-bis(isopropylamino)-s-triazine], and simazine [2-chloro-4,6-bis(ethylamino)-s-triazine], and two monodealkylated triazine metabolites, deisopropylatrazine (DIA: 2-amino-4-chloro-6-ethylamino-s-triazine) and deethylatrazine (DEA: 2-amino-4-chloro-6-isopropylamino-s-triazine) were investigated on two adjacent Eudora silt-loam plots growing corn (Zea mays L.). Results from the shallow unsaturated zone and surface-water runoff showed preferential removal of an ethyl side chain from atrazine, simazine, and DIA relative to an isopropyl side chain from atrazine, propazine, and DEA. It is hypothesized that deethylation reactions may proceed at 2-3 times the rate of deisopropylation reactions. It is concluded that small concentrations of DIA reportedly associated with the degradation of atrazine may be due to a rapid turnover rate of the metabolite in the unsaturated zone, not to small production levels. Because of continued dealkylation of both monodealkylated metabolites, a strong argument is advanced for the presence of a didealkylated metabolite in the unsaturated zone.

Environmental Science & Technology↗
USGS2002

Polychlorinated biphenyl congeners in emergent mayflies from the upper Mississippi River

We determined polychlorinated biphenyls (pcbs) in emergent mayflies (hexagenia bilineata) from a 1250-km reach of the upper mississippi river (UMR). Total pcb concentrations (sum of 125 congeners) ranged from 0.21 To 4.1 Mu g/g of dry weight (1.2-29 mu g/g of lipid weight). Concentrations were highest in pools near the twin cities and the quad cities metropolitan areas. Longitudinal movement of pcbs was extensive downstream from the twin cities (175-320 km) but was not apparent downstream from the quad cities. The pcb composition of mayflies was relatively homogeneous throughout most of the river. However, the congener composition in mayflies from two distant locations differed markedly from the other samples and contained a greater abundance of lower molecular weight congeners. Recent pcb discharges from point and nonpoint sources may account for these differences. Emergent mayflies seem to be a useful indicator of pcb contamination of the UMR.

Environmental Science & Technology↗