Spike- and blank-based procedures were applied to estimate the detection limits (DLs) for example analytes from inorganic and organic methods for water samples to compare with the U.S. Environmental Protection Agency's (EPA) Method Detection Limit (MDL) procedures (revisions 1.11 and 2.0). The multi-concentration spike-based procedures ASTM Within-laboratory Critical Level (DQCALC) and EPA's Lowest Concentration Minimum Reporting Level were compared in one application, with DQCALC further applied to many methods. The blank-based DLs, MDLb99 (99th percentile) or MDLbY (= mean blank concentration + s × t), estimated using large numbers (>100) of blank samples often provide DLs that better approach or achieve the desired ≤1% false positive risk level compared to spike-based DLs. For primarily organic methods that do not provide many uncensored blank results, spike-based DQCALC or MDL rev. 2.0 are needed to simulate the blank distribution and estimate the DL. DQCALC is especially useful for estimating DLs for multi-analyte methods having very different analyte response characteristics. Time series plots of DLs estimated using different procedures reveal that DLs are dependent on the applied procedure, should not be expected to be static over time, and seem best viewed as falling over a range versus being a single value. Use of both blank- and spike-based DL procedures help inform this DL range. Data reporting conventions that censor data at a threshold and report "less than" that threshold concentration as the reporting level have unknown and potentially high false negative risk. The U.S. Geological Survey National Water Quality Laboratory's Laboratory Reporting Level (LRL) convention (applied primarily to organic methods) attempts to simultaneously minimize both the false positive and false negative risk when <LRL is reported and data between DL and the higher LRL are allowed to be reported.

Geogenic arsenic (As) adversely affects drinking water quality in geologically diverse aquifers across the globe. Although the species of As significantly affects its fate, transport, toxicity, and As treatment technology efficacy, reported effectiveness of As species preservation methods varies widely with preservation methods and natural water geochemistry. Our study 1) evaluates the shelf life of As(III), As(V), dimethylarsinate (DMA), and monomethylarsonate (MMA) in standards prepared with ultrapure water; 2) establishes a hold time for these As species in low-iron (Fe) groundwater and surface water samples preserved with a concentration of EDTA that exceeded the sum of the molar concentrations of Al, Fe, Mn, Ca, Mg, and Sr (molar excess of EDTA); and 3) evaluates As(III) species stability in groundwater samples with detectable SO4 and up to 6.5 mg/L Fe concentrations preserved in 3 ways: less than molar excess EDTA, molar excess EDTA, and Vacuette (R) tubes with an unknown (proprietary) amount of EDTA. Arsenic species standards prepared with 2.5 mM EDTA in ultrapure water and stored at 4 degrees C had a shelf life of at least 180 days. As(III) was stable for at least 15 days and DMA and MMA were stable for at least 90 days in environmental samples with Fe less than 1 mg/L that were preserved with a molar excess of EDTA and stored in opaque containers at 4 degrees C. As(III) species were not stable for any holding time in samples with Fe greater than 1 mg/L and detectable SO4 when preserved with a molar excess of EDTA and stored in white high density polyethylene bottles at room temperature, or when preserved by storage in EDTA containing Vacuette (R) tubes at 4 degrees C. For geochemical or water quality studies where the distribution of As(III) and As(V) is a critical factor, an understanding of the sample chemistry, rapid As speciation analysis after sample collection, and collecting a field spike with the sample can be helpful for collecting accurate inorganic As species data.

Robust and sensitive methods for monitoring inorganic and organic As species As(III), As(V), dimethylarsinate (DMA), and monomethylarsonate (MMA) in environmental water are necessary to understand the toxicity and redox processes of As in a specific environment. The method is sufficiently sensitive and selective to ensure accurate and precise quantitation of As(III), As(V), DMA, and MMA in surface water and groundwater samples with As species concentrations from tens of nanograms per liter to 50 µg/L without dilution of the sample. Mean recoveries of the four species spiked into reagent water, surface water and groundwater and measured periodically over three months ranged from 87.2 % to 108.7 % and relative standard deviation of replicates of all analytes ranged from 1.1 % to 9.0 %.•A PRP-X100 column and nitrate/phosphate mobile phase was used to separate As(III), As(V), DMA, and MMA in 0.45 µm filtered surface water and groundwater matrices.•Oxygen was used in the collision cell of the inductively coupled plasma-mass spectrometer with MS/MS mode to shift the measured As mass from 75 to 91.•The analytical performance of the method and figures of merit including detection limits, precision, accuracy, and interferences when applied to surface water and groundwater matrices were investigated.

Automated, colorimetric analysis of nutrients in samples with high and variable salinity can be time consuming due to the need to matrix match calibration and reference solution matrices with those of samples-particularly when using flow-based analyzers that are prone to detector artifacts caused by optical inhomogeneities, "schlieren," that form at interfaces between samples and deionized water carrier or wash solutions. Such detector artifacts do not occur in discrete analyzers. Here we report spike recoveries when nitrite plus nitrate, nitrite, ammonia, orthophosphate, and silica were determined in estuarine waters, seawater, and hypersaline surface water samples without calibrator matrix matching using an automated discrete analyzer set up with standard colorimetric methods. Salinities of these samples varied from 0 to 22%. Spike recoveries and precision were excellent for nitrite and nitrite plus nitrate analyses in samples with salinities up to 15%, for ammonia in samples with salinities up to about 1.7%, and for orthophosphate in samples with salinities up to about 3.5%. Orthophosphate spike recoveries were high biased in hypersaline matrices (salinity >3.5%), likely due to an unidentified sample matrix interference. After applying linear correction factors to account for chemistry-related salt effects, spike recoveries were acceptable for ammonia analyses in samples with salinities in the range of 1.7-3.5%, and for silica analyses in samples with salinities in the range of 0-3.5%.

Field operations may differentially influence crop residue size distributions, altering residue decomposition rates and soil carbon (C) and nitrogen (N) dynamics. In a laboratory microcosm study modeling corn residue distributions observed in a no-till cropping system, microbial respiration was initially (first 30 d) inversely proportional to residue particle size across four size classes. Subsequently (30–60 d), respiration in the smallest particle size decreased in relation to the larger size classes. Residue particle size significantly increased soil C levels, with the smallest sizes producing the longest-lasting effects (150 d). Smaller residue size classes initially (30 d) immobilized more soil N compared with larger size classes; however, at 150 d, the smaller size classes had mobilized increasing amounts of N while the larger size classes had progressively immobilized more N. We conclude that crop residue management operations changed characteristic residue size distributions that moderate decomposition activities and result in unique soil C and N dynamics, possibly influencing soil properties, including nutrient availability.

Inorganic carbon (IC) in soil is important when considering carbon (C) fluxes and processes in the environment that involve C. Here data are presented for measurement of IC in soils using the pressure-calcimeter method of Sherrod et al. (2002) with modifications to decrease analysis time while preserving method accuracy. Inorganic C measured using a syringe to inject acid vs. the vial delivery method of the original method were not significantly different at the 95 percent confidence level when using 100-ml bottles for the analysis (R2 = 0.9946). When using 20-ml bottles, bias was introduced in the measurement when using a syringe for acid delivery, likely due to small losses of pressure from the bottle during acid delivery. There was no significant difference at the 95 percent confidence level in IC measured on unsieved finely ground and coarsely ground soil. When quantifying IC in soils using the modified pressure calcimeter method with a 100-ml bottle, a syringe can be used to inject acid into the capped bottle rather than dropping a vial into the bottle and then capping it. This modification results in a modest reduction in cost and significant reduction in time required for analysis and cleanup.

Corn (Zea mays L.) residue is being considered as a feedstock for biofuels production. The impact of removing corn residue on soil productivity is not well understood. A corn–soybean [Glycine max (L.) Merr.] rotation was established in 2000 to determine the effect of removing corn residue at three rates (37, 55, and 98%) on soil organic carbon (SOC) in the 0- to 5-cm layer of soil after 8 yr. The effect of cover crops {slender wheatgrass [Agropyron caninum (L.) Beauv.] in corn and lentil (Lens culinaris Medik. variety Morton) in soybeans} on SOC was also measured. As the rate of residue removal increased, soil organic matter (SOM), wet aggregate stability (WAS), C/N, and microbial activity decreased significantly. Although the effect was not significant, there was a decrease in SOC as the rate of removal increased. At the high residue removal rate, SOM analyzed by quantitative 13C NMR contained an abundance of aromatic C structures, suggesting that less humified pools of soil C are not being replenished. The humin fraction of the soil had a reduction in SOC under the medium and high rates of residue removal without a cover crop and is likely beginning to be depleted. Bradford-reactive soil protein and immunoreactive soil protein were higher in soils with cover crops, likely due to increased plant diversity and extending the growing season to allocate more C belowground. Overall, the data suggest that the soil properties indicative of soil quality are negatively impacted by removal of corn residue.

Many questions have surfaced regarding short-and long-term impacts of corn (Zea mays L.) residue removal for use in the biofuels industry. To address these concerns, a field study was established in eastern South Dakota in 2000 using no-till soil management within a 2-yr corn/soybean [Glycine max (L.) Merr.] rotation. The objective of this study was to examine the effects of three residue removal treatments of low (corn harvested for grain; all residues remain on soil surface), medium (corn harvested for grain; residue raked, baled, and removed), and high (aboveground corn biomass and grain removed) on soil quality, measured through particulate organic matter (POM), soil organic matter (SOM), wet aggregate stability (WAS), and dry aggregate size distribution (DASD). Following four complete rotational cycles, when residue was removed from the soil surface there was a consistent decrease in the amount of SOM and all fractions of POM regardless of aggregate size class, indicating a possible decrease in soil quality. This was further indicated by the near doubling of the erodible fraction in the high removal treatment compared to the low removal treatment. Potential further degradation of the soil structure is indicated by a shift in DASD among the residue removal treatments. Within this study, removal of corn residue had a negative impact on the soil physical and chemical properties measured, potentially illustrating the importance of crop residue to maintain our soil resource. Additional research is needed to incorporate other soil chemical and biological indicators before recommendations can be made.

We report on the chemical analysis of water samples collected from the Taylor Mountains 1:250,000-scale quadrangle, Alaska. Parameters for which data are reported include pH, conductivity, water temperature, major cation and anion concentrations, trace-element concentrations, and dissolved organic-carbon concentrations. Samples were collected as part of a multiyear U.S. Geological Survey project entitled ?Geologic and Mineral Deposit Data for Alaskan Economic Development.? Data presented here are from samples collected in June and July 2006. The data are being released at this time with minimal interpretation. This is the third release of aqueous geochemical data from this project; aqueous geochemical data from samples collected in 2004 and 2005 were published previously. The data in this report augment but do not duplicate or supersede the previous data release. Site selection was based on a regional sampling strategy that focused on first- and second-order drainages. Water sample site selection was based on landscape parameters that included physiography, wetland extent, lithological changes, and a cursory field review of mineralogy from pan concentrates. Stream water in the Taylor Mountains quadrangle is dominated by bicarbonate (HCO3-), although in a few samples more than 50 percent of the anionic charge can be attributed to sulfate (SO42-). The major-cation chemistry ranges from Ca2+/Mg2+ dominated to a mix of Ca2+/Mg2+/Na++K+. Generally, good agreement was found between the major cations and anions in the duplicate samples. Many trace elements in these samples were at or near the analytical method detection limit, but good agreement was found between duplicate samples for elements with detectable concentrations. All field blank major-ion and trace-element concentrations were below detection.

This report presents data collected as part of a reconnaissance study to evaluate the occurrence of perchlorate in rivers and streams and in shallow aquifers in selected areas of the United States. Perchlorate, a component in rocket fuels, fireworks, and some explosives is soluble in water and persists in soils and water for long periods. It is biologically active at relatively low-levels in the environment, and has been identified as an endocrine-disrupting chemical. The purpose of this reconnaissance was to determine the occurrence of perchlorate in agricultural areas of the Midwestern and North-Central United States and in arid Central and Western parts of the United States. Samples were collected from 171 sites on rivers and streams and 146 sites from wells during the summer and early fall of 2004. Samples were collected from surface-water sites in 19 states and from wells in 5 states. Perchlorate was detected in samples collected in 15 states and was detected in 34 of 182 samples from rivers and streams and in 64 of 148 groundwater samples at concentrations equal to or greater than 0.4 micrograms per liter. Perchlorate concentrations were 1.0 micrograms per liter or greater in surface-water samples from seven states and in groundwater samples in four states. Only one surface-water and one groundwater sample had concentrations greater than 5.0 micrograms per liter. Perchlorate concentrations in followup samples collected from 1 to 3 months after the initial sample were unchanged at four of five stream sites.

The isotopic composition of mercury (Hg) was determined in cinnabar ore, mine-waste calcine (retorted ore), and leachates obtained from water leaching experiments of calcine from two large Hg mining districts in the U.S. This study is the first to report significant mass-dependent Hg isotopic fractionation between cinnabar ore and resultant calcine. Data indicate that δ202Hg values relative to NIST 3133 of calcine (up to 1.52‰) in the Terlingua district, Texas, are as much as 3.24‰ heavier than cinnabar (−1.72‰) prior to retorting. In addition, δ202Hg values obtained from leachates of Terlingua district calcines are isotopically similar to, or as much as 1.17‰ heavier than associated calcines, most likely due to leaching of soluble, byproduct Hg compounds formed during ore retorting that are a minor component in the calcines. As a result of the large fractionation found between cinnabar and calcine, and because calcine is the dominant source of Hg contamination from the mines studied, δ202Hg values of calcine may be more environmentally important in these mined areas than the primary cinnabar ore. Measurement of the Hg isotopic composition of calcine is necessary when using Hg isotopes for tracing Hg sources from areas mined for Hg, especially mine water runoff.

Immune complex diseases are a group of disorders caused when …

Ingestion of food-associated antigens can cause localized and systemic reactions in sensitized individuals. Adverse food reactions have been reported throughout history. Hippocrates reported an account of an adverse reaction to milk over 2000 years ago. Diagnosis of …