The fate of oxidized mercury (Hg) in clouds and fogs is affected by the complexation of oxidized Hg(II) with other chemical species present in cloud and fog water. Metal complexation often influences the types of reactions available to a metal in an aqueous system. The influence of pH, major inorganic ions, and organic acids on the complexation of Hg(II) and methylmercury (MeHg) was examined for a range of cloud and fog water compositions. Fog water was collected in the San Joaquin Valley, CA and rain water was collected at Devil's Lake State Park, WI to provide additional measurements of the chemical conditions of atmospheric media. A thermodynamic model was used to determine the speciation of Hg(II) and methylmercury (MeHg) over a range of atmospherically-relevant cloud and fog compositions. The speciation of Hg(II) in cloud and fog water was highly dependent on pH. For conditions found in most clouds and fogs, the chloride ion was the most important major ion controlling Hg(II) complexation, even under conditions of relatively low chloride content. However, Hg(OH)(2(aq)), and HgClOH(aq) were found to dominate over HgCl2 in locations with high pH due emissions of agricultural ammonia; i.e. San Joaquin and Sacramento Valleys, CA. At concentrations relevant to typical cloud and fog waters, carboxylic acids (e. g. formate and acetate) did not play a significant role in Hg(II) speciation. Methyl mercury was speciated as MeHgCl in most locations, except for the locations with high pH, where MeHgOH dominated. These results provide constraints over potential reaction pathways that may transform oxidized Hg(II) in clouds and fogs.

Nonbiological degradation processes play an important role in the dissipation of many pesticides in soil. This chapter reviews the major types of chemical reactions contributing to pesticide degradation in soils using examples of important pesticide groups. Hydrolysis reactions are important steps in the degradation of many pesticide compounds. In soil, sorption-catalyzed reactions appear to be particularly important for two pesticide groups, namely, the chloro-s-triazine herbicides and the organophosphate insecticides. Chemical reactions induced by electromagnetic radiation represent a potentially important pathway for alteration and/or degradation of pesticides applied to soil. The wide range of pesticide compounds susceptible to photochemical reactions illustrates the potential importance of these reactions in the degradation of pesticides in soil. However, the role of photochemical reactions in soil pesticide degradation remains uncertain. Various other chemical reactions, in addition to hydrolysis and photodecomposition, are important for particular pesticides.

Bioavailability of mercury (Hg) to Selenastrum capricornutum was assessed in bioassays containing field-collected freshwater of varying dissolved organic carbon (DOC) concentrations. Bioconcentration factor (BCF) was measured using stable isotopes of methylmercury (MeHg) and inorganic Hg(II). BCFs for MeHg in low-DOC lake water were significantly larger than those in mixtures of lake water and high-DOC river water. The BCF for MeHg in rainwater (lowest DOC) was the largest of any treatment. Rainwater and lake water also had larger BCFs for Hg(II) than river water. Moreover, in freshwater collected from several US and Canadian field sites, BCFs for Hg(II) and MeHg were low when DOC concentrations were >5 mg L−1. These results suggest high concentrations of DOC inhibit bioavailability, while low concentrations may provide optimal conditions for algal uptake of Hg. However, variability of BCFs at low DOC indicates that DOC composition or other ligands may determine site-specific bioavailability of Hg.

The effects of watershed type exert a strong influence on the speciation of mercury and the delivery of mercury to Lake Superior nearshore waters. As a consequence, tributary mixing zones are important locations for enhanced bioaccumulation in Lake Superior. Methyl Hg (MeHg) bioaccumulation, however, is also observed in regions of the lake that are remote from tributary influences. Three cruises aboard the USEPA vessel R/V Lake Guardian on Lake Superior revealed that offshore concentrations of total mercury (HgT) were low, similar to Lake Michigan and oceanic waters (0.21-1.0 ng L-1 HgT). During August 2000, MeHg averaged 3.0-12.6 pg L-1, at least an order of magnitude lower than most tributaries during typical flow regimes. Despite these differences, initial comparisons of phytoplankton revealed only a two to threefold enrichment of MeHg in tributary mixing zones versus offshore regions. MeHg inputs to the open waters of the lake are dependent on three processes: mixing from nearshore zones, direct atmospheric inputs and MeHg diffusion from sediments. Direct sedimentary methylation rates are extremely low and modeling efforts suggest that photodegradation would eliminate tributary derived MeHg. Therefore, we conclude that atmospheric sources strongly influence MeHg uptake in offshore zones. A detailed profile at a deep-lake station in August 2001 suggests enhanced bioaccumulation at a subsurface chlorophyll maximum, in a zone with close contact to atmospheric fluxes.

The accumulation of total mercury (HgT) andmethylmercury (MeHg) was evaluated in sediments ofTivoli South Bay, a freshwater tidal mudflat wetlandin the Hudson River National Estuarine ResearchReserve system. HgT concentrations in sedimentcores were measured to evaluate the spatialvariability of HgT deposition, and to establisha chronology of HgT accumulation. Cores takenfrom the northern, middle, and southern sections ofthe bay had similar distribution patterns andconcentrations of HgT, suggesting a common sourceof HgT throughout the bay. Sedimentconcentrations ranged from 190 to 1040 ng Hg g−1,2 to 10 times greater than concentrations expected insediments from non-anthropogenic sources. HgTdeposition rates were similar in different regions ofthe bay, and increased from 200 ng Hg cm−2yr−1in the 1930s to a maximum of 300 ngHg cm−2 yr−1 in the 1960s. Deposition rateshave steadily declined since the 1970s and arecurrently at 80 ng Hg cm−2 yr−1. Transportof HgT by tidal waters from the Hudson River islikely the main source of HgT in the bay.Distribution patterns and absolute concentrations ofMeHg in sediment cores were similar throughout thebay, with concentrations ranging from 0.43 to 2.95ng g−1. Maxima in MeHg concentration profilesoccurred just below the sediment-water interface andat a depth of 30 cm. The maximum at 30 cm wascoincident with maximum HgT concentrations. MeHgconcentrations in suspended particulate matter (SPM)from the Hudson River suggest that MeHg in the baycould be derived from riverine SPM rather than formedin situ.

QUANTITATIVE ANALYSIS OF THE DETECTION LIMITS FOR HEAVY METAL-CONTAMINATED SOILS BY LASER-INDUCED BREAKDOWN SPECTROSCOPY Alexander, Dennis R.; Dana E. Poulain, Nebraska Univ., Lincoln NTIS: ADA328435. 34 pp, Jun 1997 Laser-induced breakdown spectroscopy (LIBS) is a rapid remote measurement method for detection of metals in the environment. A major factor in the quantitative use of this technique involves the minimum detection limits under both laboratory and field operations. Research on limits of detection of heavy metals in different types of soils under various conditions using LIBS has been carried out. Pulses from a Nd:YAG laser operating at 125 mJ at lambda = 1.06 micrometers are focused on sample surfaces to produce laser sparks (plasmas). Atomic emissions from the plasmas are recorded using an optical multichannel analyzer after delays of a few microseconds when interference from broad-band emissions is reduced. Research has been performed on the detection limits of arsenic, cadmium, chromium, mercury, lead, and zinc in soil matrices. Results are reported on the lower detection limits of these six elements in sand, silt, clay, and kaolin matrices. Detection limits are significantly lower for heavy metals in sand matrices than silt and clay matrices due to differences between surface and volume contamination.

227 We designed a resistance exercise protocol to evaluate the efficacy of ergogenic aids on short term resistance exercise performance. The purpose of the present investigation was to evaluate the reliability of this protocol. Six men (age: 32.8±1.6 yr, body mass: 89.3±8.1 kg and height: 1.81±0.10 m) participated in this investigation after giving their consent. Subjects' 10 repetition maximum (10 RM) was determined on a Nautilus leg extension device. A familiarization trial followed approximately one week later. After a warm-up set of 10 repetitions at 70% of 10 RM subjects performed six sets at 80% of 10 RM (1.5 seconds for concentric and 1.5 seconds for eccentric phases). Ten repetitions were performed during the first three sets; during the last three sets subjects exercised to fatigue which was considered the point where they were unable to attain 150 degrees of extension. Ninety seconds of seated passive recovery separated each set. Subsequently, two experimental trials were conducted in which the exercise protocol was identical to the familiarization trial. The familiarization trial and each of the experimental trials were separated by approximately one week. A one-way ANOVA with repeated measures was followed by paired t-tests (Bonferroni correction) to determine if there was significant fatigue from the 4th set to the 6th set. The intraclass correlation (ICC) and the average coefficient of variation (CV) were calculated for the 4th, 5th and 6th sets to determine reliability. There was a significant decline in performance from set 4 (13.5±0.9 reps) to set 5 (11.9±0.8 reps) and set 4 to set 6 (10.8±1.0 reps) suggesting that the protocol did induce fatigue. The ICCs were 0.999, 0.999, and 0.997 for the 4 th, 5 th, and 6th sets, respectively. The average CVs for the 4th, 5th, and 6th sets were 6.7%, 2.7% and 7.1%, respectively. These data suggest that the resistance training protocol used in this investigation is reliable and is sensitive enough to evaluate the efficacy of ergogenic aids.

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTEnrichment of micronutrients, heavy metals, and chlorinated hydrocarbons in wind-generated lake foamS. J. Eisenreich, A. W. Elzerman, and D. E. ArmstrongCite this: Environ. Sci. Technol. 1978, 12, 4, 413–417Publication Date (Print):April 1, 1978Publication History Published online1 May 2002Published inissue 1 April 1978https://doi.org/10.1021/es60140a015RIGHTS & PERMISSIONSArticle Views147Altmetric-Citations35LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (601 KB) Get e-Alerts Get e-Alerts

The adsorption of inorganic ? (Pi) and organic ? (Po) compounds by amorphous aluminum hydroxide was studied over the equilibrium ? concentration range of 8 × 10‐7 to 1 × 10‐4 M under normal lake pH conditions using the Langmuir adsorption isotherm. The isotherms for Pi and Po adsorption plotted according to a modified Langmuir equation generally exhibited multiphasic behavior indicative of more than one population of sorption sites differing in their affinity for P. Adsorption maxima and binding energy constants for the adsorption of inorganic and organic phosphorus compounds are reported. Cations, anions, and chelating agents typical of natural waters greatly affected Po adsorption. In general, Po adsorption increased with anionic charge, number of reactive phosphate groups, decreasing steric hindrance and decreasing molecular size. Results indicate that a significant fraction of the native Po in lakes differs from the model Po compounds studied.

Existing information on the presence, composition, and formation of surface organic microlayers in freshwater systems is reviewed. Present sampling techniques are also discussed. Special emphasis is put on discussing observed enrichment of microcontaminants in Lakes Ontario, Michigan, and Lake Mendota.

A simplified method for the analysis of total P(TP), total dissolved P(TDP) and dissolved reactive P (DRP) in multiple water samples has been developed. The reported modification utilizes a single digestion reagent and a single "mixed reagent" to eliminate neutralization, transfer and dilution steps normally required in total P analyses. The method results in a 70 percent decrease in analysis time for multiple samples, a reduction in the glassware required, and about a 30 percent increase in sensitivity. The method can be directly applied to water samples with P levels of 2 to 1100 ug P/l. Reproducibility and precision measurements compare to or exceed commonly used P techniques.

AbstractThe amounts and forms of inorganic and organic phosphate (P) in lake sediments are discussed in relation to sediment composition and properties. The ability of noncalcareous and calcareous sediments to sorb and desorb added P in the laboratory and in the lake environment is interpreted in terms of the amounts and reactivities of sediment components involved in the sorption of P; emphasis is placed on the role of an Fe‐rich gel complex. Factors controlling the chemical mobility and biological availability of sediment inorganic and organic P are considered. Whether sediments act as a P source or sink is determined by sediment composition and limnological conditions. The factors involved in the interchange of P between the sediment interstitial water and the overlying water column are reviewed. The role of P in lake eutrophication is discussed briefly.

AbstractThe interference from As in the colorimetric determination of inorganic P by the method of Murphy and Riley was evaluated in water and sediment extract systems. Whereas up to 20 µg As/ml as arsenite (AsIII) did not interfere, arsenate (AsV) showed a positive interference and the extent of interference was independent of the level of inorganic P in both systems. On a weight basis, 1.0 µg of As is equivalent to 0.33 µg of “apparent inorganic P.” The amounts of As extractable by 3N HCl from nine surficial Wisconsin lake sediments ranged from <0.1 to 45 µg/g. The overestimation of inorganic P in 3N HCl extracts due to the positive interference from As was less than 1% in all cases. Calculations indicate that the maximum possible interference from As in a variety of extracts of these sediments is less than 2%, even if all of the As exists as arsenate, which is unlikely in reduced sediments. Arsenic was concentrated in the most recent sediments in a core from a Wisconsin lake, indicating that As interference in the determination of inorganic P in the older sediments is also not significant in view of the very low levels of As relative to inorganic P.

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTHerbicide Clorimetric Procedures, Evaluation of Pyridine-Alkali Colorimetic Method for Determination of AtrazineR. O. Radke, D. E. Armstrong, and Gordon ChestersCite this: J. Agric. Food Chem. 1966, 14, 1, 70–73Publication Date (Print):January 1, 1966Publication History Published online1 May 2002Published inissue 1 January 1966https://doi.org/10.1021/jf60143a023RIGHTS & PERMISSIONSArticle Views98Altmetric-Citations12LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (467 KB) Get e-Alertsclose Get e-Alerts