James R. Kramer

Determination of complexing capacities of ligands in natural waters and conditional stability constants of the copper complexes by means of manganese dioxide

A dispersion of manganese dioxide is used as a weak ion exchanger in the determination of the complexing capacities of natural waters for copper and in the estimation of the stability constants of the complexes formed, at the concentration and pH at which the ligands occur in natural waters. Experiments were done at 25°C and 0.01 M ionic strength. Stability constants varied from 107.8 to 108.8 at pH 7.6 for ligands in lakes and rivers. The constant for the copper—fulvic acid complex was estimated as 107.8 at pH 7.6. Only one complexing site of major importance for natural water environments was observed.

Sulfur and oxygen isotopes of sulfate in precipitation and lakewater, Quebec, Canada

Stable isotope ratios of sulfur and oxygen of sulfate ion in precipitation and lakewater were monitored in six headwater lakes in Quebec, Canada. The lakes studied are oligotrophic and located over a wide area (350 km) on the Canadian Shield, which is known to be sensitive to acidification. The δ34S of the sulfate ion in precipitation ranges from 3.1 to 6.7‰ for all locations during the sampling period, which is very close to the values found for the lakes, from 3.5 to 6.7‰. Moreover, the δ34S of sulfate showed seasonal variations which are parallel in time for all stations. This strongly suggests that precipitation is a major source of sulfate in the lakes that were investigated. However, the δ18Ovalues of precipitation sulfate are close to each other between stations and are consistently higher (+ 8.3 to 13.5‰) than that of the lakes (+ 1.7 to 8.5‰). In addition, there is no spatial or temporal trend in lake δ18O sulfate, suggesting that a transformation occurs to sulfate in the watersheds. We suggest the hypothesis that sulfate ion is reduced and reoxidized in the runoff and lake waters so that it acquires an oxygen isotopic label different from precipitation.

Potentiometric Determination of Silver Thiolate Formation Constants Using a Ag2S Electrode

Formation constants for silver thiolates were obtained by titration of the ligand in a constant temperature, ionic strength and pH medium and measuring the potential change at a Ag2S electrode. A non-linear equation was derived from which the first and second silver formation constants, β1 and β2′, and the sulfide group acid dissociation constant, Ka′, were determined. An overall estimate of the uncertainty in the derived parameters was obtained using a Monte Carlo approach. The procedure was compared to a previous work on AgHS°. Log β1′, log β2′ and - log Ka′ results were obtained for cysteine (11.9 ± 0.5, 15.2 ± 0.4, 7.8 ± 0.1), glutathione (12.3 ± 0.3, 14.3 ± 0.8, 8.8 ± 0.3) and 3-mercaptopropanoic acid (12.0± 0.4, 14.0 ± 0.4, 10.5 ± 0.3) at 20 °C and 0.01 m ionic strength.

Multisite metal binding to fulvic acid determined using multiresponse fluorescence

Metal binding to Suwannee River fulvic acid (SRFA) is determined using multiresponse fluorescence. The fluorescence surface of SRFA is described by five average fluorescent components, determined by spectral resolution using SIMPLISMA [W. Windig, J. Guilment, Anal. Chem. 63 (1991) 1425]. Fluorescence at excitation and emission wavelengths corresponding to these components was measured during titration with Cu(II). The resultant multiresponse data were fit to a five-site speciation model for Cu‐SRFA interactions. The excitation/emission wavelengths identified for the fives sites are: 320/425, 370/450, 420/500, 480/540 and 500/550 nm. Logarithms of the conditional stability constants assuming one to one complex stoichiometry for the five sites at pH 6.02 and ionic strength of 0.1 M (KClO 4) are: 4.95 (0.23), 4.98 (0.23), 5.32 (0.21), 5.59 (0.24), and 5.62 (0.22). The respective concentrations (mmol/mg of SRFA) are 0.83 (0.44), 2.38 (0.56), 2.76 (0.29), 0.74 (0.09), 0.037 (0.005), where the bracket values indicate 95% confidence intervals. Free copper predicted using these parameters agrees within 0.1 of log unit of predicted free copper concentration from Cabaniss and Shuman’s empirical equation [S.E. Cabaniss, M.S. Shuman, Geochim. Cosmochim. Acta 52 (1988) 185]. This agreement gives additional credence to the multiresponse multisite fluorescent method used in this paper. These values are compared to existing values for Al and H binding by SRFA, for the same five sites, also determined using multi-response fluorescence. The binding of Al, Cu and H are best represented as bidentate/diprotic sites. The conditional stability constants for Al and Cu are consistent with salicylic acid-like binding.

Sulphur isotope tests of seasalt correction factors in precipitation: Nova Scotia, Canada

Sulphate in precipitation is an index of atmospheric pollution but natural sources also contribute to its concentration. One of the dominant natural sources of sulphate is seasalt and reseachers have routinely calculated its proportion using reference species such as Cl−, Na+ and Mg2+. Such a method of estimation assumes conservatism of, and a purely marine origin for, the reference species. The stable isotopes of sulphur were utilized to assess the validity of these assumptions for a coastal area in Canada by taking advantage of the sulphur isotopic signature of seasalt sulphate (+20‰). The seaspray component (PSS) was calculated for 39 coastal rain events using Cl−, Na+ and Mg2+ as reference species and these parameters were plotted against the sulphur isotopic composition of sulphate in the sample. All three regression lines yielded a value of ≈ +4‰ for a sample containing no seasalt. The regression lines extrapolated to δ34S≈+20, +17 and +16‰ using Cl−, Na+ and Mg2+ respectively for a theoretical sample whose sulphate was derived totally from seasalt. This observation confirms that for this locality, the marine component of precipitation sulphate utilizing Cl− is isotopically equivalent to sea spray sulphate, suggesting that Cl− is a suitable reference species. It also supports the use of δ34SSO4 as a constraint on the selection of the correct reference species for estimation of the seasalt component in a particular study area.

Silver speciation during chronic toxicity tests with the mysid, Americamysis bahia.

A 28-day chronic toxicity test and two 7-day chronic estimation toxicity tests were conducted with silver nitrate (AgNO(3)) and the marine invertebrate, Americamysis bahia, in 20 per thousand (parts-per thousand) salinity seawater. One 7-day test was initiated with 7-day-old mysids and the second was initiated with <24-h-old mysids. There was very good agreement between the three toxicity tests. The no-observed-effect concentration (NOEC) values from the 28-day test, the 7-day test initiated with 7-day-old mysids, and the 7-day test initiated with <24-h-old mysids were 34, 65 and 38 microg/l silver, respectively. The 96-h LC50 values from the 28-day toxicity test and the 7-day toxicity test initiated with 7-day old mysids were 260 microg/l, and the 96-h LC50 value from the 7-day toxicity test initiated with <24-h-old mysids was 280 microg/l. Free ionic silver, Ag(+), concentrations measured with a silver electrode were in good agreement with concentrations calculated using total dissolved silver and chloride concentrations. Mean measured concentrations of Ag(+) in the test solutions ranged from 0.99 to 25 ng/l for the dissolved silver concentrations that ranged from 34 to 410 microg/l silver, indicating that free ionic silver varied from 0.003 to 0.006% of the silver dissolved in the 20 per thousand salinity seawater. Understanding the relationship of salinity and silver speciation, and the effect of this relationship on chronic invertebrate toxicity, will be useful for development of a marine biotic ligand model (BLM) and a water quality criterion for silver. This model could provide an important tool for improving the relationship of laboratory toxicity test results and predicted effects in natural environments, where variations in salinity may act to modify the toxicity of silver and other metals.

Resolving uncertainty in chemical speciation determinations

Abstract Speciation determinations involve uncertainty in system definition and experimentation. Identification of appropriate metals and ligands from basic chemical principles, analytical window considerations, types of species and checking for consistency in equilibrium calculations are considered in system definition uncertainty. A systematic approach to system definition limits uncertainty in speciation investigations. Experimental uncertainty is discussed with an example of proton interactions with Suwannee River fulvic acid (SRFA). A Monte Carlo approach was used to estimate uncertainty in experimental data, resulting from the propagation of uncertainties in electrode calibration parameters and experimental data points. Monte Carlo simulations revealed large uncertainties present at high (>9–10) and low (

Multi-site proton interactions with natural organic matter

Abstract Water samples from various locations in Norway were used to isolate natural organic matter (NOM). The NOM was isolated using both reverse osmosis and low-pressure low-temperature evaporation for each sample site. These samples were titrated from −log[H+] 3 to 11 at 0.1 unit intervals. The data were analyzed using the Discrete Site Analysis (DISI) technique for pKa intervals of 0.2. The acidity constants are grouped into four classes: strong (pKa 9.3). All samples, regardless of isolation method, were found to contain strong and weak ligands, along with some intermediate ligands. For the same sample site, the concentration of these ligands were found to be dependent on isolation method and titration direction (acid then base vs. base then acid). In addition, the concentration and classes of ligands present were found to vary between sample sites. Suwannee River fulvic acid was analyzed as a reference sample, and was qualitatively similar to the NOM samples but quantitatively different. Overall, the differences in pKa spectra due to isolation method and/or titration direction are almost as significant as differences between sample location, but there are no consistent trends in effects of isolation method or titration direction on characterization of NOM.

The biotic ligand model and a cellular approach to class B metal aquatic toxicity

The biotic ligand model (BLM) and a cellular molecular mechanism approach represent two approaches to the correlation of metal speciation with observed toxicity to aquatic organisms. The two approaches are examined in some detail with particular reference to class B, or soft metals. Kinetic arguments are presented to suggest situations that can arise where the BLM criterion of equilibrium between all metal species in the bulk solution and the biotic ligand may not be satisfied and what might the consequences be to BLM predictive capability. Molecular mechanisms of toxicity are discussed in terms of how a class B metal might enter a cell, how it is distributed in a cell, and how the cell might respond to the unwanted metal. Specific examples are given for copper as an organism trace essential metal, which is toxic in excess, and for silver, a non-essential metal. As class B metals all bind strongly to sulfur, regulation of these metals requires that all S(II-) species be accounted for in aquatic systems, even under oxic conditions.

Concentration of aquatic dissolved organic matter by reverse osmosis

Abstract Dissolved organic carbon (DOC) was concentrated from natural streams using reverse osmosis equipment. Quality control tests show that from 95.6 to 98.5% of total DOC was rejected by the membrane, though only 70% could actually be recovered, most likely because of losses within the plumbing system. Comparison of the acid-base characteristics of the original water sample with re-diluted concentrate show that modifications occurred. Visual evidence showed that polycondensation reactions which modify acid-base characteristics occurred in the concentrate. Analysis of the material passing through the membrane (permeate) shows that it is