Geology topics

M. Haitzer

Publications and source records attributed to M. Haitzer.

6 recordsLinked to original sources

USGS2003

Binding of mercury(II) to aquatic humic substances: Influence of pH and source of humic substances

Conditional distribution coefficients ( K DOM ‘) for Hg(II) binding to seven dissolved organic matter (DOM) isolates were measured at environmentally relevant ratios of Hg(II) to DOM. The results show that K DOM ‘ values for different types of samples (humic acids, fulvic acids, hydrophobic acids) isolated from diverse aquatic environments were all within 1 order of magnitude (10 22.5 ± 1.0 −10 23.5 ± 1.0 L kg - 1 ), suggesting similar Hg(II) binding environments, presumably involving thiol groups, for the different isolates. K DOM ‘ values decreased at low pHs (4) compared to values at pH 7, indicating proton competition for the strong Hg(II) binding sites. Chemical modeling of Hg(II)−DOM binding at different pH values was consistent with bidentate binding of Hg(II) by one thiol group (p K a = 10.3) and one other group (p K a = 6.3) in the DOM, which is in agreement with recent results on the structure of Hg(II)−DOM bonds obtained by extended X-ray absorption fine structure spectroscopy (EXAFS).

Environmental Science & Technology↗

USGS2003

Interactions between dissolved organic matter and mercury in the Florida Everglades

Experiments were conducted using organic matter isolated from various surface waters in the Florida Everglades to study the interactions between dissolved organic matter (DOM) and Hg (II). Conditional distribution coefficients ( ), obtained using an equilibriurn dialysis ligand exchange method, were strongly affected by the Hg/DOM concentration ratio. Very strong interactions ( = 10 L kg -1 ), indicative of Hg-thiol bonds, were observed at Hg/DOM ratios below approximately 1 g Hg per mg DOM. Above approximately 10 g Hg per mg DOM much lower values ( L kg -1 ) were obtained. DOM-Hg interactions were also studied by HgS (log K ) dissolution and precipitation experiments. In the dissolution experiments, a significant amount of Hg was released from cinnabar in the presence of DOM, suggesting strong interactions. Conversely, precipitation of HgS was strongly inhibited in the presence of low concentrations ( 3 mg C/L) of DOM. In both the dissolution and precipitation experiments, organic matter rich in aromatic moities was more reactive with HgS than less aromatic fractions and sulfur-containing model compounds. These results suggest that DOM can influence the geochemistry of inorganic complexes of Hg in the Everglades, especially HgS, by strong Hg-DOM binding and colloidal stabilization.

Florida↗

USGS2002

Binding of mercury(II) to dissolved organic matter: The role of the mercury-to-DOM concentration ratio

The binding of Hg(II) to dissolved organic matter (DOM; hydrophobic acids isolated from the Florida Everglades by XAD-8 resin) was measured at a wide range of Hg-to-DOM concentration ratios using an equilibrium dialysis ligand exchange method. Conditional distribution coefficients ( K DOM ‘) determined by this method were strongly affected by the Hg/DOM concentration ratio. At Hg/DOM ratios below approximately 1 μg of Hg/mg of DOM, we observed very strong interactions ( K DOM ‘ = 10 23.2 ± 1.0 L kg - 1 at pH = 7.0 and I = 0.1), indicative of mercury−thiol bonds. Hg/DOM ratios above approximately 10 μg of Hg/mg of DOM, as used in most studies that have determined Hg−DOM binding constants, gave much lower K DOM ‘ values (10 10.7 ± 1.0 L kg - 1 at pH = 4.9−5.6 and I = 0.1), consistent with Hg binding mainly to oxygen functional groups. These results suggest that the binding of Hg to DOM under natural conditions (very low Hg/DOM ratios) is controlled by a small fraction of DOM molecules containing a reactive thiol functional group. Therefore, Hg/DOM distribution coefficients used for modeling the biogeochemical behavior of Hg in natural systems need to be determined at low Hg/DOM ratios.

Environmental Science & Technology↗

USGS2001

No enhancement in bioconcentration of organic contaminants by low levels of DOM

The aim of the present work was to systematically study the effect of low concentrations of dissolved organic matter (DOM) on the bioconcentration of organic contaminants, in order to show whether the phenomenon of enhanced bioconcentration factors (BCFs), that has been reported in the literature, is generally found at low levels of DOM or if BCF enhancements are more likely due to a random scatter in the experimental data. The first part of the study tested the hypothesis that low levels of DOM affect the uptake kinetics of organic contaminants, leading to transient enhancements of BCFs, relative to DOM-free controls, which could have been reported as BCF enhancements in short-term studies. We found that the presence of low concentrations of two different types of DOM consistently decreased the bioconcentration of benzo[a]pyrene (BaP) in the water flea Daphnia magna at all exposure times (1-24 h), and that no transient BCF enhancements occurred. The second part of the study systematically investigated if low concentrations of DOM from a wide range of different aquatic systems can cause enhancements in the bioconcentration of organic contaminants. Water fleas were exposed to combinations of four different organic contaminants (BaP, tetrachlorobiphenyl, pentachlorophenol and naphthalene) with low concentrations of 12 different types of DOM that had been collected from various regions throughout Europe. In several of the DOM treatments, we found mean BCFs being higher than mean BCFs in the controls (especially for naphthalene). This shows that the experimental setup used in this study (and similarly in previous studies) can produce seeming BCF enhancements at low concentrations of DOM. However, statistical analyses showed that treatment means were not significantly different from control means. Thus, this systematic study suggests that the BCF enhancements that have been reported in the literature are more likely the result of random, experimental variations than the result of a systematic enhancement of bioconcentration. ?? 2001 Elsevier Science Ltd.

Chemosphere↗

USGS2001

Bioavailability of atrazine, pyrene and benzo[a]pyrene in European river waters

Thirteen river waters and one humic lake water were characterized. The effects of dissolved organic matter (DOM) on the bioavailability of atrazine, pyrene and benzo[a]pyrene (B[a]P) was evaluated. Binding of the chemicals by DOM was analyzed with the equilibrium dialysis technique. For each of the water samples, 24 h bioconcentration factors (BCFs) of the chemicals were measured in Daphnia magna. The relationship between DOM and other water characteristics (including conductivity, water hardness and pH), and bioavailability of the chemicals was studied by performing several statistical analyses, including multiple regression analyses, to determine how much of the variation of BCF values could be explained by the quantity and quality of DOM. The bioavailability of atrazine was not affected by DOM or any other water characteristics. Although equilibrium dialysis showed binding of pyrene to DOM, the bioavailability of pyrene was not significantly affected by DOM. The bioavailability of B[a]P was significantly affected by both the quality and quantity of DOM. Multiple regression analyses, using the quality (ABS270 and HbA%) and quantity of DOM as variables, explainedup to 70% of the variation in BCF of B[a]P in the waters studied. ?? 2001 Elsevier Science Ltd. All rights reserved.

Chemosphere↗

USGS1999

Effects of humic substances on the bioconcentration of polycyclic aromatic hydrocarbons: Correlations with spectroscopic and chemical properties of humic substances

The presence of dissolved humic substances (HS, fulvic and humic acids) generally reduces the up take of hydrophobic organic compounds into aquatic organisms. The extent of this effect depends both on the concentration and on the origin of the HS. The aim of this study was to investigate the role of qualitative differences between HS from different origins. The effects of seven different HS on the bioconcentration of pyrene and benzo[ a ]pyrene (B a P) in the nematode Caenorhabditis elegans were related to the spectroscopic and chemical properties of the HS. The effect of each humic material on the bioconcentration of pyrene or B a P was quantified as a “biologically determined” partition coefficient K DOC . We observed significant linear relationships between K DOC and the atomic H/C ratio, the specific absorptivity at 254 nm, the content of aromatic carbons (as determined by 13 C nuclear magnetic resonance spectroscopy, the copper-complexing capacity, the content of phenolic OH groups, and the molecular weight of the HS. There was no discernible relationship of K DOC with the atomic (N + O)/C ratio, an indicator of the polarity of HS. Taken together, our results show that the variability in the effects of HS from different origins could be related to variations in bulk properties of the HS. Parameters describing the aromaticity of the humic materials seemed to be most useful for estimating effects of HS on the bioconcentration of pyrene and B a P.

Environmental Toxicology and Chemistry↗