Characterization of marine and terrestrial DOM in seawater using excitation-emission matrix spectroscopy

This book is written as a reference on organic substances in natural waters and as a supplementary text for graduate students in water chemistry. The chapters address five topics: amount, origin, nature, geochemistry, and characterization of organic carbon. Of these topics, the main themes are the amount and nature of dissolved organic carbon in natural waters (mainly fresh water, although seawater is briefly discussed). It is hoped that the reader is familiar with organic chemistry, but it is not necessary. The first part of the book is a general overview of the amount and general nature of dissolved organic carbon. Over the past 10 years there has been an exponential increase in knowledge on organic substances in water, which is the result of money directed toward the research of organic compounds, of new methods of analysis (such as gas chromatography and mass spectrometry), and most importantly, the result of more people working in this field. Because of this exponential increase in knowledge, there is a need to pull together and summarize the data that has accumulated from many disciplines over the last decade.

Organic geochemistry of natural waters

Because it is very toxic and accumulates in organisms, particularly in fish, mercury is an important pollutant and one of the most studied. Nonetheless we still have an incomplete understanding of the factors that control the bioconcentration of mercury. Elemental mercury is efficiently transported as a gas around the globe, and even remote areas show evidence of mercury pollution originating from industrial sources such as power plants. Besides elemental mercury, the major forms of mercury in water are ionic mercury (which is bound to chloride, sulfide, or organic acids) and organic mercury, particularly methylmercury. Methylmercury rather than inorganic mercury is bioconcentrated because it is better retained by organisms at various levels in the food chain. The key factor determining the concentration of mercury in the biota is the methylmercury concentration in water, which is controlled by the relative efficiency of the methylation and demethylation processes. Anoxic waters and sediments are an important source of methylmercury, apparently as the result of the methylating activity of sulfatereducing bacteria. In surface waters, methylmercury may originate from anoxic

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The chemical cycle and bioaccumulation of mercury

Mercury is one of the most hazardous contaminants that may be present in the aquatic environment, but its ecological and toxicological effects are strongly dependent on the chemical species present. Species distribution and transformation processes in natural aquatic systems are controlled by various physical, chemical, and biological factors. Depending on the prevailing environmental conditions, inorganic mercury species may be converted to many times more toxic methylated forms such as methylmercury, a potent neurotoxin that is readily accumulated by aquatic biota. Despite a considerable amount of literature on the subject, the behavior of mercury and many of the transformation and distribution mechanisms operating in the natural aquatic environment are still poorly understood. This review examines the current state of knowledge on the physicochemical behavior of mercury in the aquatic environment, and in particular the environmental factors influencing its transformation into highly toxic methylated forms.

Mercury in the Aquatic Environment: A Review of Factors Affecting Methylation

Geochemistry of Recent oxic and anoxic marine sediments: Implications for the geological record

Fluorescence quenching titration for determination of complexing capacities and stability constants of fulvic acid

Review of possible paths for abiotic methylation of mercury(II) in the aquatic environment

Inorganic tin and methyl- and n-butyltin compounds were speciated by volatilization from water samples by hydride generation, separation by a chromatographic packing material, and detection by atomic absorption spectrophotometry in an electrothermal quartz furnace at the 224.61-nm wavelength. Absolute detection limits of 20-50 pg (3sigma) as Sn and linearity of calibration curves up to 30 ng as Sn avoid preconcentration by extraction and allow direct determination of methyl- and n-butyltin compounds from environmental waters. Reproducibility for 15 ng as Sn is less than 15% for most alkyltin compounds. This study discusses optimization of parameters and results from natural waters. 26 references, 4 figures, 3 tables.

Speciation of inorganic tin and alkyltin compounds by atomic absorption spectrometry using electrothermal quartz furnace after hydride generation

A novel method for speciation and determination of Me/sub 3/Pb/sup +/ and Me/sub 2/Pb/sup 2 +/ is described. The procedure includes in situ ethylation by sodium tetraethylborate (NaBEt/sub 4/) in water, purging and trapping of alkyllead molecules, and thermal desorption in an electrically heated quartz AAS furnace. The absolute detection limits of Pb for 50 cm/sup 3/ are ca. 8.7 pg for Me/sub 3/Pb/sup +/ (0.18 pg/cm/sup 3/) and ca. 10.5 pg for Me/sub 2/Pb/sup 2 +/ (0.21 pg/cm/sup 3/). Major advantages for the technique are avoidance of solvent extraction and ample transfers because ethylation to Me/sub 3/EtPb and Me/sub 2/Et/sub 2/Pb takes place in a closed system. Reaction conditions and apparatus operating parameters were optimized by a Simplex algorithm. 24 refs., 3 figs., 1 tab.

Speciation of lead and methyllead ions in water by chromatography/atomic absorption spectrometry after ethylation with sodium tetraethylborate

Fulvic acid, which is derived from the decay of plants and animals, is being studied for its role in the transport and toxicity of metal ions in soil and water. It is discussed in relation to the origin of humic substances and its interactions with metal ions. Techniques for investigating complexes of fulvic acid and metal ions are presented. They are separation and nonseparation analyses which are applied to speciation problems. The applicability, advantages, and disadvantages of both methods are presented. Separation of free and complexed metal ions can be done by chromatography, or with membranes that exclude the metal-ion complexes. Chromatographic techniques include liquid chromatography by size exclusion. Nonseparation techniques include voltametry and potentiometry, as well as fluorescence. A comparison of methods for calculation of the conditional stability constant K for complexes containing fulvic acid and copper (II) or cadmium (II) is presented.

James H. Weber

Papers

Fluorescence quenching titration for determination of complexing capacities and stability constants of fulvic acid

Review of possible paths for abiotic methylation of mercury(II) in the aquatic environment

Speciation of inorganic tin and alkyltin compounds by atomic absorption spectrometry using electrothermal quartz furnace after hydride generation

Speciation of lead and methyllead ions in water by chromatography/atomic absorption spectrometry after ethylation with sodium tetraethylborate

Fulvic acid: modifier of metal-ion chemistry.