The chemical composition of natural water is derived from many different sources of solutes, including gases and aerosols from the atmosphere, weathering and erosion of rocks and soil, solution or precipitation reactions occurring below the land surface, and cultural effects resulting from human activities. Broad interrelationships among these processes and their effects can be discerned by application of principles of chemical thermodynamics. Some of the processes of solution or precipitation of minerals can be closely evaluated by means of principles of chemical equilibrium, including the law of mass action and the Nernst equation. Other processes are irreversible and require consideration of reaction mechanisms and rates. The chemical composition of the crustal rocks of the Earth and the composition of the ocean and the atmosphere are significant in evaluating sources of solutes in natural freshwater. The ways in which solutes are taken up or precipitated and the amounts present in solution are influenced by many environmental factors, especially climate, structure and position of rock strata, and biochemical effects associated with life cycles of plants and animals, both microscopic and macroscopic. Taken together and in application with the further influence of the general circulation of all water in the hydrologic cycle, the chemical principles and environmental factors form a basis for the developing science of natural-water chemistry. Fundamental data used in the determination of water quality are obtained by the chemical analysis of water samples in the laboratory or onsite sensing of chemical properties in the field. Sampling is complicated by changes in the composition of moving water and by the effects of particulate suspended material. Some constituents are unstable and require onsite determination or sample preservation. Most of the constituents determined are reported in gravimetric units, usually milligrams per liter or milliequivalents

Study and Interpretation of the Chemical Characteristics of Natural Water

Fenton chemistry encompasses reactions of hydrogen peroxide in the presence of iron to generate highly reactive species such as the hydroxyl radical and possibly others. In this review, the complex mechanisms of Fenton and Fenton-like reactions and the important factors influencing these reactions, from both a fundamental and practical perspective, in applications to water and soil treatment, are discussed. The review covers modified versions including the photoassisted Fenton reaction, use of chelated iron, electro-Fenton reactions, and Fenton reactions using heterogeneous catalysts. Sections are devoted to nonclassical pathways, by-products, kinetics and process modeling, experimental design methodology, soil and aquifer treatment, use of Fenton in combination with other advanced oxidation processes or biodegradation, economic comparison with other advanced oxidation processes, and case studies.

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Advanced Oxidation Processes for Organic Contaminant Destruction Based on the Fenton Reaction and Related Chemistry

Occurrence, fate and effects of pharmaceutical substances in the environment- A review

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

A surface science perspective on TiO2 photocatalysis

A rapid increase in the concentration of hydrogen peroxide was observed when samples of natural surface and ground water from various locations in the United States were exposed to sunlight. The hydrogen peroxide is photochemically generated from organic constituents present in the water; humic materials are believed to be the primary agent producing the peroxide. Studies with superoxide dismutase suggest that the superoxide anion is the precursor of the peroxide.

https://science.sciencemag.org/content/sci/220/4598/711.full.pdf

Photochemical formation of hydrogen peroxide in surface and ground waters exposed to sunlight.

Biogenic Sulfur Emissions: A Review U.S. National Biogenic Sulfur Emissions Inventory Variability in Biogenic Sulfur Emissions from Florida Wetlands Synthesis and Emission of Hydrogen Sulfide by Higher Plants Sulfur Emissions from Roots of the Rain Forest Tree Stryphnodendron excelsum: Ecosystem, Community, and Physiological Implications Origin of Hydrogen Sulfide in Freshwater Sediments Sulfur Cycling in an Experimentally Acidified Seepage Lake Reactivity of Sulfur Nucleophiles Toward Halogenated Organic Compounds in Natural Waters The Distribution of Dimethyl Sulfide in the Oceans: A Review Biogeochemical Cycling of Dimethyl Sulfide in Marine Environments Dimethyl Sulfide Production in Marine Phytoplankton Dimethyl Sulfide and (Dimethylsulfonio)propionate in European Coastal and Shelf Waters Microbial Metabolism of Dimethyl Sulfide Metabolism of Acrylate and 3-Mercaptopropionate: Decomposition Products of (Dimethylsulfonio)propionate in Anoxic Marine Sediments Mechanistic Studies of Organosulfur (Thiol) Formation in Coastal Marine Sediments Reduced Sulfur Compounds in the Marine Environment: Analysis by High-Performance Liquid Chromatography Enzymatic Steps and Dissimilatory Sulfur Metabolism by Whole Cells of Anoxyphotobacteria Thermodynamics and Kinetics of Hydrogen Sulfide in Natural Waters Hydrogen Sulfides in Oxic Seawater Dimethyl Sulfide and Hydrogen Sulfide in Marine Air Distribution of Biogenic Sulfur Compounds in the Remote Southern Hemisphere Sulfur Isotope Ratios: Tracers of Non-Sea Salt Sulfate in the Remote Atmosphere Two Automated Methods for Measuring Trace Levels of Sulfur Dioxide Using Translation Reactions Gas-Phase Atmospheric Oxidation of Biogenic Sulfur Compounds: A Review OH-Initiated Oxidation of Biogenic Sulfur Compounds: Kinetics and Mechanisms Under Atmospheric Conditions Mechanism of Atmospheric Oxidation of Sulfur Dioxide by Hydroxyl Radicals Mechanisms for the Reaction of CH[3S with NO[2 The Impact of Halogen Oxides on Dimethyl Sulfide Oxidation in the Marine Atmosphere Fourier Transform IR Studies of the Reactions of Dimethyl Sulfoxide with OH, NO[3, and Cl Radicals North Sea Dimethyl Sulfide Emissions as a Source of Background Sulfate over Scandinavia: A Model The Uptake of Gases by Liquid Droplets: Sulfur Dioxide Rate of Reaction of Methanesulfonic Acid, Dimethyl Sulfoxide, and Dimethyl Sulfone with Hydroxyl Radical in Aqueous Solution Oxidation of Biogenic Sulfur Compounds in Aqueous Media: Kinetics and Environmental Implications

Biogenic sulfur in the environment

Hydrogen peroxide is formed in most natural waters when they are exposed to sunlight. The rate at which H/sub 2/O/sub 2/ accumulates is related to the concentration of light-absorbing (>295 nm) organic substances in these waters. The photochemical accumulation rate of H/sub 2/O/sub 2/ in sunlight has been measured for several surface waters and ground waters and was found to be 2.7 /times/ 10/sup /minus/7/ to 48 /times/ 10/sup /minus/7/ mol L/sup /minus/1/ h/sup /minus/1/, in waters ranging from 0.53 to 18 mgL/sup -1/ dissolved organic carbon (DOC), respectively. These rates were determined in midday sunlight, 0.4 W m/sup /minus/2/ (295-385 nm), latitude 24.3/degrees/ N. Apparent quantum yields of H/sub 2/O/sub 2/ have been determined for natural waters at different wavelengths. These quantum yields decreased with increasing wavelength, from 10/sup /minus/3/ in the near-ultraviolet to 10/sup /minus/6/ in the visible spectral range. The quantum yields have been used in a photochemical model to calculate H/sub 2/O/sub 2/ accumulation rates of natural water samples. Model calculations agree with H/sub 2/O/sub 2/ accumulation rates obtained from exposing three different water samples to sunlight.

Photochemical formation of hydrogen peroxide in natural waters exposed to sunlight.

Sunlight-Induced Photochemistry of Humic Substances in Natural Waters: Major Reactive Species

Variability in chromophoric dissolved organic carbon (CDOM) was characterized in and around the Cape Fear River and Onslow Bay, North Carolina USA. The river end member of the study is extremely rich in CDOM, thus the Cape Fear River serves as a point source of CDOM-rich water into the southeastern Atlantic bight. The river plume is easily traceable and generally extends in a southwesterly direction along the coastline into Long Bay. Depending on physical processes and river flow, the plume can meander somewhat and may even turn northward for short periods of time. The oceanic end member of this study was the Gulf Stream. Samples from the Gulf Stream were obtained up to 97 km off shore. The experimental approach focused on the qualitative and quantitative description of CDOM from fresh-to-oceanic waters. CDOM was characterized by excitation emission matrix (EEM) fluorescence and UV/VIS spectroscopy. Variability of CDOM absorption in the relatively small area of the Cape Fear River estuary and surrounding coastal ocean was very high. The observed range of variability of CDOM absorption coefficient, a
 CDOM
 (350), extended over nearly the entire range of CDOM absorption in the literature: 0.046 = a
 CDOM
 (350) = 29.9 m–1. Changes in CDOM absorption spectrum slope coefficient S, were small in the Cape Fear River plume area, but relatively large in Onslow Bay. CDOM EEM spectra indicated that a radical change in composition of CDOM occurs along the river-to-oceanic salinity gradient. CDOM in the coastal ocean was characterized by strong reduction of the three principal intensity peaks: A, C, and M, and a prominent contribution of the T peak to the fluorescence spectrum. The fluorescence intensity is linearly related with absorption. There is a strong inverse relationship between salinity and CDOM absorption. The distribution of the slope coefficient and the percent contribution of respective peak intensities to the total EEM intensity showed that CDOM undergoes conservative mixing until it approached oceanic salinity. Thus, CDOM is so concentrated in the river that mixing and other physical processes mask photochemical or biological alteration of its composition.

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William J. Cooper

Papers

Photochemical formation of hydrogen peroxide in surface and ground waters exposed to sunlight.

Biogenic sulfur in the environment

Photochemical formation of hydrogen peroxide in natural waters exposed to sunlight.

Sunlight-Induced Photochemistry of Humic Substances in Natural Waters: Major Reactive Species

Characterization of CDOM in an organic-rich river and surrounding coastal ocean in the South Atlantic Bight