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

Aquatic chemistry is becoming both a rewarding and substantial area of inquiry and is drawing many prominent scientists to its fold. Its literature has changed from a compilation of compositional tables to studies of the chemical reactions occurring within the aquatic environments. But more than this is the recognition that human society in part is determining the nature of aquatic systems. Since rivers deliver to the world ocean most of its dissolved and particulate components, the interactions of these two sets of waters determine the vitality of our coastal waters. This significant vol ume provides not only an introduction to the dynamics of aquatic chem istries but also identifies those materials that jeopardize the resources of both the marine and fluvial domains. Its very title provides its emphasis but clearly not its breadth in considering natural processes. The book will be of great value to those environmental scientists who are dedicated to keeping the resources of the hydrosphere renewable. As the size of the world population becomes larger in the near future and as the uses of materials and energy show parallel increases, the rivers and oceans must be considered as a resource to accept some of the wastes of society. The ability of these waters and the sediments below them to accommodate wastes must be assessed continually. The key questions relate to the capacities of aqueous systems to carry one or more pollutants."

Metal pollution in the aquatic environment

Bioavailability, accumulation and effects of heavy metals in sediments with special reference to United Kingdom estuaries: a review

The purpose of this review paper is to present the technical basis for establishing sediment quality criteria using equilibrium partitioning (EqP). Equilibrium partitioning is chosen because it addresses the two principal technical issues that must be resolved: the varying bioavailability of chemicals in sediments and the choice of the appropriate biological effects concentration.

The data that are used to examine the question of varying bioavailability across sediments are from toxicity and bioaccumulation experiments utilizing the same chemical and test organism but different sediments. It has been found that if the different sediments in each experiment are compared, there is essentially no relationship between sediment chemical concentrations on a dry weight basis and biological effects. However, if the chemical concentrations in the pore water of the sediment are used (for chemicals that are not highly hydrophobic) or if the sediment chemical concentrations on an organic carbon basis are used, then the biological effects occur at similar concentrations (within a factor of two) for the different sediments. In addition, the effects concentrations are the same as, or they can be predicted from, the effects concentration determined in water- only exposures.

The EqP methodology rationalizes these results by assuming that the partitioning of the chemical between sediment organic carbon and pore water is at equilibrium. In each of these phases, the fugacity or activity of the chemical is the same at equilibrium. As a consequence, it is assumed that the organism receives an equivalent exposure from a water-only exposure or from any equilibrated phase, either from pore water via respiration, from sediment carbon via ingestion; or from a mixture of the routes. Thus, the pathway of exposure is not significant. The biological effect is produced by the chemical activity of the single phase or the equilibrated system.

Sediment quality criteria for nonionic organic chemicals are based on the chemical concentration in sediment organic carbon. For highly hydrophobic chemicals this is necessary because the pore water concentration is, for those chemicals, no longer a good estimate of the chemical activity. The pore water concentration is the sum of the free chemical concentration, which is bioavailable and represents the chemical activity, and the concentration of chemical complexed to dissolved organic carbon, which, as the data presented below illustrate, is not bioavailable. Using the chemical concentration in sediment organic carbon eliminates this ambiguity.

Sediment quality criteria also require that a chemical concentration be chosen that is sufficiently protective of benthic organisms. The final chronic value (FCV) from the U.S. Environmental Protection Agency (EPA) water quality criteria is proposed. An analysis of the data compiled in the water quality criteria documents demonstrates that benthic species, defined as either epibenthic or infaunal species, have a similar sensitivity to water column species. This is the case if the most sensitive species are compared and if all species are compared. The results of benthic colonization experiments also support the use of the FCV.

Equilibrium partitioning cannot remove all the variation in the experimentally observed sediment- effects concentration and the concentration predicted from water-only exposures. A variation of approximately a factor of two to three remains. Hence, it is recognized that a quantification of this uncertainty should accompany the sediment quality criteria.

The derivation of sediment quality criteria requires the octanol/water partition coefficient of the chemical. It should be measured with modern experimental techniques, which appear to remove the large variation in reported values. The derivation of the final chronic value should also be updated to include the most recent toxicological information.

https://setac.onlinelibrary.wiley.com/doi/pdf/10.1002/etc.5620101203

Technical basis for establishing sediment quality criteria for nonionic organic chemicals using equilibrium partitioning

Nano-silver is used in an increasing number of products. Some of the applications have resulted in the concern of governments and the public, since little is known about the potential risks of nano-silver. In this review, an inventory is made to identify knowledge gaps that have to be filled before risks for both man and the environment can be assessed as reliable as for ‘non-nanosized’ chemicals. It is hypothesized that the toxic effects of nano-silver are due to a combination of the specific properties of silver nanoparticles and the generation of ions from them. The main topic for future research is validation of our ‘0-hypothesis’ that toxic effects of nano-silver are proportional to the activity of free silver ions released by the nanoparticles. Furthermore, it must be determined whether – or to what extent – nano-silver particles will enter the body. The outcomes of these tests will determine the requirements for further toxicity testing.

Nano-silver – a review of available data and knowledge gaps in human and environmental risk assessment

https://wwwrcamnl.wr.usgs.gov/tracel/references/pdf/SciTotEnviron_v17p165.pdf

A statistical assessment of the form of trace metals in oxidized estuarine sediments employing chemical extractants

Concentrations of lead in the soft tissues of the deposit-feeding bivalve Scrobicularia plana have been compared with the physicochemical characteristics of sediments in 20 estuaries in southern and western England and one in north-west France. The results indicate that the biological availability of lead in the sediment is controlled mainly by the concentration of iron, and that the concentration of lead in the bivalve may be predicted from the Pb/Fe ratio in 1 N hydrochloric acid extracts of surface sediments.

Factors controlling the availability of sediment-bound lead to the estuarine bivalve scrobicularia plana

Multiple regression analyses indicate that the most important factors controlling Ag, Cd, Co, Cu, Pb and Zn concentrations in the estuarine bivalve Scrobicularia plana and the polychaete Nereis diversicolor are the concentrations of these metals in surface sediments and the partitioning of sediment-bound metals between different sediment constituents. Extraction of the sediments with 1-n HCl provides more information about the bioavailability of the metals than do extractions with five other techniques. Biologically available Cd and Co in solution contribute significantly to Cd and Co concentrations in both Scrobicularia and Nereis. Concentrations of Ag in Scrobicularia are reduced where Cu concentrations in sediments are high. An unexplained increase in concentrations of Cu in Scrobicularia at specific stations in six estuaries suggests that under certain very anoxic conditions the availability of copper may be exceptionally high.

A statistical study of environmental factors controlling concentrations of heavy metals in the burrowing bivalve Scrobicularia plana and the polychaete Nereis diversicolor

https://wwwrcamnl.wr.usgs.gov/tracel/references/pdf/MarPolBull_v31n1-3p44.pdf

G.W. Bryan

Papers

A statistical assessment of the form of trace metals in oxidized estuarine sediments employing chemical extractants

Factors controlling the availability of sediment-bound lead to the estuarine bivalve scrobicularia plana

A statistical study of environmental factors controlling concentrations of heavy metals in the burrowing bivalve Scrobicularia plana and the polychaete Nereis diversicolor

Fate, bioavailability and toxicity of silver in estuarine environments

Effects of tributyltin pollution on the mud snail, Ilyanassa obsoleta, from the York river and Sarah creek, Chesapeake bay