Organism transfer, soil-sediment

DHS can significantly affect the environmental behavior of hydrophobic organic compounds and lower the possibility of direct contact of such organic compounds with various solid phases. The rate of chemical degradation, photolysis, volatilization, transfer to sediments/soils, and biological uptake may be different for the fraction of organic pollutant that is bound to DHS. If this is the case, the distribution and total mass of a pollutant in an ecosystem depends, in part, on the extent of humic matter-hydrophobic binding. 

Sulfoxide Reduction Sulfoxide reduction is a two-electron-transfer reversible reaction resulting in thioethers. Organic sulfoxides are used mainly as agrochemicals, and their reduction (abiotic and microbially mediated) has been found in anaerobic soils, sediments, and groundwater (Larson and Weber 1994). 

Table I summarizes some typical distribution coefficients. Sediments become enriched in plutonium with respect to water, usually with a factor of vlO5. Also living organisms enrich plutonium from natural waters, but usually less than sediments a factor of 103 - 101 is common. This indicates that the Kd-value for sediment (and soil) is probably governed by surface sorption phenomena. From the simplest organisms (plankton and plants) to man there is clear evidence of metabolic discrimination against transfer of plutonium. In general, the higher the species is on the trophic level, the smaller is the Kd-value. One may deduce from the Table that the concentration of plutonium accumulated in man in equilibrium with the environment, will not exceed the concentration of plutonium in the ground water, independent of the mode of ingestion.

Lead enters surface water from atmospheric fallout, run-off, or wastewater. Little lead is transferred from natural minerals or leached from soil. Pb ", the stable ionic species of lead, forms complexes of low solubility with major anions in the natural environment such as the hydroxide, carbonate, sulfide, and sulfate ions, which limit solubility. Organolead complexes are formed with humic materials, which maintain lead in a bound form even at low pH. Lead is effectively removed from the water column to the sediment by adsorption to organic matter and clay minerals, precipitation as insoluble salt (the carbonate, sulfate, or sulfide) and reaction with hydrous iron, aluminum, and manganese oxides. Lead does not appear to bioconcentrate significantly in fish but does in some shellfish such as mussels. When released to the atmosphere, lead will generally occur as particulate matter and will be subject to gravitational settling. Transformation to oxides and carbonates may also occur. 

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