Abiotic processes surface

Sorption/desorption is the key property for estimating the mobility of organic pollutants in solid phases. There is a real need to predict such mobility at different aqueous-solid phase interfaces. Solid phase sorption influences the extent of pollutant volatilization from the solid phase surface, its lateral or vertical transport, and biotic or abiotic processes (e.g., biodegradation, bioavailability, hydrolysis, and photolysis). For instance, transport through a soil phase includes several processes such as bulk flow, dispersive flow, diffusion through macropores, and molecular diffusion. The transport rate of an organic pollutant depends mainly on the partitioning between the vapor, liquid, and solid phase of an aqueous-solid phase system. 

Environmental organic matter is a composite of humic and nonhumic substances, which is formed through operation and interactions of various biotic and abiotic processes. Humic substances are formed through both selected preservation (residue) and catalytic synthesis mechanisms. Both enzymatic and mineral catalyses contribute to the formation of humic substances in the environment. The relative importance of these catalytic reactions would depend on vegetation, microbial population and activity, enzymatic activity, mineralogical composition and surface chemistry of environmental particles, management practices, and environmental conditions. Selective preservation pathways would play a more important role in humification processes in poorly drained soils and lake sediments, compared with more aerated environmental conditions. 

Profiles of dissolved iron in seawater show the influence of both biotic and abiotic processes. At stations in the Northeast Pacific, dissolved iron concentrations are low in surface waters, reflecting biological uptake. Iron concentrations also show peak values at depth, corresponding to the oxygen minimum zone (Martin and Gordon, 1988), suggesting the abiotic reduction of Fe(III) back to the soluble Fe(II). 

The polygenetic model of rock varnish formation combines biotic enhancement of Mn with abiotic processes (Dorn, 1998). It builds on the mineralogy research of Potter and Rossman (1979a,b,c) and studies of bacteria fossil remains within varnish layers (Dorn and Meek, 1995 Krinsley et al., 1995 Dorn, 1998 Krinsley, 1998). In brief, weathered remains of Mn-rich bacterial casts (Figure 8.6) cement weathered clay minerals to rock surfaces. 

PCBs, particularly the highly chlorinated congeners, adsorb strongly to sediment and soil where they tend to persist with half-lives on the order of months to years (see Section 6.3.1 Gan and Berthouex 1994 Kohl and Rice 1998). There is no abiotic process known that significantly degrades PCBs in soil and sediment. However, photolysis of PCBs from surface soil may occur, and PCBs may also undergo base-... 

In two independent studies that simulated comet chemistry, racemic amino acids formed after irradiation with UV light (Bernstein et al. 2002 Munoz-Caro et al. 2002). The results indicate that the distribution of amino acids correlated with the abundance of hydrous silicates. This raises the prospect of a participation of the primary asymmetric phases of minerals in the ee observed in the a-methyl-amino acids in the Murchison meteorite. This result points to a possible inorganic catalysis on the surface of minerals as a source of the ee of amino acids formed to various extent in interstellar and planetary abiotic processes. 

When we adopt the idea that water was carried by icy ammonia hydrate bodies to the earth not only at the very beginning of the earth s formation around 4.6 Gy ago but also during the LHB 4 Gyr ago - when the oceans had already been recycled by the hot surface together with evaporation of dissolved species - there was competition between NH3 photolysis, an irreversible transformation process into N2 (no abiotic process is known on earth that produces NH3 and CH4 under natural conditions), and NH3 scavenging by rain. It also remains open to speculation how much of the ammonia was probably produced from nitrides. 

The ocean as a source of trace gases is between biogenic and abiotic processes hence we consider the ocean here in a separate subchapter. Whereas the generation of sea-salt particles from the surface of seawater is a purely physical process (see Chapter 2.6.4.2), it has been identified as a considerable global source of different nitrogen, sulfur and carbon species (Table 2.33). These species are produced in the... 

We cover each of these types of examples in separate chapters of this book, but there is a clear connection as well. In all of these examples, the main factor that maintains thermodynamic disequilibrium is the living biosphere. Without the biosphere, some abiotic photochemical reactions would proceed, as would reactions associated with volcanism. But without the continuous production of oxygen in photosynthesis, various oxidation processes (e.g., with reduced organic matter at the Earth s surface, reduced sulfur or iron compounds in rocks and sediments) would consume free O2 and move the atmosphere towards thermodynamic equilibrium. The present-day chemical functioning of the planet is thus intimately tied to the biosphere. 

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