Persistence prediction, organic compound

Black C, produced by wild fires and humic substances (HS), the natural by products of SOM decomposition in soil and water systems, are certainly the classes of organic compounds that most closely approximate this recalcitrant behavior. HS occur widely, being found in large amounts not only in the soil and sediments but also in lakes, rivers, ground waters, and even the open ocean (Stevenson, 1994). Besides these relatively refractory substances, more labile compounds can persist in soil for a much longer time than would be predicted from their inherent recalcitrance to decomposition. SOM stabilization (Figure 5.2) is generally considered to occur by three main mechanisms (i) physical protection, (ii) chemical stabilization, and (iii) biochemical stabilization (Six et al., 2002). 

Compounds released to the environment distribute among the major environmental compartments, air, water, soil, and biota as a function of their physical chemical properties and models can provide a basis to predict how different compounds behave. Adverse effects will depend on persistence in a compartment. In this context, it is readily apparent that the hydroxyl radical serves as a very efficient atmospheric scavenger. Other oxidants may show activity with a limited series of compounds, but the hydroxyl radical is unique in the broad range of organic compounds with which it reacts and the rates at which these reactions proceed. Lifetimes for selected compounds based on reactions with the hydroxyl radical are compiled in Table 6.28. 

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