Toxins soil reactions

Whatever quantity of toxin is released generally enters the soil, where several things may happen to it. The order of the second, third, and fourth steps in Figure 1 is not necessarily the order in which the reactions actually occur. In fact, if the toxin is a volatile substance, these steps may be skipped entirely. In most cases, however, it appears that allelopathic chemicals enter the soil. 

Soil colloids are capable of adsorbing most allelopathic chemicals. Such adsorption would result in temporary loss of toxin activity. Chemical changes could occur during adsorption that would permanently deactivate the toxin. The adsorption reactions are usually reversible, however, so that some or all of the toxin would still be available for uptake by a receiver plant. 

The toxin is also likely to be adsorbed or complexed by soil humic acids. If the reaction is a simple adsorption reaction, all or part of the toxin might later become available for absorption by a receiver plant. If the toxin is complexed or precipitated by its reaction with soil humic substances, then it would be deactivated. 

The reactions that a toxin undergoes in the soil are largely controlled by edaphic factors such as moisture regime, nutrient... 

We will begin with phosphotriesterase, which is an unusual (if not unique) enzyme in that it has no naturally occurring substrates. The enzyme was originally isolated from soil bacteria that were able to hydrolyze and detoxify a wide variety of organophosphate insecticides and nerve toxins. A typical reaction is the hydrolysis of the insecticide paraoxon, shown in Equation (2) ... 

Due to variations in the soil, such as humic constituents, sand fractions, clay minerals, peat minerals, wood rests, algal toxins, and deposits of shell lime, different reactions take place. The natural organic matter (NOM) in an aquifer is a complex mixture of substances, such as humic acids, fulvic acids, amino acids, carbohydrates, lipids, lignin, and waxes. 

---