Subject lead, water solubility

In water, tetraalkyl lead compounds are subject to photolysis and volatilization with the more volatile compounds being lost by evaporation. Degradation proceeds from trialkyl lead to dialkyl lead to inorganic lead. Tetraethyl lead is susceptible to photolytic decomposition in water. Triethyl and trimethyl lead are more water-soluble and therefore more persistent in the aquatic environment than tetraethyl or tetramethyl lead. The degradation of trialkyl lead compounds yields small amounts of dialkyl lead compounds. Removal of tetraalkyl lead compounds from seawater occurs at rates that provide half-lives measurable in days (DeJonghe and Adams 1986). 

The one-phase liquid system is more frequently encountered since many organic reactions are carried out in solution. Direct fractional distillation may separate the product, if it is a liquid, from the solvent and other liquid reagents, or concentration or cooling may lead to direct crystallisation of the product if this is a solid. However, it is often more appropriate, whether the required product is a liquid or solid, to subject the solution to the acid/base extraction procedure outlined above and considered in detail on p. 162. This acid/base extraction procedure can be done directly if the product is in solution in a water-immiscible solvent. A knowledge of the acid-base nature of the product and of its water solubility is necessary to ensure that the appropriate fraction is retained for product recovery. In those cases where the reaction solvent is water miscible (e.g. methanol, ethanol, dimethylsulphoxide, etc.) it is necessary to remove all or most of the solvent by distillation and to dissolve the residue in an excess of a water-immiscible solvent before commencing the extraction procedure. The removal of solvent from fractions obtained by these extraction procedures is these days readily effected by the use of a rotary evaporator (p. 185) and this obviates the tedium of removal of large volumes of solvent by conventional distillation. 

PAHs also react with OH. Removal of PAHs from the atmosphere by photolytic production of OH may be an important natural remediation mechanism. Because these compounds have limited water solubility, most studies have investigated gas phase reactions. Naphthalene was shown to be subject to a complex series of hydroxylations and peroxyl-induced ringopening reactions leading to the production of organic acids [37]. Although PAHs have low water solubility, they are often important water pollutants, attached to particles or colloids suspended in solution, or in aqueous sediments. PCBs have been shown to be susceptible to OH attack, resulting in dechlorination [38]. 

Based on effects observed in water (Navy 1984b), tetryl released to soil is expected to be susceptible to slow hydrolysis in acidic and neutral soils and to relatively rapid hydrolysis in highly alkaline soils (HSDB 1994). Samples of water collected from lysimeters containing tetryl-contaminated soil indicated that the major transformation products were picric acid (5-14%) and other polar, water- soluble decomposition products no tetryl was detected in the water, or in the soil at the end of the study, suggesting complete hydrolysis (Kayser and Burlinson 1988 Navy 1982). The specific reaction leading to these products was not determined. Because tetryl is subject to photolysis in water, it may be susceptible to photolysis on sunlit soil surfaces (HSDB 1994). 

Once in the organism, solvents will undergo biotransformation which essentially takes place in the liver. This metabolism very often leads to more water-soluble products than the parent compound and, as such, more easily excreted by the kidneys. This detoxication process is beneficial for the individual but varies greatly from one subject to another. Unfortunately, this metabolic detoxication can be complicated by the appearance of reactive intermediates which, if not rapidly inactivated, will destroy the essential constituents of the cells (proteins, nucleic acids, unsaturated lipids) and cause INTOXICATION. The latter ranges from a simple allergic reaction to tissue necrosis or, at worst, to cancer. Table 16.2.1 summarizes the different events which can occur in the organism. 

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