Hydrolysis of environmental contaminants as an experimental tool for indication of their persistency

To predict the persistency of a chemical in the environment, the chemical's physical-chemical properties and its reactivity in the environment need to be known or at least estimated. The partitioning of a chemical can be described on the basis of its water solubility, its octanol/water partitioning coefficient, and its vapor pressure. The mechanisms by which a chemical can be transformed may be categorized as being hydrolysis, oxidation, reduction, and photolysis. This study establishes a method for estimating the relative susceptibility of some potential environmental pollutants to undergo hydrolysis reactions. The method used the second-order rate constant for the reaction with sodium methoxide in methanol/N,N-dimethylformamide (DMF) as an indicator of relative susceptibility toward hydrolysis. The decabromodiphenyl ether is rapidly hydrolyzed, that is, undergoes nucleophilic aromatic substitution, while the rate of reaction of less brominated diphenyl ethers decreased by roughly a factor of 10 for each decrease in the level of bromination. Hexachlorobenzene was found to have a similar rate to a nonabromodiphenyl ether. 2,2-Bis(4-chlorophenyl)-1,1,1-trichloroethane (DDT) was transformed to 2,2-bis(4-chlorophenyl)-1,1-dichloroethene (DDE) immediately under these conditions, while DDE showed no apparent reaction. The results show that chemicals that can undergo elimination reactions are rapidly transformed, as are perhalogenated chemicals that can undergo substitution reactions. These chemicals are not likely to persist in the environment, while those that did not show any observable reactivity under similar hydrolytic conditions may persist for a very long time.