Chemical hydrolysis of 2-chloro-4,6-bis(alkylamino)-1,3,5-triazine herbicides and their breakdown in soil under the influence of adsorption

The determination of rate constants and the calculation of the activation parameters [activation energy (E_a), free energy of activation(ΔG^≠)and entropy of activation (ΔS^≠)] demonstrated the identity of the reaction kinetics of chemical hydrolysis of the chlorinated triazine herbicides simazine, atrazine, propazine and terbuthylazine. Persistence in soil could be estimated, from the hydrolytic half-life time, only in pH regions where these compounds were also sensitive to chemical hydrolysis. In general, the rate of hydrolysis increased in the presence of soil as the result of a catalysing effect of the soil in their breakdown. When half-lives in soil of these triazine herbicides were compared with adsorption constants, a functional relationship was observed in both soil types; as adsorption increased the half-life in soil also increased.