Desorption of DDT from a contaminated soil using cosolvent and surfactant washing in batch experiments

1,1-bis(p-chlorophenyl)- 2,2,2-trichloroethane ( p, p'-DDT) is a recalcitrant organic compound that is difficult to remove from contaminated soil due to its low solubility. In this study we investigated the effectiveness of both cosolvents and surfactants in enhancing the solubility of p, p'-DDT from a soil that has been contaminated with DDT for nearly 40 yr. The presence of selected surfactants removed less than 1 to 11% of p, p'-DDT compared to cosolvents, which removed less than 1 to 77% of p, p'-DDT from the same soil. The low solubility of p, p'-DDT in the presence of surfactants was attributed to the decreased surfactant concentration to below critical micelle concentration following sorption by soil surfaces. Enhanced solubility of p, p'-DDT was achieved with the use of cosolvents that released up to 77% of p, p'-DDT from a contaminated soil. Increasing the solution concentration and hydrophobicity of the cosolvent increased the amount of p, p'-DDT desorbed. For example, the amount of p, p'-DDT desorbed increased in the order 5% 1-propanol much less than 50% ethanol much less than 50% 1-propanol. Repeated washing of the soil with various cosolvents, in all but two cases, markedly increased the total amount of p, p'-DDT desorbed from the soil. For example, repeated washing of the soil with 50% ethanol increased the amount of p, p'-DDT removed by 42% while repeated washings of the soil with 50% 1-propanol had little effect on the amount of p, p'-DDT desorbed. Increasing the soil-solution ratio from 1: 2 to 1: 10 in the presence of 40% 1-propanol increased the amount of p, p'-DDT desorbed by 100%; suggesting that the soil-solution ratio was an important parameter in controlling the amount of p, p'-DDT desorbed.