Temperature dependence of slow adsorption and desorption kinetics of organic compounds in sediments

The purpose of the present study was to determine the temperature dependence of slow adsorption and desorption kinetics of some chlorobenzenes, polychlorinated biphenyls (PCBs), and polycyclic aromatic hydrocarbons (PAHs) in a lab-contaminated and a field-contaminated sediment. The kinetics of desorption were measured by means of a technique in which Tenax TA beads are used as ''sink'' for desorbed solute. A first-order kinetic model with three sediment compartments described the desorption of the test compounds from the sediments. Apart from a rapidly desorbing fraction, two sediment fractions were distinguished, one slowly desorbing with a rate constant of (1-4) x 10(-3) h(-1) and a very slowly desorbing one with rate constants approximately 10-50 times smaller. From temperature dependence studies, the a activation enthalpies for slow desorption appeared to be 60-70 kJ mol(-1) for both the lab-contaminated and the field-contaminated sediments; the values were approximately constant for all compounds studied. From adsorption studies at two temperatures, enthalpies of sorption to the slow sediment compartment appeared to be slightly negative. Because slow desorption is much faster al elevated temperatures, the measurement of high-temperature desorption kinetics can provide information on long-term desorption kinetics and, probably, on the feasibility of bioremediation of aged contaminants.