Two-stage desorption kinetics and in situ partitioning of hexachlorobenzene and dichlorobenzenes in a contaminated sediment

The desorption kinetics of in situ hexachlorobenzene (HCB), 1,3-dichlorobenzene (1,3-DCB) and 1,4-dichlorobenzene (1,4-DCB) from a sediment were determined by a method in which the aqueous phase was kept solute-free with Tenax TA beads. Slowly desorbing fractions were 47–98% for HCB, 58–76% for 1,3-DCB and 36–63% for 1,4-DCB. Also, in situ partition coefficients (Kocin situ) were measured; they were 0.24–1.4 log-unit higher than literature Koc-values measured using short-term laboratory incubations Koc values for the rapid fractions (Kocrap), calculated with Kocin situ and the rapidly desorbing fractions, were similar to literature Koc values. From this, it is concluded that the slowly desorbing contaminant fractions and the fractions not available for rapid equilibrium partitioning are the same.