Competitive effects on the slow desorption of organic compounds from sediments

Experiments were carried out concerning competition effects in slow desorpt ion. Excess lab-added 1,2,4-trichlorobenzene (TCB) decreased the slowly des orbing amounts of aged in situ polychlorinated biphenyls (PCBs) and chlorob enzenes in sediment from Lake Ketelmeer (KM), The Netherlands, after 14 d o f TCB-sediment contact time (factor of 1.2-2.7). Another experiment showed that the presence of large quantities of in situ oil (15 g/kg) and polycycl ic aromatic hydrocarbons (PAHs; 1.5 g/kg) strongly inhibited the formation of slowly desorbing amounts of lab-added pentachlorobenzene, PCB-30 and PCB -65. These results imply that (i) freshly sorbed contaminants can influence the desorption behavior of aged contaminants within weeks, and (ii) PAH, o il, PCBs and chlorobenzenes show competition for the same slow sorption sit es in sediment. So, the occurrence of competitive effects on slow desorptio n indicates that the number of slow sorption sites is limited. This is in a ccordance with the recent finding that part of the sorption of organic comp ounds in soils and sediments occurs in a nonlinear way, the slowly desorbin g fractions showing this nonlinear sorption. (C) 1999 Elsevier Science Ltd. All rights reserved.