Influence of long contact times on sediment sorption kinetics of spiked chlorinated compounds

Abstract

The desorption kinetics of hexachlorobenzene (HCB) and 2,4,4'-trichlororbiphenyl (PCB 28) spiked to a field sediment were studied using a gas-purge technique. A contact time of up to 1,461 d was used to assess long-term changes in desorption kinetics. Purge-induced desorption experiments lasted from 300 to more than 4,000 h. Fast-, slow-, and very-slow-desorbing fractions could be distinguished. The desorption patterns changed with contact time from mainly fast- and slow-desorbing fractions toward the domination of slow- and very-slow-desorbing fractions. The desorption pattern for HCB after a contact time of 1,461 d became comparable to previously reported desorption patterns observed for in situ contaminants. An additional spike of HCB, PCB 28, 2,4,6-trichlorobiphenyl, and 2,2',4,5'-tetrachlorobiphenyl applied to the sediment purged for more than 4,000 h showed that very slow sites were accessible for these compounds within a few hours. Only very small fast-desorbing fractions could be detected after a contact time of just 48 h. These results indicate that domination of very slow desorption is caused not only by long contact times but, perhaps, also by the accessibility of specific sites within the sediment matrix.

Kinetics of adsorption and desorption of some organochlorine compounds on black carbon in a sediment

“…The times to equilibrium in Table 2 indicate that equilibrium would have been reached in approximately 1 to 6 d. The trend in the data for increasing chlorination further suggests that the time to equilibrium for higher‐chlorinated benzenes and PCBs is less than 1 day. That supports our earlier finding [8] that domination of very slowly desorbing fractions not only may occur on long contact times but also may be diminished by reduced availability of sites. In that study, it was observed that an additional spike of hexachlorobenzene, 2,4,4′‐trichlorobi‐phenyl, 2,4,6‐trichlorobiphenyl, and 2,2′,4,5′‐tetrachlorobi‐phenyl to a Ketelmeer sediment (not heated at 375°C as in the present study) purged for more than 4,000 h resulted in these sorbates being almost exclusively in the very slow desorbing domain, whereas spiking the sediment with some of these compounds before the gas purge resulted in sorbates being predominantly in the rapidly desorbing domain instead.…”

“…Recently, we found that sorption to so-called ''very slow'' sites also can be accomplished in a short period of time [8]. This occurred in sediment used for desorption experiments over an extended time period: desorption experiments with gas purging lasted several months.…”

Effect of aging on desorption kinetics of sediment‐associated pyrethroids

“…Using a gas‐purge method, ten Hulscher et al [23] showed that decreases of F rapid for hexachlorobenzene and 2,4,4′‐trichlorobiphenyl in sediment followed a first‐order trend ( r 2 = 0.98), with a t 1/2 of 288 d. White et al [30] found that desorption and mineralization rates of phenanthrene in soils decreased by an order of magnitude after 50 or 60 d of aging and that plots of normalized rates of mineralization and desorption practically coincided. Therefore, the decrease of F rapid found for pyrethroids during the present study fell within the range found in the previous studies.…”

Modeling intragranular diffusion in low‐connectivity granular media

“…Characterizing the diffusive exchange of solutes between bulk water in an aquifer and water in the intragranular pores of the solid phase is still challenging despite decades of study. For organic solutes, the exchange is complicated by such issues as partitioning into various kinds of organic matter [ Huang et al , 2003; Warren et al , 2003; Ten Hulscher et al , 2005], bioavailability and biological activity [ Reichenberg and Mayer , 2006], and nonlinear isotherms [ McGinley et al , 1996; Ran et al , 2002]. Exchange of inorganic solutes such as contaminant uranium is complicated by multiple redox states, precipitation in multiple minerals, and interaction with other solutes [ Zachara et al , 2007; Liu et al , 2008].…”