Triphasic Desorption of Highly Resistant Chlorobenzenes, Polychlorinated Biphenyls, and Polycyclic Aromatic Hydrocarbons in Field Contaminated Sediment

Abstract

Pollutants in aged field sediments seem to differ from spiked sediments in their chemical and biological availability. Biphasic desorption is often used as an explanation. In the present study, desorption kinetics and partitioning of chlorobenzenes (CBs), polychlorinated biphenyls (PCBs), and polycyclic aromatic hydrocarbons (PAHs) in long term field contaminated sediment cores and top layer sediment were measured by gas-purging. Desorption from sediment was deduced to be triphasic: fast, slowly, and very slowly desorbing fractions were distinguished. In both the sediment core and the top layer sediment no detectable fast fractions were present for all the compounds studied, so these were estimated as upper limits from the desorption curves. This observation coincided with very high in situ distribution coefficients for several PCBs and PAHs: 10−1000 times higher than literature values for short contact time experiments. Rate constants were (3−8) × 10-3 h-1 for slow desorption and (0.16−0.5) × 10-3 h-1 for very slow desorption. In some cases only a very slowly desorbing fraction was detectable. Desorption from field contaminated sediments with extended contact times may not be readily estimated from laboratory experiments in which contaminants have contact times with the sediment in the order of weeks.

Influence of Desorption and Contact Time on Sediment–water Distribution of Spiked Polychlorinated Biphenyls and Polycyclic Aromatic Hydrocarbons: Relation With in Situ Distribution

“…The extraction and clean-up (including recoveries) of the Tenax traps was described earlier [16]. The procedure for PAH extraction, clean-up, and analyses was as described earlier [16]. The PCBs were analyzed with a Hewlett-Packard (Amstelveen, The Netherlands) 5890 gas chromatography-electron capture detector as described previously [17].…”

Benchscale Assessment of the Efficacy of a Reactive Core Mat to Isolate PAH-Spiked Aquatic Sediments

“…At the end of spiking, the sediment-naphthalene mixture was immediately used in the experiment with no significant post-mixing storage duration. It has been shown that sorption/desorption chemistry and bioavailability of the spiked compounds differ from those in the native contaminants (Alexander, 1995; Ten Hulscher et al, 1999), with higher mobility that would be advantageous considering the limited experimental durations.…”

Environmental bioavailability of hydrophobic organochlorines in sediments—A review

“…Furthermore, the nonlabile, slowly desorbing fraction in sediment has recently been shown to be composed of two fractions (slow and very slow), resulting in triphasic desorption kinetics. The slow-and very slow-desorbing phases differ in their first order rate constants by about two orders of magnitude for chlorobenzenes, PCBs, and PAHs (Cornelissen et al, 2000, Kan et al, 2000Ten Hulscher et al, 1999). Equilibrium sorption of compounds at these two nonlabile, kinetically different sorption domains could be described by Langmuir isotherms, whereas the sorption of compounds at rapidly desorbing sites follows linear isotherms (Cornelissen et al, 2000).…”