Labile and non-labile desorption rate constants for 33 PCB congeners from lake sediment suspensions

Lake sediments contaminated with polychlorinated biphenyls (PCBs) were purged using a gas stripping technique to estimate desorption rate constants. Desorption profiles and modeling of the data clearly show a two-step release of PCBs from sediment suspensions that can be described as a labile (fast) release followed by a non-labile (slow) release. Data are summarized by labile and non-labile rate constants and by mass in each phase as a function of suspended solids concentration for twelve pure congeners and nine co-eluting data sets (twenty-one chromatograph peaks total). Labile desorption rate constants range from 113 days−1 to 1.43 days−1 for the 100 mg/l sediment suspension, from 67.7 days−1 to 2.45 days−1 for the 1000 mg/l sediment suspension, and from 8.41 days−1 to 0.946 days−1 for the 5000 mg/l sediment suspension. Labile rate constants consistently decreased with increasing suspended solids, and, in general, decreased with increasing degree of chlorination (reflected in increasing retention time in the chromatogram). No consistent trend was observed for the non-labile rate constants with suspended solids concentration or degree of chlorination. The average non-labile rate constant for the PCB congeners studied here was 0.154 days−1 (s.d. = 0.158; n = 63). The distribution between the labile and non-labile phases also failed to indicate dependence on suspended solids concentration, chlorine substitution pattern, or molecular weight of the congener, although the data from the 5000 mg/l suspension consistently contained less labile components. The average distributions (n = 63) were 60.1% in the labile phase and 39.9% in the non-labile phase.