Incubation, slurries sediment

Bedard et al. [245] reported that PCB dechlorination was stimulated by adding 2,5,3, 4 -tetrachlorobiphenyl (25-3 4 -CB) to slurries (incubated under methanogenic conditions) of sediments contaminated with Aroclor 1260 from Woods Pond (MA). The 25-3 4 -CB was converted stoichio-metrically to 25 - 3 -CB and stimulated a selective para-dechlorination which decreased the penta- through heptachlorobiphenyls containing 234-, 245-, or 2345-chlorophenyl groups by up to 83% in 12 weeks. 

Wu et al. (1998) investigated the microbial reductive dechlorination of PCB-1260 in anaerobic slurries of estuarine sediments from Baltimore Harbor, MD. The slurries were amended with 800 ppm PCB-1260 with and without the addition of 2,3,4,5-tetrachlorobiphenyl or 2,3,5,6-tetrachlorobiphenyl and incubated at 30 °C under methanogenic conditions. Without the addition of the tetrachlorobiphenyls, chlorine atoms at the meta and ortho positions on the PCB congeners decreased by 45 and 9%, respectively. When 2,3,4,5-tetrachlorobiphenyl and 2,3,5,6-tetrachlorobiphenyl were added, chlorine atoms at the meta position decreased by 65 and 55% and chlorines at the ortho positions decreased by 18 and 12%, respectively. After 181 d, hexa- and nonachlorobiphenyls decreased by 65, 75, and 88% In PCB-1260 alone, PCB-1260 + 2,3,5,6-tetrachlorobiphenyl, and PCB-1260 + 2,3,4,5-tetrachlorobiphenyl. The investigators concluded that the addition of a single congener stimulated the dechlorination of PCB-1260. 

In order to provide additional evidence In support of the proposed Michael addition reaction, a sediment study was also performed. Acrylic acid was added directly to slurries of reducing sediments from Blscayne Bay and the formation of 3-mercaptopropionate In the porewater, relative to unsplked controls, was monltered by HPLC. The concentration of added acrylic acid was 0.1 mmol per liter slurry ( 0,2 mM In the porewater) and the slurries were Incubated under argon at 37 C for 2 hours prior to thiol analysis. Figure 6 clearly shows that addition of acrylic acid to reducing sediment gives rise to 3-mercaptopropionate, the main product expected from the Michael addition of HS to acrylic acid. 

Sediment slurries were Incubated at 30 C (approximate In situ temperature) with and without trlbutylphosphlne. Aliquots of porewater were periodically removed for thiol analysis over the following 2-4 days. During the course of this study, a total of 7 such Incubations were performed on freshly collected sediment. Results were similar In all cases and typically showed that trlbutylphosphlne Induced a dramatic and rapid release of bound (or oxidized) thiols (Table IV and Figure 8). Bound thiols were present at approximately 20 times greater concentrations than free thiols (I.e., 95% of all thiols released from sediment were Initially bound). If air Is not excluded during the Incubation, released thiols become reoxldlzed after several days (Figure 8) probably due to the oxidation of the protective phosphine. Addition of fresh trlbutylphosphlne regenerated the thiols. 

Figure 8. Release of thio ls (3-mercaptoproplonate -MP and methanethlol - MeS) and HS upon addition of tributylphosphine (50pl per 100 ml slurry) to a Biscayne Bay sediment slurry incubated at 25°C control slurries received no tributylphosphine.

Westerman, P., The effect of incubation temperature on steady-state concentrations of hydrogen and volatile fatty acids during anaerobic degradation in slurries from wetland sediments, FEMS Microbiol. EcoL, 13, 295-302, 1994. 

In the absence of any one standardized method, many investigators have used laboratory batch incubation of wetland soils and aquatic sediments and measured ammonium production as a measure of nitrogen mineralization rates (Wang et al., 2001 White and Reddy, 2001) (Figure 8.20). These methods range from simple batch incubation experiments in which ammonium accumulation is measured over time to stable isotope dilution technique in which soil cores or anaerobic soil slurries are injected with N-labeled ammonium nitrogen. This method allows to estimate both gross and net mineralization rates (Blackburn, 1979). 

Figure 5 Effect of electron donors on the reduction of arsenate (O) to arsenite ( ) in anoxic estuarine sediment slurries incubated (a) without additions, (b) with lactate, (c) with glucose, and (d) with acetate. (From Ref. 39.)...

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