Reductive dechlorination of aroclor 1242 in anaerobic sediments: Pattern, rate and concentration dependence

Abstract

Anaerobic biotransformation of polychlorinated biphenyls of Hudson River sediment microorganisms was investigated using the commercial mixture Aroclor 1242 in the laboratory at six different concentrations: 120, 300, 500, 800, 1,000, and 1,500 μg/g (on a sediment dry‐weight basis). Dechlorination was concentration dependent. No change in congener composition was found at 1,000 and 1,500 μg/g during seven months of incubation, but significant shifts were observed in sediments with concentrations below 800 μg/g. A mass balance of the transformation indicated that, despite the shifts, the total molar concentration remained the same. An optimum concentration, based on the decrease of Cl per biphenyl, was 500 μg/g, but based on Cl removed per gram sediment it had a range from 500 to 800 μg/g. Dechlorination (total Cl removed per biphenyl) at 300 and 500 μg/g appeared to be first order, with rate constants of —0.039 and —0.059 per month, respectively. The rate also varied with the substitution position; it was faster for m‐Cl, followed by p‐Cl, but no o‐Cl was removed. However, the faster rate of m‐dechlorination in Aroclor 1242 was probably due to a high concentration of congeners in the Aroclor with Cl substitution patterns favoring its removal, rather than the meta‐position itself.

Reductive Dechlorination of Preexisting Sediment Polychlorinated Biphenyls With Long-Term Laboratory Incubation

“…2a). Interestingly, additional dechlorination of these same identical congeners was also noted in our earlier long-term studies of Aroclor 1242 [5] and 1254 [29]. With further incubation of the natural sediments a second phase of dechlorination ensued after 15 months, with the total chlorines per biphenyl decreasing slightly further from 2.5 to 2.4 (Fig.…”

“…All sediment slurry preparation took place within an anaerobic chamber (Coy Laboratory Products, Ann Arbor, MI, USA) containing an oxygen-free atmosphere of N 2 :CO 2 :H 2 (85:5:10). We previously reported that the PCB extraction efficiency of this method is greater than 96% and does not change with length of sediment incubation [5]. The sediment slurries contained 20% (w/v) of each type of sediment on a dryweight basis.…”

“…The Aroclor 1248-spiked and native PCB-contaminated sediments were separately made into slurries by adding either reduced synthetic minimal medium [5] or filtered (Whatman GF/C; Whatman International Ltd., Maidstone, UK) and reduced St. Lawrence River water, respectively. All sediment slurry preparation took place within an anaerobic chamber (Coy Laboratory Products, Ann Arbor, MI, USA) containing an oxygen-free atmosphere of N 2 :CO 2 :H 2 (85:5:10).…”

“…This standard mix was also used for quality assurance/quality control to check instrument performance, reproducibility, and sensitivity, as previously described [5]. The initial oven temperature of 100ЊC was maintained for 2 min and then increased at a rate of 10ЊC/min to 160ЊC, held for 1 min, and finally to 250ЊC by 2ЊC/min.…”

“…Reductive dehalogenation is an important and widespread form of biodegradation for a variety of haloaromatic compounds including halogenated biphenyls [1][2][3][4][5] and benzenes [6][7][8][9], chlorophenols [10][11][12][13], and dioxins [14][15][16][17][18]. In situ reductive dechlorination of polychlorinated biphenyls (PCBs) has been observed in contaminated sediments from various locations [19][20][21][22][23][24].…”