Biotransformations of Aroclor 1242 in Hudson River test tube microcosms

Abstract

A microcosm system to physically model the fate of Aroclor 1242 in Hudson River sediment was developed. In the dark at 22 to 25 degrees C with no amendments (nutrients, organisms, or mixing) and with overlying water being the only source of oxygen, the microcosms developed visibly distinct aerobic and anaerobic compartments in 2 to 4 weeks. Extensive polychlorinated biphenyl (PCB) biodegradation was observed in 140 days. Autoclaved controls were unchanged throughout the experiments. In the surface sediments of these microcosms, the PCBs were biologically altered by both aerobic biodegrading and reductive dechlorinating microorganisms, decreasing the total concentration from 64.8 to 18.0 micromol/kg of sediment in 1140 days. This is the first laboratory demonstration of meta dechlorination plus aerobic biodegradation in stationary sediments. In contrast, the primary mechanism of microbiological attack on PCBs in aerobic subsurface sediments was reductive dechlorination. The concentration of PCBs remained constant at 64.8 micromol/kg of sediment, but the average number of chlorines per biphenyl decreased from 3.11 to 1.84 in 140 days. The selectivities of microorganisms in these sediments were characterized by meta and para dechlorination. Our results provide persuasive evidence that naturally occurring microorganisms in the Hudson River have the potential to attack the PCBs from Aroclor 1242 releases both aerobically and anaerobically at rapid rates. These unamended microcosms represent a unique method for determining the fate of released PCBs in river sediments.

Site‐specific microbial communities in three PCB‐impacted sediments are associated with different in situ dechlorinating activities

“…Interestingly, the concentrations of PCBs detected in Anacostia, Buffalo and Grasse Rivers were only 1.3%, 0.16% and 20%, respectively, of the threshold concentrations (25 p.p.m.) reported as the limit for dechlorination for Aroclor mixtures (Fish and Principe, 1994). However, the adherence to an absolute threshold value below which no dechlorination can occur may not apply in all circumstances.…”

Interspecific differences of parental polychlorinated biphenyl exposure on nutrient availability, egg production and brooding in two Syngnathus species

“…Exposure concentrations differed considerably from target Aroclor 1254 levels even though concentration of the stock solution was confirmed. PCB congeners with a high degree of chlorination such as Aroclor 1254 biodegrade slowly, are less soluble and readily adsorb to glass and biological tissue (Boyle et al, 1992;Schwarzenbach et al, 1993;Fish & Principe, 1994). Considering the short period between water changes and thereby a likely absence of biotransforming microbial colonies, the instantaneous difference in nominal v. measured exposure concentration is most likely due to adsorption and not biodegradation.…”

Influence of incubation temperature on the microbial reductive dechlorination of 2,3,4,6-tetrachlorobiphenyl in two freshwater sediments

“…It is likely that PCB-dechlorinating microorganisms function in syntrophic communities, and they may be dependent on such communities for electron donors, micronutrients, and maintenance of an optimal hydrogen concentration (5). Furthermore, it appears that the PCB dechlorination observed in sediments may result from the actions of multiple PCB-dechlorinating populations that exhibit different substrate specificities (5,12,13,20). Some of these populations may compete with each other for the same PCB substrates and produce PCB congeners with fewer chlorines that are not substrates for either population.…”

“…Some of these populations may compete with each other for the same PCB substrates and produce PCB congeners with fewer chlorines that are not substrates for either population. The most extensive dechlorination occurs when several PCBdechlorinating populations act simultaneously or sequentially to attack different suites of congeners (5,13). For example, the terminal dechlorination products of one population may serve as substrates for a different PCB-dechlorinating population (5,13), leading to more extensive removal of chlorines.…”