The present study has investigated a correlation between the kinetics of polychlorinated biphenyl (PCB) dechlorination and the growth of dechlorinating microbial populations. Microorganisms were eluted from Aroclor 1248-contaminated St. Lawrence River (NY, USA) sediments and inoculated into clean sediments spiked with Aroclor 1248 at 10 concentrations ranging from 0 to 3.12 micromol/g sediment (0-900 ppm). The time course of PCB dechlorination and population growth were concurrently determined by congener-specific analysis and the most probable number technique, respectively. The specific growth rate was a saturation function of PCB concentrations above the threshold concentration (0.14 micromol/g sediment, or 40 ppm), below which no dechlorination or growth of dechlorinations were observed. The maximum growth rate was 0.20/d with a half-saturation constant of 1.23 micromol/g sediment. The yield of dechlorinating microorganisms showed a peak at 0.70 micromol/g sediment (200 ppm), with a value of 10.3 x 10(12) cells/mol Cl removed, and decreased below and above this concentration. The dechlorination rate (micromol Cl removed/g sediment/d) was a linear function of Aroclor concentration. Both the log of this rate and the maximum level of dechlorination were significantly correlated with growth rate. The biomass-normalized dechlorination rate (micromol Cl removed/g sediment/cell/d) was first order because of the exponential manner of the population growth. The first-order rate constant was a saturation function of Aroclor concentrations, with a maximum of 0.24/d (a half-life of 2.9 d) and a half-saturation constant of 1.18 micromol/g sediment, which are similar to the constants for growth. These results indicate that the dechlorination rate is tightly linked to the population growth of dechlorinating microorganisms.

Reductive dechlorination of individual PCB congeners in Aroclor 1248 was investigated using sediment microorganisms from the St. Lawrence River (NY). No dechlorination was observed at Aroclor concentrations below 40 ppm [137 nmol (g of sediment)(-1)]. Above this threshold, congeners could be divided into three categories: group A, congeners that dechlorinated above 40 ppm; group B, congeners that dechlorinated only at high concentrations above 60 ppm [206 nmol (g of sediment)(-1)]; and group C, lower chlorinated congeners that increased in concentration. The dechlorination rate of congeners in groups A and B was a linear function of their initial sediment concentration. For group A congeners, the concentration intercepts of this linear function were the same as their concentrations in the Aroclor at the threshold concentration, and these therefore represented the threshold values. However, the intercepts of group B congeners were significantly higher than their levels at the threshold Aroclor concentration and were equivalent to their concentrations in Aroclor 1248 at about 75 ppm [258 nmol (g of sediment)(-1)]. The final concentrations of group A and group B congeners at the end of dechlorination were the same, regardless of their initial concentrations. These final concentrations were significantly lower than their threshold values. The accumulation rate of group C congeners was a linear function of their initial concentrations, and the total accumulation was greater at higher Aroclor concentrations in sediments.

The present study has investigated a correlation between the kinetics of polychlorinated biphenyl (PCB) dechlorination and the growth of dechlorinating microbial populations. Microorganisms were eluted from Aroclor 1248-contaminated St. Lawrence River (NY, USA) sediments and inoculated into clean sediments spiked with Aroclor 1248 at 10 concentrations ranging from 0 to 3.12 micromol/g sediment (0-900 ppm). The time course of PCB dechlorination and population growth were concurrently determined by congener-specific analysis and the most probable number technique, respectively. The specific growth rate was a saturation function of PCB concentrations above the threshold concentration (0.14 micromol/g sediment, or 40 ppm), below which no dechlorination or growth of dechlorinations were observed. The maximum growth rate was 0.20/d with a half-saturation constant of 1.23 micromol/g sediment. The yield of dechlorinating microorganisms showed a peak at 0.70 micromol/g sediment (200 ppm), with a value of 10.3 x 10(12) cells/mol Cl removed, and decreased below and above this concentration. The dechlorination rate (micromol Cl removed/g sediment/d) was a linear function of Aroclor concentration. Both the log of this rate and the maximum level of dechlorination were significantly correlated with growth rate. The biomass-normalized dechlorination rate (micromol Cl removed/g sediment/cell/d) was first order because of the exponential manner of the population growth. The first-order rate constant was a saturation function of Aroclor concentrations, with a maximum of 0.24/d (a half-life of 2.9 d) and a half-saturation constant of 1.18 micromol/g sediment, which are similar to the constants for growth. These results indicate that the dechlorination rate is tightly linked to the population growth of dechlorinating microorganisms.