The effect of a rhamnolipid biosurfactant on the reductive dechlorination of polychlorinated biphenyls was investigated
with the use of clean sediments spiked with Aroclor 1248. The surfactant was added to the contaminated sediments at four different
concentrations (5, 10, 25, and 50 mg/g sediment [ppm] on a sediment dry wt basis), and dechlorination was followed over a 40-
week period. The rate of overall dechlorination was enhanced at the three highest concentrations. Dechlorination at the lowest
concentration (5 ppm) was not different from that in surfactant-free sediments. On a congener basis, enhanced dechlorination was
mostly found in the congeners that have high threshold concentrations for dechlorination. These congeners are characterized by an
initial increase in concentration before dechlorination starts. At the three highest biosurfactant concentrations, this initial concentration
increase was absent or dramatically reduced. Therefore, the enhancement in dechlorination appears to be caused by an increase in
bioavailability at high surfactant concentrations. The biosurfactant also reduced the lag time before dechlorination began in these
congeners. Among those congeners that have low threshold concentrations, dechlorination enhancement was found only in two
peaks. For these two, there was no lag period, either with or without the rhamnolipids. The maximum level of dechlorination and
the congener pattern of final dechlorination products were identical, regardless of biosurfactant concentration.