The role of black carbon in the sorption and desorption of phenanthrene on river sediments

Black carbon (BC) is ubiquitous in an aquatic environment. In the present study, the role of BC in the sorption and desorption of phenanthrene on the sediments sampled from the Yangtze River and the Yellow River of China has been studied. The BC content in total organic carbon ranged from 23 to 50% in sediment samples and BC accounted for 52.7–79.1% of the overall sorption, revealing the important role of BC in the sorption of phenanthrene on natural river sediments. The mean value of BC-water distribution coefficient ( k BC ) was about 50 times that of organic carbon (OC)-water distribution coefficient ( k OC ) for phenanthrene. The values of log k BC for the CTO375-combusted sediments ranged from 5.66 to 5.95, and the Freundlich exponent ranged from 0.40 to 0.67, suggesting that a difference exists among sorption capacities of BC from different river sediments. Therefore, the sources of BC should be taken into account when assessing its sorption capacity. For the desorption process, approximately 10.5–21.4 and 27.1–49.2% phenanthrene was desorbed from CTO375-combusted and original sediments, respectively. The results revealed that the OC-sorbed phenanthrene could not all desorb, and a fraction of BC-sorbed phenanthrene could desorb, although BC is considered a strong sorbent.