Effects of suspended sediment on the biodegradation and mineralization of phenanthrene in river water.

High suspended sediment (SPS) concentration commonly exists in many Asian rivers. Furthermore, climate change can cause high floods and lead to the resuspension of sediments and soil erosion, resulting in high SPS concentration in many natural waters. This research studied the impact of the presence of SPS and organic C composition of SPS on the biodegradation and mineralization of phenanthrene (PHE). Three sediments, including original sediment (OS), 375 degrees C (S375), and 600 degrees C (S600) combusted sediment, were studied. A flask-based 14C-respirometer system was applied to study the mineralization of [14C]PHE by Agrobacterium sp. The mineralization rate of PHE in the absence of SPS was significantly lower than that with the presence of OS and S600 but higher than that with S375, suggesting that the effect of the presence of sediment on PHE mineralization depended on its organic C composition. The residual levels of PHE in the S375 and OS systems were about 1.5 times that of the S600 system after incubation for 2 d. After 26-d incubation, the mineralization rates of PHE were 34.64, 29.40, and 14.00% in the OS, S600, and S375 systems, respectively. The first-order rate constants of the OS and S600 systems were about three times that of the S375 system. The net influence of SPS on the biodegradation and mineralization rates of PHE was dependent on its effects on compound bioavailability and bacteria population. This study suggested that black C played a key role in reducing the mineralization rates of PHE in sediments-even without aging.

Bioavailability of adsorbed phenanthrene by black carbon and multi-walled carbon nanotubes to Agrobacterium.

Carbonaceous sorbents including black carbon (BC) and carbon nanotubes have attracted research attention around the world because of their effects on bioavailability of hydrophobic organic compounds (HOCs) in sediments and soils. In this research, (14)C-labeled and unlabeled phenanthrene were spiked into three artificial sediments: (i) a sediment sample without amorphous organic carbon (OC) and with BC collected from the Yangtze River (BC-YR), (ii) a sediment without OC and with multi-walled carbon nanotubes (MWCNTs), and (iii) a sediment without OC and with fresh wood char. Biodegradation and mineralization of adsorbed phenanthrene by Agrobacterium and XAD-2 assisted abiotic desorption of adsorbed phenanthrene were studied. The results showed that microbes could utilize a fraction of adsorbed phenanthrene by BC and MWCNTs after aging for 21-40d. With aging for 28d, the biodegradation efficiencies of phenanthrene after incubation for 21d were 83.8%, 73.5% and 54.2% for BC-YR, char and MWCNTs, respectively; with aging for 40d, the mineralization rates of (14)C-labeled phenanthrene after incubation for 25d were 38.3%, 25.1% and 24.6%, respectively. The desorption and biodegradation processes showed similar residual concentration of phenanthrene. However, the biodegradation rates were higher than the desorption rates during the fast biodegradation stage, suggesting that bacteria could promote desorption or access and utilize the sorbed phenanthrene. The biodegradation and mineralization efficiencies of phenanthrene associated with MWCNTs were significantly lower than with BC (p<0.01), implying adsorption by MWCNTs may lead to a greater decrease of HOCs bioavailability in the environment.

Distribution and sources of polycyclic aromatic hydrocarbons in Wuhan section of the Yangtze River, China.

Polycyclic aromatic hydrocarbons (PAHs) are important organic contaminants with great significance for China, where coal burning is the main source of energy. In this study, concentrations, distribution between different phases, possible sources and eco-toxicological effect of PAHs of the Yangtze River were assessed. PAHs in water, suspended particulate matters (SPM) and sediment samples at seven main river sites, 23 tributary and lake sites of the Yangtze River at the Wuhan section were analyzed. The total concentrations of PAHs in the studied area ranged from 0.242 to 6.235 microg/l in waters and from 31 to 4,812 microg/kg in sediment. The average concentration of PAHs in SPM was 4,677 microg/kg, higher than that in sediment. Benzo(a)pyrene was detected only at two stations, but the concentrations were above drinking water standard. The PAHs level of the Yangtze River was similar to that of some other rivers in China but higher than some rivers in foreign countries. There existed a positive relationship between PAHs concentrations and the TOC contents in sediment. The ratio of specific PAHs indicated that PAHs mainly came from combustion process, such as coal and wood burning. PAHs may cause potential toxic effect but will not cause acute biological effects in sedimentary environment of the Wuhan section of the Yangtze River.