Print PageThe Mahoning River flows 208 km through Northeast Ohio and Western Pennsylvania and indirectly discharges into the Ohio River. For over 150 years the river served as an industrial sewer receiving high volumes of organic and inorganic waste from Youngstown’s coke and steel industries. Today the riparian zone is habitat for aquatic and woodland organisms and is slowly recovering its biodiversity. However high concentrations of polycyclic aromatic hydrocarbons (PAHs) and heavy metals remain in river bank sediments along the riparian corridor. These contaminated sediments are considered the main factor limiting aquatic life over a 51 km stretch. The Mahoning River is one of the most contaminated in the U.S. and is in dire need of an effective remediation strategy. In addition, information on microbial communities and biogeochemical processes that control contaminated river systems is limited. The purpose of this investigation is to fully characterize anaerobic riverbank sediment towards future implementation of in situ bioremediation. Triplicate riverbank sediment samples were collected in December 2010 using stainless steel cores to a depth of 80 cm. Cores were capped, placed in bags, transported, and processed under nitrogen. PAHs were determined by GC-MS. Nitrate and sulfate were measured by standard methods and ion chromatography respectively. Metals were measured using sequential extraction followed by ICP-AES and X-Ray Fluorescence (XRF) analysis. Total bacteria and sulfate reducers were enumerated by DAPI staining and by most probable number respectively. Microbial respiration was measured using reduction of 2-(p-iodophenyl)-3(p-nitrophenyl)-5-phenyl tetrazolium chloride (INT). DNA was extracted to characterize the microbial community by T-RFLPs.
Results/Conclusions
Results showed that total PAHs ranged from 47,000 to 85,000 μg/kg. Sediments presented low nitrate concentrations (4 to 14 μg/g) and surprisingly high sulfate concentrations (195 -325 μg/g). Metal sequential extraction revealed high concentrations of total iron (~100,000 ppm) of which 20% corresponded to iron oxides. Other metals associated with iron oxides included arsenic, cadmium, chromium, and lead. In addition, XRF confirmed that 60% of the metals present in the sediments corresponded to iron. Total bacteria were abundant (3x1010 g-1) despite PAH contamination while high numbers of sulfate reducing bacteria (3x104 g-1) were also present. Anaerobic microbial respiration (1.6 - 1.7 μmol/g/min) was much higher than reported previously.
These preliminary findings (microbial activity, bacterial numbers, sulfate concentrations, and sulfate reducers) indicate that indigenous microbes might have potential for anaerobic PAH degradation. Additionally, the high iron concentration may serve as a suitable terminal electron acceptor for microbial respiration.
