Biogeochemistry of Chromium in Marine SedimentsEPA Grant Number: U915757
Title: Biogeochemistry of Chromium in Marine Sediments
Investigators: Murray, Karen J.
Institution: University of California - San Diego
EPA Project Officer: Michaud, Jayne
Project Period: August 1, 2000 through August 1, 2003
Project Amount: $148,963
RFA: STAR Graduate Fellowships (2000) RFA Text | Recipients Lists
Research Category: Aquatic Ecosystems , Academic Fellowships , Fellowship - Oceanography
The purpose of this project is to examine the biogeochemical cycling of chromium (Cr) in the harbor sediments in San Diego Bay, CA, or another Cr-contaminated site. The focus will be on elucidating the processes responsible for Cr(VI) reduction under environmental conditions, and the relative significance of biotic versus abiotic factors.
Mesocosm experiments mimicking marine systems exposed to Cr(VI) through pollution from the water column will be set up to determine the effects of Cr(VI) pollution on the redox conditions and bacterial communities in the sediments. Sediment from San Diego Bay will be placed in 37.85 L aquaria, and overlain with 20 L of natural seawater, which will be gently mixed with slow moving paddles to prevent stagnation. Two aquaria will be kept for approximately 3 months at each of three Cr conditions: 0 mM, 0.05 mM, and 0.25 mM Cr(VI). After the aquaria has been running for several months, redox conditions in the six aquaria will be examined using solid-state gold amalgam voltammetric microelectrodes. Depth profiles of oxygen, manganese(II), iron species, and sulfur species are being taken at millimeter scale in approximately the first 2-3 centimeters of the sediment. At the end of the experiment, the mesocosms will be cored and analyzed for solid phase and porewater chemical species and microbial community composition. The results for the different aquaria will be compared to assess the effect of Cr(VI) on chemical profiles and microbial populations. Laboratory experiments to determine the potential for Cr(III) oxidation by bacterial consortia obtained from San Diego Bay sediments will be started, and experiments to measure the precipitation of Cr at different depths in the mesocosm and environmental cores are planned. The removal of Cr(VI) by live and killed sediments will be compared to examine the relative importance of abiotic and biotic reduction.
The potential for biologically catalyzed in situ reduction of Cr(VI) and subsequent precipitation of nontoxic Cr(III) suggests that there may be methods for bioremediation or accelerated natural attenuation of chromium contamination in the environment. If it can be shown that the Cr(III) is stable in sediments, then bacterial Cr(VI) reduction and the effect of other environmental conditions may be explored as a method for the detoxification of hazardous Cr(VI).