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Industrial activities in the Baltimore Harbor, Baltimore, Maryland, USA, have resulted in widespread chromium contamination of sediments. A comprehensive analysis of Cr speciation in sediment and porewater collected from 22 locations in the Baltimore Harbor was completed to understand Cr bioavailability and probability of toxicity due to Cr in sediments. The analysis employed a reverse-phase ion-pair high-performance liquid chromatography-inductively coupled plasma-mass spectrometry (HPLCICP- MS) method. Sub-microgram-per-liter determination of Cr(III) and Cr(VI) in environmental samples was found, with method validation revealing broad method applicability of HPLC-ICP-MS to a wide range of sample types. The major limitation of the method was poor Cr species separation in high ionic strength solutions (greater than 0.1 M NaCl). Total Cr concentrations in Baltimore Harbor sediments ranged from 2.5 to 1,050 mg/kg with 11 of the 22 sites containing total Cr in excess of the 370 mg/ kg effects range-median (ER-M) sediment quality guideline. The Cr(VI) concentrations in sediments, however, were markedly lower, ranging from 0.10 to 0.38 mg/kg with Cr(VI) not detected in 14 of the 22 stations. Porewater concentrations, both for total Cr and Cr(VI), were quite low, with total Cr ranging from 0.20 to 2.16 μg/L and Cr(VI) ranging from 0.73 to 1.17μg/L. The Cr(VI)-reducing capacity of the sediments, based on a sediment-spiking experiment, was found to be strongly correlated with the acid volatile sulfides content of the sediment. Overall, our results provide field validation of the hypothesis that Cr(VI) will not persist in sediments with excess acid volatile sulfides. Given the low concentrations of Cr(VI) in sediment and porewater, it appears unlikely that Cr in Baltimore Harbor sediments contributes appreciably to previously observed sediment toxicity. [ABSTRACT FROM AUTHOR]

Directly adjacent to the Chesapeake Bay lies the Aberdeen Proving Ground, a U.S. Army facility where testing of armor-piercing ammunitions has resulted in the deposition of >70,000 kg of depleted uranium (DU) to local soils and sediments. Results of previous environmental monitoring suggested limited mobilization in the impact area and no transport of DU into the nation's largest estuary. To determine if physical and biological reactions constitute mechanisms involved in limiting contaminant transport, the sorption and biotransformation behavior of the radionuclide was studied using geochemical modeling and laboratory microcosms (500 ppb U(VI) initially). An immediate decline in dissolved U(VI) concentrations was observed under both sterile and non-sterile conditions due to rapid association of U(VI) with natural organic matter in the sediment. Reduction of U(VI) to U(IV) occurred only in non-sterile microcosms. In the non-sterile samples, intrinsic bioreduction of uranium involved bacteria of the order Clostridiales and was only moderately enhanced by the addition of acetate (41% vs. 56% in 121 days). Overall, this study demonstrates that the migration of depleted uranium from the APG site into the Chesapeake Bay may be limited by a combination of processes that include rapid sorption of U(VI) species to natural organic matter, followed by slow, intrinsic bioreduction to U(IV).