The role of organic carbon in facilitating mercury sorption and retention in the soil: Some field evidence from Oak Ridge, Tennessee-10391

ABSTRACT Potential binding ability of mercury (Hg) to soil is an important aspect in selecting bioremediation technologies. Two studies were carried out to evaluate affinity of Hg to soil organic carbon. The first study was conducted with soil samples obtained from Hg-contaminated areas close to the Department of Energy Site at Oak Ridge, Tennessee. The soil samples were analyzed for total Hg and total organic carbon (TOC), and later tested for Hg desorption in aqueous phase. The second study was conducted using peat (Sphagnum moss) as a carbon source for sorption of Hg in the aqueous phase. The study was undertaken as a confirmatory test to understand the interaction of Hg with the organic carbon under controlled conditions. Both studies revealed higher degree of association of Hg with peat/soil organic carbon, for a given condition. The soil samples were found to contain higher concentrations of Hg with increasing percentages of TOC in the soil. The soils with TOC of 1.18% and 6.05% had total Hg concentrations of 0.92 and 436 parts per million (ppm), respectively. Furthermore, desorption of Hg from the contaminated soils was directly related to TOC content of the soil. The results revealed an inverse relationship between Hg desorption from the soil and the TOC content of the soil, thus indicating the role of soil organic carbon in binding and retaining Hg in the soil. In a similar way, Hg sorption on peat substrate increased with increasing concentrations of Hg in the aqueous phase, thus showing a high affinity of Hg towards organic carbon. The ratio of the initial to final concentrations of Hg in the aqueous phase was as high as 144.09 for the experiments conducted at 0.50 ppm aqueous Hg concentration. Such Hg-TOC relationships might have a significant impact on the bioavailability of Hg in soils, hence on the ability of microorganisms or plants to uptake, transform or mobilize Hg during remediation process

Susceptibility of Bridge Steel and Concrete Components to Microbiological Influenced Corrosion (MIC) and Microbiological Influenced Deterioration (MID) in Florida

BDV29-977-26Submerged steel piles had localized corrosion associated with microbiologically influenced corrosion (MIC). The site also had heavy marine growth. The effect of crevice environments created by the macrofoulers may support MIC. Also, concrete may be subject to deterioration by microbiologically influenced deterioration (MID). Field visits to Florida natural water sites and a review of the literature and databases indicated that there are locations in Florida that support MIC. Steel samples were installed at three sites (brackish and fresh waters). The presence of marine fouling was an important part of the corrosion system. Laboratory testing identified the effects of crevices and availability of bacteria and nutrients on MIC. The use of steel coatings and galvanic cathodic protection was assessed for mitigation of MIC in environments with marine fouling. The use of polyurea and a water-based copper-free antifouling coating was examined to identify mitigation. The anti-fouling coating showed less barnacle growth compared to polyurea and had generally lower surface populations of SRB, IRB, APB, and SFB. Complications in cathodic protection (CP) arise with the presence of MIC and marine fouling. Steel field specimens were coupled to a zinc anode at the test sites. Application of CP reduced the corrosion rate, but results indicated that there were portions of the steel array under marine fouling that did not receive sufficient cathodic polarization. In field testing of concrete immersed in the test sites, heavy marine fouling and bacteria developed on the specimen surface. No differentiation in bulk concrete characteristics relating to MID were identified. Application of a polyurea did not mitigate marine fouling or bacteria formation