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Long-term speciation and lability of silver (Ag-), silver chloride (AgCl-), and silver sulfide nanoparticles (Ag2S-NPs) in soil were studied by X-ray absorption spectroscopy (XAS), and newly developed “nano” Diffusive Gradients in Thin Films (DGT) devices. These nano-DGT devices were designed specifically to avoid confounding effects when measuring element lability in the presence of nanoparticles. The aging profile and stabilities of the three nanoparticles and AgNO3 (ionic Ag) in soil were examined at three different soil pH values over a period of up to 7 months. Transformation of ionic Ag, Ag-NP and AgCl-NPs were dependent on pH. AgCl formation and persistence was observed under acidic conditions, whereas sulfur-bound forms of Ag dominated in neutral to alkaline soils. Ag2S-NPs were found to be very stable under all conditions tested and remained sulfur bound after 7 months of incubation. Ag lability was characteristically low in soils containing Ag2S-NPs. Other forms of Ag were linked to higher DGT-determined lability, and this varied as a function of aging and related speciation changes as determined by XAS. These results clearly indicate that Ag2S-NPs, which are the most environmentally relevant form of Ag that enter soils, are chemically stable and have profoundly low Ag lability over extended periods. This may minimize the long-term risks of Ag toxicity in the soil environment.

Divalent cationic strontium (Sr2+) adsorption to and desorption from iron corrosion products were examined in two model drinking water distribution systems (DWDS). One system was maintained with chlorine-disinfected drinking water and the other with the same water with secondary chloramine disinfection. Flow conditions simulated primary transmission lines (constant flow) and residential mains (periods of stagnation). Accumulation of Sr2+ to iron corrosion products in model DWDS was independent of disinfection type. Adsorption and desorption mechanisms are discussed. x-ray adsorption near edge structure (XANES) spectroscopy and linear combination fitting determined Sr2+ was primarily associated with iron oxyhydroxide corrosion products. At the end of the desorption study, the amount of Sr2+ remaining in iron corrosion products equilibrated to approximate levels observed at the end of the constant flow adsorption experiments. These results suggest that enhanced iron corrosion product loading of Sr2+ during stagnation could be short lived under constant flow conditions. Differences between adsorption and desorption based on disinfection type (chlorine versus chlorine plus chloramine) cannot be used to control Sr2; desorption., The original document contains color images. Pub in Journal of Water Supply: Research and Technology_AQUA, v63 n6 p449-460, 2014.

The capability of iron pipe corrosion products in active drinking water systems to concentrate metal ions, such as Pb, Sr and V from treated drinking water and mechanisms that can cause consumer exposures and releases back into the environment will be presented. We propose that sorption is the main mechanism concentrating metal ions on the surfaces of iron corrosion products. Typically metal concentrations in the corrosion products are an order(s) of magnitude greater than in the water entering the distribution system. Several mechanisms, including hydraulic disturbances, chemical disassociations, road work, or earthquakes, can result in acute exposures of consumers or concentrated releases of toxic metals back into the environment., Presented at the NACE International CORROSION 2013 Conference & Expo, Orlando, FL, 17-21 March 2013.

In situ amendments are a promising approach to enhance removal of metal contaminants from diverse environments including soil, groundwater and sediments. Apatite and chitin were selected and tested for copper, chromium, and zinc metal removal in marine sediment samples. Microbiological, molecular biological and chemical analyses were applied to investigate the role of these amendments in metal immobilization processes. Both apatite and chitin promoted microbial growth. These amendments induced corresponding bacterial groups including sulfide producers, iron reducers, and phosphate solubilizers; all that facilitated heavy metal immobilization and removal from marine sediments. Molecular biological approaches showed chitin greatly induced microbial population shifts in sediments and overlying water: chitin only, or chitin with apatite induced growth of bacterial groups such as Acidobacteria, Betaproteobacteria, Epsilonproteobacteria, Firmicutes, Planctomycetes, Rhodospirillaceae, Spirochaetes, and Verrucomicrobia; whereas these bacteria were not present in the control. Community structures were also altered under treatments with increase of relative abundance of Deltaproteobacteria and decrease of Actinobacteria, Alphaproteobacteria, and Nitrospirae. Many of these groups of bacteria have been shown to be involved in metal reduction and immobilization. Chemical analysis of pore- and overlying water also demonstrated metal immobilization primarily under chitin treatments. X-Ray absorption spectroscopy (XAS) spectra showed more sorbed Zn occurred over time in both apatite and chitin treatments (from 9% - 27%). The amendments improved zinc immobilization in marine sediments that led to significant changes in the mineralogy: easily mobile Zn hydroxide phase was converted to an immobile Zn phosphate (hopeite). In-situ amendment of apatite and chitin offers a great bioremediation potential for marine sediments contaminated with heavy metals., Published in the Open Journal of Metal, v3 p51-61, Jul 2013. The original document contains color images. Prepared in collaboration with the Stroud Water Research Center, Avondale, PA, the Department of Earth Sciences, University of Southern California, Los Angeles, and the National Risk Management Research Laboratory, Environmental Protection Agency, Cincinnati, OH.

The United States Environmental Protection Agency (US EPA) will require some U.S. drinking water distribution systems (DWDS) to monitor nonradioactive strontium (Sr2+) in drinking water in 2013. Iron corrosion products from four DWDS were examined to assess the potential for Sr2+ binding and release. Average Sr2+ concentrations in the outermost layer of the corrosion products ranged from 3 to 54 mg kg -1 and the Sr2 + drinking water concentrations were all /=0.3 mg L -1. Micro-X-ray adsorption near edge structure spectroscopy and linear combination fitting determined that Sr2+ was principally associated with CaCO3. Sr2+ was also detected as a surface complex associated with -FeOOH. Iron particulates deposited on a filter inside a home had an average Sr2+ concentration of 40.3 mg kg -1 and the associated drinking water at a tap was 210 g L -1. The data suggest that elevated Sr2+ concentrations may be associated with iron corrosion products that, if disturbed, could increase Sr2+ concentrations above the 0.3 g L -1 US EPA reporting threshold. Disassociation of very small particulates could result in drinking water Sr2+ concentrations that exceed the US EPA health reference limit (4.20 mg kg -1 body weight)., The original document contains color images. Published in Environmental Science and Technology, v47 p5171-5177, 22 Apr 2013. Prepared in collaboration with the U.S. Environmental Protection Agency, ORD, NRMRL, LRPCD, Cincinnati, OH, and in cooperation with the Department of Geology, University of Cincinnati, OH.

Dynamic templating as a result of cathodic hydrogen gas production is suggested as a possible mechanism for the formation of tube-like corrosion products on an unlined cast iron pipe in a drinking water distribution system. Mounds of corrosion product, with protruding tubes and freestanding tubes, were observed within a single 30 cm section of piping. Internal morphologies for all shapes were texturally complex although mineralogically simple, composed of two iron oxide/oxyhydroxides minerals: alpha-FeOOH (goethite) and Fe304 (magnetite). Static templating by either microorganisms or minerals was rejected as a possible mechanism for tube formation in this study.

Sediment amendments provide promising strategies of enhancing sequestration of heavy metals and degradation of organic contaminants. The impacts of sediment amendments for metal and organic remediation including apatite, organoclay (and apatite and organoclay in geotextile mats), acetate, and chitin on environmental microbial communities in overlying water and sediment profiles are reported here. These experiments were performed concurrent with an ecotoxicity evaluation (data submitted in companion paper) and X-ray absorption spectroscopy of zinc speciation post apatite amendments. X-ray absorption spectra showed that a modest modification of zinc speciation occurred in amended treatments. Significant changes in both bacterial cell densities and populations were observed in response to amendments of apatite+organoclay, chitin, and acetate. The enriched bacteria and breakdown of these amendments were likely attributed to water quality degradation (e.g. ammonia and dissolved oxygen). Molecular fingerprints of bacterial communities by denaturant gradient gel electrophoresis (DGGE) showed that distinct bacterial populations occurred in overlying waters from different amendments: aapatite+rganoclay led to the dominance of Gammaproteobacteria, acetate enriched Alphaproteobacteria, and chitin treatment led to a dominance of Bacteroidetes and Alphaproteobacteria. In amended sediments, Firmicutes, Bacteroidetes, and Deltaproteobacteria (Desulfovibrio) were commonly found with chitin and apapatite+itin treatments. Finally, sulfate-reducing bacteria (e.g. Desulfovibrio) and metal-reducing bacteria were also recovered with most probable number (MPN) analyses in treatments with acetate, chitin, and apaapatite+tin. These geochemically important bacteria were stimulated by amendments and may play critical functional roles in the metal and organic contaminant remediation process for future investigations of contaminated sediments., Pub. in Ecotoxicology and Environmental Safety, v74, p1931-1941, 2012. The original document contains color images.