Methylmercury in marine ecosystems : spatial patterns and processes of production, bioaccumulation, and biomagnification

Author Posting. © International Association for Ecology and Health, 2008. This is the author's version of the work. It is posted here by permission of Springer for personal use, not for redistribution. The definitive version was published in EcoHealth 5 (2008): 399-408, doi:10.1007/s10393-008-0201-1.The spatial variation of MeHg production, bioaccumulation and biomagnification in marine food webs is poorly characterized but critical to understanding the links between sources and higher trophic levels such as fish that are ultimately vectors of human and wildlife exposure. This paper discusses both large and local scale processes controlling Hg supply, methylation, bioaccumulation and transfer in marine ecosystems. While global estimates of Hg supply suggest important open ocean reservoirs of MeHg, only coastal processes and food webs are known sources of MeHg production, bioaccumulation, and bioadvection. The patterns observed to date suggest that not all sources and biotic receptors are spatially linked and that physical and ecological processes are important in transferring MeHg from source regions to bioaccumulation in marine food webs and from lower to higher trophic levels.Supported by NIH Grant Number P42 ESO7373 from the NIEHS, SERDP funds from the Department of Defense, the ESSRF (Environmental Science Strategic Research Fund) DFO, Canada, Woods Hole Sea Grant, Woods Hole Coastal Ocean Institute, National Science Foundation, and RI-INBRE Grant #P20RR016457 from NCRR, NIH

Experimental study and steady-state simulation of biogeochemical processes in laboratory columns with aquifer material

Abstract Packed bed laboratory column experiments were performed to simulate the biogeochemical processes resulting from microbially catalyzed oxidation of organic matter. These included aerobic respiration, denitrification, and Mn(IV), Fe(III) and SO 4 reduction processes. The effects of these reactions on the aqueous-and solid-phase geochemistry of the aquifer material were closely examined. The data were used to model the development of alkalinity and pH along the column. To study the independent development of Fe(III)-and SO 4 -reducing environments, two columns were used. One of the columns (column 1) contained small enough concentrations of SO 4 in the influent to render the reduction of this species unimportant to the geochemical processes in the column. The rate of microbially catalyzed reduction of Mn(IV) changed with time as evidenced by the variations in the initial rate of Mn(II) production at the head of the column. The concentration of Mn in both columns was controlled by the solubility of rhodochrosite (MnCO 3(S) ). In the column where significant SO 4 reduction took place (column 2), the concentration of dissolved Fe(II) was controlled by the solubility of FeS. In column 1, where SO 4 reduction was not important, maximum dissolved Fe(II) concentrations were controlled by the solubility of siderite (FeCO 3(S) ). Comparison of solid-phase and aqueous-phase data suggests that nearly 20% of the produced Fe(II) precipitates as siderite in column 1. The solid-phase analysis also indicates that during the course of experiment, approximately 20% of the total Fe(III) hydroxides and more than 70% of the amorphous Fe(III) hydroxides were reduced by dissimilatory iron reduction. The most important sink for dissolved S(-II) produced by the enzymatic reduction of SO 4 was its direct reaction with solid-phase Fe(III) hydroxides leading initially to the formation of FeS. 0169-7722/03/$ -see front matter

Highly Efficient Iron Oxide Nanoparticles Immobilized on Cellulose Nanofibril Aerogels for Arsenic Removal from Water

The application and optimal operation of nanoparticle adsorbents in fixed-bed columns or industrial-scale water treatment applications are limited. This limitation is generally due to the tendency of nanoparticles to aggregate, the use of non-sustainable and inefficient polymeric resins as supporting materials in fixed-bed columns, or low adsorption capacity. In this study, magnesium-doped amorphous iron oxide nanoparticles (IONPs) were synthesized and immobilized on the surface of cellulose nanofibrils (CNFs) within a lightweight porous aerogel for arsenic removal from water. The IONPs had a specific surface area of 165 m2 g−1. The IONP-containing CNF aerogels were stable in water and under constant agitation due to the induced crosslinking using an epichlorohydrin crosslinker. The adsorption kinetics showed that both As(III) and As(V) adsorption followed a pseudo second-order kinetic model, and the equilibrium adsorption isotherm was best fitted using the Langmuir model. The maximum adsorption capacities of CNF-IONP aerogel for As(III) and As(V) were 48 and 91 mg As g-IONP−1, respectively. The optimum IONP concentration in the aerogel was 12.5 wt.%, which resulted in a maximum arsenic removal, minimal mass loss, and negligible leaching of iron into water

Kinetics of Homogeneous and Surface-Catalyzed Mercury(II) Reduction by Iron(II)

Production of elemental mercury, Hg(0), via Hg­(II) reduction is an important pathway that should be considered when studying Hg fate in environment. We conducted a kinetic study of abiotic homogeneous and surface-catalyzed Hg(0) production by Fe­(II) under dark anoxic conditions. Hg(0) production rate, from initial 50 pM Hg­(II) concentration, increased with increasing pH (5.5–8.1) and aqueous Fe­(II) concentration (0.1–1 mM). The homogeneous rate was best described by the expression, <i>r</i>_<i>hom</i> = <i>k</i>_<i>hom</i> [FeOH⁺] [Hg­(OH)₂]; <i>k</i>_<i>hom</i> = 7.19 × 10⁺³ L (mol min)⁻¹. Compared to the homogeneous case, goethite (α-FeOOH) and hematite (α-Fe₂O₃) increased and γ-alumina (γ-Al₂O₃) decreased the Hg(0) production rate. Heterogeneous Hg(0) production rates were well described by a model incorporating equilibrium Fe­(II) adsorption, rate-limited Hg­(II) reduction by dissolved and adsorbed Fe­(II), and rate-limited Hg­(II) adsorption. Equilibrium Fe­(II) adsorption was described using a surface complexation model calibrated with previously published experimental data. The Hg(0) production rate was well described by the expression <i>r</i>_<i>het</i> = <i>k</i>_<i>het</i> [>SOFe^(II)] [Hg­(OH)₂], where >SOFe^(II) is the total adsorbed Fe­(II) concentration; <i>k</i>_<i>het</i> values were 5.36 × 10⁺³, 4.69 × 10⁺³, and 1.08 × 10⁺² L (mol min)⁻¹ for hematite, goethite, and γ-alumina, respectively. Hg(0) production coupled to reduction by Fe­(II) may be an important process to consider in ecosystem Hg studies