Properties influencing flux and diatom uptake of mercury and methylmercury from estuarine sediments.

Mercury (Hg) is a conspicuous and persistent global pollutant. Ionic Hg can be methylated into noxious methylmercury (CHHg), which biomagnifies in marine tropic webs and poses a health risk to humans and organisms. Sediment Hg methylation rates are variable, and the output flux of created CHHg are dependent on sediment characteristics and environmental factors.

The interaction of mercury and methylmercury with chalcogenide nanoparticles.

Mercury (Hg) and methylmercury (CHHg) bind strongly to micro and nano (NP) particles and this partitioning impacts their fate and bioaccumulation into food webs, and, as a result, potential human exposure. This partitioning has been shown to influence the bioavailability of inorganic Hg to methylating bacteria, with NP-bound Hg being more bioavailable than particulate HgS, or organic particulate-bound Hg. In this study we set out to investigate whether the potential interactions between dissolved ionic Hg (Hg) and CHHg and NPs was due to incorporation of Hg into the core of the cadmium selenide and sulfide (CdSe; CdS) nanoparticles (metal exchange or surface precipitation), or due purely to surface interactions.

Mercury flux from salt marsh sediments: Insights from a comparison between Ra/Th disequilibrium and core incubation methods.

In aquatic environments, sediments are the main location of mercury methylation. Thus, accurate quantification of methylmercury (MeHg) fluxes at the sediment-water interface is vital to understanding the biogeochemical cycling of mercury, especially the toxic MeHg species, and their bioaccumulation. Traditional approaches, such as core incubations, are difficult to maintain at conditions during assays, leading to over/underestimation of benthic fluxes.

The precipitation, growth and stability of mercury sulfide nanoparticles formed in the presence of marine dissolved organic matter.

The methylation of mercury is known to depend on the chemical forms of mercury (Hg) present in the environment and the methylating bacterial activity. In sulfidic sediments, under conditions of supersaturation with respect to metacinnabar, recent research has shown that mercury precipitates as β-HgS(s) nanoparticles (β-HgS(s)nano). Few studies have examined the precipitation of β-HgS(s)nano in the presence of marine dissolved organic matter (DOM).

Enhanced availability of mercury bound to dissolved organic matter for methylation in marine sediments.

The forms of inorganic mercury (Hg) taken up and methylated by bacteria in sediments still remain largely unknown. From pure cultures studies, it has been suggested that dissolved organic matter (DOM) may facilitate the uptake either by acting as a shuttle molecule, transporting the Hg atom to divalent metal transporters, or by binding Hg and then being transported into the cell as a carbon source. Enhanced availability of Hg complexed to DOM has however not yet been demonstrated in natural systems.

Dimethylmercury Formation Mediated by Inorganic and Organic Reduced Sulfur Surfaces.

Underlying formation pathways of dimethylmercury ((CH3)2Hg) in the ocean are unknown. Early work proposed reactions of inorganic Hg (Hg(II)) with methyl cobalamin or of dissolved monomethylmercury (CH3Hg) with hydrogen sulfide as possible bacterial mediated or abiotic pathways. A significant fraction (up to 90%) of CH3Hg in natural waters is however adsorbed to reduced sulfur groups on mineral or organic surfaces.