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Contaminants in sediments are less available than their concentrations might imply, but measures of this availability have been generally lacking. Sediments ingested by benthic animals can be expected to undergo a unique chemical environment controlled by the digestive chemistry of the organism. We measured solubilization of sedimentary contaminantsCu, Pb, and polycyclic aromatic hydrocarbons (PAH)by digestive fluids extracted from marine invertebrates. Bioavailability of these contaminants, thus measured, is a small fraction of total contaminant loadingtypically 1−10%. The amounts of metals solubilized by digestive fluids were orders of magnitude greater than would be predicted from water−solid partitioning with clean seawater, although they correlated well with solubilization by seawater. Digestive fluids from two different animal species solubilized different amounts of metals, indicating that bioavailability varies among species even under constant mode of uptake. High concentrations of solubilizing agents, such as amino acids for metals and surfactants for PAH, in the digestive fluids can explain the enhanced solubilization. This biomimetic approach to contaminant measurement provides the basis for more accurate mechanistic and routine assessments of environmental impact.

Sr:Ca and Ba:Ca ratios in water from the Adour estuary show a clear relationship with the salinity of the surrounding water for salinities <20, while ratios are almost constant above this level of salinity. A positive relationship was observed for the Sr:Ca ratio, whereas it was inverse for the Ba:Ca ratio. These two elemental ratios were measured in the otoliths of the European eels (Anguilla anguilla L.) using femtosecond laser ablation linked to an ICP-MS (fs-LA-ICP-MS). There was a direct relationship between the elemental ratios recorded in eel otoliths and those found in water from fresh and marine areas, suggesting that Sr:Ca and Ba:Ca ratios in eel otoliths can be used as markers of habitat in this estuary. Continuous profiling allowed the determination of three behaviour patterns in terms of habitat: freshwater, estuary and migratory individuals. Finally, the above results support the simultaneous use of both ratios for a better understanding of the migratory contingents and also as a relevant method to avoid a misidentification of environmental migratory history due to the presence of vaterite crystal in the otolith matrix.

This study presents the determination and comparison of isotopic compositions of Hg in sediments, plankton, roach, and perch of two freshwater systems in the Lake Baikal-Angara River aquatic ecosystem: the man-made Bratsk Water Reservoir contaminated by Hg from a chlor-alkali factory and the noncontaminated Lake Baikal. Isotopic ratios of biota exhibit both significant mass-independent fractionation (MIF) (Δ(199)Hg from 0.20 to 1.87‰) and mass-dependent fractionation (MDF) (δ(202)Hg from -0.97 to -0.16‰), whereas sediments exhibit high MDF (δ(202)Hg from -1.99 to -0.83‰) but no MIF. δ(15)N and δ(13)C are correlated with methylmercury in organisms from both sites, indicating bioaccumulation and biomagnification through food webs of both regions. Combining this with isotopic composition of samples shows that δ(202)Hg increases with the trophic level of organisms and also with methylmercury in fish from Lake Baikal. This study demonstrates that MIF in fish samples from Bratsk Water Reservoir allow to trace anthropogenic Hg, since fish with the highest levels of Hg in muscle have the same isotopic composition as the sediment in which anthropogenic Hg was deposited. Less contaminated fish do not exhibit this anthropogenic signature accumulating relatively lower Hg amount from the contaminated sediments. This work reveals that Hg isotopic composition can be used to track the contribution of anthropogenic sources in fish from a contaminated lake.

Mercury undergoes several transformations that influence its stable isotope composition during a number of environmental and biological processes. Measurements of Hg isotopic mass-dependent (MDF) and mass-independent fractionation (MIF) in food webs may therefore help to identify major sources and processes leading to significant bioaccumulation of methylmercury (MeHg). In this work, δ(13)C, δ(15)N, concentration of Hg species (MeHg, inorganic Hg), and stable isotopic composition of Hg were determined at different trophic levels of the remote and pristine Lake Baikal ecosystem. Muscle of seals and different fish as well as amphipods, zooplankton, and phytoplankton were specifically investigated. MDF during trophic transfer of MeHg leading to enrichment of heavier isotopes in the predators was clearly established by δ(202)Hg measurements in the pelagic prey-predator system (carnivorous sculpins and top-predator seals). Despite the low concentrations of Hg in the ecosystem, the pelagic food web reveals very high MIF Δ(199)Hg (3.15-6.65‰) in comparison to coastal fish (0.26-1.65‰) and most previous studies in aquatic organisms. Trophic transfer does not influence MIF signature since similar Δ(199)Hg was observed in sculpins (4.59 ± 0.55‰) and seal muscles (4.62 ± 0.60‰). The MIF is suggested to be mainly controlled by specific physical and biogeochemical characteristics of the water column. The higher level of MIF in pelagic fish of Lake Baikal is mainly due to the bioaccumulation of residual MeHg that is efficiently turned over and photodemethylated in deep oligotrophic and stationary (i.e., long residence time) freshwater columns.

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