Increasing Hg Concentration Research Articles

Exploring the applicability of nano-selenium for capture of mercury vapor: Paper based sorbent and a chemical modifier in graphite furnace atomic absorption spectrometry

The ability of the selenium nanoparticles (SeNPs) to capture mercury (Hg) is a subject of interest as this concept can be applied to reduce mercury poisoning cases to certain extent. In this work, SeNPs were fabricated on a paper and used as sorbent for capturing mercury vapor. The formation of the stable HgSe on the paper sorbent after the sequestration was visible to the naked eye for mercury concentration of higher than 200 μg L−1, corresponding with the discoloration of the paper sorbent from dark orange to gray color. The gray color was more intense with increasing Hg concentrations from 200 to 300, 500, and 1000 μg L−1. Therefore, color analysis software was used as a semi-quantitative technique for mercury analysis. The mercury captured was also analyzed with the inductively coupled plasma mass spectrometry (ICP-MS). After confirming that SeNPs helps capture mercury, it was further applied as a chemical modifier in graphite furnace atomic absorption spectrometry (GFAAS) for mercury determination. The SeNPs (410 mg L−1) allowed the use of pyrolysis temperature up to 300 °C with adequate sensitivity. Calibration curve was constructed from 100 to 500 μg L−1 with good linearity (R2 = 0.9968). With the use of SeNPs, 15 times sensitivity improvement was obtained compared to that without the use of any chemical modifier. The detection limit (N = 10 at 3σ) was calculated at 2 μg L−1 for the Hg standard. The proposed modifier was used for analyzing mercury in the saliva sample. Apart from minimizing extensive sample pretreatment process, the recovery percentage of Hg from the spiked sample was found to be approximately 90% (RSD 0–2%) with the help of the SeNPs modifier. This work exhibits multi-dimensional applications of SeNPs towards mercury analysis.

Total and methyl mercury distribution in water, sediment, plankton and fish along the Tapajós River basin in the Brazilian Amazon

Mercury (Hg) is known as one of the major contaminants in the Amazon. The Tapajós River basin, in the Brazilian Amazon, has diverse anthropogenic activities which increase Hg concentrations in the aquatic ecosystem. Moreover, high concentrations of Hg are naturally found in this basin. Distribution of total (THg) and methyl (MeHg) mercury were assessed in unfiltered water (n = 47), suspended particulate matter (SPM, n = 30), superficial sediment (BS, n = 29), plankton (n = 28) and fishes (n = 129) from the Tapajós River basin. Suspended particles were the main carrier of Hg in the water column and sediment. Increased erosion, prompted by anthropic activities, led to higher Hg concentrations in water from the most impacted areas. Hg is transported mainly in particulate matter; thus, anthropic disturbances influence Hg concentrations downstream. Limnological parameters such as organic matter content influenced MeHg concentrations in water, plankton and sediment of the Tapajós basin. Hg methylation in total plankton was more efficient in lakes (13-66%) than in Tapajós River main channel (2-14%). Biotic and abiotic factors interact in a complex way in the aquatic ecosystem, making Hg concentrations to vary in food web. Gold mining and deforestation probably increase Hg levels in the Tapajós basin. Thus, in addition to Hg monitoring, prevention and remediation efforts should be focused on soil and sediment erosion control.

Multiple Lines of Evidences Reveal Mechanisms Underpinning Mercury Resistance and Volatilization by Stenotrophomonas sp. MA5 Isolated from the Savannah River Site (SRS), USA.

A largely understudied microbially mediated mercury (Hg) bioremediative pathway includes the volatilization of Hg2+ to Hg0. Therefore, studies on Hg resistant bacteria (HgR), isolated from historically long-term contaminated environments, can serve as models to understand mechanisms underpinning Hg cycling. Towards this end, a mercury resistant bacterial strain, identified as Stenotrophomonas sp., strain MA5, was isolated from Mill Branch on the Savannah River Site (SRS); an Hg-impacted ecosystem. Minimum inhibitory concentration (MIC) analysis showed Hg resistance of up to 20 µg/mL by MA5 with 95% of cells retaining viability. Microcosm studies showed that the strain depleted more than 90% of spiked Hg2+ within the first 24 h of growth and the detection of volatilized mercury indicated that the strain was able to reduce Hg2+ to Hg0. To understand molecular mechanisms of Hg volatilization, a draft whole genome sequence was obtained, annotated and analyzed, which revealed the presence of a transposon-derived mer operon (merRTPADE) in MA5, known to transport and reduce Hg2+ into Hg0. Based on the whole genome sequence of strain MA5, qRT-PCR assays were designed on merRTPADE, we found a ~40-fold higher transcription of mer T, P, A, D and E when cells were exposed to 5 µg/mL Hg2+. Interestingly, strain MA5 increased cellular size as a function of increasing Hg concentrations, which is likely an evolutionary response mechanism to cope with Hg stress. Moreover, metal contaminated environments are shown to co-select for antibiotic resistance. When MA5 was screened for antibiotic resistance, broad resistance against penicillin, streptomycin, tetracycline, ampicillin, rifampicin, and erythromycin was found; this correlated with the presence of multiple gene determinants for antibiotic resistance within the whole genome sequence of MA5. Overall, this study provides an in-depth understanding of the underpinnings of Stenotrophomonas-mercury interactions that facilitate cellular survival in a contaminated soil habitat.

The role of benthic macrofauna in the trophic transfer of mercury in a low-diversity temperate coastal ecosystem (Puck Lagoon, southern Baltic Sea)

Mercury (Hg) is a global pollutant that affects human and ecosystem health. Hg is a serious threat especially for the marine environment, in which it undergoes bioaccumulation and biomagnification, reaching elevated concentrations in fish and other seafood. The research aimed at investigating the trophodynamics of Hg in the basal links of the marine food chain: benthic macrofauna and its main food sources (i.e. suspended and sediment organic matter, micro- and macrophytobenthos). The results showed that both the amount and the origin of organic matter affected the Hg level in particular trophic groups of macrozoobenthos. The intensive inflow of terrestrial material influenced the enrichment of suspended particles and microphytobenthos in Hg, leading to increased Hg concentrations in filter-feeding macrofauna. The input of Hg-rich marine matter transported from the deeper parts of the Gulf of Gdańsk along with the near-bottom currents caused higher Hg levels in deposit feeders. The biomagnification factor (BMF) of Hg through benthic food web was dependent on environmental conditions occurring in the studied areas, in particular, factors favouring the growth and fecundity of macrofauna. Consequently, as a result of biodilution, the trophic transfer of Hg was less effective in a more productive region, despite the elevated Hg concentrations in dietary components of the macrofauna and in the surrounding environment.

Cleaning and sampling protocol for analysis of mercury and dissolved organic matter in freshwater systems

Mercury (Hg), and in particular its methylated form (methylmercury, MeHg), is a hazardous substance with the potential to produce significant adverse neurological and other health effects. Enhanced anthropogenic emissions and long-range transport of atmospheric Hg have increased Hg concentrations above background levels in aquatic systems. In this context, the Minamata Convention, a global legally binding agreement that seeks to prevent human exposure to Hg, was signed and enforced by 128 countries, and today more than 90 Parties have ratified it. All these Parties have committed to develop Hg monitoring programs to report the effectiveness of the convention. For this purpose, we provide a standardized cleaning and water sampling protocol for the determination of total-Hg and MeHg in freshwaters at ambient levels. As Hg and organic matter are tightly bound, the protocol also describes sample collection for dissolved organic carbon (DOC) concentration and characterization of dissolved organic matter (DOM) composition by fluorescence spectroscopy. This protocol is highly useful to non-experts without a prior background in Hg sampling and analysis, and can serve as a useful basis for national monitoring programs. Furthermore, this protocol should help increase quantitative inventories of DOC, inorganic-Hg (IHg) and MeHg concentrations and DOM composition in freshwater, which are severely lacking at a global scale.•Provides a standardized method to collect water samples for IHg, MeHg, DOC and DOM composition from freshwater ecosystems.

Interactive effect of dietary vitamin E and inorganic mercury on growth performance and bioaccumulation of mercury in juvenile olive flounder, Paralichthys olivaceus treated with mercuric chloride.

A 6-week feeding trial was carried out to evaluate the effects of dietary vitamin E (dl-α-tocopheryl acetate, TA) on growth and mercury (Hg) accumulation in juvenile olive flounder (Paralichthys olivaceus) treated with mercuric chloride (HgCl2). Vitamin E and HgCl2 were added to the semi-purified basal diet. Six semi-purified diets in a 2 × 3 factorial design were formulated to contain 2 levels of Hg (0 or 20 mg HgCl2/kg diet) and 3 levels of vitamin E (0, 100, or 200 mg TA/kg diet). Experimental fish (n = 360, 9.99 ± 0.15 g) were randomly allocated into 30-L tanks at a density of 20 fish per tank with 3 replicates in each treatment and were fed twice a day. At the end of the feeding trial, dietary Hg depressed the growth performances in terms of weight gain (WG), specific growth rate (SGR), feed efficiency (FE) and protein efficiency ratio (PER) in fish, while fish fed the diets supplemented with vitamin E showed significant growth improvement in both presence and absence of HgCl2 in the diets (P < 0.05). Survival rate was not affected in fish fed the experimental diets. Whole body compositions of fish such as lipid and moisture contents were influenced by dietary vitamin E supplementation. Total Hg contents of muscle, liver and kidney tissues were significantly reduced in fish fed diets supplemented with vitamin E (P < 0.05), while the two-way ANOVA showed that increasing Hg concentration has resulted in a reduction in vitamin E. Whole body fatty acids of fish like eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) contents were decreased by dietary Hg. However, supplementation of dietary vitamin E improved the α-linolenic acid (ALA) and EPA contents in fish. Our results suggest that dietary supplementation of vitamin E has potential effects on growth improvement and ameliorating inorganic Hg bioaccumulation in juvenile olive flounder.

Photosynthetic pigments and peroxidase activity of Lepidium sativum L. during assisted Hg phytoextraction

The study was conducted to evaluate metabolic answer of Lepidium sativum L. on Hg, compost, and citric acid during assisted phytoextraction. The chlorophyll a and b contents, total carotenoids, and activity of peroxidase were determined in plants exposed to Hg and soil amendments. Hg accumulation in plant shoots was also investigated. The pot experiments were provided in soil artificially contaminated by Hg and/or supplemented with compost and citric acid. Hg concentration in plant shoots and soil substrates was determined by cold vapor atomic absorption spectroscopy (CV-AAS) method after acid mineralization. The plant photosynthetic pigments and peroxidase activity were measured by standard spectrophotometric methods. The study shows that L. sativum L. accumulated Hg in its aerial tissues. An increase in Hg accumulation was noticed when soil was supplemented with compost and citric acid. Increasing Hg concentration in plant shoots was correlated with enhanced activation of peroxidase activity and changes in total carotenoid concentration. Combined use of compost and citric acid also decreased the chlorophyll a and b contents in plant leaves. Presented study reveals that L. sativum L. is capable of tolerating Hg and its use during phytoextraction assisted by combined use of compost and citric acid lead to decreasing soil contamination by Hg.

Isotopic signatures of mercury contamination in latest Permian oceans

Abstract Sedimentary records from the northwest margin of Pangea and the Tethys show anomalously high Hg levels at the latest Permian extinction boundary. Background δ202Hg values are consistent with normal marine conditions but exhibit negative shifts coincident with increased Hg concentrations. Hg isotope mass-independent fractionation (Δ199Hg) trends are consistent with volcanic input in deep-water marine environments. In contrast, nearshore environments have Δ199Hg signatures consistent with enhanced soil and/or biomass input. We hypothesize that the deep-water signature represents an overall global increase in volcanic Hg input and that this isotope signature is overwhelmed in nearshore locations due to Hg from terrestrial sources. High-productivity nearshore regions may have experienced stressed marine ecosystems due to enhanced Hg loading.

Mercury toxicity to Eisenia fetida in three different soils.

Three different soils were spiked with 12 different concentrations of inorganic mercury (Hg). Sub-chronic Hg toxicity tests were carried out with Eisenia fetida in spiked soils by exposing the worms for 28days following standard procedures. The toxicity studies revealed that Hg exerted less lethal effect on earthworms in acidic soil with higher organic carbon (S-3 soil) where water soluble Hg recovery was very low compared to the water soluble Hg fractions in soils with less organic carbon and higher pH (S-1 and S-2 soils). The concentrations of total Hg that caused 50% lethality to E. fetida (LC50) after 28days of exposure in S-1, S-2 and S-3 soils were 152, 294 and 367mgkg-1, respectively. The average weight loss of E. fetida in three soils ranged from 5 to 65%. The worms showed less weight loss in the organic carbon-rich soil (S-3) compared to less organic carbon containing soils (S-1 and S-2). The bioconcentration of Hg in E. fetida increased with increased Hg concentrations. The highest bioaccumulation took place in the acidic soil with higher organic carbon contents with estimated bioaccumulation factors ranging from 2 to 7.7. The findings of this study will be highly useful for deriving a more robust soil ecological guideline value for Hg.

Bioaccumulation of trace element concentrations in common dolphins (Delphinus delphis) from Portugal

The common dolphin (Delphinus delphis) is one of the most abundant species in Atlantic Iberia, representing a potentially important tool to assess the bioaccumulation of trace elements in the Iberian marine ecosystem. Nine elements (As, Cd, Cu, Hg, Mn, Ni, Pb, Se and Zn) were evaluated in 36 dolphins stranded in continental Portugal. Dolphins had increasing Hg concentrations (16.72μg·g−1 ww, liver) compared with previous studies in Atlantic Iberia, whereas Cd concentrations (2.26μg·g−1 ww, kidney) fell within reported ranges. The concentrations of some trace elements (including Cd and Hg) presented positive relationships with dolphin length, presence of parasites and gross pathologies. Common dolphins may help biomonitoring more offshore Atlantic Iberian areas in future studies, which would otherwise be difficult to assess.

The ground beetle Parallelomorphus laevigatus is a potential indicator of trace metal contamination on the eastern coast of Sicily

Carabids are generally considered to be non-specialized predators, and they have been considered useful ecological indicators. They can play a key role in clarifying the route of contaminants in food webs because they are predators of small invertebrates and, in turn, part of the diet of several vertebrates. The Mediterranean species Parallelomorphus laevigatus, which so far has not been studied from an ecotoxicological point of view, is an excellent ecological indicator in sandy coastal environments.We investigated the accumulation of trace elements in Ionian populations of P. laevigatus and evaluated the transfer of metal through the food chain of the coastal ecosystem. We analyzed 15 metals, including 11 essential metals (Co, Cr, Cu, Fe, Mn, Mo, Ni, Se, Sn, V and Zn) and four toxic metals (As, Cd, Hg and Pb). Significant differences were found in metal concentration in animal tissues among sites.Our results support the existence of defense mechanisms for the studied species.High values of As, Cd, Cr, Pb, Ni, and Hg detected in the beetles from the control site can be explained by both the emission sources from the nearby industrial plants and the intense agricultural activity.The present paper shows increasing Hg concentrations in the simplified trophic web of sandy beaches and confirms the capability of this pollutant to biomagnify. Moreover, the high value of biomagnification factor (BMF) points to the severe pollution level in this protected area.

High precision analysis modeling by backward elimination with attitude on interaction effects on Au (Ag)-polymetallic mineralization of Glojeh, Iran

Identification of possible relationship between the elements, in mineralization and geochemical modeling is very important. The Full Cubic Model (FCM) with 90 Predictors including the main effects, quadratic terms, and interaction effects of Ag, As, Cu, Hg, Mn, Nb, P, Pb, Sn, Sr, Zn and U elements was used to create an Optimal and Reduced Cubic Model (ORCM) at vein-style Au (Ag)-polymetallic mineralization of Glojeh. It was generated with multiple regression and variance analysis and enhanced by Backward Elimination Procedure (BEP) for insignificant predictors through 15 steps. All the predictors contributed in ORCM by lowest p-value of 0.07 at degree of freedom (DF) equaled to 36. F ratio and R2 (pred.) criteria showed increasing trend from 0% to 77.80% and 6.12–262.51, respectively in model optimization. The main and interacted elements at ORCM are Sn, U, Pb, Cu and Ag × Sn, As × Mn, As × Zn, Hg × P, P × Sn, Sn2, P2, respectively based on related t-values. Interaction occurred when a pair of elements produces no similar trend on the response at different levels (associated to populations) of another element. Therefore, interaction of two elements on Au concentration was considered, simultaneously. By investigation, a disordinal interaction effect occurs on deposit for Au-As–Mn, Au-Ag-As and Au-Hg-Mn when the third element changes across the background level to vein values. Whereas, ordinal effects was observed at both population for Au-Ag-Hg and Au-As-Hg, since the lines were parallel. It implies that As has similar trend on Au for each value of Hg. The Au-Ag line explains the general downward shift by increasing Hg concentrations from vein to background. It revealed that Hg is more concentrated in background area. The accuracy and precision of this approach have been studied extensively for sample analysis, parameter identification, and modeling to ensure about BEP.

Thunderstorms Increase Mercury Wet Deposition.

Mercury (Hg) wet deposition, transfer from the atmosphere to Earth's surface by precipitation, in the United States is highest in locations and seasons with frequent deep convective thunderstorms, but it has never been demonstrated whether the connection is causal or simple coincidence. We use rainwater samples from over 800 individual precipitation events to show that thunderstorms increase Hg concentrations by 50% relative to weak convective or stratiform events of equal precipitation depth. Radar and satellite observations reveal that strong convection reaching the upper troposphere (where high atmospheric concentrations of soluble, oxidized mercury species (Hg(II)) are known to reside) produces the highest Hg concentrations in rain. As a result, precipitation meteorology, especially thunderstorm frequency and total rainfall, explains differences in Hg deposition between study sites located in the eastern United States. Assessing the fate of atmospheric mercury thus requires bridging the scales of global transport and convective precipitation.

Is mercury from small-scale gold mining prevalent in the southeastern Peruvian Amazon?

There is an ongoing debate on the fate of mercury (Hg) in areas affected by artisanal and small-scale gold mining (ASGM). Over the last 30 years, ASGM has released 69 tons of Hg into the southeastern Peruvian Amazon. To investigate the role of suspended matter and hydrological factors on the fate of ASGM-Hg, we analysed riverbank sediments and suspended matter along the partially ASGM-affected Malinowski-Tambopata river system and examined Hg accumulation in fish. In addition, local impacts of atmospheric Hg emissions on aquatic systems were assessed by analysing a sediment core from an oxbow lake. Hg concentrations in riverbank sediments are lower (20–53 ng g−1) than in suspended matter (∼400–4000 ng g−1) due to differences in particle size. Elevated Hg concentrations in suspended matter from ASGM-affected river sections (∼1400 vs. ∼30–120 ng L−1 in unaffected sections) are mainly driven by the increased amount of suspended matter rather than increased Hg concentrations in the suspended matter. The oxbow lake sediment record shows low Hg concentrations (64–86 ng g−1) without evidence of any ASGM-related increase in atmospheric Hg input. Hg flux variations are mostly an effect of variations in sediment accumulation rates. Moreover, only 5% of the analysed fish (only piscivores) exceed WHO recommendations for human consumption (500 ng g−1). Our findings show that ASGM-affected river sections in the Malinowski-Tambopata system do not exhibit increased Hg accumulation, indicating that the released Hg is either retained at the spill site or transported to areas farther away from the ASGM areas. We suspect that the fate of ASGM-Hg in such tropical rivers is mainly linked to transport associated with the suspended matter, especially during high water situations. We assume that our findings are typical for ASGM-affected areas in tropical regions and could explain why aquatic systems in such ASGM regions often show comparatively modest enrichment in Hg levels.

Long-Term (2002-2015) Changes in Mercury Contamination in NE Brazil Depicted by the Mangrove Oyster Crassostraea rhizophorae (Guilding, 1828).

Mercury concentrations in oysters from four estuaries in northeastern Brazil varied following source changes during the past 13years. Concentrations were higher in urban estuaries relative to rural areas, but decreased in the 13-years interval following improvements in solid wastes disposal and sewage treatment. In rural estuaries, the one located in an environmental protection area showed no changes in Hg concentrations in the period. However, in the Jaguaribe estuary, remobilization from soils and sediments due to regional environmental changes, increased Hg concentrations in oysters to values similar to the most contaminated metropolitan sites.

Mercury profiles in sediment from the marginal high of Arabian Sea: an indicator of increasing anthropogenic Hg input.

Total Hg distributions and its speciation were determined in two sediment cores collected from the western continental marginal high ofIndia. Total Hg content in the sediment was found to gradually increase (by approximately two times) towards the surface in both the cores. It was found that Hg was preferentially bound to sulfide under anoxic condition. However, redox-mediated reactions in the upper part of the core influenced the total Hg content in the sediment cores. This study suggests that probable increase in authigenic and allogenic Hg deposition attributed to the increasing Hg concentration in the surface sediment in the study area.

Translocation of mercury from substrate to fruit bodies of Panellus stipticus, Psilocybe cubensis, Schizophyllum commune and Stropharia rugosoannulata on oat flakes

The cultivation and fructification of 15 saprotrophic and wood-rotting fungal strains were tested on three various semi-natural medium. The formation of fruit bodies was observed for Panellus stipticus, Psilocybe cubensis, Schizophyllum commune and Stropharia rugosoannulata in the frame of 1–2 months. Mercury translocation from the substrate to the fruit bodies was then followed in oat flakes medium. Translocation was followed for treatments of 0, 1.25, 2.5, 5, 10 and 20ppm Hg in the substrate. All four fungi formed fruit bodies in almost all replicates. The fruit body yield varied from 0.5 to 15.3g dry weight. The highest bioconcentration factor (BCF) of 2.99 was found for P. cubensis at 1.25ppm Hg. The BCF decreased with increasing Hg concentration in the substrate: 2.49, 0, 2.38, 1.71 and 1.82 for P. stipticus; 3.00, 2.78, 2.48, 1.81 and 2.15 for P. cubensis; 2.47, 1.81, 1.78, 1.07 and 0.96 for S. commune; and 1.96, 1.84, 1.21, 1.71 and 0.96 for S. rugosoannulata. The Hg contents in the fruit bodies reflected the Hg contents in the substrate; the highest contents in the fruit bodies were found in P. cubensis (43.08±7.36ppm Hg) and P. stipticus (36.42±3.39ppm).

Toxicity of mercury to the earthworm Pontoscolex corethrurus in a tropical soil of French Guiana

Mercury is one of the most hazardous environmental pollutants due to its toxicity and bioaccumulation in the trophic web. In the Amazonian tropical forests, human activities, especially gold mining and coal burning, have increased the levels of mercury in soil, modified its mobilization and locally induced acute contamination. In order to evaluate the threat of such contamination for soil organisms, accumulation and toxic effects of mercury on the geophagous tropical earthworm Pontoscolex corethrurus was assessed in a laboratory test lasting 56 days. The toxicity test was done using a natural tropical soil amended with HgCl2 (from 5 to 100μgg−1 soil) under controlled conditions. While Hg body burden exponentially increased with increasing Hg concentration in soil, mortality, growth and cocoon production were affected only at the highest concentrations (50 and 100μgg−1 soil), confirming the broad tolerance of this species.

Phytoextraction of HG by parsley (Petroselinum crispum) and its growth responses

ABSTRACTThe effect of mercury (Hg) on the growth and survival of parsley (Petroselinum crispum) was explored at various treatments. The plants were grown in pots having Hoagland's solution to which various Hg treatments were applied and placed under greenhouse conditions. The treatments were: no metal applied (control) and six doses of Hg as mercuric chloride for 15 days. Linear trend of Hg accumulation was noted in roots, stems, and leaves with increasing Hg treatments. The maximum Hg concentration in root, stem and leaf was 8.92, 8.27, and 7.88 at Hg treatments of 25 mg l–1, respectively. On the whole, Hg accumulation in different plant parts was in the following order: leaves > stem > roots. Linear trend was also observed for Bioaccumulation Factor (BF) and Translocation Factor (TF) with increasing Hg concentrations in the growth medium. The highest respective BFHg and TFHg values were 9.32 and 2.02 for the Hg treatments of 25 and 50 mg l–1. In spite of the reduced growth in the presence of Hg, the plant has phytoremediation potential. It is recommended that parsley should not be cultivated in Hg contaminated sites in order to avoid dietary toxicity.

Mercury biomagnification and contemporary food web dynamics in lakes Superior and Huron

Trophic structure is an integral part of understanding the flow of contaminants within an aquatic system. Persistent, bioacccumulative, and toxic substances and food web perturbations by invasive species are critical ecological issues with far-reaching consequences for the health of the Laurentian Great Lakes. The historically-different aquatic ecosystems of Lakes Superior and Huron were evaluated for mercury (Hg) biomagnification using stable carbon (δ 13C) and nitrogen (δ 15N) isotope ratios. The results showed that δ values vary significantly with sampling depth, particularly for the lower food web components, reflecting depth- and diet-specific patterns of δ values. The stable isotope assessment of the Lake Superior food webs was consistent with previous results, underscoring the temporal stability of this ecosystem. However, based on stable isotope data, the Lake Huron lake trout appear to be incorporating the exotic round goby in their diet, possibly compensating for the collapse of alewife populations, historically their principal food. Our results suggest that the well-documented perturbations in the Lake Huron ecosystem have likely contributed to increasing Hg concentrations in the lake trout. Similar Hg biomagnification rates were observed suggesting strong similarities in the contemporary contaminant flow in Lakes Superior and Huron.