Relationship between mercury accumulation in young-of-the-year yellow perch and water-level fluctuations

A three-year (2001-2003) monitoring effort of 14 northeastern Minnesota lakes was conducted to document relationships between water-level fluctuations and mercury bioaccumulation in young-of-the-year (YOY) yellow perch (Perca flavescens) collected in the fall of each year at fixed locations. Six of those lakes are located within or adjacent to Voyageurs National Park and are influenced by dams on the outlets of Rainy and Namakan lakes. One site on Sand Point Lake coincides with a location that has nine years of previous monitoring suitable for addressing the same issue over a longer time frame. Mean mercury concentrations in YOY yellow perch at each sampling location varied significantly from year to year. For the 12-year monitoring site on Sand Point Lake, values ranged from 38 ng gww(-1) in 1998 to 200 ng gww(-1) in 2001. For the 14-lake study, annual mean concentrations ranged by nearly a factor of 2, on average, for each lake over the three years of record. One likely factor responsible for these wide variations is that annual water-level fluctuations are strongly correlated with mercury levels in YOY perch for both data sets.     

Elimination of mercury by yellow perch in the wild

The rate of methylmercury (MeHg) elimination by fish is important in determining the extent of bioaccumulation and for predicting recovery times of MeHg-contaminated fisheries. Rates of MeHg elimination remain uncertain in existing bioaccumulation models due to a lack of field studies. We addressed this problem by monitoring fish that had naturally accumulated isotopically enriched MeHg (spike MeHg) during a whole-ecosystem experiment. We transported yellow perch (Perca flavescens) from the experimental lake to an untreated lake and monitored spike total mercury (THg, most of which was MeHg) losses over 440 d. Spike THg was distributed among fish tissues in a similar way as ambient THg (background non-spike THg). We observed rapid loss of spike THg from liver and other visceral tissues (approximately 90 d) followed by a plateau. Subsequently, there was prolonged redistribution of spike THg into muscle (180 d). Loss of spike THg from the whole fish occurred > 5 times slower (half-life of 489 d) than in past laboratory studies using this species. We determined that MeHg bioaccumulation models with laboratory-based elimination rates produced faster losses than those observed in wild fish. The present findings provide support for refining elimination rates in MeHg models and show the importance of examining biological processes under natural conditions.     

Increasing mercury in yellow perch at a hotspot in Atlantic Canada, Kejimkujik National Park

In the mid-1990s, yellow perch (Perca flavescens) and common loons (Gavia immer) from Kejimkujik National Park and National Historic Site (KNPNHS), Nova Scotia, Canada, had among the highest mercury (Hg) concentrations across North America. In 2006 and 2007, we re-examined 16 lakes to determine whether there have been changes in Hg in the loon's preferred prey, yellow perch. Total Hg concentrations were measured in up to nine perch in each of three size classes (5-10 cm, 10-15 cm, and 15-20 cm) consumed by loons. Between 1996/97 and 2006/07, polynomial regressions indicated that Hg in yellow perch increased an average of 29% in ten lakes, decreased an average of 21% in three, and were unchanged in the remaining three lakes. In 2006/07, perch in 75% of the study lakes had Hg concentrations (standardized to 12-cm fish length) equal to or above the concentration (0.21 μg·g(-1) ww) associated with a 50% reduction in maximum productivity of loons, compared with only 56% of these lakes in 1996/97. Mercury contamination currently poses a greater threat to loon health than a decade ago, and further reductions in anthropogenic emissions should be considered to reduce its impacts on ecosystem health.     

Rapid release of mercury from intertidal sediments exposed to solar radiation: a field experiment

There is increasing evidence of the primary importance of photochemical reactions and transfer of gaseous mercury to the atmosphere. Although mercury in aquatic sediments is efficiently retained, resuspension and bioturbation in intertidal sediments may expose temporarily anoxic sediments to solar radiation. Field experiments were performed to investigate these processes. Anoxic sediments from two areas in the Tagus estuary with different degrees of Hg contamination (experiments I and II) were homogenized and distributed into two sets of 36 uncovered Petri dishes. The samples were placed on the intertidal sediments and exposed to direct solar radiation and kept under dark (control) for 6-8 h. The decrease rates of acid volatile sulfides (abrupt in the first 3 h) and of pyrite (linear) were the same in sediments under solar radiation and dark. The total Hg concentrations were relatively constant in sediments kept in dark, but decreased from 17.6 to 7.65 and 3.45 to 1.35 nmol g(-1) in experiments I and II, respectively. In those exposed to solar radiation during the period of higher UV intensity. Similar evolutions were found in nonreactive Hg in pore waters (3.00-2.59 and 0.725-0.105 nM). On the contrary, reactive Hg was higher in pore waters of the sediments exposed to solar radiation and increased with time, from 424 to 845 pM and 53 to 193 pM. These results indicate that most mercury released in pore waters was photochemically reduced in a short period of time and escaped rapidly to the atmosphere. Episodes of bottom resuspension and bioturbation in the intertidal sediments enhance the transfer of gaseous mercury to the atmosphere.     

PCB elimination by yellow perch (Perca flavescens) during an annual temperature cycle

The significance of temperature on aquatic species ecology and physiology is well recognized yet its effects on chemical bioaccumulation kinetics are less well understood under natural conditions. In this study, yellow perch were dosed with a polychlorinated biphenyl (PCB) mixture and allowed to depurate the chemicals over 1 year under an ambient temperature cycle characteristic of northern temperate latitudes. PCB elimination kinetics during the summer months at optimal water temperature for perch (23 degrees C) were similar to those observed in lab studies with other species reared at their optimal temperature. During the fall and winter seasons, however, elimination of only 11 PCB congeners of log K(ow) < or = 5.7 was observed and half-lives averaged > 1000 d for these PCBs. PCB elimination was again observed with the onset of spring temperatures but elimination rates averaged 2.6 times slower for readily metabolized congeners and 7.5 times slower for more persistent PCBs than observed during the summer. Bioenergetics modeling efforts predicted maximum values for respiration, fecal egestion, and growth rates during summer months but also predicted rapid declines in these chemical dilution processes during the fall and winter concurrent with changes in temperature. As temperature increased into the spring, bioenergetic rates were predicted to increase but only achieved approximately 85% of maximum rates predicted for summer peak temperatures. These results indicate that minimal chemical elimination occurs in perch when metabolic functioning falls to low maintenance levels during the fall and winter. These seasons encompass approximately 8 months of the year at northern temperate latitudes and therefore these patterns have significant consequences for understanding mechanisms of food-web biomagnification of hydrophobic organic chemicals in aquatic systems.     

Atmospheric mercury speciation: laboratory and field evaluation of a mist chamber method for measuring reactive gaseous mercury

Knowledge of atmospheric mercury speciation is critical to modeling its fate. Thus there is a crucial need for reliable methods to measure the fraction of gaseous atmospheric Hg which is in the oxidized Hg(II) form (termed reactive gaseous mercury, RGM). We have developed a novel method for measurement of RGM using a refluxing mist chamber, and we recently reported the results of sampling campaigns for RGM in Tennessee and Indiana. In general, measured RGM levels were about 3% of total gaseous mercury (TGM), and our results support prevailing hypotheses about the nature and behavior of RGM in ambient air. Because its use for RGM is growing, we now report in more detail the development and testing of the mist chamber method. Several styles of mist chambers have been investigated. The most versatile design employs a single nebulizer nozzle and can operate at flows of 15-20 L/min. The water-soluble Hg is collected in ca. 20 mL of absorbing solution, which is then analyzed for Hg(II) by SnCl2 reduction and CVAFS. One-hour samples (ca. 1 m3 of air) generally contain 50-200 pg of RGM. The method detection limit for 1-h samples is approximately 6-10 pg/m3. Thus short sample times can reveal temporal variations in RGM that would not otherwise be observable. The efficiency of collecting RGM in mist chambers is highly dependent on Cl- concentration in the absorbing solution, in keeping with equilibrium calculations. Artifact formation of Hg(II) by oxidation of Hg0 under ozone ambient conditions appears to be sufficiently slow so as to be negligible for the short (ca. 1 h) runs that are typically employed. We observed no significant error from cosampled particles or aerosols in rural nonimpacted air samples. We have developed a simple approach to analyzing mist chamber samples in the field using an automated Hg sampler.     

Experimental evidence of a linear relationship between inorganic mercury loading and methylmercury accumulation by aquatic biota

Developing effective regulations on mercury (Hg) emissions requires a better understanding of how atmospheric Hg deposition affects methylmercury (MeHg) levels in aquatic biota. This study tested the hypothesis that MeHg accumulation in aquatic food webs is related to atmospheric Hg deposition. We simulated a range of inorganic Hg deposition rates by adding isotopically enriched Hg(II) (90.9% 202Hg) to 10-m diameter mesocosms in a boreal lake. Concentrations of experimentally added ("spike") Hg were monitored in zooplankton, benthic invertebrates, and fish. Some Hg(II) added to the mesocosms was methylated and incorporated into the food web within weeks, demonstrating that Hg(II) deposited directly to aquatic ecosystems can become quickly available to biota. Relationships between Hg(II) loading rates and spike MeHg concentrations in zooplankton, benthic invertebrates, and fish were linear and significant. Furthermore, spike MeHg concentrations in the food web were directly proportional to Hg(II) loading rates (i.e., a percent change in Hg(II) loading rate resulted in, statistically, the same percent change in MeHg concentration). This is the first experimental determination of the relationship between Hg(II) loading and MeHg bioaccumulation in aquatic biota. We conclude that changes in atmospheric Hg deposition caused by increases or decreases in Hg emissions will ultimately affect MeHg levels in aquatic food webs.     

Dietary intake of pesticide residues: cadmium, mercury, and lead.

Information on the dietary intake of chemical contaminants has been obtained from institutions participating in GEMS/Food. Contaminants studied include certain organochlorine and organophosphorous pesticides, PCBs, cadmium, mercury, and lead. The intakes are compared with toxicologically acceptable intake levels established by international expert groups. In most cases, dietary intakes of organochlorine and organophosphorous pesticides are well below the Acceptable Daily Intake (ADI) of the respective pesticide. Of some 21 countries providing information on the average dietary intake of cadmium, only in one case is the Provisional Tolerable Weekly Intake (PTWI) exceeded. Several countries identified cereals and cereal products and root and tuber vegetables as the main contributors to the dietary intake of cadmium. For mercury, all reported intakes are below the PTWI of methylmercury. The contribution of fish to the total intake of mercury varied from 20% to 85%, depending on the country. Therefore, the general assumption that fish is the main contributor to the total dietary intake of mercury may, at times, not be justified. Average dietary intake of lead exceeding or approaching the PTWI are reported for adults and infants and children in some countries. Foodstuffs which contribute most to the intake of lead vary from country to country, and have been identified as being alternately drinking water, beverages, cereals, vegetables and fruit.     

Foliar mercury accumulation and exchange for three tree species

The goals of this study were to (1) investigate plant mercury (Hg) uptake using different air and soil Hg concentrations near natural background values for three tree species, and (2) test if measured foliar Hg fluxes could explain observed foliar Hg concentrations. Plants were exposed to three soil treatments (<0.01, 0.09 +/- 0.02, and 0.92 +/- 0.27 microg Hg g(-1)), and to three atmospheric exposure concentrations (5.9 +/- 2.3, 14.3 +/- 2.7, and 30.1 +/- 3.5 ng Hg m(-3)). Foliar Hg concentrations were found to be influenced primarily by atmospheric Hg concentrations and to a lesser extent by soil Hg exposures. Data indicated that deciduous species might play a more active role in ecosystem Hg cycling than evergreen trees. Foliar mercury fluxes quantified using a dynamic single-plant gas-exchange chamber for two species were variable and accumulation rates were lower than those predicted based on foliar Hg concentrations. A hypothesis to explain this discrepancy is that the plant gas-exchange chamber measures net flux which includes emission, deposition, adsorption, and reemission of Hg at the leaf surface, while total foliar accumulation represents only deposition and assimilation.     

Field,laboratory, and X-ray absorption spectroscopic studies of mercury accumulation by water hyacinths

We have studied water hyacinth (Eichhornia crassipes), a non-native nuisance plant found in the in San Francisco Bay Delta region, for its potential to phytoremediate mercury. Mercury is a common contaminant in San Francisco Bay Area waters because of gold mining activities. In this study, speciation of mercury in hyacinth roots and shoots, rates of mercury uptake by hyacinths in the laboratory, and mercury levels near the Big Break Region in the Delta were studied. In the speciation studies, Hg L3 edge X-ray absorption spectroscopic analysis of Hg model compounds and water hyacinth roots and shoots revealed that Hg was initially bound ionically to oxygen ligands in roots, most likely to carboxylate groups, and was bound covalently to sulfur groups in shoots. In laboratory uptake studies, we found that water hyacinths grown in 1 ppm Hg and one-quarter strength Hoagland's solution accumulated a maximum of 0.20 ppm in shoots and 16.0 ppm in roots, both reaching maximum concentrations after approximately 16 days. Mercury concentrations were found to be 0.26 +/- 0.20 ppm in the water and 0.86 +/- 1.70 ppm in sediment at Big Break. It was proposed that water hyacinths have the potential to phytoremediate mercury in the water at Big Break if the current herbicide treatments are replaced by physical removal.     

Climate change and mercury accumulation in Canadian high and subarctic lakes

Mercury (Hg) profiles were compared to profiles of climate indicators including microfossil remains and algal-derived or S2 carbon (C) in dated sediment cores from 14 lakes spanning latitudinal and longitudinal gradients across the Canadian high and subarctic. Hg fluxes increased postindustrialization (post-～1850) in 11 of these lakes (postindustrialization Hg fluxes (ΔHgF(F)) = 2-24 μg m(-2) y(-1)). Correction of HgF(F) for catchment contributions demonstrated that Hg deposition originating from catchment-independent factors, such as atmospheric deposition, increased since industrialization in all 14 lakes. Several of these lakes also showed postindustrial shifts in algal assemblages consistent with climate-induced changes. Eleven lakes showed post-1850s increases in S2F(F), suggesting that lake primary productivity has recently increased in the majority of our sites (ΔS2F(F) = 0.1-4 g m(-2) y(-1)). Other studies have interpreted significant relationships between Hg:S2 concentrations in Arctic sediment as support for the algal scavenging hypothesis, which postulates that Hg fluxes to Arctic sediments are largely driven by S2. However, in six of our lakes we observed no Hg:S2 relationship, and in one lake a significant negative Hg:S2 relationship was observed due to increased Hg and decreased S2 C deposition during the postindustrialization period. In six of the seven lakes where a significant positive Hg:S2 relationship was observed, algal assemblages either did not change through time or the timing of the shifts did not correspond to changes in Hg deposition. Our results demonstrate that, although Arctic lakes are experiencing a myriad of changes, including increased Hg and S2 deposition or changing algal assemblages, increased lake primary productivity does not appear to be driving changes in Hg fluxes to sediments.     

Deposition and cycling of sulfur controls mercury accumulation in Isle Royale fish

Mercury contamination of fish is a global problem. Consumption of contaminated fish is the primary route of methylmercury exposure in humans and is detrimental to health. Newly mandated reductions in anthropogenic mercury emissions aim to reduce atmospheric mercury deposition and thus mercury concentrations in fish. However, factors other than mercury deposition are important for mercury bioaccumulation in fish. In the lakes of Isle Royale, U.S.A., reduced rates of sulfate deposition since the Clean Air Act of 1970 have caused mercury concentrations in fish to decline to levels that are safe for human consumption, even without a discernible decrease in mercury deposition. Therefore, reductions in anthropogenic sulfur emissions may provide a synergistic solution to the mercury problem in sulfate-limited freshwaters.     

Dietary exposure to lead, cadmium, mercury and radionuclides of an adult urban population in Lebanon: a total diet study approach.

Human exposure to toxic chemicals is suspected of being responsible for a wide range of human health disorders. This study is the first in Lebanon to evaluate the dietary exposure of an adult urban population to three heavy metals (lead, cadmium and mercury) and to radionuclides. Exposure assessment was performed by means of the total diet study approach as recommended by the Word Health Organization. Five 'total diets' were collected during 2003-04. Average and maximal consumer exposure estimates to heavy metals were calculated and compared with appropriate reference values and with intakes reported from other countries. The average dietary intakes of lead, cadmium and mercury represented 7, 17 and 5.6%, respectively, of the appropriate provisional tolerable weekly intakes (PTWI). The mean dietary intake of methylmercury represented 17.5% of the appropriate PTWI. Cs-134 and I-131 were not detected in any of the food samples. Traces of Cs-137 were only found in five food samples. The exposure assessment conducted places Lebanon among countries least exposed to heavy metals through the diet and it highlights the safety of the food supply from radioactive contamination.     

Dietary mercury has no observable effects on thyroid-mediated processes and fitness-related traits in wood frogs

Mercury (Hg) is a neurotoxicant known to cause developmental and behavioral abnormalities in vertebrates. Increasing evidence suggests that Hg can also disrupt endocrine functions and endocrine-dependent processes. For example, dietary Hg has been shown to delay tail resorption during metamorphic climax in amphibians, a process mediated by thyroid hormones. However, a direct link between Hg, hormone disruption, and developmental delays in amphibians has not been explored. Therefore, we examined the effects of dietary Hg (0.01, 2.5, and 10 μg/g total Hg, dry wt) on thyroid hormone concentrations, development, growth, performance, and survival of wood frogs (Rana sylvatica). Tadpoles accumulated Hg in a concentration-dependent manner; total Hg concentrations in tadpoles at the beginning of metamorphic climax (Gosner stage 42) were 0.03, 1.06, 3.54 μg/g, dry wt, for control, low, and high Hg diets, respectively. During metamorphic climax, tadpoles eliminated 35% of the inorganic Hg from their tissues but retained most of their accumulated methylmercury. Contrary to our predictions, we found no effect of Hg on the duration of tadpole development, size at metamorphosis, tail resorption time, or hopping performance. Consistent with the lack of effects on development, we also detected no differences in whole-body thyroid hormone concentrations among our dietary treatments. Our results, when compared with the effects of Hg on other amphibians, suggest that amphibian species may differ substantially in their sensitivity to dietary Hg, emphasizing the need for data on multiple species when establishing toxicity benchmarks.     

Dietary exposure to antimony, lead and mercury of secondary school students in Hong Kong

The aim of this first study was to determine the dietary exposure of antimony, lead, mercury in foodstuffs consumed by secondary school students in Hong Kong. Around 100 composite food items were purchased and then cooked prior to analysis. Antimony was measured by hydrogen generation (HG)/inductively coupled plasma-mass spectrometry (ICP-MS), while lead was determined by ICP-MS. Total mercury was measured by cold vapour atomic absorption spectrometry. The detection limits for antimony, lead and total mercury were 1, 0.6 and 3 microg kg(-1), respectively. The dietary intake of antimony, lead and total mercury for an average secondary student were estimated to be 0.252, 1.98 and 0.92 microg (kg bw)(-1) week(-1), respectively. The dietary intake of antimony, lead and total mercury for high-consumer secondary student were estimated to be 0.567, 5.09 and 2.33 microg (kg bw)(-1) week(-1), respectively. The main contribution to antimony, lead and mercury were milk, vegetables and seafood, respectively. The Tolerable Daily Intake (TDI) of antimony, as recommended by WHO, is 6 microg (kg bw)(-1) week(-1), while the Provisional Tolerable Weekly Intakes (PTWI) of lead and mercury, as recommended by JECFA, are 25 and 5 microg (kg bw)(-1) week(-1), respectively. The estimated exposure values for secondary school students were compared to these safety reference values. For the relevant population, this study confirms the low probability of health risks from these metals via food consumption.     

Influence of snow and ice crystal formation and accumulation on mercury deposition to the Arctic

Mercury is deposited to the Polar Regions during springtime atmospheric mercury depletion events (AMDEs) but the relationship between snow and ice crystal formation and mercury deposition is not well understood. The objective of this investigation was to determine if mercury concentrations were related to the type and formation of snow and ice crystals. On the basis of almost three hundred analyses of samples collected in the Alaskan Arctic, we suggestthat kinetic crystals growing from the vapor phase, including surface hoar, frost flowers, and diamond dust, yield mercury concentrations that are typically 2-10 times higher than that reported for snow deposited during AMDEs (approximately 80 ng/L). Our results show that the crystal type and formation affect the mercury concentration in any given snow sample far more than the AMDE activity prior to snow collection. We present a conceptual model of how snow grain processes including deposition, condensation, reemission, sublimation, and turbulent diffusive uptake influence mercury concentrations in snow and ice. These processes are time dependent and operate collectively to affect the retention and fate of mercury in the cryosphere. The model highlights the importance of the formation and postdeposition crystallographic history of snow or ice crystals in determining the fate and concentration of mercury in the cryosphere.     

Dietary Polyphenols and Human Gut Microbiota: a Review

Dietary polyphenols are substrates for colonic microbiota. They and their metabolites contribute to the maintenance of gastrointestinal health by interacting with epithelial cells, and largely by modulating the gut microbial composition. Polyphenols may act as promoting factors of growth, proliferation, or survival for beneficial gut bacteria—mainly Lactobacillus strains—and thus, exerting prebiotic actions and inhibiting the proliferation of some pathogenic bacteria such as Salmonella and Helicobacter pylori species. To date the interactions affecting metabolic pathways and numerous metabolites of dietary polyphenols have been widely documented. However, the effects of dietary polyphenols on the modulation of the intestinal ecology and on the growth of gut microbial species are still poorly understood. This paper summarizes data on the influence of dietary polyphenols on gut microbiota and the main interactions between dietary polyphenols and beneficial and pathogenic intestinal bacteria.     

Dietary exposure of Hong Kong secondary school students to total mercury and methylmercury from fish intake

Fish is the main source of dietary exposure to methylmercury (MeHg), which is a public health concern owing to its potential neurotoxicity. To evaluate the public health risk, this study estimated the total mercury (tHg) and MeHg exposure from fish intake in Hong Kong secondary school students. Median tHg and MeHg concentrations of 280 samples purchased from different commercial outlets (covering 89 species of whole fish and three types of canned tuna), together with the local food consumption data of secondary school students obtained by semi-quantitative food frequency questionnaire in 2000, were used to estimate dietary exposure from fish intake for the average and high consumer (95th percentile exposure). For tHg, the median concentration was 63 µg kg^–1 (range 3–1370 µg kg^–1) and estimated exposures ranged 0.5–0.6 µg kg^–1 body weight (bw) week^–1 for an average consumer and 1.6–1.9 µg kg^–1 bw week^–1 for a high consumer. For MeHg, median concentration was 48 µg kg^–1 (range 3–1010 µg kg^–1) and estimated dietary exposures were 0.4–0.5 µg kg^–1 bw week^–1 for an average consumer and 1.2–1.4 µg kg^–1 bw week^–1 for a high consumer. These values are below the respective provisional tolerable weekly intake (PTWI) established by the Joint Food and Agriculture Organization/World Health Organization Expert Committee on Food Additives (JECFA). The health risk is greater for high consumers since MeHg exposures may approach or exceed the PTWI when other dietary sources are taken into account.     

Atmospheric mercury accumulation rates between 5900 and 800 calibrated years BP in the High Arctic of Canada recorded by peat hummocks

In this paper, we present the first comprehensive long-term record of preanthropogenic rates of atmospheric mercury accumulation in dated peat deposits for the High Arctic of Canada. Geochemical studies of two peat hummocks from Bathurst Island, Nunavut reveal substantial inputs from soil dust (titanium), marine aerosols (bromine), and mineral-water interactions (uranium). Mercury, however, was supplied to these peat mounds exclusively by atmospheric deposition. Mercury concentration measurements and age dating of the peat profiles indicate rather constant natural "background" mercury flux of ca. 1 microgram per square meter per year from 5900 to 800 calibrated years BP. These values are well within the range of the mercury fluxes reported from other Arctic locations, but also by peat cores from southern Canada that provide a record of atmospheric Hg accumulation extending back 8000 years. Thus, preanthropogenic Hg fluxes in the Arctic were not significantly different from atmospheric Hg fluxes in the temperate zone. In preindustrial times, therefore, the High Arctic was no more important as a sink for global atmospheric mercury than was the temperate zone.