Methylated mercury species in Canadian high Arctic marine surface waters and snowpacks

We sampled seawater and snowpacks in the Canadian high Arctic for methylated species of mercury (Hg). We discovered that, although seawater sampled under the sea ice had very low concentrations of total Hg (THg, all forms of Hg in a sample; on average 0.14-0.24 ng L(-1)), 30-45% of the THg was in the monomethyl Hg (MMHg) form (on average 0.057-0.095 ng L(-1)), making seawater itself a direct source of MMHg for biomagnification through marine food webs. Seawater under the ice also contained high concentrations of gaseous elemental Hg (GEM; 129 +/- 36 pg L(-1)), suggesting that open water regions such as polynyas and ice leads were a net source of approximately 130 +/- 30 ng Hg m(-2) day(-1) to the atmosphere. We also found 11.1 +/- 4.1 pg L(-1) of dimethyl Hg (DMHg) in seawater and calculated that there could be a significant flux of DMHg to the atmosphere from open water regions. This flux could then resultin MMHg deposition into nearby snowpacks via oxidation of DMHg to MMHg in the atmosphere. In fact, we found high concentrations of MMHg in a few snowpacks near regions of open water. Interestingly, we discovered a significant log-log relationship between Cl- concentrations in snowpacks and concentrations of THg. We hypothesize that as Cl- concentrations in snowpacks increase, inorganic Hg(II) occurs principally as less reducible chloro complexes and, hence, remains in an oxidized state. As a result, snowpacks that receive both marine aerosol deposition of Cl- and deposition of Hg(II) via springtime atmospheric Hg depletion events, for example, may contain significant loads of Hg(II). Overall, though, the median wet/dry loads of Hg in the snowpacks we sampled in the high Arctic (5.2 mg THg ha(-1) and 0.03 mg MMHg ha(-1)) were far below wet-only annual THg loadings throughout southern Canada and most of the U.S. (22-200 mg ha(-1)). Therefore, most Arctic snowpacks contribute     

Importance of the forest canopy to fluxes of methyl mercury and total mercury to boreal ecosystems

The forest canopy was an important contributor to fluxes of methyl mercury (MeHg) and total mercury (THg) to the forest floor of boreal uplands and wetlands and potentially to downstream lakes, at the Experimental Lakes Area (ELA), northwestern Ontario. The estimated fluxes of MeHg and THg in throughfall plus litterfall below the forest canopy were 2 and 3 times greater than annual fluxes by direct wet deposition of MeHg (0.9 mg of MeHg ha(-1)) and THg (71 mg of THg ha(-1)). Almost all of the increased flux of MeHg and THg under the forest canopy occurred as litterfall (0.14-1.3 mg of MeHg ha(-1) yr(-1) and 110-220 mg of THg ha(-1) yr(-1)). Throughfall added no MeHg and approximately 9 mg of THg ha(-1) yr(-1) to wet deposition at ELA, unlike in other regions of the world where atmospheric deposition was more heavily contaminated. These data suggest that dry deposition of Hg on foliage as an aerosol or reactive gaseous Hg (RGM) species is low at ELA, a finding supported by preliminary measurements of RGM there. Annual total deposition from throughfall and litterfall under a fire-regenerated 19-yr-old jack pine/birch forest was 1.7 mg of MeHg ha(-1) and 200 mg of THg ha(-1). We found that average annual accumulation of MeHg and THg in the surficial litter/fungal layer of soils since the last forest fire varied between 0.6 and 1.6 mg of MeHg ha(-1) and between 130 and 590 mg of THg ha(-1) among sites differing in drainage and soil moisture. When soil Hg accumulation sites were matched with similar sites where litterfall and throughfall were collected, measured fluxes of THg to the forest floor (sources) were similar to our estimates of longterm soil accumulation rates (sinks), suggesting that the Hg in litterfall and throughfall is a new and not a recycled input of Hg to forested ecosystems. However, further research is required to determine the proportion of Hg in litterfall that is being biogeochemically recycled within forest and wetland ecosystems and, thus, does not represent new inputs to the forest ecosystem.     

Total and organic mercury concentrations in the white muscles of swordfish (Xiphias gladius) from the Indian and Atlantic oceans

A total of 226 swordfish samples collected from Taiwanese fishing vessels in the Indian and Atlantic oceans were examined for total mercury (THg) and organic Hg (OHg). Analysis of 56 pooled white muscle samples showed that THg and OHg concentrations ranged from 0.056 to 3.97 (1.3 ± 0.97) and from 0.043 to 3.92 (1.01 ± 0.82) µg g^-1 flesh mass, respectively. These values were similar to those from various previous studies during the past three decades. THg and OHg were significantly linearly correlated with fork length (FL, cm) of the fish from Indian and Atlantic oceans; however, there was no significant OHg%-FL relationship. OHg and THg also were significantly correlated. Fishes with FL ≤ 140 cm met the methyl Hg (meHg) regulatory standard set by the European Commission Decision (meHg ≤ 1.0); and fish with FL ≤ 211 cm met the Taiwanese Food and Hygiene Standard (meHg ≤ 2.0). Weekly swordfish consumption rates and amounts are recommended accordingly.     

Spatial and Temporal Assessment of Mercury and Organic Matter in Thermokarst Affected Lakes of the Mackenzie Delta Uplands, NT, Canada

We examined dated sediment cores from 14 thermokarst affected lakes in the Mackenzie Delta uplands, NT, Arctic Canada, using a case-control analysis to determine how retrogressive thaw slump development from degrading permafrost affected the delivery of mercury (Hg) and organic carbon (OC) to lakes. We show that sediments from the lakes with retrogressive thaw slump development on their shorelines (slump-affected lakes) had higher sedimentation rates and lower total Hg (THg), methyl mercury (MeHg), and lower organic carbon concentrations compared to lakes where thaw slumps were absent (reference lakes). There was no difference in focus-corrected Hg flux to sediments between reference lakes and slump-affected lakes, indicating that the lower sediment Hg concentration in slump-affected lakes was due to dilution by rapid inorganic sedimentation in the slump-affected lakes. Sedimentation rates were inversely correlated with THg concentrations in sediments among the 14 lakes considered, and explained 68% of the variance in THg concentration in surface sediment, further supporting the dilution hypothesis. We observed higher S2 (algal-derived carbon) and particulate organic carbon (POC) concentrations in sediment profiles from reference lakes than in slump lakes, likely because of dilution by inorganic siliciclastic matter in cores from slump-affected lakes. We conclude that retrogressive thaw slump development increases inorganic sedimentation in lakes, and decreases concentrations of organic carbon and associated Hg and MeHg in sediments.     

Hair mercury levels and food consumption in residents from the Pearl River Delta: South China

The Pearl River Delta (PRD) is located in the Southern part of China and is the main region for fish culture in Guangdong Province. In order to assess the potential health risks associated with dietary consumption of mercury, hair samples from 91 urban, town and fishing village residents, 37 species of fish, cereal, vegetables, and meat samples were collected. The average total mercury (THg) and methylmercury (MeHg) concentrations in hair were 1.08 ± 0.94 and 0.58 ± 0.59 μg/g, respectively. Daily Hg intake via fish consumption is significantly correlated with THg and MeHg accumulated in human hair (r = 0.48, p < 0.01; r = 0.43, p < 0.01). The estimated daily intake of Hg via different food types showed that both fish and cereal consumption were the two main routes of Hg exposure for residents in the sampling areas. Besides food intake, smoking was also an important source for daily THg intake in the smoke group, contributing 11–18% to EDI of THg.     

Legacy and fate of mercury and methylmercury in the Florida Everglades

Mass inventories of total Hg (THg) and methylmercury (MeHg) and mass budgets of Hg newly deposited during the 2005 dry and wet seasons were constructed for the Everglades. As a sink for Hg, the Everglades has accumulated 914, 1138, 4931, and 7602 kg of legacy THg in its 4 management units, namely Water Conservation Area (WCA) 1, 2, 3, and the Everglades National Park (ENP), respectively, with most Hg being stored in soil. The current annual Hg inputs account only for 1-2% of the legacy Hg. Mercury transport across management units during a season amounts to 1% or less of Hg storage, except for WCA 2 where inflow inputs can contribute 4% of total MeHg storage. Mass budget suggests distinct spatiality for cycling of seasonally deposited Hg, with significantly lower THg fluxes entering water and floc in ENP than in the WCAs. Floc in WCAs can retain a considerable fraction (around 16%) of MeHg produced from the newly deposited Hg during the wet season. This work is important for evaluating the magnitude of legacy Hg contamination and for predicting the fate of new Hg in the Everglades, and provides a methodological example for large-scale studies on Hg cycling in wetlands.     

Rapid reduction and reemission of mercury deposited into snowpacks during atmospheric mercury depletion events at churchill, Manitoba, Canada

Mercury (Hg) in some Arctic marine mammals has increased to levels that may be toxic to Northern peoples consuming them as traditional food. It has been suggested that sunlight-induced atmospheric reactions called springtime atmospheric Hg depletion events (AMDEs) result in the loading of -150-300 tons of Hg to the Canadian Arctic archipelago each spring and that AMDEs are the ultimate source of Hg to Arctic foodwebs. AMDEs result from the oxidation of gaseous elemental Hg0 (GEM) in Arctic atmospheres to reactive gaseous Hg (RGM) and particulate Hg (pHg), both of which fall out of the atmosphere to snowpacks. We studied the springtime cycling of Hg between air and snowpacks near Churchill, Manitoba, for 2 years to determine the net input of Hg to Hudson Bay from AMDEs. In 2004, we monitored atmospheric concentrations of GEM, pHg, and RGM while simultaneously measuring concentrations of total Hg (THg) in surface snow collected over the sea ice on Hudson Bay. During numerous springtime AMDEs, concentrations of THg in surface snow increased, often to over 60 ng/L, demonstrating that AMDEs resulted in deposition of oxidized Hg (Hg(II)) to snowpacks. However, immediatelyfollowing AMDEs, average concentrations of THg in snow declined drastically from between 67.8+/-7.7 ng/L during AMDEs to only 4.25+/-1.85 ng/L four or more days following them. In 2003, we measured THg in surface snow collected daily over the sea ice and total gaseous Hg (TGM) concentrations in the interstitial airspaces of snowpacks. When concentrations of THg in the surface snow decreased, concentrations of TGM in interstitial airspaces of the snowpack increased sharply from between approximately 1.4-3.4 ng/m(3) to between approximately 20-150 ng/m(3), suggesting thatthere was a reduction of deposited Hg(II) to GEM, which then diffused out of snowpacks. At snowmelt in both 2003 and 2004, average concentrations of THg in meltwater collected over Hudson Bay were only 4.04+/-2.01 ng/L. Using concentrations of THg in meltwater and snow water equivalent, we estimated a net springtime loading of only 2.1+/-1.7 mg/ha of Hg to Hudson Bay from AMDEs, indicating that only a small portion of the Hg(II) deposited during AMDEs enters Hudosn Bay each spring.     

Differences in mercury bioaccumulation between polar bears (Ursus maritimus) from the Canadian high- and sub-Arctic

Polar bears (Ursus maritimus) are being impacted by climate change and increased exposure to pollutants throughout their northern circumpolar range. In this study, we quantified concentrations of total mercury (THg) in the hair of polar bears from Canadian high- (southern Beaufort Sea, SBS) and sub- (western Hudson Bay, WHB) Arctic populations. Concentrations of THg in polar bears from the SBS population (14.8 ± 6.6 μg g(-1)) were significantly higher than in polar bears from WHB (4.1 ± 1.0 μg g(-1)). On the basis of δ(15)N signatures in hair, in conjunction with published δ(15)N signatures in particulate organic matter and sediments, we estimated that the pelagic and benthic food webs in the SBS are ～ 4.7 and ～ 4.0 trophic levels long, whereas in WHB they are only ～ 3.6 and ～ 3.3 trophic levels long. Furthermore, the more depleted δ(13)C ratios in hair from SBS polar bears relative to those from WHB suggests that SBS polar bears feed on food webs that are relatively more pelagic (and longer), whereas polar bears from WHB feed on those that are relatively more benthic (and shorter). Food web length and structure accounted for ～ 67% of the variation we found in THg concentrations among all polar bears across both populations. The regional difference in polar bear hair THg concentrations was also likely due to regional differences in water-column concentrations of methyl Hg (the toxic form of Hg that biomagnifies through food webs) available for bioaccumulation at the base of the food webs. For example, concentrations of methylated Hg at mid-depths in the marine water column of the northern Canadian Arctic Archipelago were 79.8 ± 37.3 pg L(-1), whereas, in HB, they averaged only 38.3 ± 16.6 pg L(-1). We conclude that a longer food web and higher pelagic concentrations of methylated Hg available to initiate bioaccumulation in the BS resulted in higher concentrations of THg in polar bears from the SBS region compared to those inhabiting the western coast of HB.     

Monitoring mercury in the loggerhead sea turtle, Caretta caretta

The validity of using blood samples and keratinized scutes for nonlethal routine monitoring of mercury (Hg) in loggerhead sea turtles, Caretta caretta, is evaluated in the context of how effectively these matrixes predict internal tissue Hg burdens and the different temporal scales of exposure they represent. Total Hg (THg) was measured in blood and scutes collected from live captures (n = 34) and liver, kidney, muscle, spinal cord, blood, and scutes collected from freshly stranded loggerhead turtles (n = 6) along the coast of the southeastern United States. Linear regressions between monitoring compartments and internal tissues from stranded animals were all statistically significant (r2 > 0.805, p < 0.015) but varied in their utility as a predictive tool depending on which tissues were paired. Blood was an effective predictor of THg in muscle (r2 = 0.988, p < 0.0001) and spinal cord (r2 = 0.988, p < 0.0001), while scute was the most accurate predictor of THg in liver (r2 = 0.948, p = 0.0010). The strength of the relationship between tissues types is believed to reflect the similarity in the temporal scales they represent and the variability in the fraction of methylmercury present. The stability of Hg in the scute matrix makes this tissue preferable for approximating long-term exposure, while blood Hg levels can be affected by recent changes in Hg intake. THg levels in blood and scutes from live captures were highly correlated (linear regression r2 = 0.926, p < 0.0001) and increased significantly with body mass (r2 = 0.173, p = 0.016 and r2 = 0.187, p = 0.012 respectively), further supporting thatthere is a component reflecting long-term accumulation of Hg in these matrixes. We also present a novel technique using the residuals from the blood-scute regression as an index of recent exposure (IRE). The interpretation of this value is derived from the comparison between the most recent Hg intake (which contributes to the Hg measured in the blood) relative to the average past intake (which is recorded in the scute). A stepwise multiple regression revealed a significant positive relationship between the IRE and the proximity of the capture site to the nearest major industrial river mouth (p = 0.0102). This suggests that there is an elevation of bioavailable Hg in nearshore habitats where terrestrial influences and anthropogenic impacts are high. Seasonal foraging site fidelity and the variability in environmental Hg may explain the high intraspecific variability and occasional highly contaminated turtle seen in this and previous studies.     

Estimate of mercury and methyl mercury intake associated with fish consumption from Sagua la Grande River,Cuba

This paper provides an estimate of the weekly intake of total mercury (THg) and methyl mercury (MeHg) from consumption of fish from the Sagua la Grande River, Villa Clara, Cuba, by determining the THg levels in different fish species. The levels varied between 0.143 and 0.484 μg g^?1 on a fresh weight basis. None of the analysed fish was found to have levels above the national and international regulatory levels, although THg levels over 0.2 μg g^?1, the threshold concentration established by the World Health Organization (WHO) for the consumption by vulnerable population groups, were found in 75% of samples. The MeHg level was found to be 84% of the THg content. A Food Frequency Survey was given to 127 townspeople to estimate river fish consumption. The weekly intake of MeHg was found to be greater than the value established by the provisional tolerable weekly intake (PTWI) in 50% of children, in 80% of pregnant women, and in 75% of women in childbearing age. These weekly intakes can represent an important risk to the population's health, especially for vulnerable groups.