Tissue composition and storage duration affect the usefulness of generic wet-to-dry mass conversion factors in toxicology studies.

All ecosystems are exposed to a variety of anthropogenic contaminants. The potential threat posed by these contaminants to organisms has prompted scores of toxicology studies. Contaminant concentrations in wildlife toxicology studies are inconsistently expressed in wet or dry mass units, or even on a lipid-normalized basis, but tissue composition is rarely reported, and the conversion between dry and wet mass units, notably, is often based on assumed empirical moisture contents in tissues. However, diverse factors (e.g., tissue, storage conditions) may affect tissue composition and render comparisons between studies difficult or potentially biased. Here, we used data on the concentration of mercury, a global pollutant, in tissues of red foxes (Vulpes vulpes) to quantify the effects of diverse variables on moisture and lipid contents, and their consequences on contaminant concentration in different tissues, when converting between wet and dry mass units (lipid extracted or not). We found that moisture content differed largely between organs, enough to preclude the use of a single conversion factor, and decreased by 1% per year when stored at -80 °C. Although most fox tissues had low lipid concentrations, lipid content affected water content and their extraction affected the wet to dry mass conversion factor. We thus recommend reporting tissue composition (at least water and lipid contents) systematically in toxicology studies of mercury specifically and of contaminants in general, and using tissue/species specific conversion factors to convert between dry and wet mass concentration.

Total and methylated mercury in Arctic multiyear sea ice.

Mercury is one of the primary contaminants of concern in the Arctic marine ecosystem. While considerable efforts have been directed toward understanding mercury cycling in the Arctic, little is known about mercury dynamics within Arctic multiyear sea ice, which is being rapidly replaced with first-year ice. Here we report the first study on the distribution and potential methylation of mercury in Arctic multiyear sea ice. Based on three multiyear ice cores taken from the eastern Beaufort Sea and McClure Strait, total mercury concentrations ranged from 0.65 to 60.8 pM in bulk ice, with the highest values occurring in the topmost layer (∼40 cm) which is attributed to the dynamics of particulate matter. Methylated mercury concentrations ranged from below the method detection limit (<0.1 pM) to as high as 2.64 pM. The ratio of methylated to total mercury peaked, up to ∼40%, in the mid to bottom sections of the ice, suggesting the potential occurrence of in situ mercury methylation. The annual fluxes of total and methylated mercury into the Arctic Ocean via melt of multiyear ice are estimated to be 420 and 42 kg yr(-1), respectively, representing an important and changing source of mercury and methylmercury into the Arctic Ocean marine ecosystem.

Large mercury release from the Greenland Ice Sheet invalidated.

The major input of mercury (Hg) to the Arctic is normally ascribed to long-range transport of anthropogenic Hg emissions. Recently, alarming concentrations of Hg in meltwater from the Greenland Ice Sheet (GrIS) were reported with bedrock as the proposed source. Reported Hg concentrations were 100 to 1000 times higher than in known freshwater systems of Greenland, calling for independent validation of the extraordinary concentrations and conclusions. Here, we present measurements of Hg at 21 glacial outlets in West Greenland showing that extreme Hg concentrations cannot be reproduced. In contrast, we find that meltwater from below the GrIS is very low in Hg, has minor implications for the global Hg budget, and pose only a very limited risk for local communities and the natural environment of Greenland.

Metal distributions in human hair strand cross-section: Advanced analysis using LA-ICP-MS in dentistry.

Human hair is a biomarker that is crucial in investigating toxic metal exposures. Thirteen elements (Li, Mg, Cr, Mn, Fe, Co, Ni, Cu, Zn, Sr, Ag, Ba, and Hg) commonly found in hair strands from dentistry environments were investigated using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). Previous studies have employed partial ablation along hair strands to avoid contamination from mounting materials. The partial ablation can be problematic if element chemistry within the hair is not homogeneous. In this study, element variations along cross-sections of human hair strands were investigated. A number of elements showed internal variations with most elements enriched at the cuticle, emphasizing the importance of complete ablation for the characterization of human hair element chemistry. Complete and partial ablation LA-ICP-MS results were verified against solution nebulization SN-ICP-MS. Complete LA-ICP-MS showed a better agreement with SN-ICP-MS. Therefore, the developed LA-ICP-MS method can be applied to monitor the health of dental workers and students exposed to dental environments.

Total and methylated mercury in the Beaufort Sea: the role of local and recent organic remineralization.

Mercury is a major contaminant in the Arctic marine ecosystem. While extensive studies have been conducted on mercury in the Arctic's atmosphere and biota, far less is known about the distribution and dynamics of mercury species in the Arctic Ocean. Here, we present vertical profiles for total mercury (Hg(T)) and total methylated mercury (MeHg(T), sum of monomethylmercury and dimethylmercury) from the Beaufort Sea of the Arctic Ocean at locations with differing sea ice conditions. The concentration of Hg(T) ranged from 0.40 to 2.9 pM, with a surface enrichment that can be attributed to a combination of sea ice-modified atmospheric deposition and riverine input. The concentration of MeHg(T) ranged from <0.04 to 0.59 pM, with a subsurface peak occurring at the same depth as a nutrient maximum with lower dissolved oxygen, which is consistent with the recent findings in the Pacific Ocean, Southern Ocean, and Mediterranean Sea. However, unlike the interior ocean regions, the nutrient maximum in the Beaufort Sea is predominantly an advective feature produced over the Chukchi Shelf. On the basis of the short lifetime of monomethylmercury in seawater, we propose that the MeHg(T) profile in the Beaufort Sea reflects the local, short-term remineralization of labile organic matter, and not the larger signal of organic remineralization advected from the Chukchi Sea in the halocline. The finding that MeHg(T) is produced locally, reflecting recent strength of organic matter cycling, not only explains wide variance in MeHg(T) in seawater and biota over time and space, but also implies that MeHg(T) could be used as an indicator of the recent export flux of labile organic matter.

Mercury distribution and deposition in glacier snow over western China.

Western China is home to the largest aggregate of glaciers outside the polar regions, yet little is known about how the glaciers in this area affect the transport and cycling of mercury (Hg) regionally and globally. From 2005 to 2010, extensive glacier snow sampling campaigns were carried out in 14 snowpits from 9 glaciers over western China, and the vertical distribution profiles of Hg were obtained. The Total Hg (THg) concentrations in the glacier snow ranged from <1 to 43.6 ng L(-1), and exhibited clear seasonal variations with lower values in summer than in winter. Spatially, higher THg concentrations were typically observed in glacier snows from the northern region where atmospheric particulate loading is comparably high. Glacier snowpit Hg was largely dependent on particulate matters and was associated with particulate Hg, which is less prone to postdepositional changes, thus providing a valuable record of atmospheric Hg deposition. Estimated atmospheric Hg depositional fluxes ranged from 0.74 to 7.89 µg m(-2) yr(-1), agreeing very well with the global natural values, but are one to two orders of magnitude lower than that of the neighboring East Asia. Elevated Hg concentrations were observed in refrozen ice layers in several snowpits subjected to intense melt, indicating that Hg can be potentially released to meltwater.

Widespread elevated concentrations of gaseous elemental mercury in Guanajuato, Mexico, centuries after historical silver refining by mercury amalgamation.

Silver (Ag) production in Hispanic America between the 16th and 19th centuries is thought to be one of the largest sources of anthropogenic mercury (Hg) emissions in history. Recent reviews of the chemistry behind the patio process, which used Hg amalgamation to extract Ag from ore, reveal that a large amount of the Hg may not have been immediately released to the atmosphere; instead, it may have been captured in the form of calomel (Hg2Cl2, in which Hg exists as monovalent HgI) and remained in the local environment. Here we show that Hg used in the patio process centuries ago in the Guanajuato Mining District of Mexico continues to elevate present-day concentrations of gaseous elemental mercury (GEM) throughout the region. In the ground-level air, GEM ranged from 8 to 454 ng m-3, exceeding the Northern Hemispheric average (~1.4 ng m-3) by up to two orders of magnitude. Much higher concentrations, up to 44,700 ng m-3, were found in the interstitial air of reprocessed mineral wastes, sediment, and soil. These highly elevated present-day GEM values are due, at least in part, to the disproportionation of legacy calomel, as supported by the presence of HgI in the reprocessed wastes and by the GEM release pattern from calomel disproportionation. Our results imply that the contribution of historical Ag refining to atmospheric Hg emissions must be re-evaluated to account for calomel and its subsequent disproportionation and releases of GEM to the present-day.

Mercury distribution and transport across the ocean-sea-ice-atmosphere interface in the Arctic Ocean.

The Arctic sea-ice environment has been undergoing dramatic changes in the past decades; to which extent this will affect the deposition, fate, and effects of chemical contaminants remains virtually unknown. Here, we report the first study on the distribution and transport of mercury (Hg) across the ocean-sea-ice-atmosphere interface in the Southern Beaufort Sea of the Arctic Ocean. Despite being sampled at different sites under various atmospheric and snow cover conditions, Hg concentrations in first-year ice cores were generally low and varied within a remarkably narrow range (0.5-4 ng L(-1)), with the highest concentration always in the surface granular ice layer which is characterized by enriched particle and brine pocket concentration. Atmospheric Hg depletion events appeared not to be an important factor in determining Hg concentrations in sea ice except for frost flowers and in the melt season when snowpack Hg leaches into the sea ice. The multiyear ice core showed a unique cyclic feature in the Hg profile with multiple peaks potentially corresponding to each ice growing/melting season. The highest Hg concentrations (up to 70 ng L(-1)) were found in sea-ice brine and decrease as the melt season progresses. As brine is the primary habitat for microbial communities responsible for sustaining the food web in the Arctic Ocean, the high and seasonally changing Hg concentrations in brine and its potential transformation may have a major impact on Hg uptake in Arctic marine ecosystems under a changing climate.

Atmospheric transport of mercury to the Tibetan Plateau.

The Tibetan Plateau (including the Himalayas) is one of the most remote and cold regions in the world. It has very limited to nonexistent industry but is adjacent to the two most populous and rapidly industrializing countries (China and India) and thus provides a unique location for studying the atmospheric transport of mercury. Here we report the first study on the atmospheric transport of mercury to the Tibetan Plateau. The total mercury profiles in four snowpits from glaciers above 5700 m asl along a southwest-northeast transect across the central Tibetan Plateau were obtained in 2005-2006. In general, the total mercury concentrations in the snow samples ranged from < 1 to 9 ng L(-1), increasing northeastward from the southernmost site at Mount Everest. Higher total mercury concentrations were found in the snow deposited in the nonmonsoon season, as indicated by seasonal variation of delta18O values and major ions in the snowpack. The annual atmospheric depositional flux of total Hg was estimated to range from 0.74 to 2.97 microg m(-2) yr(-1) in the region, the majority of which occurred via particulate matter deposition.