Academic literature on the topic 'IHg/MeHg'

Mercury (Hg) remains hazardous in aquatic environments, because of its toxicity and high biomagnification in food webs. In phytoplankton and macrophytes, Hg compounds at high concentration have been reported to affect the growth, photosynthesis, and nutrient metabolism, as well as to induce oxidative stress and damage. Here, we reviewed the recent knowledge gained on cellular toxicity of inorganic and methyl Hg (IHg; MeHg) in aquatic primary producers at more relevant environmental concentrations, with a particular focus on omics data. In addition, we compared a case study conducted with transcriptomic on the green microalga Chlamydomonas reinhardtii and the macrophyte Elodea nuttallii. At lower concentrations, IHg and MeHg influenced similar gene categories, including energy metabolism, cell structure, and nutrition. In addition, genes involved in the cell motility in the microalgae, and in hormone metabolism in the macrophyte were regulated. At equivalent intracellular concentration, MeHg regulated more genes than IHg supporting a higher molecular impact of the former. At the organism level in C. reinhardtii, MeHg increased reactive oxygen species, while both IHg and MeHg increased photosynthesis efficiency, whereas in E. nuttallii MeHg induced anti-oxidant responses and IHg reduced chlorophyll content. Data showed differences, according to species and characteristics of life cycle, in responses at the gene and cellular levels, but evidenced a higher molecular impact of MeHg than IHg and different cellular toxicity pathways in aquatic primary producers.

Between May and December 1996, monthly samples of surface sediment (0–1 cm), settling matter, and water were taken at a shallow site and a deep site in each of two consecutive Hg-polluted riverine lakes. In the upper lake, the sediment was polluted also with cellulose fiber. Both hypolimnia turned anoxic, but sulfide was detected only in the upper lake. When sulfide appeared, hypolimnetic methyl mercury (MeHg) increased and reached 47 pM (9.4 ng·L–1), whereas MeHg in the sediment below decreased. The increase in hypolimnetic inorganic Hg (IHg = total Hg – MeHg), which reached a peak of 40 pM (8.0 ng·L–1), was slower, possibly because mobilized IHg was methylated. In the lower lake, hypolimnetic MeHg and IHg increased less dramatically during summer stratification, reaching only 5 and 24 pM (1.0 and 4.8 ng·L–1), respectively. There was no detectable concomitant decrease in sediment MeHg. In both lakes, MeHg appeared to increase simultaneously with total Fe and Mn in the hypolimnion, as did IHg in the lower lake. Our observations suggest that the presence of hydrous ferric and manganese oxides decreased the mobility of Hg in both lakes but increased MeHg production in the upper lake.

Prenatal exposure to methylmercury (MeHg) affects child development after birth. However, many epidemiological studies have evaluated total mercury levels without analyzing speciation. Biomonitoring of MeHg and inorganic mercury (IHg) is essential to reveal each exposure level. In this study, we compared a high-throughput analysis for mercury speciation in blood using liquid chromatography-inductively coupled plasma-mass spectrometry (LC-ICP-MS) and liquid chromatography-cold vapor atomic fluorescence spectrometry (LC-CVAFS). The validated LC-ICP-MS method was applied to 101 maternal blood and 366 cord blood samples in the pilot study of the Japan Environment and Children’s Study (JECS). The accuracy of the LC-CVAFS method ranged 90–115% determined by reference material analysis. To evaluate the reliability of 366 cord blood samples, fifty cord blood samples were randomly selected and analyzed using LC-CVAFS. The median (5th–95th percentile) concentrations of MeHg and IHg were 5.4 (1.9–15) and 0.33 (0.12–0.86) ng/mL, respectively, in maternal blood, and 6.3 (2.5–15) and 0.21 (0.08–0.49) ng/mL, respectively, in cord blood. Inter-laboratory comparison showed a relatively good agreement between LC-ICP-MS and LC-CVAFS. The median cord blood:maternal blood ratios of MeHg and IHg were 1.3 and 0.5, respectively. By analyzing speciation, we could focus on the health effects of each chemical form.

Rice consumption is the main methylmercury (MeHg) exposure route for residents in mercury (Hg) mining areas. However, there is limited studies on mercury in commercial rice, which has high liquidity and can be directly consumed by urban residents. This study measured the total Hg (THg) and MeHg concentrations in 146 rice samples purchased from the markets in Guiyang city, southwest China, and both the inorganic Hg (IHg) and MeHg estimated daily intakes (EDIs) and hazard quotients (HQs) were calculated according to rice consumption. The THg concentrations in all rice samples (range: 0.97 to 13.10 μg·kg−1; mean: 3.88 μg·kg−1) were lower than the Chinese national standard (20 μg·kg−1). The average MeHg concentration in rice was 1.16 μg·kg−1. The total HQs (THQs) ranged from 0.0106 to 0.1048, with a mean of 0.0462, which was far lower than 1. This result suggests that there were low Hg exposure levels through consumption of commercial rice in residents of Guiyang.

Background In comparison to organic mercury (MeHg), the environmental inorganic mercury (IHg) can be found in some skin-lightening cosmestics were considered “harmless” for a long time. However, recent studies have shown that long-term exposure to low doses of IHg may affect biological systems. Therefore, this study investigated the effects of IHg long-term exposure to the alveolar bone of adult rats. Methods Adult Wistar rats were distributed in control and HgCl2 exposed (0.375 mg/kg/day). After 45 days, the rats were euthanized and both blood and hemimandibles were collected. Total blood Hg levels were measured and both inorganic and organic components of the alveolar bone were determined through XRD and ATR-FTIR. The microstructure of the alveolar bone was assessed by using micro-CT and the morphometric analysis was performed by using stereomicroscopy. Results Alterations in the physicochemical components of the alveolar bone of exposed animals were observed. The bone changes represented a tissue reaction at the microstructural level, such as bone volume increase. However, no significant dimensional changes (bone height) were observed. Conclusion Exposure to IHg at this dose can promote microstructural changes and alteration in the organic and inorganic components in the alveolar bone.

Abstract. Rice paddy plantation is the dominant agricultural land use throughout Asia. Rice paddy fields have been identified as important sites for methylmercury (MeHg) production in the terrestrial ecosystem and a primary pathway of MeHg exposure to humans in mercury (Hg) mining areas. We compared the source and distribution of Hg species in different compartments of the rice paddy during a complete rice-growing season at two different typical Hg-contaminated mining sites in Guizhou province, China: an abandoned site with a high Hg concentration in soil but a low concentration in the atmosphere and a current-day artisanal site with a low concentration in soil but a high concentration in the atmosphere. Our results showed that the flux of new Hg to the ecosystem from irrigation and atmospheric deposition was insignificant relative to the pool of old Hg in soil; the dominant source of MeHg to paddy soil is in situ methylation of inorganic Hg (IHg). Elevated MeHg concentrations and the high proportion of Hg as MeHg in paddy water and the surface soil layer at the artisanal site demonstrated active Hg methylation at this site only. We propose that the in situ production of MeHg in paddy water and surface soil is dependent on elevated Hg in the atmosphere and the consequential deposition of new Hg into a low-pH anoxic geochemical system. The absence of depth-dependent variability in the MeHg concentration in soil cores collected from the abandoned Hg mining site, consistent with the low concentration of Hg in the atmosphere and high pH of the paddy water and irrigation water, suggested that net production of MeHg at this site was limited. We propose that the concentration of Hg in ambient air is an indicator for the risk of MeHg accumulation in paddy rice.

During most of an annual cycle, we studied the temporal variation of total mercury (HgT) and methyl mercury (MeHg) in unfiltered and filtered (0.45 µ) peat water from a minerotrophic peat bog in southeastern Sweden. MeHg in bulk water ([MeHgT]) and total Hg in filtered water in discharge water from the peat bog ([HgD]) were an order of magnitude higher than in upland runoff water entering the peat bog. At the discharge end, peat-water [HgD] and [MeHgD] ranged from 8 to 54 pmol·L–1 and from 1 to 32 pmol·L–1, respectively. Whereas the variation of [MeHgT] was explained by changes in [MeHgD], the variation of inorganic HgT [IHgT] = [HgT] – [MeHgT] was explained by changes in particle-bound IHg [IHgP] = [IHgT] – [IHgD]. Filterable organic matter and sulfide in the water both correlated poorly with [HgD]. Neither did the amount of HgT in precipitation and upland runoff water correlate well with the estimated discharge of HgD from the peat bog. However, there was a strong correlation between [HgD] and [MeHgT] in the peat water (r = 0.96). Furthermore, a significant fraction of HgD was MeHg (mean 28%; range 8–60%). These results suggest that methylation increased the mobility of Hg.

Mercury (Hg) is a toxic environmental contaminant associated with oxidative stress in freshwater fish. A known antagonist to Hg, selenium (Se), may reduce the toxic effects of Hg. In this study, the relation among Se, methylmercury (MeHg), inorganic mercury (IHg), total mercury (THg), and the expression of biomarkers of oxidative stress and metal regulation in livers of northern pike were examined. Livers from northern pike were collected from 12 lakes in Isle Royale National Park, Pictured Rocks National Lakeshore, Sleeping Bear Dunes National Lakeshore, and Voyageurs National Park. The concentrations of MeHg, THg, and Se were measured in liver tissue, and the expression of superoxide dismutase (sod), catalase (cat), glutathione s-transferase (gst), and metallothionein (mt) was assessed. There was a positive relationship between the concentrations of THg and Se, with a Hg:Se molar ratio less than one in all livers examined. There was no significant relation between sod, cat, gst, or mt expression and Hg:Se molar ratios. cat and sod expression were significantly related to increases in percent MeHg, relative to THg; however, gst and mt expression were not significantly altered. This suggests that incorporating biomarkers containing Se may be a better indicator than non-selenium-containing proteins of assessing the long-term effect of Hg and the interactions between Hg and Se in the livers of fish, such as northern pike, especially when molar concentrations of Se are greater than Hg.

Abstract Human exposure to organic mercury (Hg) as methylmercury (MeHg) from seafood consumption is widely considered a health risk because pure methylmercury is extremely neurotoxic. In contrast, the clinical significance of Hg exposure from amalgam (AMG) dental restorations, the only other major non-occupational source of Hg exposure, has long been debated. Here we examined data from the two most recent National Health and Nutrition Examination Surveys (NHANES) on 14,181 subjects to assess the contributions of seafood consumption versus AMG to blood total mercury (THg), inorganic mercury (IHg), and methyl mercury (MeHg) and to urine creatinine corrected mercury (UTHg). All subjects were also classified as to their self-reported qualitative consumption of seafood (59% fish and 44% shellfish). Subjects with restorations were grouped into three groups, (0) those without AMG (64.4%), (1) those with 1-5 dental AMG restorations (19.7%), (2) those with more than five AMG (16%). Seafood consumption increased total mercury in urine (UTHg) and total mercury (THg) and methyl mercury (MeHg) in blood, but unlike AMG, seafood did not increase blood inorganic mercury (IHg). Using stratified covariate (ANOVA) and multivariate (GLM) analyses revealed a strong correlation of blood (THg and IHg) and urine (UTHg) levels with the number of AMGs. In a subpopulation without fish consumption, having more than five AMG restorations raised blood THg (103%), IHg (221%), and urine UTHg (221%) over the group without AMG. The most striking difference was noted in classification by age: subjects under six years old with more than five AMG restorations had the highest blood IHg and urine UTHg among all age groups. Elevation of bivalent IHg on a large scale in children warrants urgent in-depth risk assessment with specific attention to genetic- and gender-associated vulnerabilities.

La seiche commune, Sepia officinalis, est un céphalopode côtier connu pour ses performances écophysiologiques soutenues par un large répertoire de comportements lui permettant, malgré son cycle de vie court, de tenir un rôle central dans les réseaux trophiques. Cependant, elle est également connue pour accumuler efficacement les éléments métalliques tel que le mercure (Hg), un contaminant neurotoxique sous sa forme organique (methylmercure ; MeHg). De plus, dans le contexte des changements environnementaux globaux, l’acidification des océans (AO) induite par l’augmentation des émissions de CO2, peut impacter le métabolisme, le développement et le système nerveux central, notamment chez les jeunes stades de vie. Le présent travail a donc pour but d’étudier les effets de l’AO sur la bioaccumulation du Hg et les effets de ces deux neurotoxiques (Hg et CO2) sur le comportement et les performances cognitives chez les juvéniles de seiches. Préalablement, des mesures in-situ ont montré que le Hg s’accumulait dans le cerveau des céphalopodes sous forme méthylé (MeHg). Par ailleurs, les approches expérimentales utilisant des traceurs isotopiques (stables et radioactif) du Hg ont démontré que l’accumulation du Hg total provenait majoritairement de l’assimilation du MeHg présent dans les proies, en comparaison à l’accumulation du mercure inorganique (iHg) par voie dissoute. Ce MeHg est ensuite très fortement retenu malgré la mise en évidence de processus de déméthylation du Hg dans la glande digestive. Étonnamment, l’AO n’a aucun effet sur les efficacités de la bioaccumulation et le métabolisme du Hg. En termes d’effets, des essais comportementaux ont montré que le Hg et CO2, seuls ou combinés, n’impactaient pas l’acuité visuelle et les performances de prédation chez les juvéniles. Par contre, ces deux derniers induisent une augmentation de l’activité locomotrice, compromettant le comportement défensif à travers notamment une altération de la coloration disruptive et un non-alignement de la latéralisation. Parmi les processus neuronaux susceptibles d’être impactés par le Hg et le CO2, le système GABAergique a été analysé dans les lobes optiques mais n’a montré aucun lien évident avec les réponses comportementales suggérant des processus d’effets plus complexes. L’ensemble de ce travail questionne donc les effets des conditions futures de l’océan sur les juvéniles de seiches, et plus largement les impacts sur les populations de céphalopodes
The common cuttlefish, Sepia officinalis, is a coastal cephalopod known for its eco physiological performance supported by a wide repertoire of behaviors that allows it, despite its short life cycle, to play a central role in food webs. However, it is also known to efficiently accumulate metallic elements such as mercury (Hg), a neurotoxic contaminant in its organic form (methylmercury; MeHg). Moreover, in the context of global changes, ocean acidification (OA) induced by the increase of CO2 emissions, can impact metabolism, development and the central nervous system, especially in young life stages. The present work therefore aims to study the effects of OA on Hg bioaccumulation and the effects of these two neurotoxicants (Hg and CO2) on behavior and cognitive performance in juvenile cuttlefish. In the first place, in-situ measurements showed that Hg accumulated in the brain of cephalopods in methylated form (MeHg). Moreover, experimental approaches using isotopic tracers (stable and radioactive) of Hg have shown that the accumulation of total Hg comes mainly from the assimilation of MeHg present in preys, compared to the accumulation of inorganic mercury (iHg) dissolved in seawater. This MeHg is then very strongly retained despite evidence of Hg demethylation processes in the digestive gland. Surprisingly, OA has no effect on the bioaccumulation efficiencies and metabolism of Hg. In terms of effect, behavioral assays showed that Hg and CO2, alone or in combination, did not impact visual acuity and predation performance in juveniles. However, both induced an increase in locomotor activity, compromised defensive behavior through, in particular, an alteration of disruptive coloration and a non-alignment of lateralization. Among the neural processes likely to be impacted by Hg and CO2, the GABAergic system was analyzed in the optic lobes but showed no obvious link with behavioral responses suggesting more complex effect processes. All of this work therefore questions the effects of future ocean conditions on juvenile’s cuttlefish, and more broadly the impacts on cephalopod populations