Increase In Hg Levels Research Articles

Mercury exposure in Antarctic seabirds: Assessing the influence of trophic position and migration patterns

Although naturally present in the environment, mercury (Hg) input is significantly amplified by anthropogenic activities on a global scale, leading to a growing concern about the recent increase in Hg levels observed in Antarctica. This study investigated total mercury (THg) concentrations in feathers and eggs of resident and migratory Antarctic seabirds. Stable isotope data (δ15N, δ13C, and δ34S) were employed to ascertain the key factors influencing the exposure of these species to Hg. We gathered feathers and eggs from three resident species - Adélie, Gentoo, and Chinstrap penguins, as well as five migratory species - Snowy Sheathbill, Antarctic Tern, Southern Giant Petrel, Kelp Gull, and South Polar Skua. These samples were collected from Admiralty Bay, King George Island, in the Antarctica Peninsula. For all species, THg concentrations were higher in feathers (mean ± SD: 2267 ± 2480 ng g−1 dw) than in eggs (906 ± 1461 ng g−1 dw). Species occupying higher trophic positions, such as the Southern Giant Petrel (5667 ± 1500 ng g−1 dw) and South Polar Skua (4216 ± 1101 ng. g−1 dw), exhibited higher THg levels in their feathers than those at lower positions, like Antarctic Tern (1254 ± 400 ng g−1 dw) and Chinstrap Penguin (910 ± 364 ng g−1 dw). The δ15N values, which serve as a proxy for the trophic position, significantly correlated with THg concentrations. These findings reveal that trophic position influences THg concentrations in Antarctic seabirds. Migration did not appear to significantly affect the exposure of seabirds to THg, contrary to initial expectations. This research highlights the importance of evaluating the impacts of THg contamination on the Antarctic ecosystem by considering a variety of species. This multi-species approach offers critical insights into the factors that may potentially influence the exposure of these species to contaminants.

Understanding Food Web Mercury Accumulation Through Trophic Transfer and Carbon Processing along a River Affected by Recent Run-of-river Dams.

Unlike large dams which favor methylation of Hg in flooded soils over long periods, run-of-river dams are designed to flood a limited area of soils and are therefore not expected to significantly affect mercury (Hg) cycling or carbon processing. We studied the Hg and carbon cycles within food webs from several sectors along the Saint-Maurice River, Quebec, Canada, that differ in how they are influenced by two run-of-river dams and other watershed disturbances. We observed peak Hg concentrations in fish five-year postimpoundment, but these levels were reduced three years after this peak. Methylmercury concentrations in low trophic level fish and invertebrates were related to their carbon source (δ13C) rather than their trophic positions (δ15N). Biomagnification, measured by trophic magnification slopes, was driven mainly by methylmercury concentrations in low-trophic level organisms and environmental factors related to organic matter degradation and Hg-methylation. River sectors, δ13C and δ15N, predicted up to 80% of the variability in food web methylmercury concentrations. The installation of run-of-river dams and the related pondages, in association with other watershed disturbances, altered carbon processing, promoted Hg-methylation and its accumulation at the base of the food web, and led to a temporary increase in Hg levels in fish.

Bioaccumulation and trophic transfer of metals, As and Se through a freshwater food web affected by antrophic pollution in Córdoba, Argentina

The concentration of metals (Al, Cr, Mn, Fe, Ni, Cu, Zn, Ag, Cd, Hg, Pb, U), As and Se in different ecosystem components (water, sediment, plankton, shrimp, and fish muscle) has been determined in a eutrophic reservoir in the Province of Córdoba (Argentina). Los Molinos Lake (LML) was sampled during the dry (DS) and wet seasons (WS) in order to examine the bioaccumulation and transfer of these inorganic elements through the food web. Stable nitrogen isotope (δ15N) was used to investigate trophic interactions. According to this, samples were divided into three categories: plankton, shrimp (Palaemonetes argentinus) and fish (Silverside, Odontesthes bonariensis). The bioaccumulation factor (BAF) was calculated for the organisms, and it was determined that the elements analyzed undergo bioaccumulation, especially in organisms such as plankton. The invertebrates were characterized by the highest BAF for Cu and Zn in both seasons, As (DS), and Cd and Hg (WS). The fish muscle was characterized by the highest BAF for Se (WS), Ag and Hg (DS). On the other hand, a significant decrease in Al, Cr, Mn, Fe, Ni, Cu, Zn, As, Se, Cd and U concentrations through the analyzed trophic web during both seasons was observed. Moreover, a significant increase in Hg levels was observed with increasing trophic levels in the DS, indicating its biomagnification.Despite the increasing impact of metals, As and Se pollution in the studied area due to urban growth and agricultural and livestock activities, no previous study has focused on the behavior and relationships of these pollutants with the biotic and abiotic components of this aquatic reservoir. We expect that these findings may be used for providing directions or guidance for future monitoring and environmental protection policies.

One century of sedimentation and Hg pollution at the mouth of the Sagua la Grande River (Cuba)

The Sagua la Grande River is the largest of northern Cuba. The socioeconomic development in this region during the last 100 years has caused changes in its natural conditions, such as an increase in Hg levels. In 1981, a chlor-alkali plant with mercury-cell technology was built on the river bank and has released several contaminants to the environment. Sedimentation along the river and the nearby coastal zone was reconstructed using the radionuclides 210Pb, 226Ra, 137Cs, and 239,240Pu in sediment cores. The changes in sediment accumulation were related to important changes in the river basin after 1950, such as the channeling of the river in 1955 and the construction of the Alacranes Dam in 1972. Maximum sediment accumulation rates were attributed to large floods in 1933, 1948, and 1985 (Hurricane Kate). The 210Pb chronology allowed the reconstruction of Hg pollution during the last four decades. In the locations with greatest fluvial influence, Hg concentrations increased since the early 1980s exceeding the Effects Range-Median (0.71 mg kg–1). The accumulated Hg inventories released from the plant were one order of magnitude larger than those due to other sources. These results show the impact of Hg releases from this industry on the estuary, especially in the coastal zone close to the river mouth.

The putative multidrug resistance proteinMRP‐7 inhibits methylmercury‐associated animal toxicity and dopaminergic neurodegeneration inCaenorhabditis elegans

Parkinson's disease (PD) is the most prevalent neurodegenerative motor disorder worldwide, and results in the progressive loss of dopamine (DA) neurons in the substantia nigra pars compacta. Gene-environment interactions are believed to play a significant role in the vast majority of PD cases, yet the toxicants and the associated genes involved in the neuropathology are largely ill-defined. Recent epidemiological and biochemical evidence suggests that methylmercury (MeHg) may be an environmental toxicant that contributes to the development of PD. Here, we report that a gene coding for the putative multidrug resistance protein MRP-7 in Caenorhabditis elegans modulates whole animal and DA neuron sensitivity to MeHg. In this study, we demonstrate that genetic knockdown of MRP-7 results in a twofold increase in Hg levels and a dramatic increase in stress response proteins associated with the endoplasmic reticulum, golgi apparatus, and mitochondria, as well as an increase in MeHg-associated animal death. Chronic exposure to low concentrations of MeHg induces MRP-7 gene expression, while exposures in MRP-7 genetic knockdown animals results in a loss of DA neuron integrity without affecting whole animal viability. Furthermore, transgenic animals expressing a fluorescent reporter behind the endogenous MRP-7 promoter indicate that the transporter is expressed in DA neurons. These studies show for the first time that a multidrug resistance protein is expressed in DA neurons, and its expression inhibits MeHg-associated DA neuron pathology.

Steady-state transfer and depletion kinetics of mercury from amalgam fillings

In 29 volunteers with a low amalgam load, the number of amalgam-covered tooth surfaces and the occlusal area of the fillings were determined. Before and at select times after removal of all amalgams, concentrations of total mercury were measured by cold-vapor atomic absorption in plasma and erythrocytes as well as in urine together with the excretion rate. Absorbed daily doses were estimated from intraoral Hg emission by two separate methods. The transfer of Hg from the fillings via the oral cavity and blood to urinary excretion was evaluated according to the most representative combination of parameters. This consisted of occlusal area (1), absorbed dose (2), Hg concentration in plasma (3) and urinary excretion (4). Pairwise correlation coefficients were 0.49 for parameters 1 vs. 2, and 0.75 each for parameters 2 vs. 3 and 3 vs. 4. Within 9 days after removal of the fillings, a transient increase in Hg levels was observed in plasma only; in the group without a rubber dam, concentrations increased significantly above pre-removal values at days 1 and 3, whereas they decreased significantly below pre-removal values at day 30 in the rubber-dam group and at day 100 in both groups. Excretion rates decreased significantly at day 100 in the protected group. Peak plasma-Hg was 0.6 ng/ml on average at day 1 and decreased with halftimes of 3 and 43 days in subjects protected by a rubber dam. The results indicated that concentrations of total mercury in plasma responded rapidly to changes in the amalgam status and reflected the actual absorption most reliably. Notably, plasma-Hg levels were sensitive enough to detect a transient attenuation of the additional exposure after using a rubber dam during the removal of only a few fillings. However, being small in magnitude and lasting 100 days at best, the rubber-dam effect had minor toxicological relevance.

Re-examination of Hg pollution in the Ashtabula area, Astabula County, Ohio

Environmental concern about Hg pollution in Lake Erie peaked in 1970 with most investigations being directed to the west end of the lake and problems associated with Lake St. Clair. The Ohio Geological Survey subsequently (1970–1971) collected and analyzed stream and lake sediments in the vicinity of several industrial areas that border Lake Erie and reported indications of Hg pollution along the lower reaches of the Ashtabula River. Neither the intensity, nor the center, of the contamination was recognized in that study. In 1970, however, the state began to monitor the levels of Hg in the industrial effluent of the area. During a re-investigation of pollution at Ashtabula, 68 sediment samples were collected across an area of 90 km 2 in the late spring and early summer of 1982. The Hg that was released by heating the samples on a hot plate for one minute at 290°C was determined with a gold-film Hg detector. Mercury concentrations in the sediments had a median (background) value of 24.4 ppb and a mean content of 422 ppb, and exhibited a lognormal distribution that was bimodal. Three samples that ranged from 1550 to 20,600 ppb Hg are considered anomalous and come from the drainage of Fields Brook. Although no single industrial operation could be targeted as a source, high Hg levels apparently are due to the past accumulation of industrial waste. Mean Hg levels in the Ashtabula River samples from south and north of the junction with Fields Brook were 42.8 and 118.5 ppb Hg, respectively, indicating that contamination of the latter had occurred. The Lake Erie samples (mean ppb Hg) can be separated by the mouth of the Ashtabula River and the depth of the lake bottom as follows: west side (9.7), east side (59.8); and shoreline (15.8), nearshore (64.5). The six-fold increase on the eastern side of the harbor relative to the western side is believed to be due to the direction of the longshore currents which, in the Ashtabula area, run from southwest to northeast. The four-fold increase in Hg levels in nearshore sediments relative to those from the shoreline is due to preferential concentration in the finer size fraction. The Hg levels obtained for nearshore sediments just east of the Ashtabula River are six times higher than those reported earlier by the Geological Survey, suggesting that accumulation of Hg may have occurred.

A stationary cold vapor method for atomic absorption measurement of mercury in blood and urine used for exposure screening

A method is provided for rapid, accurate flameless atomic absorption Hg determinations in blood and urine used for exposure screening of mercury. Instead of the conventional apparatus requiring separate reduction and absorption containers, a one-piece reduction-absorption cell was fitted on the burner mount of an atomic absorption spectrophotometer. A five mL aliquot of the digested urine or blood sample was pipetted into the cell and one mL reductant added. The background corrected absorbance was recorded after three minutes of mixing. Heating the absorption cell at 60°C eliminated the formation of water vapor on the quartz windows of the tube. Sensitivity of the method was 1.0 ng which corresponds to a concentration of 0.2 ng/mL using a 5 mL sample size. The accuracy of Hg determinations in human blood and urine was confirmed by the method of standard additions of Hg to undigested samples. In order to test the applicability of the method to biological samples from Hg exposed individuals, rats were injected i.p. with 0.0 to 0.10 mg Hg as HgCl2. A dose related increase in Hg levels was observed in blood and urine collected at 24 hours after dosing. In addition, Hg was measured in human blood and urine samples obtained from 11 males not known to be recently exposed to Hg, indicating that the method is applicable to Hg exposure screening commonly used in industrial hygiene. The analysis can be conducted in less than 4 minutes each with a semi-automated sampling and cleaning capability and multiple Hg determinations performed on a single sample digest.