Torunn Berg

Selenium moderates mercury toxicity in free-ranging freshwater fish.

Due to the extremely high affinity of selenium (Se) to mercury (Hg), Se sequesters Hg and reduces its biological availability in organisms. However the converse is also true. Hg sequesters Se, causing Hg to inhibit the formation of Se dependent enzymes while supplemental Se supports their continued synthesis. Hence, whether or not toxic effects accompany exposure to Hg depends upon the tissue Se:Hg molar ratio of the organism. The main objective of the present study was to investigate how levels of Hg and Se affected metallothionein (MT) induction in free-ranging brown trout, Salmo trutta, from Lake Mjøsa, Norway (a Se depauperate lake). MT is proposed as a sensitive biomarker of potential detrimental effects induced by metals such as Hg. Emphasis was addressed to elucidate if increased tissue Se:Hg molar ratios and Se levels affected the demands for MT in the trout. The Se:Hg molar ratio followed by tissue Se levels were most successful for assessing the relationship between metal exposure and MT levels in the trout. Thus, Hg in molar excess over Se was a stronger inducer of MT synthesis than tissue Hg levels in the trout, supporting the assumption that Se has a prominent protective effect against Hg toxicity. Measuring Hg in animals may therefore provide an inadequate reflection of the potential health risks to humans and wildlife if the protective effects of Se are not considered.

Three decades of atmospheric metal deposition in Norway as evident from analysis of moss samples

Monitoring of atmospheric deposition of metals in Norway on a nationwide scale using samples of terrestrial moss started in 1977 and has been repeated every 5 years. This has facilitated a detailed record of temporal and spatial trends of metal deposition all over the country as a supplement to measurements based on bulk deposition sampling on a small number of sites. Pb, Zn, Cd, As, Sb, V, Sn, Mo, and Bi all show highest deposition in the far south due to trans-boundary pollution from other parts of Europe, but the contribution from long-range atmospheric transport to metal deposition has decreased substantially over the years. The distributions of Fe, Ni, Cu, Cr, and Co are more affected by local sources, but a decreasing time trend is also evident for these elements. Se is mainly derived from processes in the marine environment. Deposition of metals from Cu-Ni smelters in Russia situated close to the Norwegian border has shown a steadily increasing trend over the time period concerned.

Mercury in Molar Excess of Selenium Interferes with Thyroid Hormone Function in Free-Ranging Freshwater Fish

Thyroid hormones (THs) are essential for cellular metabolism, somatic growth and development, and reproduction. Mercury (Hg) entering aquatic systems and accumulated as highly toxic methylmercury (MeHg) represents a threat to wildlife and human health. Selenium (Se) is an essential element critical for TH activation and regulation. In organisms, binding of Hg in a Se-Hg complex results in a detoxification of Hg. However, formation of Se-Hg complexes also affects Se bioavailability, disrupting functions of Se-dependent enzymes, such as TH deiodinases, which convert thyroxine (T4) to the physiologically active TH, triiodothyronine (T3). The main aim of the present study was to investigate how tissue Se:Hg molar ratios, tissue levels of Se and Hg, and other potential TH disruptive contaminants (metals and organic chemical compounds) affect plasma TH levels in free-ranging brown trout, Salmo trutta , from Lake Mjøsa (a Se-deprived lake) and Lake Losna (a reference lake), Norway. Among the wide range of potential TH disruptive pollutants investigated, tissue Se:Hg molar ratios in muscle and liver were the most significant predictors of plasma TH levels in the trout. Moreover, lower plasma levels of the biological active hormone, T3, in the Lake Mjøsa trout co-occurred with their low Se:Hg molar ratios. This suggests that Se availability is impaired by Hg and results in altered selenoenzyme activities and loss of optimal control of TH balance in free-ranging freshwater fish.

Decline in atmospheric mercury deposition in London.

Bulk atmospheric deposition samples were continuously collected using a standard IVL-type mercury (Hg) bulk deposition collector from January 1999 to December 2005 in order to monitor Hg deposition in London. The volume-weighted annual Hg concentrations in deposition gradually declined from 76.0 ng L(-1) in 1999 to 43.8 ng L(-1) in 2005. Correspondingly, Hg fluxes in deposition declined from 45.3 microg m(-2) yr(-1) in 1999 to 15.0 microg m(-2) yr(-1) in 2005. However, this decline in Hg deposition does not agree with trends in UK Hg emissions which are relatively stable over the sampling period. Comparison with contemporaneous data collected at Lochnagar, a remote site in Scotland, suggests that the high Hg concentrations in London deposition are likely to be due to local or regional sources. Surface sediments taken from lakes across London show that the environment has been heavily contaminated by Hg and suggest that Hg re-emission from depositional sinks (e.g. soils, water bodies) may be an important source to Londons atmosphere, thereby delaying response to the major reductions in direct emissions to the atmosphere since the 1970s.

Atmospheric monitoring at the Norwegian Antarctic station Troll: measurement programme and first results

The Troll Atmospheric Station in Antarctica (72°01′S, 2°32′E, 1309 m a.s.l.) was established and put into operation in early 2007. The main foci of the measurement programme are pollution and aerosols in the transition zone between the coastal zone and the inland ice plateau, complementing existing observation programmes along the Antarctic coast and on the Antarctic Plateau. After one year of operation, the monitoring programme is fully operative, and a comprehensive set of data is being analysed. As far as comparable data are available, there is satisfactory agreement between previous and new data. Both aerosol data and measurements of pollution indicate the episodic influence of coastal air masses throughout the year. Background values of medium long-lived pollutants such as CO, O3 and Hg are up to 50% lower than at corresponding Arctic sites (depending on the season), but are still significant. Total ozone and UV doses manifest the recurring Antarctic stratospheric ozone hole, which was moderately severe, but very persistent in 2007. Specific episodes of elevated aerosol concentration and mercury activation are currently under detailed investigation, and will be published separately.

Acute and sub-lethal response to mercury in Arctic and boreal calanoid copepods

Acute lethal toxicity, expressed as LC50 values, is a widely used parameter in risk assessment of chemicals, and has been proposed as a tool to assess differences in species sensitivities to chemicals between climatic regions. Arctic Calanus glacialis and boreal Calanus finmarchicus were exposed to mercury (Hg(2+)) under natural environmental conditions including sea temperatures of 2° and 10°C, respectively. Acute lethal toxicity (96 h LC50) and sub-lethal molecular response (GST expression; in this article gene expression is used as a synonym of gene transcription, although it is acknowledged that gene expression is also regulated, e.g., at translation and protein stability level) were studied. The acute lethal toxicity was monitored for 96 h using seven different Hg concentrations. The sub-lethal experiment was set up on the basis of nominal LC50 values for each species using concentrations equivalent to 50, 5 and 0.5% of their 96 h LC50 value. No significant differences were found in acute lethal toxicity between the two species. The sub-lethal molecular response revealed large differences both in response time and the fold induction of GST, where the Arctic species responded both faster and with higher mRNA levels of GST after 48 h exposure. Under the natural exposure conditions applied in the present study, the Arctic species C. glacialis may potentially be more susceptible to mercury exposure on the sub-lethal level.

Characterisation of individual aerosol particles on moss surfaces: implications for source apportionment

The size, morphology and chemical composition of 8405 particles on moss surfaces (Hylocomium splendens) was investigated by scanning electron microscopy and energy-dispersive X-ray microanalysis. Two moss samples from three locations in Southern Norway (Algård, Birkeland, Neslandsvatn) and two sampling years (1977 and 2005) each were selected leading to a total of 12 samples investigated. At all three locations, particle deposition decreased substantially with time. The major particle groups encountered include silicates, iron-rich silicates, metal oxides/hydroxides, iron oxides/hydroxides, carbonates, carbon-rich particles, silicate fly ashes, iron-rich silicate fly ashes, and iron oxide fly ashes. Between 1977 and 2005, the relative number abundance of the three fly ash groups decreased substantially from approximately 30-60% to 10-18% for the small particles (equivalent projected area diameter <1 microm), and from 10-35% to 2-9% for large particles with diameters ≥1 microm. This decrease of fly ash particles with time was overlooked in previous papers on atmospheric input of pollutants into ecosystems in Southern Norway. In general, the presence of fly ash particles is ignored in most source apportionment studies based on bulk chemical analysis. Consequently, the geogenic component (crustal component) derived from principal component analysis is overestimated systematically, as it has a similar chemical composition as the fly ash particles. The high abundance of fly ashes demonstrates the need to complement source apportionment based on bulk chemistry by scanning electron microscopy in order to avoid misclassification of this important anthropogenic aerosol component.

Essential and non-essential elements in natural vegetation in southern Norway: contribution from different sources.

Concentrations of essential and non-essential elements in five widespread species of natural boreal vegetation were studied with respect to seasonal variation and contribution from different sources. The plant species included in the study were Betula pubescens, Sorbus aucuparia, Vaccinium myrtillus, Vaccinium uliginosum, Calluna vulgaris and Deschampsia flexuosa. Concentrations of elements essential to plants remained essentially constant or decreased slightly throughout the growing season. Concentrations of most non-essential elements increased or tended to increase on a dry mass basis from June to July as well as from July to September. The increasing trend for these elements was observed for all species except C. vulgaris. Principal component analysis (PCA) of the material indicated a common source for many of the non-essential elements; Sc, Ti, V, Ga, As, Y, Sb, lanthanides, Pb, Bi, and U, i.e. both elements presumably of geogenic origin and elements associated with trans-boundary air pollution. Uptake by plant roots appeared to be the main source of nutrient elements as well as some non-essential elements.