Effects of mercury intoxication on the response of horizontal cells of the retina of thraira fish (Hoplias malabaricus)

Methyl mercury (MeHg) is highly neurotoxic, affecting visual function in addition to other central nervous system functions. The effect of mercury intoxication on the amplitude of horizontal cell responses to light was studied in the retina of the fish Hoplias malabaricus. Intracellular responses were recorded from horizontal cells of fish previously intoxicated with MeHg by intraperitoneal injection (IP group) or by trophic exposure (T group). Only one retina per fish was used. The doses of MeHg chloride administered to the IP group were 0.01, 0.05, 0.1, 1.0, 2.0, and 6.0 mg/kg. The amplitudes of the horizontal cell responses were lower than control in individuals exposed to 0.01 (N = 4 retinas), 0.05 (N = 2 retinas) and 0.1 mg/kg (N = 1 retina), whereas no responses were recorded in the 1.0, 2.0, and 6.0 mg/kg groups. T group individuals were fed young specimens of Astyanax sp previously injected with MeHg corresponding to 0.75 (N = 1 retina), 0.075 (N = 8 retinas) or 0.0075 (N = 4 retinas) mg/kg fish body weight. After 14 doses, one every 5 days, the amplitude of the horizontal cell response was higher than control in individuals exposed to 0.075 and 0.0075 mg/kg, and lower in individuals exposed to 0.75 mg/kg. We conclude that intoxication with MeHg affects the electrophysiological response of the horizontal cells in the retina, either reducing or increasing its amplitude compared to control, and that these effects are related to the dose and/or to the mode of administration.

Evolucao materno-infantil da contaminacao por mercurio: Estudo em duas populacoes indigenas brasileiras

Considering the severity of Hg intoxication to human health and the frequent use of the metal in gold prespection on Brazilian Amazonia, an extensive project in being developed in order to quantify such conditions in two indigenous Kayapo populations, inhabitants of South of Para State, Gorotire and Djudjetikitire. This paper reports evolution of this contamination on mothers and babies. During puerperium, it was registered both an important decline on dosimetric values observed before in pregnancy and the occurrence of expressive levels in the babies. Such data are discussed based on contemporary medical-biologic conceptions, since it raises conceptual review of the matter.

Exposição humana ao metilmercúrio em comunidades ribeirinhas da Região do Tapajós, Pará, Brasil

Avaliou-se a exposição humana ao metilmercúrio e ao mercúrio total em comunidades ribeirinhas do rio Tapajós e da região metropolitana de Belém, no Estado do Pará, Brasil, através da determinação de mercúrio total e metilmercúrio em amostras de cabelo nos anos de 1994 e 1995. Observou-se que as concentrações médias de mercúrio total variaram de 2 ± 1µg/g-1 a 20,5 ± 12,1µg/g-1, enquanto que as concentrações médias de metilmercúrio variaram de 1,4 ± 0,7µg/g-1 a 18,5 ± 11µg/g-1. Estes resultados confirmam a contaminação mercurial na região do rio Tapajós, admitem a possibilidade do aparecimento de sinais e sintomas de intoxicação mercurial e recomendam a manutenção da monitorização do mercúrio total e do metilmercúrio nas amostras de cabelo, bem como a necessidade de estudos clínico-epidemiológicos para implantação de medidas de prevenção e controle da intoxicação mercurial.

Exposição à concentração subletal de metilmercúrio: genotoxicidade e alterações na proliferação celular

O mercúrio é um metal que se destaca dos demais por se apresentar líquido em temperatura e pressão normais. Este xenobiótico se apresenta como a maior fonte de poluição em várias partes do mundo e tem como característica ser altamente tóxico ao Sistema Nervoso Central (SNC). O despejo é na forma líquida diretamente no solo e leito dos rios. Este metal pesado é complexado com vários elementos presentes no solo ou sedimentos sendo convertido à metilmercúrio (MeHg) pela microbiota aquática. O MeHg apresenta a capacidade de se acumular ao longo da cadeia trófica, um evento conhecido como biomagnificação, o qual afeta diretamente a vida humana. Nesse sentido, a Região Amazônica se destaca por possuir todos os componentes necessários para a manutenção do ciclo biogeoquímico do mercúrio, além de populações cronicamente expostas a este metal pesado, sendo este fato considerado um problema de saúde pública. Tem-se conhecimento que este xenobiótico após a exposição aguda a altas doses promove desordens relacionadas ao surgimento de processos degenerativos no SNC, entretanto, os efeitos a baixas concentrações ainda não são totalmente conhecidos. Nesse sentido, se destacam as células gliais que atuam como mediadores no processo de neurotoxicidade desse metal, principalmente em baixas concentrações. Apesar de este tipo celular exibir um importante papel no processo de intoxicação mercurial, a ação deste metal sobre as células glias é pouco conhecida, principalmente sobre o genoma e a proliferação celular. Desta forma, este trabalho se propõe a avaliar o efeito da exposição a este xenobiótico em baixa concentração sobre o material genético e a proliferação celular em células da linhagem glial C6. As avaliações bioquímica (atividade mitocondrial – medida pelo ensaio de MTT –) e morfofuncional (integridade da membrana – avaliada pelo ensaio com os corantes BE e AA –) confirmaram a ausência de morte celular após a exposição ao metal pesado na concentração de 3 μM por um intervalo de 24 horas. Mesmo sem promover processos de morte celular, o tratamento com esta concentração subletal de MeHg foi capaz de aumentar significativamente os níveis dos marcadores de genotoxicidade (fragmentação do DNA, formação de micronúcleos, pontes nucleoplásmica e brotos nucleares). Ao mesmo tempo, foi possível observar uma alteração no ciclo celular através do aumento do índice mitótico e uma mudança no perfil do ciclo celular com aumento da população celular nas fases S e G2/M, sugerindo um aprisionamento nessa etapa. Esta mudança no ciclo celular, provocada por 24h de exposição ao MeHg, foi seguida de uma redução no número de células viáveis e confluência celular 24h após a retirada do MeHg e substituição do meio de cultura, além do aumento no tempo de duplicação da cultura do mesmo. Este estudo demonstrou pela primeira vez que a exposição ao metilmercúrio em concentração baixa e subletal é capaz de promover eventos genotóxicos e distúrbios na proliferação celular em células de origem glial.

Irreversible color vision losses in patients with chronic mercury vapor intoxication

This longitudinal study addresses the reversibility of color vision losses in subjects who had been occupationally exposed to mercury vapor. Color discrimination was assessed in 20 Hg-exposed patients (mean age = 42.4 +/- 6.5 years; 6 females and 14 males) with exposure to Hg vapor during 10.5 +/- 5.3 years and away from the work place (relative to 2002) for 6.8 +/- 4.2 years. During the Hg exposure or up to one year after ceasing it, mean urinary Hg concentration was 47 +/- 35.4 mu g/g creatinine. There was no information on Hg urinary concentration at the time of the first tests, in 2002 (Ventura et al., 2005), but at the time of the follow-up tests, in 2005, this value was 1.4 +/- 1.4 mu g/g creatinine for patients compared with 0.5 +/- 0.5 mu g/g creatinine for controls (different group from the one in Ventura et al. (2005)). Color vision was monocularly assessed using the Cambridge Colour Test (CCT). Hg-exposed patients had significantly worse color discrimination (p < 0.02) than controls, as evaluated by the size of MacAdam`s color discrimination ellipses and color discrimination thresholds along protan, deutan, and tritan confusion axes. There were no significant differences between the results of the study in Ventura et al. (2005) and in the present follow-up measurements, in 2005, except for worsening of the tritan thresholds in the best eye in 2005. Both chromatic systems, blue-yellow and red-green, were affected in the first evaluation (Ventura et al., 2005) and remained impaired in the follow-up testing, in 2005. These findings indicate that following a long-term occupational exposure to Hg vapor, even several years away from the source of intoxication, color vision impairment remains irreversible.

Electrophysiological evidence for impairment of contrast sensitivity in mercury vapor occupational intoxication

Contrast sensitivity (CS) was evaluated in 41 former workers from a lamp manufacturing plant who were on disability retirement due to exposure to mercury and 14 age-matched controls. The CS was measured monocularly using the sweep visual evoked potential (sVEP) paradigm at 6 spatial frequencies (0.2, 0.8, 2.0, 4.0, 15.0, and 30 cpd). Statistical difference (p < 0.05) was found between the controls and the patient right and left eyes for 2.0 and 4.0 cpd. According the results in those spatial frequencies the eyes were classified in best and worst. Statistical differences were found between the controls and the best eyes for 2.0 and 4.0 cpd and for 0.8, 2.0, and 4.0 cpd for their worst eyes. No correlation was found between CS results and the time of exposure (mean 8.9 yr +/- 4.1), time away from the mercury source (mean = 6.0 yr +/- 3.9), urinary mercury level at the time of work (mean = 40.6 mu g/g +/-36.3) or with the mercury level at the CS measurement time (mean = 1.6 mu g/g +/-1.1). We show the first evidence of a permanent impairment in CS measured objectively with the sVEP. Our data complement the previous psychophysical works reporting a diffuse impairment in the CS function showing a CS reduction in the low to middle spatial frequencies. In conclusion, non-reversible CS impairment was found in occupational exposure to mercury vapor. We suggest that CS measurement should be included in studies of the mercury effects of occupational exposure. (C) 2007 Elsevier Inc. All rights reserved.

Methylmercury intoxication and histochemical demonstration of NADPH-diaphorase activity in the striate cortex of adult cats

The effects of methylmercury (MeHg) on histochemical demonstration of the NADPH-diaphorase (NADPH-d) activity in the striate cortex were studied in 4 adult cats. Two animals were used as control. The contaminated animals received 50 ml milk containing 0.42 µg MeHg and 100 g fish containing 0.03 µg MeHg daily for 2 months. The level of MeHg in area 17 of intoxicated animals was 3.2 µg/g wet weight brain tissue. Two cats were perfused 24 h after the last dose (group 1) and the other animals were perfused 6 months later (group 2). After microtomy, sections were processed for NADPHd histochemistry procedures using the malic enzyme method. Dendritic branch counts were performed from camera lucida drawings for control and intoxicated animals (N = 80). Average, standard deviation and Student t-test were calculated for each data group. The concentrations of mercury (Hg) in milk, fish and brain tissue were measured by acid digestion of samples, followed by reduction of total Hg in the digested sample to metallic Hg using stannous chloride followed by atomic fluorescence analysis. Only group 2 revealed a reduction of the neuropil enzyme activity and morphometric analysis showed a reduction in dendritic field area and in the number of distal dendrite branches of the NADPHd neurons in the white matter (P<0.05). These results suggest that NADPHd neurons in the white matter are more vulnerable to the long-term effects of MeHg than NADPHd neurons in the gray matter.

Preliminary Findings on the Effects of Occupational Exposure to Mercury Vapor Below Safety Levels on Visual and Neuropsychological Functions

Objective: To evaluate whether there are visual and neurophysical decrements in workers with low exposure to Hg vapor. Methods: Visual fields, contrast sensitivity, color vision, and neuropsychological functions were measured in 10 workers (32.5 +/- 8.5 years) chronically exposed to Hg vapor (4.3 +/- 2.8 years; urinary Hg concentration 22.3 +/- 9.3 mu g/g creatinine). Results: For the worst eyes, we found altered visual field thresholds, lower contrast sensitivity, and color discrimination compared with controls (P < 0.05). There were no significant differences between Hg-exposed subjects and controls on. neuropsychological tests. Nevertheless, duration of exposure was statistically correlated to verbal memory and depression scores. Conclusions: Chronic exposure to Hg vapor at currently accepted safety levels was found to be associated with visual losses but not with neuropsychological dysfunctions in the sample of workers studied. (J Occup Environ Med. 2009,51:1403-1412)

Visual field losses in workers exposed to mercury vapor

Visual field losses associated with mercury (Hg) exposure have only been assessed in patients exposed to methylmercury. Here we evaluate the automated visual field in 35 ex-workers (30 males; 44.20+/-5.92 years) occupationaly exposed to mercury vapor and 34 controls (21 males; 43.29+/-8.33 years). Visual fields were analyzed with the Humphrey Field Analyzer II (model 750i) using two tests: the standard automated perimetry (SAP, white-on-white) and the short wavelength automated perimetry (SWAP, blue-on-yellow) at 76 locations within a 27 degrees central visual field. Results were analyzed as the mean of the sensitivities measured at the fovea, and at five successive concentric rings, of increasing eccentricity, within the central field. Compared to controls, visual field sensitivities of the experimental group measured using SAP were lower for the fovea as well as for all five eccentricity rings (p<0.05). Sensitivities were significantly lower in the SWAP test (p<0.05) for four of the five extra-foveal eccentricity rings; they were not significant for the fovea (p = 0.584) or for the 15 degrees eccentricity ring (p = 0.965). These results suggest a widespread reduction of sensitivity in both visual field tests. Previous reports in the literature describe moderate to severe concentric constriction of the visual field in subjects with methylmercury intoxication measured manually with the Goldman perimeter. The present results amplify concerns regarding potential medical risks of exposure to environmental mercury sources by demonstrating significant and widespread reductions of visual sensitivity using the more reliable automated perimetry. (C) 2007 Elsevier Inc. All rights reserved.

Recent cases on intoxication

Intoxication of a plaintiff raises many issues in a negligence action – duty of care, breach of duty, causation and the defence of contributory negligence. Recently intoxication has been examined by the Full Court of Tasmania in relation to duty and breach and by the New South Wales Court of Appeal in respect of causation and contributory negligence.

Pore structure characterization of North American shale gas reservoirs using USANS/SANS, gas adsorption, and mercury intrusion

Small-angle and ultra-small-angle neutron scattering (SANS and USANS), low-pressure adsorption (N2 and CO2), and high-pressure mercury intrusion measurements were performed on a suite of North American shale reservoir samples providing the first ever comparison of all these techniques for characterizing the complex pore structure of shales. The techniques were used to gain insight into the nature of the pore structure including pore geometry, pore size distribution and accessible versus inaccessible porosity. Reservoir samples for analysis were taken from currently-active shale gas plays including the Barnett, Marcellus, Haynesville, Eagle Ford, Woodford, Muskwa, and Duvernay shales. Low-pressure adsorption revealed strong differences in BET surface area and pore volumes for the sample suite, consistent with variability in composition of the samples. The combination of CO2 and N2 adsorption data allowed pore size distributions to be created for micro–meso–macroporosity up to a limit of �1000 Å. Pore size distributions are either uni- or multi-modal. The adsorption-derived pore size distributions for some samples are inconsistent with mercury intrusion data, likely owing to a combination of grain compression during high-pressure intrusion, and the fact that mercury intrusion yields information about pore throat rather than pore body distributions. SANS/USANS scattering data indicate a fractal geometry (power-law scattering) for a wide range of pore sizes and provide evidence that nanometer-scale spatial ordering occurs in lower mesopore–micropore range for some samples, which may be associated with inter-layer spacing in clay minerals. SANS/USANS pore radius distributions were converted to pore volume distributions for direct comparison with adsorption data. For the overlap region between the two methods, the agreement is quite good. Accessible porosity in the pore size (radius) range 5 nm–10 lm was determined for a Barnett shale sample using the contrast matching method with pressurized deuterated methane fluid. The results demonstrate that accessible porosity is pore-size dependent.

Creating gold nanoprisms directly on quartz crystal microbalance electrodes for mercury vapor sensing

A novel electrochemical route is used to form highly {111}-oriented and size-controlled Au nanoprisms directly onto the electrodes of quartz crystal microbalances (QCMs) which are subsequently used as mercury vapor sensors. The Au nanoprism loaded QCM sensors exhibited excellent response–concentration linearity with a response enhancement of up to ~ 800% over a non-modified sensor at an operating temperature of 28 °C. The increased surface area and atomic-scale features (step/defect sites) introduced during the growth of nanoprisms are thought to play a significant role in enhancing the sensing properties of the Au nanoprisms toward Hg vapor. The sensors are shown to have excellent Hg sensing capabilities in the concentration range of 0.123–1.27 ppmv (1.02–10.55 mg m − 3), with a detection limit of 2.4 ppbv (0.02 mg m − 3) toward Hg vapor when operating at 28 °C, and 17 ppbv (0.15 mg m − 3) at 89 °C, making them potentially useful for air monitoring applications or for monitoring the efficiency of Hg emission control systems in industries such as mining and waste incineration. The developed sensors exhibited excellent reversible behavior (sensor recovery) within 1 h periods, and crucially were also observed to have high selectivity toward Hg vapor in the presence of ethanol, ammonia and humidity, and excellent long-term stability over a 33 day operating period.

The influence of perpetrator and victim intoxication on perceivers' ratings of a sexual perpetrator's own awareness of wrongdoing for his sexually aggressive behaviour

Rape-perception studies have examined the influence of alcohol intoxication on perpetrator blame attributions: However, no studies have examined how intoxication affects perceptions of a sexual perpetrator’s awareness of the wrongfulness of his behaviour despite its relevance to the conceptualisation of responsibility and blame. This experiment investigated the impact of perpetrator and victim intoxication on perceptions of a perpetrator’s own awareness of wrongdoing for acquaintance rape. Undergraduate students (N = 314) read one of four rape-scenarios in which intoxication was manipulated and rated the perpetrator’s awareness of the consequences and wrongfulness of his sexual aggression. Findings supported the hypothesis that participants would assign less awareness of wrongdoing to an intoxicated, compared to sober, perpetrator. Further, males ascribed more awareness of wrongdoing to the perpetrator of an intoxicated, compared to sober, victim. Findings indicate that intoxicated sexual perpetrators are seen as not fully aware of the nature and consequences of their crime.