S16 (II) Mercury in contaminated sites: Biogeochemistry and human health

Mercury was discovered in Idrija around the year 1490, and the mercury mine operated for 500 years. Ore appears in two forms, 70% as cinnabar and 30% as native-elemental mercury (Hg(0)). In the 16^th century, Paracelsus and Mattioli first described mercurialism among miners of the Idrija Mine and in 1754 J.A. Scopoli was the first company physician appointed. He described in detail the symptoms and signs of mercurialism, and recommended adequate preventive measures. In the years immediately following the Second World War, Hg intoxication in miners reached up to as many as 145 cases per year. After 1964, a continuous decrease in the incidence of mercury intoxication was observed despite the fact that native mercury was still being mined. The clinical picture of intoxication was dominated by tremor, oropharyngeal syndrome, erethismus mercurialis, and occasionally proteinuria, urine Hg excretion varied from 300 to 1000 mg/24^h urine. Post-mortem studies have shown that Hg in ex-miners accumulated predominantly in the endocrine glands (pituitary, thyroid), kidneys, and brain tissue (dentate nucleus). Selenium co-accumulation (Hg/Se molar ratio 1:1) was notable only in samples with mercury concentrations over 2 mg/g. The results of research conducted in collaboration with the Jožef Stefan Institute have enabled us to define the ratio of air-blood mercury concentration (1 g/m³:0.54 mg/L), blood-urine mercury concentration (1 mg/L:2,7 mg/L), and air-urine mercury concentration (1 mg/L:1.0 mg/L), which served as a basis for the application of biological action levels in miners intermittently exposed to Hg(0). The results of our studies support the assumption that long-term occupational exposure to Hg(0): (i) enhances the formation of free radicals and increases lipid peroxidation, (ii) in co-exposure to silica dust, could increase the known nephrotoxic effect, and (iii) in interaction with alcohol, enhances depression and negative self-concept in ex-miners. Biological monitoring helped to prevent mercury intoxication, but not the increased absorption of Hg(0), which appeared in about 40 % of exposed miners. Long-term increased Hg(0) absorption, co-exposure to silica dust and radon, and miners’ lifestyle-related factors could be responsible for the mortality causes observed in miners of the Idrija Mercury Mine: increased risk of mortality from lung cancer, nephritis-nephrosis, ischaemic heart diseases, and suicide.

Background:
Gold miners use mercury to extract gold from the ore. Liquid mercury is added to the crushed gold ore binding to an amalgam. This amalgam is smelted without any protection to extract the gold from the amalgam. The amalgam burners, who are directly exposed to mercury vapor, are extremely burdened.

Methods:
Gold miners were assessed in different small-scale gold mining areas in the Philippines, Mongolia, Tanzania, Zimbabwe and Indonesia (1-4). Urine, blood and hair samples were taken from each participant, (and also additional control groups), and consequently analyzed for mercury (n=1077). The participants were medically investigated, following a standardized protocol. In each country, volunteers from unburdened areas served as controls (n=143). Amalgam burners (n=418) and miners using mercury for panning (n= 179) are especially exposed, but also the general population in mining areas is seriously at risk (n=337). The medical data was statistically analyzed (Chi-square, Mann-Whitney test, Kruskal-Wallis test, correlation coefficient).

Results:
Mercury concentrations in all three specimens were elevated (control versus exposed groups p<0.001 Mann Whitney test, Kruskal Wallis test). In some cases very high mercury concentrations were found. Symptoms, characteristic for a chronic mercury vapor exposure were frequent. Ataxia of gait was found in 7% of the control group and 35% of the amalgam smelters (Chi-square p<0.001). Dysdiadochokinesia was found in 18% of the control group and 34% of the amalgam smelters (Chi-square p<0.001). Neuro-psychological tests such as the match-box test, a test for co-ordination, intentional tremor and concentration, show poorer results in comparison to the control group (significant correlation p<0.001). 74.3% of the amalgam burners were diagnosed as mercury intoxicated, compared to 0.8% within the control group (Chi-square p<0.001).

Conclusion:
Many of the miners have health problems related to the mercury exposure in the immediate environment. The most important conclusion is that the exposure has to be reduced. The use of mercury needs to be reduced as a first priority. Mining and housing areas need to be separated. Mercury free technologies have to be developed and used. Health care systems need to be prepared and trained for this new emerging “amalgam burner disease”.

1. Steckling STOTEN 2011;409:994-1000.
2. Bose-O’Reilly STOTEN 2010;408:796-805.
3. Bose-O’Reilly STOTEN 2010;408:713-25.
4. Drasch STOTEN. 2001;267(1-3):151-68.

The epidemic known as “Minamata disease” was the first instance on record of severe methylmercury poisoning caused by man-made environmental pollution. It was caused by the consumption of large amounts of fish and shellfish contaminated with methylmercury, which was generated as a by-product of an acetaldehyde production process and discharged from the Chisso Minamata plant. Since an accurate appreciation of individual methylmercury exposure levels was impossible, neither the actual time-course nor regional distribution of methylmercury pollution in the Minamata area could be determined at the time of heavy pollution. However, Japanese people even today have long observed an ancient custom of preserving the infant’s umbilical cord as a memento of its birth. The present study was conducted to investigate the historical time-course changes and regional distribution of methylmercury concentrations in preserved umbilical cords collected from Minamata-area inhabitants born between 1947 and 1990. The data from Miyazaki, Tottori, Akita, Tsushima, Fukuoka and Tokyo were used as controls. A total of 325 data were analyzed to estimate the temporal and spatial distribution of methylmercury among inhabitants born in the Minamata area. Elevated methylmercury concentrations (≥1 µg/g) were mainly observed in inhabitants born between 1947 and 1968. That peak coincided with the period of acetaldehyde production in Minamata. The methylmercury concentrations started to decrease in keeping with the decline of acetaldehyde production, which ceased in 1968, and thereafter the methylmercury levels gradually decreased to the control levels. Elevated methylmercury concentrations were first observed in the districts of Minamata, followed by Izumi, Tsunagi and Ashikita, indicating the time-course-dependent regional distributions of methylmercury pollution.The methylmercury concentrations in the preserved cords reflected not only the historical time-course but also the regional distribution of methylmercury exposure among inhabitants born in this area.

Traditional foods offer tremendous social, health, and economic benefits to Indigenous Peoples in Canada. However, the presence of environmental contaminants such as mercury in traditional foods may present health risks. In this talk, we will present results from two case studies of elevated mercury exposure as a result of mercury contamination. The first case study is from a small First Nations reserve in northern Ontario named Grassy Narrow which is located downstream of a chemical plant that dumped approximately ten metric tonnes of inorganic mercury into the river system between 1962 and 1970. This mercury was converted to the toxic methylated form by sulfide-reducing bacteria in the water, and was subsequently incorporated into the river ecosystem. All fish species from the river system were considered to be so contaminated as to be unfit for human consumption. Four decades after the initial pollution, we still found elevated though much lower than the peak levels of mercury in the predatory fish species in river system. The residents of the communities had lower hair mercury compared to the historical record but many have complains of neurological symptoms. The second case study is from the Arctic Canada where the mercury was originated from the south and reached the Arctic through long-range atmospheric transport. Elevated levels were found in animals of higher trophic levels such as marine mammals and predatory fish. As a result, the Inuit who depend on these species for subsistence living have high mercury exposure. Our results show that concerted efforts are needed to decrease the release of mercury in the environment globally. Experience learned from mercury contaminated sites will help us to develop the proper public health interventions to lower the risk of health effects as well as to lobby for international regulations for the use and release of mercury in the environment.

Mercury (Hg) species were investigated in 50 varieties of rice grain, grown in 3 sites along a contamination gradient in Guizhou province, southwestern China, including 2 sites near the Wanshan Hg mine (Wukeng and Gouxi) and one background site (Xiaohe). Interestingly, in polished white rice average total Hg (Hg_T) and methylmercury (MeHg) levels were both significantly higher in Gouxi compared to the other two sites (Hg_T: Xiaohe 2.8 ± 0.97 ng/g; Wukeng 18 ± 4.3 ng/g; Gouxi: 120 ± 33 ng/g) (MeHg: Xiaohe 2.0 ± 0.78; Wukeng 9.9 ± 5.1; Gouxi 63 ± 19). However, sediment and pore water Hg_T levels were more elevated near Wukeng, which bordered the capped mine tailings, while MeHg levels between Wukeng and Gouxi were similar, and both were significantly higher than Xiaohe. Partitioning coefficients (K_d) for Hg_T and MeHg did not differ between Wukeng and Gouxi (Log₁₀ K_d Hg_T, Wukeng: 4.9, Gouxi: 5.1; Log₁₀ K_d MeHg, Wukeng: 3.3, Gouxi: 3.5), indicating bioavailability was similar between the two highly contaminated sites. Lower concentrations of Hg species in white rice from Wukeng may be due to elevated pore water Hg_T (Wukeng 650 ± 350 ng/L; Gouxi: 92 ± 12 ng/L), which may reduce nutrient uptake by creating cellular plant stress or by inhibition of aquaporins through binding of inorganic Hg(II) to cysteine. Lastly, 15 varieties of bran were analyzed from each site (total n=45), and dimethylmercury was observed (although not quantified) in all samples, but was not observed in polished white rice (n=147). Results indicated there was a barrier to dimethylmercury between the maternal tissue (i.e., bran) and the filial tissue (i.e., polished white rice), which was not previously reported for rice grain. Differences between varieties were observed in Wukeng and Gouxi, but not in Xiaohe, although the same 50 rice species were planted in all 3 sites. Results from this study suggested some plant responses, including nutrient uptake, were dictated by environmental pollutant levels.

Numerous populations face multiple Hg exposure pathways, such as air pollution, occupational exposure, like gold or Hg mining or dietary exposure from fish and rice consumption. Populations may be exposed to both monomethylmercury (MMHg) and inorganic Hg (InHg) species. There is now a substantial interest in developing a tracer tool that may identify the different types of Hg exposure to limit the risks for human health.

The use of Hg stable isotope signatures to trace processes and sources of Hg in the environment has emerged over the last decade. Our objective is to investigate the possibility to trace and quantify natural and anthropogenic Hg sources in human tissue by using Hg stable isotope signatures coupled to Hg speciation. Human hair has been recognized as a good tracer to evaluate MMHg contamination in the body. People that are also exposed to liquid or vapor Hg(0) have both Hg species in their hair. In this work, hair samples of different populations are studied: 1) native communities from the Bolivian Amazon and French Guiana, 2) European people, and 3) gold-miners.

Similar to the progressive enrichment of heavy nitrogen isotopes along food chains, the heavy Hg stable isotopes also tend to become enriched between a food source and human hair. Hair samples of native communities from both Bolivia and French Guiana are enriched by +2‰ in d²⁰²Hg relative to freshwater fish they consume. Similar mass dependent Hg isotope fractionation of +2‰ is observed between European hair and published data on marine fish and shellfish. As these populations are mainly exposed to MMHg via fish diet, this enrichment is attributed to MMHg species metabolism in the human body. On the other hand, in gold miner’s hair, the fraction of InHg can reach 96% of total hair Hg. Unlike MMHg, InHg d²⁰²Hg appears not to be enriched in the heavier isotopes relative to the d²⁰²Hg of the liquid Hg exposure source. Across all gold miner’s hair samples, d²⁰²Hg is positively correlated to MMHg percentage (r²=0.66; n=23) and appears to reflect binary mixing between the InHg and MMHg sources. Anomalous mass independent Hg isotope fractionation (MIF) is also observed in all hair samples and for all populations. For dominant MMHg exposure, MIF anomalies are conservative and a direct indicator of the exposure source. For populations with substantial InHg presence in hair, more work is needed to interpret MIF anomalies.

Three different locations near Almadén (Ciudad Real, Spain) with high (Almadenejos), medium (Las Cuevas) and low (San Quintín) soil Hg concentrations were selected for legume-nodule and soil sample collection. In order to study the biodiversity of rhizobia in mercury-contaminated areas, we preceded to the isolation and phenotypic and genetic characterization of rhizobia from legume-nodule grown in the above mentioned soils. We have identified 19 strains of rhizobia from 5 different plant species able to survive in areas contaminated with mercury. The phenotypic characterization has allowed us to classify the bacteria in relation to mercury tolerance and to identify mercury-tolerant strains. This represents a very important finding because, up to date no rhizobia strains with this characteristics have been identified. Minimal inhibitory concentrations (MICs) of more resistant strains are in the range of 12.5-30 µM of Cl₂Hg which is significantly high as compared to the standard values. The degree of toxicity of Hg on these strains, as measured by the effective concentration that produces 50% mortality, has permitted to define the concentrations of mercury to be used in trials with these bacteria. Genetic analyses of the 16S rDNA and nodC gene have determined that there are 3 strains of Rhizobium leguminosarum bv. viciae, 2 of Bradyrhizobium canariense, 7 of R. leguminosarum bv. trifolii, 6 of Ensifer (Sinorhizobium) medicae and 1 of Agrobacterium tumefaciens. Furthermore, trap plants (lupin, chick pea and bean) were planted in all collected soils to determine their Hg absorption and accumulation capacity and to isolate rhizobia. The results showed that Hg accumulation was particularly high in roots and nodules from lupin plants grown in Almadenejos soil. Therefore, lupin was chosen to study the effect of different concentrations of Hg in the watering solution of plants inoculated with two strains of Bradyrhizobium canariense, L3 (control of Hg-sensitive) and L7AH (native Hg-resistant). The results showed that Hg affected the growth of lupin plants decreasing the mass of their aerial parts and the number and weight of their nodules. The L7AH Hg-resistant strain seemed to confer lupin plants some resistance regarding their nitrogenase activity, since it remained constant through the different Hg treatments.

Research experience of cases of groundwater mercury contamination in Northern industrial area in Pavlodar City, Kazakhstan, within the territory of Kiev City, Ukraine and in Northern industrial zone of the town of Usolie-Sibirskoe, Russia (in all three cases mercury cell chlor-alkali production was a source of mercury contamination) allows coming to a conclusion that character of contamination depends substantially on hydro-geological conditions and technogenic factors influencing it.

In Pavlodar region water-bearing rocks involve sands interlaid with uneven layers of clay. In Kiev relatively uniform thick water-bearing stratum prevails which involves sands predominantly. In Usolie-Sibirskoe groundwater are enclosed within sands with clay interlayers which are underlain with karstic rocks.

Methods of mathematical modeling which enable to assess risks and predict application of different technological solutions for remediation were used in the research along with field and laboratory methods. In case of Pavlodar the prognosis was managed to compare with results of post-demercurization monitoring.

Hydro-geological conditions determine configuration of contamination aureole as well as direction and rate of its spread. Alteration of these conditions as a result of reconstruction of sewerage and water supply systems, construction of extensive underground engineering structures including protective ones can result in quite quick change of direction of the contamination spread as well as in substantial decrease in both concentration of dissolved mercury there and the contamination aureole itself.