Preparation and characterization of a soil reference material from a mercury contaminated site for comparability studies.

The preparation and characterization of a soil reference material (SOIL-1) from a site polluted with mercury due to the past mercury mining in Idrija, Slovenia is reported. Homogeneity tests and intercomparison exercises for total (T-Hg) and methylmercury (MeHg) were performed. In addition, selective sequential extraction was applied for Hg fractionation, and multielemental analyses were performed by k(0) standardization neutron activation analysis (k(0)-INAA) and inductively coupled mass spectrometry (ICP-MS) for other trace elements. Comparison of different analytical methods, as well as the distribution of data were critically evaluated using descriptive statistics and analysis of variance (ANOVA). Due to the nugget effect (cinnabar particles representing more than 90% of the mercury), homogeneity for T-Hg determination was difficult to achieve. The intercomparison exercise indicated that in order to obtain comparable results for total mercury (T-Hg) sample decomposition by HF must be performed. These data are then in good agreement with non-destructive methods such as k(0)-INAA. Accepted reference values calculated taking into account the results obtained by six and three laboratories, respectively, were 67.1+/-11.3 mg kg(-1) for T-Hg and 4.0+/-1.3 ng g(-1) for MeHg (95% confidence intervals). However, the results obtained for Hg fractionation displayed significant differences in the organically bound fraction and elemental Hg. Results obtained by two laboratories using totally different analytical protocols for other elements showed excellent agreement for most elements. In summary, the results obtained for the SOIL-1 sample were of sufficient quality to suggest its use for quality control in laboratories dealing with mercury contaminated soils.

Reduction and methylation of mercury in the terrestrial isopod Porcellio scaber (Crustacea) and its environment.

Reduction and methylation of inorganic mercury in Porcellio scaber (Isopoda, Crustacea) and its environment were studied, using a purpose-built experimental setup where Hg cycling was followed using 203Hg2+ tracer in experiments without and with isopods. In experiment without isopods, daily reduction of 203Hg2+ to 203Hg0 under sterile and nonsterile conditions was measured for three weeks to assess the contribution of bacteria to this process. In experiments with isopods, daily release of 203Hg0 was measured for two weeks. Total mercury (T203Hg) and monomethylmercury (Me203Hg) in whole animals, gut, digestive glands (hepatopancreas), food (hazelnut leaves), and feces were measured to obtain the assimilation and distribution of mercury in the animals, to investigate the origin and fate of Me203Hg, and, finally, to assess the mass balance of mercury in the experimental system. Experiment without isopods showed the important role of bacteria in reduction of 203Hg2+ to 203Hg0, especially in the first day of the experiment. Experiments with isopods showed that formation of 203Hg0 depended on the 203Hg2+ concentration in the food. The contribution of the isopod's digestive flora in reduction of 203Hg2+ to 203Hg0 was negligible. Approximately 3% of T203Hg and 2% of Me203Hg consumed was assimilated by the animals. Methylation of 203Hg2+ occurred already in the leaves before they were consumed by the isopods. Assimilation of Me203Hg from the food surprisingly was low. Also, a loss of Me203Hg was noticed when comparing assimilated and excreted Me203Hg versus consumed Me203Hg. This may be explained by the assumption that demethylation of MeHg prevailed over methylation of Hg2+ in the animal's digestive system, leading to excretion of ingested mercury as Hg2+.

Total mercury, methylmercury and selenium in mercury polluted areas in the province Guizhou, China.

The province of Guizhou in Southwestern China is currently one of the world's most important mercury production areas. Emissions of mercury from the province to the global atmosphere have been estimated to be approximately 12% of the world total anthropogenic emissions. The main objective of this study was to assess the level of contamination with Hg in two geographical areas of Guizhou province. Mercury pollution in the areas concerned originates from mercury mining and ore processing in the area of Wanshan, while in the area of Quingzhen mercury pollution originates from the chemical industry discharging Hg through wastewaters and emissions to the atmosphere due to coal burning for electricity production. The results of this study confirmed high contamination with Hg in soil, sediments and rice in the Hg mining area in Wanshan. High levels of Hg in soil and rice were also found in the vicinity of the chemical plant in Quingzhen. The concentrations of Hg decreased with distance from the main sources of pollution considerably. The general conclusion is that Hg contamination in Wanshan is geographically more widespread, due to deposition and scavenging of Hg from contaminated air and deposition on land. In Quingzhen Hg contamination of soil is very high close to the chemical plant but the levels reach background concentrations at a distance of several km. Even though the major source of Hg in both areas is inorganic Hg, it was observed that active transformation of inorganic Hg to organic Hg species (MeHg) takes place in water, sediments and soils. The concentration of Hg in rice grains can reach up to 569 microg/kg of total Hg of which 145 microg/kg was in MeHg form. The percentage of Hg as MeHg varied from 5 to 83%. The concentrations of selenium can reach up to 16 mg/kg in soil and up to 1 mg/g in rice. A correlation exists between the concentration of Se in soil and rice, indicating that a portion of Se is bioavailable to plants. No correlation between Hg and Se in rice was found. Exposure of the local population to Hg may occur due to inhalation of Hg present in air (in particular in Hg mining area) and consumption of Hg contaminated food (in particular rice and fish) and water. Comparison of intake through these different routes showed that the values of Hg considerably exceed the USA EPA Reference Concentration (RfC) for chronic Hg exposure (RfC is 0.0004 mg/m(3)) close to the emission sources. Intake of Hg through food consumption, particularly rice and fish, is also an important route of Hg exposure in study area. In general, it can be concluded that the population mostly at risk is located in the vicinity of smelting facilities, mining activities and close to the waste disposal sites in the wider area of Wanshan. In order to assess the real level of contamination in the local population, it is recommended that biomonitoring should be performed, including Hg and MeHg measurements in hair, blood and urine samples.

Transformations of mercury in the terrestrial isopod Porcellio scaber (Crustacea).

The biological cycle of mercury in the terrestrial isopod Porcellio scaber was investigated. Testing the possibility of in vivo Hg(2+) methylation was divided into two methodologically different parts. Firstly, concentrations of total mercury and MeHg in isopods P. scaber and their environment from a Hg-unpolluted area were measured by the use of validated methods (CV AAS, CV AFS). The data obtained show that the percentage of MeHg in leaves, soil and faeces was less than 1%. In contrast, the percentage of MeHg in gut and hepatopancreas was increased to 14 and 77%, respectively, indicating methylation of Hg(2+) in the gut and its further accumulation in glands. To confirm this assumption, the second methodology was applied-a radiotracer technique with 203Hg(2+) of high specific activity. There are few radiotracer techniques for Hg-methylation assays; for our work we chose the method of Czuba et al. which includes alkaline leaching of Hg species, their extraction into dithizone-toluene, followed by specific separation of Hg dithizonates by thin-layer chromatography and gamma counting. All steps of the analytical protocol were checked and optimised by the use of aqueous solutions of 203Hg(2+) and Me(203)Hg(+). The most important finding was that cleaning-up the extract through a florisil column is not appropriate, because the column retains different percentages of Hg(2+) and MeHg(+) and consequently affects the accuracy of the final result. This optimised protocol was then applied to Hg transformation studies in the terrestrial isopod P. scaber. Leaching Hg species from P. scaber fed with 203Hg(2+) or Me(203)Hg(+) dosed food was completely efficient only at elevated temperatures. Preliminary results of methylation/demethlytion studies are rather variable but they show that both processes (Hg(2+)<-->MeHg(+)) take place in the isopod P. scaber. Additionally, an assessment of the mass balance of Hg in isopods P. scaber exposed to 203Hg(2+) indicates that volatile Hg species are also formed.