Ô nhiễm thủy ngân do các hoạt động khai thác vàng ở Bắc Việt Nam

Ô nhiễm thủy ngân do các hoạt động khai thác vàng ở Bắc Việt Nam.

189Journal of Chemistry, Vol. 40, No. DB, P.189 - 193, 2002 Mercury pollution due to gold mining activities in the North of Viet Nam Received 06-8-2002 Trinh Xuan Gian, Le Lan Anh, Vu Duc Loi, Tran Van Huy1, Hirokatsu Akagy2, Mineshi Sakamoto21Institute of Chemistry, Viet Nam National Center for Natural Science and Technology 2National Institute for Minamata dissease, Japan Summary To obtain the basic information on human exposure to mercury (Hg) due to gold mining activities in North of Viet Nam, total mercury was determined for human hair and blood samples collected from population living in gold mining area. The results indicate that the mercury concentrations measured in 98 blood samples with ranging from 1.128 to 22.751 ppb and 65 hair samples with ranging from 0.379 to 2.440 ppm, the good correlation between concentration of mercury in hair and blood samples was found in people and the ratios of hair Hg to blood hair were 195 for males and 142 for females I - Introduction Environmental mercury pollution due to gold mining in the North of Viet Nam has been concerned in recent years. In the gold mining processes an enormous amount of metallic Hg has been used and released in an abusive way into local ecosystems over the last 15 years, of which are discharged in to the river system and the atmosphere. Owing to this metal, therefore, there is a possibility of causing two types of health hazards in near gold mining: Firstly, accumulation inorganic mercury poisoning by direct inhalation of mercury vapor during the processes of burning and re-burning Hg-Au amalgam. Secondly, a part of mercury discharged into the river system is methylated and ultimately bio-accumulated to a significant level in fish. Thus, people living along the river and depending on riverine products are easily exposed to methyl mercury (MeHg) and may develop toxically levels through repeated consumption of these contaminated fish. The people living near gold mining areas may be contaiminated with at least two forms of mercury - Inorganic Hg and MeHg - simultaneously from surrounding air and diets. Therefore, the present study aimed at evaluating the actual human exposure to Hg due to gold mining activities by measuring total mercury in human hair, blood samples collected from people living near gold mining areas. The second past, we will show the result of methyl mercury measured in the samples above. II - Materials and methods 1. Samples Human hair and blood were used in this study, blood samples were collected from the inhabitants living near gold mining of Vietnamese North. The subjects consisted of 82 males and 16 females. The personal data (age, 190sex, address and occupation) were obtained at the time of sampling. 2. Analytical procedures for mercury In the present work, the determination of total mercury was made with sensitive and reliable methods recently developed in National institute for Minamata disease (H. Agaki et al 2001) Total mercury analysis in hair samples: The procedure for total mercury in hair is shown in figure 1. A known amount of 10 mg hair sample was placed in a 50 ml volumetric flask, to which 1 ml of water, 2 ml concentrated sulfuric acid were added and heated at 200oCon a hotplate for 30 min. After cooling until the room temperature, the digested sample was made up to 50 ml with mercury-free water. An aliquot of sample solution was introduced into an automated circulating air flow system with the addition of 10% stannous chloride solution (SnCl2). After air circulation for 30 s, the mercury in circulating air was measure by cold pavor atomic absorption spectrometry. The detection limit is around 0.5 ng. Total mercury analysis in blood sample: The procedure for total mercury in blodd is shown in Fig 2. The 500 mg of blood sample was weighed, sample was placed in the 50-ml volumetric flask, to which 1 ml of water, 2 ml of concentrated nitric/pechloric (1:1) and 5 ml of concentrated sulfuric acid were added and heated at 200oC on a hotplate for 30 min. After cooling until the room temperature, the digested sample solution was made up to 50 ml with mercury-free water. The measurement of mercury in sample solution was carried out like method above. For determination of Hg in hair samples, also using a sample combustion method, one advantage of this method is its ability to quanlitify mercury with direct heat processing without any pre-treatment procedures. In principle, mercury vapor is generated by direct combustion of the sample. Mercury released from the sample is concentrated by amal-gamation. The amalgam is heated to 800oC to free the mercury vapor and measured by CV-AAS. The procedure for analyzing total mercury by sample combustion method is following. The 5-mg hair sample was placed to quartz combustion boat, 1 drops additive was added. Place the boat in a combustion furance, heat at 800oC while introducing oxygen at 0.5 l/min to release mercury which can then be collected in a golden tube. Heat the golden tube to 700oC to produce mercury vapor and measured by a CVAA analyzer. Accuracy of method was assesed with certified reference material NIES, No 13 - Human hair (National institute for environmental studies, Environment agency, Japan). A recovery of Hg is 98.65%. III - Results and discussion 1. Concentration of mercury in hair samples The comparison of T-Hg measurement in hair samples by two different methods showed fairly good agreement, as is shown in figure 3. There indicated that not only the two difference analytical procedures gave comparable data, but also mercury was lost during digesting samples. The concentration of T-Hg is shown in Tab 1. The distibution of mercury concentration in hair sample from males and females is shown in Fig 4. The contents in males (0.908 ppm). were about 1.51 times higher than those in females (0.606 ppm). The T-Hg in hair samples is not high compared with Minamata disease patients. These comparison results indicate that, Minamata exposed to Hg occurs mosly through the consumption of fish contaminated with Me-Hg. In case of people living near gold mining, the contribution of inorganic Hg to the human exposure through atmosphere or diet is small. There are very little available data of mercury content in human hair of Vietnamese. Vu Duc Loi et al. (2000) reported the mercury concentration in normal people were 0.224 ppm. In present study, concentration of T-Hg in hair is idue to samples were collected from near gold mining areas, Hg was used very 191much through gold mining activities and released into atmosphere and streams Hair sample Washed with neutral detergent and water Washed with acetone Dried under reduced pressure Cut finely with scissors in a 20 ml counting vial Blood sample, 500 mg or less H2O, 1 ml Conc. HNO3- HClO4(1:1), 2 ml Conc. H2SO4, 5 ml Heat at 200oC for 30 min Hair sample, 10 - 20 mg Digested sample H2O, 1 ml Conc. HNO3- HClO4(1:1), 2 ml Conc. H2SO4, 5 ml Heat at 200oC for 30 min Cooled down to room temperature Made up to 50 ml with water Digested sample Sample solution Cooled down to room temperature Made up to 50 ml with water 10% SnCl2in 1N HCl, 0.5 ml Sample solution Hg vapor 10% SnCl2in 1N HCl, 0.5 ml Hg vapor AAS AAS Fig. 1: Analytical procedure for T-Hg in hair sample Fig. 2: Analytical procedure for T-Hg in blood sample 2. Concentration of mercury in blood samples Base on the results of mercury analyses in blood samples, the relationships between T-Hg in blood and hair were investigated. The correlation between T-Hg in blood and hair was found, with the correlation coefficient r = 0.405 times for male and 142 for females. These ratios were not only different to people living near gold mining in Tapaijos river basin, Amazon of Brazil (250 times) but also different to between males and females (H. Akagi et al 1998). The difference between concentration of T-Hg in males and females was found, the contents in females were about 1.5 times lower than in males. The sex difference in mercury. Concentration in blood (Nishima et al., 1976) and the hair (Shimomura et al. 1980; Nakano and Wakisaka, 1976; Ando, 1998) has been reported. This diference may be explained by the amount of fish consumption, monthly blood loss among females, and mercury metabolism. Futashuka et al (1982) reported that males consumed larger amount of fish and and shellfish. Miettinen et al. (1997) found that methyl mercury was excreted with a mean biological half-time of 79 days for males and 71 days for females and that inorganic mercury was excreted for 48 days by females and 37 days by females. 192Fig. 3: Correlation of T-Hg determination in two different methods Fig. 4: Concentration of T-Hg in hair samples Table 1: Concentration of mercury in hair samples Mercury concentration, ppm Sex Sample N X ± SD Range Males Hair sample 49 0.908 ± 0.4220.432 - 2.440 Females Hair sample 16 0.606 ± 0.3210.379 - 0.382 Hair sample from Minamata disease patient 41.200 Fig. 5: Correlation between T-Hg in hair and blood samples for males Fig. 6: Correlation between T-Hg in hair and blood samples for females 193Fig. 7: Concentration of T-Hg in blood samples IV - Conclusions The curent situation of mercury pollution and resulting effects on the local people living near gold mining have been clarified in the present study. The result to date has confirmed that mercury concentration in hair and blood was high. The comprasion between the control group and studying group is different; the control group is (about 2.5 - 5.0 times) lower than studying group. The correlation between concentration of T-Hg in hair and blood was found. T-Hg in hair is about 195 times (Males) and 142 times (Females) higher than blood. Accuracy of method was assesed with certified reference material NIES, No 13 - Human hair (National institute for environmental studies, Environment agency, Japan). A recovery of Hg is 98.65%. There are a need more to investigate concentration of mercury in these areas. Inorganic mercury and methyl mercury in fish also should be often determined. References 1. H. Akagi. Study on mercury pollution in Amazon, Brazil. Golbal Environmental research Vol. 2, No. 2, P. 193 - 202 (1998). 2. H. Akagi et al. Human exposure to mercury due to gold mining in tapajos river basin, Amazon, Brazil: Speciation of mercury in human hair, blood and urine. Water, air, soil pollution 80: 85 - 94 (1995). 3. Mineshi Sakamoto et al. Ecotoxicology and evironmental safety 22, P. 58 - 66 (1991). 4. H. Akagi, H. Nishimura. Advances in mercury Toxicology, Plenum press, USA, 57 - 76 (1991). 5. Suzuki, T., T. Hongo, J. Yoshinaga, H. Imai, M. Nakagawa, N, Matsuo and H. Akagi. Archives of environmental health Vol. 48, No. 4, P. 221 - 229 (1993). . Viet Nam Received 06-8-2002 Trinh Xuan Gian, Le Lan Anh, Vu Duc Loi, Tran Van Huy1, Hirokatsu Akagy2, Mineshi Sakamoto21Institute of Chemistry, Viet Nam. for Minamata dissease, Japan Summary To obtain the basic information on human exposure to mercury (Hg) due to gold mining activities in North of Viet Nam,