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.

Journal 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 Sakamoto2

1 Institute of Chemistry, Viet Nam National Center for Natural Science and Technology

2 National 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,

sex, 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 200oC

on 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

much 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

Cooled down to room temperature

Made up to 50 ml with water 10% SnCl2in 1N HCl, 0.5 ml

10% SnCl2in 1N HCl, 0.5 ml

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

Fig 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

Males Hair sample 49 0.908 ±0.422 0.432 - 2.440 Females Hair sample 16 0.606 ±0.321 0.379 - 0.382

Hair sample from

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

Fig 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-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)