Figure
1. Schema of distribution of goitre on the world
(WHO, 1990).
Table 1. Interrelation between
iodine content in soil with the
ratio of goitre [30].
|
Localities |
Ratio
of people suffering goitre (%) |
I
content |
|
Taranaki |
4 |
1.4.10-3 |
|
|
4 |
1.2.10-3 |
|
Dunedine |
19 |
3.2.10-4 |
|
|
40 |
4.0.10-5 |
|
|
62 |
3.0.10-5 |
When examining the geochemical state of areas where the endemic goitre is widespread, A.P. Vinogradov [31] found that beside the very low content of iodine in the environment, the pedologo-climatic factors influence also to the disease level, from this he determined iodine-deficient bio-geochemical provinces with manifes-tation of endemic goitre.
Table 2. Iodine
quantity in soil and water in different areas
where there is endemic goitre (ppm)
[31].
|
Studied countries |
Studied objects |
Area of heavy endemic goitre |
Area of medium endemic goitre |
Area without endemic goitre |
|
Ukraina |
Soil |
1,222 |
2,687 |
15,970 |
|
Water |
1-2 |
2-3 |
8-20 |
|
|
|
Soil |
1,000-2,000 |
2,000-3,000 |
5,000-20,000 |
|
( |
Soil |
0-2 |
2-4 |
7.6-9.0
µg/l |
|
Water |
0-0.5
µg/l |
|
>
8 µg/l |
Studying on bio-geochemical characteristics of iodine in soil related to endemic goitre, V.V. Kovaskij [16] has been determining the threshold of iodine content as follows (Table 3):
Table 3. Iodine contents related to disease [16]
|
Areas |
I
content in soil, ppm |
Ability
of causing disease |
|
Deficient
in I |
<2-5 |
Goitre, stupidity
and disorder diseases caused by deficient in I |
|
Enough
in I |
5-40 |
Enough in
nutrient need, body normally developed |
|
Abundant
in I |
>40 |
Basedow occurs |
2.
Influence of the geochemical environment to the biological ability of iodine
absorption
Studying results let see that biological effect of iodine to human body, apart from its essence, depends on geochemical situation and the increasing or decreasing action of a/some accompanying elements. For instance, in such environment deficient in iodine, at the same time, in Co, Cu, Se or deficient in iodine, but exceeding in Mn, F the endemic goitre happens more seriously. Many scientists have been emphasizing the role of some micro-elements, such as Sr, Mo, Cu as well as Co and Mn in the synthesis of iodine compounds of the thyroid [16].
Studying works by C. Thilly and colleagues in Zaire published in 1990 have been letting see that, the deficiency of Se nutrient will diminish the enzyme of glutathion peroxydaza, leading to the decrease of up to 15-20% of iodine total in the thyroid T4 and T3, at the same time, decreasing the transfer of T4 to T3 acting in cellular organizations causing the enhancement of goitre.
Qian Qidong et al. (1985) studying on goitre in areas of salted-alkaline soil of Xiaoyi District, Shanxi Province let see that there, people use water from shallow wells having the bitter and salted taste with rather great iodine content - 534 µg/l, at the same time, Ca, Mn, Mo are all high, and the ratio of inhabitants getting the goitre reaches up to 43.9%. As for inhabitants in other areas using water from deep wells having normal physico-chemical factors, they have the ratio of goitre in the community is very low, reaching only 0.96%, and the iodine level in urine is normal.
So, there are 2 causes for the goitre: deficiency in iodine, and superfluousness in iodine. Goitre caused by superfluousness in iodine occurs in coastal areas, and maybe even in mainland. Wang Xin (IDD Journal, N010, 1991) let know that, in the Shanggai City, there is not the endemic goitre; as for in retired areas of Hebei, Shanxi, Shantung, Phujian, the endemic goitre is rather developed due to the exceeding iodine level.
The endemic goitre developed in some areas still is caused by the disproportional ratio of some nutritious micro-elements in the environment. Studies by Jhuski Liu (IDD Journal, N03, 1993) have been finding that the increase of goitre is caused by the high increase of nitrate content in soil and water. The endemic goitre and arthritis in some areas is related to the deficiency of Se in the environment, and this even is the factor causing the endemic stupidity. R.C. Cooksey et al. (1985) in the Institute of Incretology of Prague studying on the goitre in Bohemia after 20 years of prophylaxis by iodine salt let know that in Prague the ratio of goitre is high, but it is worthy to pay attention that, the living environment in this area is not defficient in iodine. Maybe, other factors are the main cause of endemic goitre in this area. B.A. Lamlerg (1985) in the Helsinsky University studying on disorders of thyroid combined with iodine deficiency showed that the prophylaxis by iodine salt has been carried out in 25 countries in all corners of the world, but the results let see that in some areas, the goitre still exists although the environment is enough in iodine (IDD, Journal No. 9, 1993). It is clear that in these areas, goitre-causing matters need to be determined. Just because of this, during recent years goitre-causing matters have been attracting the attention of many scientists of the world and in our country.
3.
Biological significance of iodine for human and animals
We can see that, all iodine of our body is concentrated in the thyroid. Iodine is associated with a proteine (globuline) containing much thyroxine (T4). Ordinarily, everyday the thyroid in adults produces 85 µg T4 and 32 µg T3. Everyday, children below 10 years take in 40-120 µg and adults – 150 µg. From the serum, the most part of iodine is concentrated in the thyroid; the remaining part is eliminated through urine and sweat. Ordinarily, in each hour 1 litre of blood passes on the thyroid 2.5 µg of iodine. In the case of low iodine in the blood, the circulation must be enhanced for providing the thyroid with iodine. In the case of very low iodine in the blood, the production of T4 diminishes, while the production of T3 increases for maintaining the normal state to the body and saving iodine. If iodine is strongly deficient, both T3 and T4 decrease.
4. State of endemic goitre in Việt Nam
Results of epidemiologic investigation before 1990 in some localities of 17 mountainous provinces let see that the ratio of goitre patients reaches in average 34.2%, among them a dangerous area of about 1 million people has the ratio of patient reaching about 66.36%, an area of medium state with about 6 million people – about 31.56%, and an area of light state with about 2 million people – about 27.78%.
The most awesome is that in deficient in iodine areas many dullards are found; in some areas the ratio of dullards reaches from 1 to 8% of people quantity [3].
In 1993, for the first time the Health branch carried out the investigation on iodine deficiency in the whole country. The results showed that about 84% of people is deficient in iodine, among this, 16% is in hardly deficient state, 45% – in medium state, and 23% – in slight state. The common ratio of goitre in the country belongs to the medium type. Realizing the Decree No. 148 CP/1993 of the Government, since the beginning of 1994 the Program of Protection against iodine deficiency by measure of using iodine salt has been widely deployed in the whole country that has been reaching such result as after 5-7 years, the ratio of goitre patients has been diminished.
The epidemiologic investigation in 2000 year in 7 ecological areas of the country let see that the average ratio of goitre was 10.1%. The evaluation on the iodine urine (12.6 µg/dl) let see that 2.2% of people is hardly deficient in iodine, 13.6% – in medium state, and 23.4%t – in slight state. In the Nam Bộ Plain, the ratio of goitre is rather high, in average of 14.1% of people, but the iodine urine level is low.
After the study on the cause of
goitre in the Nam Bộ Plain, Phan Văn Duyệt [27] let know that
the ratio of goitre patients in
The endemic goitre in the Bắc
Bộ Plain has also many points to be paid attention. The investigation
results in Văn Côn (Hoài Đức District) and Vân
For recognizing goitrogenous
factors, Phan Huy Nhu carried out epidemiologic investigation on the goitre and
related factors in Cát Bà Island,
II.
SOME FEATURES OF IODINE CHEMISTRY IN THE NATURAL ENVIRON-MENT
1. Some
physico-chemical characteristics of iodine
Iodine element (I) belongs to the VII group in the Cyclic table of chemical elements with the order number as 53. The iodine atom includes 1 stable isotope I127 and radioactive isotopes I 131, I125, I126, I129, I133, I134, and I135. Iodine is the heaviest element in the halogen group, having characters almost near to fluorine (F), but its chemical activity is stronger, manifesting the submetallic character.
The basic geochemical characteristic of iodine is organophile, halogeno-phile, and accumulating in natural objects, mainly in the biosphere and hydrosphere.
2.
Distribution of iodine in natural objects
2.1. Iodine in the Earth’s crust
Volcanic eruption and hydrothermal activities in
volcanic areas are main iodine sources supplying to the Earth’s surface. The
estimation on the geochemical side of volcanic activity consequences in the
Kuril Archipelago (
2.2. Iodine
in minerals
Minerals contain little iodine; there are 9 iodides: marshite - CuI, hydroiodide - HI, ammonium iodide - NH4I, salocite - CuIO3(OH), lautarite - Ca(IO3)2, etc.. The isomorphous compound of I and Br in some halogenes (Ag, Hg) and phosphates reaches up to 5 mg/l of iodine. The iodine quantity in sulfate minerals is as follows (ppm): cinnabar, chalcopyrite, galenite - 2, sphalerite, pyrite, pyrrhotine – 0.5.
2.3. Iodine in rocks
- Iodine in intrusive and effusive rocks: The iodine content in magmatic rocks oscillates in the limit of 0.07-0.55 ppm; in liparite - 0.52 ppm, in serpentinite - 0.6-3.96 ppm. The average content of iodine in effusives is about 0.3 ppm.
- Iodine in sedimentary rocks: The iodine content in terrigenous sediments í about 0.2-13.0 ppm, among this, sandstone – 3.75 ppm, clay shale – 4.4 ppm. Factual materials let see that the correlation between iodine concentration and organic content and clay composition has rule character. When the organic quantity is smaller than 5%, the dependence is clearly expressed; in the case of its increase (over 5%), the correlation is very close.
- Iodine content in limestone: oscillating from trace to 6.1 ppm. Some other forms, such as cherty limestone, have very high iodine content, from 23.0 to 29.0 ± 7 ppm.
- Rock salts have different iodine contents, from trace to 0.05 ppm. The iodine content in anhydrite (cartenite), xivine (leopondite), halite (rock salt) and potassium saltpetre reaches up to 400 ppm. In general, the average content of iodine in salt sediments is about 0.8 ppm.
- Iodine content in peat depends on its forming conditions, as well
as on the composition of the bio-block and the level of transformation, usually
with the level oscillating from 0.05 to 41.0 ppm. In coaly shale and
bitumen, the iodine concentration is rather high, reaching up to 17-242 ppm.
The iodine content in oil mines, such as in those in
2.4. Iodine in the air
The average content of iodine in the air of the convection horizon is about 1 µg/m3; the total quantity of iodine in the air within the limit of 12 km is estimated of 12.106 tons. The iodine quantity supplemented annually to the atmosphere is about 511.3.103 tons, in which iodine from the disintegration of organic matters is about 0.1.103 tons, from fuel burning – 5.103 tons, from evaporation of sea-water – 500.103 tons.
2.5. Iodine in water
The iodine content in sea and oceanic water is in average 0.052 mg/l, but, near the shore, it is lower. The iodine form existing in sea water is mainly iodate (about 73-80%), lesser, iodide. The iodide content in water of all oceans is similar, while the total of iodine quantity (I-+IO3) is very different, because IO3- in oceanic water is stable, the oscillation of total content is the oxidized products I- that is hypoiodide. A great part of iodine in the surface of sea-water in the free form is lost, furthermore the loss of iodine increases due to the influence of ultraviolet rays:
2I-
+ 1/2 O2 + H2O + hv = I2 + 2
A part of iodine in sea-water is separated and concentrated by marine organisms.
2.6. Iodine in soil
The iodine content in different soil types oscillates in very large limits, from 0.05 to 80 ppm. Soil rich in clay, organic humus, peat is richer in iodine. Iodine is highly concentrated in forest soil, from 12 to 30 ppm, in black soil - 10.8 ppm. Soil of light mechanical composition in humid areas is usually poor in iodine.
2.7. Iodine in organisms
The iodine content in fresh-water vegetation is from 40 to 80 ppm, in marine multicellular vegetation of large dimension oscillates from 10 to 600 ppm of fresh weight (in red and brown algae usually higher than in green algae), in the ash of continental flora – 5.0 ppm. Some coral, fish, bryozoan species have the very high concentration level of iodine, such as in corals - 44-7790 ppm. The concentration of iodine in some fish species depends on the concentration level of this element in ephemera, food of fishes. The iodine content in some fish species is 0.5-1.0 ppm. The average iodine content in human body is about 0.2 ppm.
III. RELATION BETWEEN
ENVIRON-MENTAL GEOCHEMISTRY AND ENDEMIC GOITRE IN VIỆT
1.
Environmental geochemistry related to endemic goitre in
1.1. Iodine content and some microelements
in rocks of West Bắc Bộ
- Iodine content in rocks: The average content of iodine in different geological formations, such as syenite of the Pu Cam Cáp Complex and granite of the Pu Sa Ph́n Complex, is about 0.2 ppm, diorite and gabbrodiorite of the Điện Biên Complex – about 0.23 ppm; plagiogranite, granodiorite of the Cù Vân Complex – 0.21 ppm, granodiorite-granite – 0.16 ppm.
The average content of iodine in gneisses in West Bắc Bộ is about 0.16 ppm, among this, in gneiss of the Sông Hồng Group – 0.11-0.22 ppm, in sericite rocks of the Nậm Cô Formation - 0.18-0.23 ppm, in average: 0.20 ppm.
Effusives and carbonate rocks are distributed mainly in the Lai Châu - Thuận Châu - Sơn La - Mộc Châu and through Hoà B́nh to Ninh B́nh band and in some other formations, such as Cẩm Thuỷ - 0,25 ppm, Văn Chấn - 0,3 ppm, Bản Páp - 0,07-0,25 ppm. The iodine content in limestone of the Đồng Giao Formation is lowest, of about 0.05 ppm.
In terrigenous sediments,
conglome-rate, gravelstone and sandstone have lowest iodine content, usually
from 0.06 to 0.17 ppm, among this, sandstone and siltstone of the Yên Châu
Formation – 0.06 ppm, Pia Phương Formation – 0.04 ppm. Clay shale is
richer in iodine, usually of 0.17-0.70 ppm, among this, clay shale of the
In general, the distribution of iodine in rocks in West Bắc Bộ observes the common rule that is the content in sediments is richer than in magmatic rocks, in clay shale – richer than others.
- Content of other elements in rocks in West Bắc Bộ: Apart from iodine, some other elements are possible to be related to endemic goitre that attract the attention of many scientists, such as Se, Co, Cu, F, Mn, Zn, As, and Ca. The geochemical characteristics of these elements depend very much on geological structure features, petrographic composition and history of regional geology development.
+ Arsenic (As) content: The As content oscillates from 0.29 to 1.33 ppm, among this limestone of the Bản Páp Formation has rather high level in As, in average: 1.33 ppm, but still lower in comparing with Clarke content of As in the lithosphere – 1.7 ppm.
+ Calcium content (Ca): The Ca content oscillates from 0.07 to 28.9%, among this, gravelstone and sandstone of the Sông Bôi Formation has the lowest Ca content, ~ 0.07 ppm, in granite – 0.12%. The Ca content in limestone of the Bản Páp Formation is rather high, up to 28.9%.
1.2. Content
of iodine and some other elements in soil in West Bắc Bộ
- Iodine content in soil in
- Distribution of iodine in soil following high belts: Iodine is usually concentrated in soil in high belt more than in low belt (Table 3). This lets see that iodine is concentrated in organic humus. This phenomenon is still manifested in the correlation between iodine content in soil and in surface water. Investigation results let see that the iodine content in soil in different areas is very different, from high mountainous belt to low mountainous one and hilly areas (Table 4). In general, soil in low-mountain and hilly landscape has lower iodine content than in high-mountain landscape.
Table 4. Iodine
distribution in soil of high-mountain belts in
|
Belt height (m) |
Features
of natural factors |
Humus
content % |
Geological
formations |
|||||
|
Terrige-nous
|
Carbo-nate |
Volcano-
terr. with carbonate |
Metam |
Metam.
with carb. |
Magmatic
itrus. & effusives |
|||
|
>1700 |
Yellow-grey humic
soil, with feeble weathering, high humus quantity, soil mixed with many rock fragments
|
>
8 |
|
|
3.26 |
|
3.20 |
3.83 |
|
700-1700 |
Yellow-red soil,
with medium humus, feebly lateritized, mixed with rock clasts. |
3-8 |
|
2.58 |
2.86 |
4.08 |
|
3.91 |
|
<700 |
Yellow-red soil, with
strong weathering and washing, humus quantity from medium to low, strong
lateritization. |
<
3 |
2.51 |
2.73 |
2.68 |
2.67 |
2.88 |
2.72 |
Table 5. Landscape-geochemical
section on the Văn Chấn Formation in Tú Lệ area
|
No |
Investigated
areas |
Belt
height (m) |
Iodine
content, ppm |
|
1 |
Kim Nọi, Mù
Cang Chải District |
>
1700 |
3.29 |
|
2 |
Khau Pha, Mù Cang
Chải District |
- |
3.15 |
|
3 |
Ngă Ba Kim, Mù
Cang Chải Distr. |
700-1700 |
2.97 |
|
4 |
Liên Sơn,
Văn Chấn District |
<
700 |
2.90 |
|
5 |
Nậm Búng,
Văn Chấn District |
- |
2.83 |
|
6 |
Đông Khê, Văn Chấn District |
- |
2.97 |
|
7 |
Trần Phú,
Văn Chấn District |
- |
2.42 |
|
8 |
Lương
Thịnh, Văn Chấn District |
- |
2.54 |
|
9 |
Hưng Thịnh,
Trấn Yên District |
- |
3.07 |
|
10 |
Mường
Cơi, Phù Yên District |
- |
2.58 |
- Solubility of iodine in soil developed in different geological formations: For determining the solubility of iodine (and other elements in soil), the soil is soaked in water 2 times in 4 hours, then dissolved iodine (and other elements) quantity is determined. The solubility of iodine (and of other elements) is the ratio between element content in the water and its total content. The analytic results let see that the solubility of iodine (and other chemical elements) in soil depends on soil types and their forming conditions, it means the geochemical landscape conditions (Table 6).
Table 6.
Solubility of chemical elements in soil types in mountainous areas of
|
No |
Studied
areas |
Number
of sp. |
|
|||||||
|
1 |
Chư Va, Phong Thổ areas, yellow-grey soil
developed on syenite and akaline granite |
5 |
8 |
6 |
0.6 |
3 |
5 |
0.2 |
0.5 |
4 |
|
2 |
Ṭng Quá Ĺn,
Phong Thồ areas, yellow-brown soil on amphibolite gneiss of the Sông Chảy
Complex |
2 |
15 |
100 |
0.2 |
0.1 |
0.6 |
0.07 |
0.4 |
20 |
|
3 |
Phan Su Ĺn, Śn
Hồ areas, red soil on limestone of the Bản Páp Formation |
4 |
9 |
16 |
0.2 |
0.8 |
0.3 |
0.1 |
0.3 |
0.9 |
|
4 |
Na Ngám, Điện
Biên areas, yellow-red soil on gritty sandstone, clay shale of the Sông Bôi
Formation |
5 |
13 |
10 |
0.2 |
0.9 |
4 |
0.2 |
0.7 |
7.0 |
- Content of other elements in soil in West Bắc Bộ: Together with iodine, some other elements having significance in epidemiology of goitre have been also touched upon, such as Se, Co, Cu, F, Zn, Mn, As, and Ca.
+ Copper (Cu) content: The average content of Cu in soil and
weathering crust in West Bắc Bộ region is about 8.4 ppm, under the
normal bio-geochemical limit of cu in soil (15-60 ppm). The most part of soil
types contains Cu with the content of from 6.5 to 15.0 ppm. In the contrary,
some soil types, such as soil on limestone of the Bản Páp Formation in
Phan Su Ĺn area have highest Cu content, in average 46 ppm, and soil on
terrigenous sediments of the Sông Bôi Formation in Na Ngám area (Điện
+ Arsenic (As) content: In general, the As content in soil in West Bắc Bộ region lies within the permitted bio-geochemical limit of this element as from 1 to 10 ppm. In soil lying on limestone of the Đồng Giao Formation has the As average content of 5.87 pm (4.17-6.05 ppm), on limestone of the Bắc Sơn Formation – a little higher, of 11.05 ppm, and on mafic effusives interbedded with carbonate – about 7.1 ppm (3.8-13.75 ppm). The soil developed on metamorphic rocks of the Sông Chảy Formation has lowest As content, in average 2.60 ppm.
- Ratio of iodine content with some other elements in soil of West Bắc Bộ region: When the environment is deficient in iodine, at the same time, if its ratio with some other elements, such as Se, Co, Cu, Zn, F, Mn, As, Ca, … is unproportional, this will diminish the nutritious function of iodine for human body that makes the goitre more serious. In West Bắc Bộ, many areas have the ratio of iodine with other elements not guaranteeing the normal biological requirements, such as in Ṭng Quá Ĺn (Phong Thổ District) belonging to mountainous landscape of over 1100 m in altitude, the soil developed in gneiss, amphibolite, migmatite has the content of many elements in low level, such as: Se ~0.12 ppm, Mn ~132 ppm, F ~160 ppm, while the Zn content is rather high, reaching up to 359 ppm. Epidemiologic investigations let see that in this area the goitre ratio in the community is rather high, of over 50%.
The above study results let see that the characteristics of different geochemical ratio of iodine in the environment are worth to pay attention in the epidemiologic study on goitre, and consist of scientific basis of explaining the cause of the existence and development of goitre, as well as suggesting rational measures in the protection against iodine deficiency in different population areas.
1.3. Content
of iodine and of some other elements in water sources
- Iodine content in water sources: The average content of iodine in the most part of natural water sources in West Bắc Bộ is of about 0.9-23.0 µg/l, depending on the composition of geological formations lying in the basement of these sources. Water lying in magmatic intrusions has the average content of iodine of 1 µg/l, in volcano-terrigenous sediments interbedded with carbonate of the Pia Phương Formation in Vĩnh Kiên area, and in volcanogenous beds of Văn Chấn and Cẩm Thuỷ Formations – of from 8.0 to 17.0 µg/l, in metamorphic rocks of the Sin Quyền Formation distributed in Đại Sơn and Mậu Đông areas (Văn Yên District) – of about 0.9-13.0 µg/l.
- Migration coefficient (Kx) of iodine in water lying in geological formations: The migration coefficient of iodine expresses its moving ability: if it is high, the washing level and moving with water intensity of iodine is great, and in the contrary, if it is low, iodine compounds is stable and the ability of biological absorption is low. The migration coefficient of iodine depends on some factors, such as topography, petrographic composition of rocks and soil, and geochemical environment. The migration ability of iodine in water lying in different geological formations is also different. The study results have been letting see that, in sericite schist iodine has rather high migration coefficient Kx, of about 188, Kx of iodine in carbonate sediments – of about 26-40 (Table 6).
- Iodine/calcium (I/Ca) ratio in water: Analytic results let see that if water samples have the Ca content of from 50 to 100 mg/l the I/Ca ratio is usually smaller than 1; this usually is water sources lying in carbonate or interbedded with carbonate formations, such as Bản Páp, Cẩm Thuỷ, C̣ Ṇi, Đồng Giao, Văn Chấn, etc. Formations. In these water sources, I/Ca ratio is usually from 2 to 4, but water sources in other geological formations have this ratio of about 1. In areas having the ratio I/Ca of <1 usually have the rather high ratio of goitre in population. On the diagram of correlation between the I/Ca ratio and Ca content in water, Ca is concentrated in areas, which have been proposed to be named by us as “calcium geochemical field of goitre”. In these areas, nests of goitre exist with high ratio of goitre patients, usually of over 40% (Fig. 2).
- Content of some other elements in water sources in
Table 7. Migration
coefficient of iodine in water lying in geological formations in Sơn La
area
|
Geological
formations |
Studied
localities |
Migration
coefficient Kx |
||
|
>
100 |
100-50 |
<
50 |
||
|
Sericite schist |
Chiềng
Cang, Chiềng Pấc (Sông Mă) |
188 |
|
|
|
Volcano-terrigenous
sediments |
Đông Khùa,
Tú Nang (Yên Châu) Nậm Pù, Huổi Một (Sông Mă) |
120 |
72 |
|
|
Volcano-terrigenous
sediments interbedded with carbonate |
Bản Pàn, Tô Múa (Mộc Châu),
Bản Bí, Mường Cơi (Phù Yên) |
|
93 58 |
|
|
Carbonate
sediments |
Bản Sôi, Cộng Hoà, Mộc
Châu Tea collective farm (Mộc Châu) Bản Có, Chiềng Sinh
(Sơn La Town) Bản Dọi (Tân Lập) |
|
|
40 30 40 26 |
The Co content in water sources is usually from 0.5 to 1.7 µg/l, the most part of >1 µg/l. The Cu content in spring, stream and groundwater of shallow horizon sources in some areas of Thuận Châu District (Chiềng Ngàm, Chiềng Pắc, Chiềng Ơn), Sông Mă District (Huổi Một, Chiềng Cang), Mộc Châu District (Bản Pàn, Mộc Châu Townlet), Sơn La Town, Mường Cơi (Phù Yên District) is usually lower than 1 µg/l, in remaining part, usually of about 4.0-6.0 µg/l. Some water sources in Phong Thổ and Śn Hồ have low F content, of under 100 µg/l (60-90 µg/l).
- Iodine ratio with some micro-elements in water environment: Many scientists on the world have been emphasizing on the unproportionality between iodine and some other elements in the environment that is also a cause of the endemic goitre.
1.4.
Bio-geochemical characteristics of iodine and some micro-elements in vegetation
- Iodine content in
vegetation in Sơn La area: Vegetation samples in this area consist of some main food plants for human
and domestic animals, such as rice, maize and manioc. Analytic results have
been showing that the average content of iodine in rice (dry rice grains),
maize (dry corn kernels), and manioc (dried manioc slices) from studied areas
oscillates from 0.01 to 0.17 ppm, among this the average content in rice is
about 0.11 ppm (0.05-0.17 ppm), in corn kernels – 0.11 ppm (0.01-0.16 ppm), and
in manioc (manioc root) – 0.09 ppm (0.04-0.15 ppm).
We can see that iodine content in food samples
from West Bắc Bộ is not high, especially in manioc sample. The
disparity in iodine concentration in samples is not high, from this we can
understand that beside the environment features, the low iodine content in soil
and water is the main factor. The value of bio-geochemical ratio K in rice is
higher than in maize and manioc (0.044; 0.038 ; and 0.034 respectively),
but this disparity is not great.
The study results in West Bắc Bộ let see that in many areas exists this environment state: in Phan Su Ĺn, the water environment is poor in iodine, but rich in Co; in Mường Cơi area (Phù Yên District) and Sơn La Town, the water sources are poor in iodine, Cu and Mn; in Chiềng Ngàm, Chiềng Pắc, and Chiềng Ơn (Thuận Châu District) the iodine content is low together with very low Cu and Zn content; in Huổi Một and Chiềng Cang (Sông Mă District), water sources are poor in iodine and Zn, as for in Bản Pàn, Mộc Châu Townlet the iodine, Mn, and Zn content in water sources is all poor; in Phong Thổ and Śn Hồ, the iodine, F, and Zn content is all poor. The disproportional phenomenon of environment is still observed in many other areas in West Bắc Bộ. These are areas of goitre distribution with high ratio (in major part of over 40%).
- Bio-geochemical characteristics of some other microelements in
vegetation:
Figure 2. Correlation between iodine and calcium content in water (Đỗ Văn Ái, 1993).
+ Arsenic content (As): The average As content in rice, maize and manioc in the studied area oscillates in about 0.2-0.97 ppm, among this, the highest is in rice, about 0.97 ppm, then in maize ~0.76 ppm, and the lowest is in manioc, about 0.20 ppm. Vegetations on without carbonate sedimentary formations have also the highest As content in rice, of ~1.23 ppm; in maize it is lower than ~0.40 ppm (Table 7). Maize planted on carbonate formations has rather high As content, up to 1.50 ppm; as for in rice, it is only of 0.26 ppm.
+ Copper content (Cu): The average Cu content in rice, maize and manioc in the whole area is about 0.85-1.02 ppm, among this, maize and manioc – 1.02 ppm and 1.0 ppm respectively, in rice, it is lower than ~0.85 ppm. Rice planted on un-carbonate formations contains Cu content of about 0.92 ppm, as for in maize, it is a bit higher, of ~1.18 ppm. Rice and maize planted on carbonate formations have lower Cu content, in average 0.66 ppm and 0.70 ppm.
2.
Study on environmental geochemistry related to endemic goitre in
2.1. Brief outlines on endemic
goitre in the studied area
Thái B́nh has been selected
as studied area represented the Bắc Bộ Plain, because in this
province the goitre is rather widespread in the community, although the alluvia
of the
For selecting areas and points of epidemiologic investigation on the goitre, we have been collecting and processing epidemiologic materials on goitre from the whole province. The analysis of materials has been showing that 2 groups of epidemiologic data can be divided: group of high ratio of inhabitants suffering goitre (over 12% of population) and group of low ratio (5-12%). Based on this, the two Hưng Hà and Vũ Thư Districts have been selected for carrying the investigation in epidemiology and environmental geochemistry, and recognizing the relation between endemic goitre and factors of environment of forming and developing iodine deficiency troubles in this area.
The results of investigation in 1473 pupils in the Vũ Thư District and 1755 in the Hưng Hà District have been showing that the goitre ratio in Vũ Thư is of 14.5%, Hưng Hà – 16.5%; the commune having lowest ratio of goitre in children belongs to the Vũ Thư District – of 5%, while in Hưng Hà – of 6.5% (Table 10).
A worth to pay attention epidemiologic characteristic is that the goitre ratio in children in the two commune groups increases in accordance to the age. In the group of 7 years exists the goitre of the Ia degree, but in the group of 8-12 years occurs the goitre of the Ib degree, and this degree increases in the group of 13-15 years in all these two commune group.
Table 8. Situation of goitre in some localities
(according to data from Centre of Preventive Medicine of Thái B́nh Province)
|
No. |
Group
of communes having goitre >12% |
Group
of communes having goitre of 5-12% |
||
|
Commune
name |
Ratio
(%) |
Commune
name |
Ratio
(%) |
|
|
1 |
Vũ
Thư District |
13.4 |
|
6.5 |
|
1.1 |
Bách Thuận Song Lăng Vũ Vân Dũng Nghĩa Hồng Lư |
12.6 14.0 13.0 13.0 14.5 |
Đông
Thanh Song An Vũ Hội Vũ Ninh Tân Lập |
7.0 7.0 5.0 7.0 6.6 |
|
1.2 |
||||
|
1.3 |
||||
|
1.4 |
||||
|
1.5 |
||||
|
2 |
Hưng
Hà District |
13.8 |
|
6.8 |
|
2.1 |
Điệp
Nông Đông Đô B́nh Lăng Độc lập Phú Sơn |
12.5 13.0 16.5 14.0 13.0 |
Minh Tân Minh Khai Hồng An Thái Hưng Phúc Khánh |
7.0 7.0 7.0 6.8 6.5 |
|
2.2 |
||||
|
2.3 |
||||
|
2.4 |
||||
|
2.5 |
||||
|
Average of commune group 1 |
13.6 |
Average of commune group 2 |
6.7 |
|
If living in the same geochemical environment, the
ratio of deficiency in iodine is not different between age groups. But, in the
time of puberty the goitre ratio is higher, and the wen is greater. This is
proved by that in the group of 7 years there is only the goitre of Ia degree,
while goitre of Ib degree occurs mainly in the group of 13-15 years.
The results of iodine urine analysis in the
Central Hospital of Incretology and Bạch Mai Hospital have been showing
that in the commune group I the urine iodine content in children not suffering
goitre is of 11.9 µg / 100 ml, in comparison with children suffering goitre –
17.2 µg / 100 ml. At the same time, in communes of the group 2 the urine iodine
content in goitre patients is 15.7 µg / 100 ml, equivalent to that in children
not suffering goitre (15.6 µg / 100 ml). This lets see that apart from iodine
deficiency the goitre cause in children of the community still is originated
from other factors, which play the role of goitrogenous matters existing in the
environment.
So, we can see that communes being of high ratio
of goitre patients have clear difference in urine iodine content between
children suffering goitre and those not suffering it; as for areas having low
ratio of goitre patients, the influence of iodine deficiency to goitre ratio is
not clear.
The results of epidemiologic investigation let see
that the ratio of iodine deficiency in children in the commune group 1 is
28.4%, while in the commune group 2 is a bit higher, ~31.1%.
Children in these commune groups are deficient in iodine in low level (commune
group 1 of 22.0%, commune group 2 of 21.9%), the medium level is rarer (commune
group 1 - 6.4%, commune group 2 – ~9.2%), the high level is not met.
In school children suffering goitre the illness is
mainly in the Ia, Ib degree, the goitre of II degree is not met. This lets see
that the goitre state in the studied area is in low level. It conforms with the
analytic results of iodine content in urine. Based in the classification of
iodine deficient areas of WHO/CCIDD (1997) the studied area belongs to the low
level of iodine deficiency.
2.2. Characteristics of environmental geochemistry related to endemic
goitre in the sudied area
- Characteristics of geochemical
factors and environment
+ pH index
of water: The pH index of water sources, such as groundwater (in wells),
surface water (in pounds and lakes), rainy water in cisterns of apartments is
mainly of alkaline type. The average value of pH of wells, the widespread water
source of inhabitants is 7.27 (oscillating in 6.8-7.65). The pH index of wells
of the commune group 1 is in average 7.46 (7.20-7.65), commune group 2 - 7.08
(6.08-7.30).
+ Bicarbonate
content (HCO3-): The results of investigation on environmental
state of the studied area let see that water sources, such as well water,
groundwater, water in pounds, lakes and cisterns containing rainy water, have
high content of HCO3-, the most part is of high
alkalinity.
The average content of HCO3-
in digged wells is 520.6 mg/l (433.1-597.8 mg/l), among this the HCO3-
content in the commune group 2 has the average value of about 530.7 mg/l
(497.2-579.5 mg/l), a bit higher than that in the water from digged wells in
the commune group 1 - 513.9 mg/l (433.1-597.5 mg/l). Water from drilled wells
has the HCO3- content lower than that from digged wells,
in average of 267.2 mg/l, among this that in the commune group 1 - 311.1 mg/l
(48.8-658.8 mg/l); in Vân Đông, Phú Sơn (Hưng Hà District) there
is sample having only 91.5 mg/l.
+ Chlorine
content (Cl): Many studied areas consist of salted or aluminous soil. The
average Cl content in digged wells is about 234.7 mg/l (56.8-539.6 mg/l), among
this water from digged wells of the commune group 2 has the average value of
331.0 mg/l (234.3-539.6 mg/l), while in the commune group 1 - lower, about
147.3 mg/l (56.8-326.6 mg/l).
+ Sulfate content (SO42):
The evaluation on SO42 content in water
sources of the studied area lets see that the SO42-
average content in water of digged wells is about 6.4 mg/l, among this water
from digged wells in the commune group 2 is 8.75 mg/l, and in the commune group
1 - 4.8 mg/l.
- Content of some
poly-elements and microelements in the Thái B́nh area:
+ Calcium content (Ca): The average Ca content in
soil of the studied area is 166.96 ppm (26.8-624.62 ppm), among this the Ca
content in soil of the commune group 2 is 183.83 ppm (48.50-377.30 ppm) and of the
commune group 1 is 145.48 ppm (70.05-213.85 ppm). In general, there is not
great diffence in the distribution of calcium in soil of different areas.
+ Copper
content (Cu): The average content of Cu in soil of the studied areas is
36.17 ppm (23.24-62.30 ppm), among this Cu content in soil of the commune group
2 is 35.28 ppm (27.02-40.79 ppm) and of the commune group 1 is 37.29 ppm
(34.13-43.20 ppm). So, we can see that cu is distributed rather equally in
different areas with the content not lower than Clarke of Cu in soil in the
world (20 ppm). With this content, organisms have the ability of regulate
oneself normal physiological functions in their living activities and
development.
- Iodine (I) content in
environment of the Thái B́nh Province: For studying on the geochemical environment
aiming to evaluate its influence to the formation and existence of endemic goitre in the studied
areas we have been carrying out the investigation on geochemical
characteristics of iodine and of some other elements in the soil, water, and
cultivated plants of these areas. The results have been showing that the
average of iodine in soil is 5.10 ppm (4.25-7.50 ppm), among this about 65% of
samples have the iodine content of >5 ppm and 35% of samples have the iodine
content of <5 ppm. These results have been showing that the environment in
these areas has not great iodine deficiency (Table 11).
The iodine distribution is different in areas. The
iodine content in soil of commune group 2 has the average value of 5.47 ppm
(4.25-7.50 ppm), among this 65% of samples have the iodine level of over 5 ppm,
and 35% of samples – of under 5 ppm. The
iodine content in soil of commune group 1 has the average value lower than that
of the group 2 – 4.63 ppm (4.25-5.75 ppm), among this about 90% of samples have
the iodine level of <5.0 ppm, and 10% have the content of higher level. This
clearly expresses the correlation between iodine content in the environment and
goitre existing in the community of these areas.
The iodine content in water sources is also
different: in surface water – 0.23 µg/l (0.10-0.31 µg/l). The difference
between iodine content of surface water in pounds and lakes and that of
groundwater in digged wells of the studied area is 0.27 µg/l (0.11-0.48 µg/l),
among this water from digged wells of the commune group 2 is 0.26 µg/l
(0.11-0.32 µg/l), and in the commune group 1 is 0.28 µg/l (0.12-0.48 µg/l).
The average content of iodine in rice is 11.69 ppm
(6.8-15 ppm). We have been knowing that the average content of iodine in soil
of the commune group 1 is lower than that of the commune group 2, but the
iodine content in rice produced from these localities has the contrary value.
This phenomenon expresses that the ability of biological absorption of iodine
of rice plant cultivated in land of the commune group 2 is higher than that of
the commune group 1.
- Evaluation of
state of geochemical environment related to endemic goitre in Thái
B́nh Province:
+ The study on geographic distribution of endemic
goitre in the studied area lets see that nests of goitre of high ratio are
usually situated along the Red River banks (occupying up to 70% of goitre
nests) and along the Tiền Giang River (occupying about 30%). Goitre nests
of low level are usually distributed farer from the Red River and extend in the
NW-SE direction.
+ Results of investigation on geochemical
environment associated with epidemiologic investigation on goitre in some areas
of the Thái B́nh Province let see that the average content of iodine in soil of
the studied area is >5 ppm. In comparison with the iodine bio-geochemical
threshold of soil stipulated by world scientists as 5-40 ppm for soil
sufficient in iodine, the soil in Thái B́nh Province is not deficient (or very
slightly deficient) in iodine.
The comparison of pollution level in organic
matters and nitrogene in water sources used in living activities of the local
community in the studied area with permitted standards lets see that it is from
hard to very hard, especially in the Quang Trung (Vũ Thư District),
Vân Đông, Phú Sơn (Hưng Hà District) Communes. Many scientists
have been determining the existing form of iodine in the nature and the stable
integration of iodine with organic matters, its difficult in dissolution and
displacement form, influencing the ability of biological absorption of iodine
of organisms.
+ The study on composition and character of water
sources in the studied area lets see that the most part of surface water, water
in shallow horizon, water in deep horizon, and rainy water in cisterns belong
to from neutral to feebly alkaline type. The HCO3-
content of water sources in the area has all the high value. Just the high
alkalinity of bicarbonate causes the water hardness and forms stable compounds,
among them, iodine compounds.
+ Many areas have rather high content of Cl and
some other elements, such as Ca, Mg… . With the high content of Ca and Mg, yhe
water source can be attributed to the medium hard water. Comparing to the
standard of WHO on the limit of Cl concentration in living water sources of 250
mg/l, many water sources from digged wells in this area have all high Ca
content. Ca2+ and Mg2+ cations in water originated from
chlorite or nitrite is easier to be dissolved than other replaced ions.
+ The Fe and Mn content in the surface and shallow
horizon waters is in rather high level. With this content water in many areas
does not conform to the permitted standard for living water.
In this area, a worth to pay attention
characteristic is that the cultivating soil has high pH and oxidizing factors (Fe3+,
Mn3+, Mn4+); I- is transformed into IO3-.
Therefore, the rich in Fe3+, Mn4+ and other oxidizers
environmental conditions will increase the loss of move of iodine in the
environment into the air through chemical reactions, causing the fact that the
total iodine quantity in soil is high, but the iodine content in water sources,
such as surface water (in pounds and lakes) and groundwater (in digged and
drilled wells), is low.
+ Apart from factors of deficiency in nutritious
iodine causing goitre, long ago scientists have been emphasizing the role of
some microelements which influence the ability of synthesizing iodine matter of
the thyroid when they are superfluous or insufficient. It is worth to pay
attention that the environment of many areas has the rather high Mn content
level in soil in comparing with the Clarke index. The Cu and Zn content in soil
is rather abundant, and higher than Clarke index of Cu and Zn in the
world ; as for in water sources, the content level of these elements is
lower than the permitted threshold.
3.
Study on the environmental geochemistry related to goitre in the Cát Bà Island
area,
3.1.
Epidemiologic state of goitre in the Cát Bà Island area
In the natural side, the Cát Bà Island is an area
of limestone mountain with 3 main soil groups as follows:
- Soil weathered from limestone accumulated in
rock cracks and in the piedmont. It is weathered from light grey, brown-grey
limestone of the Cát Bà Formation mixed with many limestone fragments, but in
loose state. Soil weathered from limestone of the Quang Hanh Formation is of
red-yellow colour with higher clay quantity.
- Soil weathered on Devonian terrigenous
formation, including sandstone, siltstone, and claystone, distributed in a
narroe band in Xuân Đám area, covering limestone soil from the Cát Bà and
Quang Hanh Formations. The soil and weathering crust lying upon these
formations are of red-yellow colour, with a thickness of over 10 m.
- Apart from these two soil groups, there still is
the soil group accumulated in intermontane valleys and open valleys situated
near the sea-shore with small area, that were transformed into rice fields
cultivated with different cereals. Some valleys situated close to the sea-shore
have the salt-polluted groundwater.
The living water in the Cát Bà Island is very
limited, mainly is fissure water flowing from limestone formations. In valleys,
water is usually salt-polluted, especially in the dry season. Island
inhabitants usually use cisterns for containing rainy water, and when it becomes
deficient, it supplemented by water of other sources for living aims.
Based on characteristics of environment,
geochemistry, population distribution, and state of endemic goitre in the
community, the studied area has been investigated and determined related
factors to epidemiologic characteristics of goitre.
On the theoritic side, a natural area is not
deficient in iodine, but according to survey data in 1992-1994 years of the
Centre of Medicine and Marine Environment the goitre ratio in the community of
this area reaches up to 25%. So, where is the main cause ? Because of the
iodine deficient living environment, or of other factors ? The study on
this problem will contribute in the clarification of the forming factor of
endemic goitre nests in islands and coastal areas, as well as in other areas on
the mainland, especially, limestone areas which occupy up to 20% of the
territory of the country.
The investigation on iodine deficiency in the
community has been carried out in the school age of 7-15 years, that is,
according to the advice of WHO-ICCIDD and UNICEF the age giving most reliable
data in comparing to other age groups. The investigation results in the 2 Xuân
Đám (in island centre) and Trân Châu (near the shore) communes has been
showing that the common goitre ratio in these 2 communes is 24.3%, among this
in the Trân Châu Commune is 22.4%, and in the Xuân Đám one - 25.8%.
Comparing to WHO standards, the studied area in the Cát Bà Island has been
attributed to the medium level of iodine-deficient areas (20-29%). These
results show that there is not difference in goitre ratio between these 2
communes (P >0.05).
Table 9. Ratio of houses using iodine salt in the
Cát Bà Island
|
Object |
Trân
Châu Commune |
Xuân
Đám Commune |
Total |
|||
|
House
number |
% |
House
number |
% |
House
number |
% |
|
|
Using of iodine
salt |
77 |
97.4 |
108 |
93.9 |
185 |
95.4 |
|
Non using iodine
salt |
2 |
2.6 |
7 |
6.1 |
9 |
4.6 |
|
Total |
79 |
100 |
115 |
100 |
194 |
100 |
|
|
|
|
|
|
|
|
The results of determining the urine iodine content in children of the 2 Trân Châu and Xuân Đám Communes let see that the urine iodine content in children suffering goitre is clearly lower, with 8.833.97 µg/dl in comparison with normal children. Comparing with WHO standards this urine iodine level is attributed to area of low level of deficiency in iodine (5.0-9.9 µg/dl). The study still lets know that only 36.9% of children in the 2 studied communes have enough iodine content, and up to 2/3 of children have the urine iodine level of under 10 µg/dl. So, the most part of children are in the state of light deficiency in iodine. But, it is worth to pay attention that the goitre ratio does not correspond to the urine iodine content, maybe due to following causes:
- During recent years, almost all families in the studied area have been using iodine salt (up to 95%), thanks to this the urine iodine content somewhat increases, but the goitre ratio still does not decrease (Table 9). The problem is in the 2 Trân Châu and Xuân Đám Communes there truly is the deficiency in iodine or not, or there exists another factor causing the goitre?
In the epidemiologic
investigation on goitre in the Cát Bà Island, for the first time the ultrasonic
technique has been used by specialists of the
Table 10. Thyroid
volume of goitre suffering and not suffering children in the studied area
|
Object |
n |
x ± SD (ml) |
|
Suffering goitre |
27 |
14.21
± 3.15 |
|
Not suffering goitre |
84 |
7.25
± 3.03 |
|
In general (suffering and not suffering) |
111 |
8.40
± 3.97 |
|
|
|
|
For studying the function activity of the thyroid, the determination of the hormone T3, T4, FT4, and TSH has been carried out. The results have been showing that children suffering goitre in the 2 studied communes have the increasing concentration of T3 and TSH, and decrease of FT4 in comparing with children not suffering goitre (P <0.01). For the 2 groups of suffering and not suffering goitre children the concentration of T3 and TSH increases, and FT4 decreases also in comparing with normal children of the same age living in Hà Nội.
The T3 concentration in children suffering goitre in the 2 Xuân Đám and Trân Châu Communes increases higher in comparing to children not suffering goitre, and the total T3 concentration of children suffering and not suffering in the two above communes is similar, of 2.55 ± 0.41 nmol/l (among this, Trân Châu of 2.53 ± 0.39 nmol/l and Xuân Đám – 2.56 ± 0.48 nmol/l) (Table 11).
Similar to those in the Trân Châu Commune, children in the Xuân Đám one suffering goitre have lower FT4 concentration in comparing to those not suffering. The FT4 concentration in Trân Châu children has the tendency to be lower than that in Xuân Đám children (Table 12).
Table 11. Total
T3 concentration in blood of children in the studied areas
|
Objects |
Trân
Châu Commune (x±SD nmol/l) |
Xuân
Đám Commune (x±SD nmol/l) |
|
Children
suffering goitre |
2.99
± 0.31 (n = 11) |
2.98
± 0.16 (n = 16) |
|
Children not
suffering goitre |
2.42
± 0.7 (n = 38) |
2.48
± 0.47 (n = 46) |
|
Common state |
2.53
± 0.39 (n = 49) |
2.56
± 0.48 (n = 62) |
Table 12. FT4
concentration (pmol/l) in blood of children suffering and not suffering goitre
in the studied area
|
Objects |
Trân Châu Commune (X±SD) |
Xuân
Đám Commune (X±SD) |
|
Suffering goitre |
10.37
± 0.82 (n = 11) |
10.74
± 0.97 (n = 16) |
|
Not suffering
goitre |
14.65
± 2.75 (n = 38) |
14.82
± 2.02 (n = 46) |
|
Common state |
13.05
± 3.01 (n = 49) |
14.10
± 2.44 (n = 62) |
Table 13. TSH
concentration (mU/l) in blood of children suffering and not suffering goitre in
the studied area
|
Objects |
Trân Châu Commune (X±SD) |
Xuân
Đám Commune (X±SD) |
|
Suffering goitre |
3,77
± 0.72 (n = 11) |
3.81
± 0.78 (n = 16) |
|
Not suffering
goitre |
2.57
± 0.64 (n = 38) |
2.52
± 0.77 (n = 46) |
|
Common state |
2.75
± 0.77 (n = 49) |
2.72
± 0.90 (n = 62) |
The TSH concentration in children suffering goitre in the Trân Châu and Xuân Đám Communes is also higher in comparing to children not suffering goitre.
The comparison of the TSH concentration in children of the two Trân Châu and Xuân Đám Communes have been letting see that there is not difference in TSH concentration in them.
The change in T3, FT4 (or T4), and TSH concentration in children of the two studied communes is expressed similarly, while in children living in typical areas deficient in iodine the T4 (or FT4) decreases, T3 and TSH increases. The above change has been proving that there is deficient state in the body. Besides, the above change is also the phenomenon of adaptation of the body when the iodine supply is insufficient for the synthesis process.
The analytic results have been letting see that iodine in urine of children suffering goitre in the two Trân Châu and Xuân Đám Communes is lower than that in children not suffuring goitre.
Table 14. Iodine
content in urine of children suffering and not suffering goitre in the studied
area
|
Objects |
Trân Châu Commune (X ± SD
µg/l) |
Xuân Đám Commune (X ± SD
µg/l) |
|
Suffering goitre |
3.62
± 1.35 (n = 11) |
4.18
± 1.75 (n = 16) |
|
Not suffering
goitre |
9.26
± 3.61 (n = 38) |
9.81
± 3.90 (n = 46) |
|
Common state |
8.45
± 3.88 (n = 49) |
9.20
± 4.20 (n = 62) |
The above data have been showing that there is not great difference in urine iodine between studied communes. In these areas there is only 36.4% of children having the urine iodine level of ≥10 µg/dl, belonging to the sufficient in iodine kind (according to the classification of WHO), in the remaining part, there is up to 38.7% having the slight deficiency level (5.0-9.9 µg/dl), 20.7% – medium level (2.0-4.9 µg/dl), and about 1.8% – heavy level (< 2 µg/dl). So, the main part of children in the studied area is of slightly deficient in iodine (Table 14).
The epidemiologic investigation has been letting see that during a long time of from 1992 to 2005, although over 95% of families frequently use iodine salt, but the goitre ratio still stands in high level, of ~24.3% of population, nearly equivalent to the Gia Lâm area, Hà Nội City (26.1%), and Cửu Long Plain (18-24%). However, the goitre degree in children in Cát Bà Island is mainly in the I degree (including Ia and Ib), the II degree occupies low ratio and,especially, there is not the III degree.
So, the occurrence and existence of endemic goitre in the Cát Bà Island, apart from nutritious iodine content there still are other causes influencing the absorbing ability of biological iodine of the body. The geochemical study has been carried out aiming to contribute in the answer to the above question.
3.3.
Environmental geochemistry related to endemic goitre of the Cát Bà Island area
* Characteristics of
environmental factors:
+ pH index in the environment: Results of analysis of soil types in the Cát Bà Island have been letting see that the pH degree of soil depends mainly on the material composition of parent rocks. The average pH degree of soil type formed on carbonate formations is 7.4% (6.03-8.03%); this soil has strong alkalinity. The soil type formed in the antemontane valleys and near-shore open valleys has also the pH index from neutral to strongly alkaline, in average 7.15, in some samples up to 8.31. As for the soil type formed on terrigenous formations with low pH, the average is only 5.10 (4.60-5.45) belonging to the acid type.
+ Bicarbonate content (
): all in high level, in spring and
stream water reaching 252.13 mµg/l (244.0-280.6 mg/l), in groundwater from
wells – 230.69 mg/l (61.0-305.0 mg/l), while in cisterns containing rainy water
of houses – 79.30 mg/l, hundred times higher than bicarbonate quantity in rainy
water on the world (0.12 mg/l). If comparing to the content of continental streams emptying into
ocean on the world being 47.6 mg/l, natural water sources in the Cát Bà Island
have the content of very high level.
The medium content of matter existing in natural water sources in the Cát Bà Island is about 6.8-11.2 mg/l, among this groundwater of shallow horizon in digged wells, water in fissures and streams have the average content of 8.66-8.79 mg/l. As for water in cisterns containing rainy water in houses, it contains organic matter of about 7.28 mg/l (6.8-8.0 mg/l).
+ Chlorine and (Cl) sulfate content (
): Analytic data let see that the Cl content in continental streams emptying into
oceans is respectively 6.4 mg/l and 11.9 mg/l, while in sea water –
respectively 19000 mg/l and 2650 mg/l. Results of analysis of natural water
sources in the Cát Bà Island have been letting see that the average content of
Cl and in spring and stream water is respectively
76.28 mg/l and 11.91 mg/l, in groundwater – 256.7 mg/l and 47.29 mg/l. Many
wells in valleys and piedmonts are salt contaminated, especially in dry season.
Comparing the Cl (7.8 mg/l) and (11.2 mg/l) contents with those of riverine
water on the world, those in natural water sources in the Cát Bà Island are in
rather high level.
+ Content of iodine and some other elements in the environment:
- Calcium (Ca) content: The average content of Ca in soil of the Cát Bà Island is 963.52 ppm (2.03-11318.38 ppm), among this soil accumulated between limestone is very high, in average 1825.75 ppm; sediments in valleys have the Ca average content of about 126.02 ppm (16.21-231.66 ppm), while red-yellow soil formed upon siltstone, sandstone, and claystone has the very low Ca content, in average only 7.41 (2.03-15.49 ppm). Such geochemical characteristics of calcium in the Cát Bà Island, the environment is easy to form sulfate or chlorine with calcium and magnesium for forming compounds of iodine with the everlasting hardness (existing after boiling).
- Copper content (Cu): The bio-geochemical limit of the lower threshold of Cu in soil is ≤6-15 ppm and that of the upper threshold, possible of causing different endemic illnesses, is >60 ppm. Results of investigation on soil types in the Cát Bà Island have been letting see that the average content of Cu in soil types is 38.20 ppm, among this soil formed upon limestone has rather high Cu content, reaching up to 45.15 ppm; in some samples, such as ĐCB-14 is 60.64 ppm, ĐCB 14-1 – 76.12 ppm, ĐCB-17 – 80.72 ppm, and ĐCB-20 – 159.33 ppm. Comparing to the bio-geochemical threshold, this content is high, surpassing the permitted limit, and possible of causing different endemic illnesses to human and organisms. In general, the Cu content in environment of the Cát Bà Island is not low, even there are areas having manifestation of surplus.
- Selenium content (Se): The average content of Se in soil types in
the Cát Bà Island is 0.82 ppm, higher than Clarke in soil of the world – 0.01
ppm, in soil of
- Iodine content (I): The Clarke value of iodine in soil is 5 ppm, in oceanic water – 50 µg/l, and in sea water – 60 µg/l. The average iodine content in soil types of the Cát Bà Island is about 3.49 ppm, among this that in ferralite soil formed upon terrigenous formations is in average 3.71 ppm (2.28-4.83 ppm), in soil formed upon sediments in valleys – 3.56 ppm (1.05-5.66 ppm). Soil formed upon carbonate formations has the average iodine content of 3.17 ppm (1.89-5.49 ppm). It is worth to pay attention that the red-yellow soil formed upon carbonate of the Quang Hanh Formation is richer in iodine, as in ĐCB-14, ĐCB-01, ĐCB-02, ĐCB-31… samples, having the content of 4.83-5.66 ppm. This iodine content in soil has been evaluated as not low.
The iodine content in water sources in the Cát Bà Island is also different one from another. Groundwater in shallow horizon has usually higher iodine content than groundwater of deep horizon, such as water of shallow horizon in digged wells in Phú Cường, Bến Villages (Trân Châu Commune), 4th Village (Xuân Đám Commune) has the iodine content up to 12.21 µg/l (8.32-28.07 µg/l), while in drilled wells giving water of deep horizon the water usually has lower iodine content, such as wells in the 3rd Village (Xuân Đám Commune), but the iodine content in water reaches also up to 4.28 µg/l.
The iodine content in rice, maize and manioc cultivated in localities is different. That in rice has the average level of 0.49 ppm (0.048-1.54 ppm), in maize – 0.77 ppm (0.033-1.48 ppm), in manioc planted in hill slopes – 0.55 ppm (0.22-1.74 ppm). This lets see that the iodine content in maize is higher than in manioc and rice, and that in rice is lowest.
3.4.
Characteristics of geochemical environment related to endemic goitre in the Cát
Bà Island
The results of epidemiologic investigation on goitre let see that the goitre ratio in children in the age of 7-15 years in the Cát Bà Island, Hải Pḥng City is in average 24,3%, that has been attibuted to the medium deficiency in iodine level, but the urine iodine content is in the lightly insufficient in iodine content level (8.83 µg/l in comparing with 5.0-9.9 µg/l of WHO). The goitre level is mainly in the I level (14.4%), the II level is smaller – 9.9%, while the III level does not occur. The volume of thyroid of children suffering goitre in this area reaches in average 13.44-14.82 ml, and the TF4 concentration in blood of children suffering goitre is in average 10.37-10.74 mol/l.
The Program of Protection against iodine deficiency illnesses was carried out in the Cát Bà Island since 1992, and there are up to 95.4% of houses use regularly iodine salt. This has the ability of increasing slightly the urine iodine content, but the goitre ratio is still not ameliorated. So, the problem is in the Cát Bà Island, there is only the deficiency in iodine or there still are other factors causing goitre? It needs the investment aiming to deeply understand the geochemical environment and other related factors.
The pH degree in the soil and water environment in the Cát Bà Island is in the from neutral to strongly alkaline level. The content of organic matters in the soil environment and water sources is all high, in average 6.8-11.2 mg/l. The nitrogen content in water sources is higher than permitted standards.
The Cl- and content in water sources is all high.
Groundwater in valleys is usually salted, especially in the dry season. The Mg
and Fe content in soil and water sources is higher than normal level.
Just the geographic position of this island that is a limestone one situated offshore has been causing factors of geochemical environment influencing the possibility of concentrating, the existing form and the movement of iodine and some other elements.
The average content of iodine in soil types of the Cát Bà is about 3.56 ppm, among which, soil in the Trân Châu Commune is up to 4.87 ppm. The iodine content in water sources is also not of low level: in fissure and stream water sources it is in average 4.90 µg/l; as for groundwater in digged wells, it is in average of 11.4 µg/l, some samples – of up to 28.09 µg/l. The average content of iodine in water of cisterns of houses is 3.6 µg/l, some samples – 5.06 µg/l.
Compring with study results
of foreign countries, the suchlike iodine content in water of the Cát Bà Island
cannot cause the endemic goitre. In fact, this
Apart from iodine geochemistry, the study on environmental geochemistry together with epidemiologic investigation on goitre needs to be combined with the investigation on some factors obstructing the ability of synthesizing iodine-bearing hormones of the thyroid.
Many studies on geochemical environ-ment related to endemic goitre have been letting see that together with the state of iodine deficiency or superfluousness, the existing form of iodine, or deficiency of some chemical elements in the environment, such as Mn, Cu, Co, Mo, Zn, Se, F,… influences to the ability of synthesizing iodine of the thyroid. These elements consist of important biological ones, and during the process of nutrition if there is not the proportion between them and iodine, this can makes the goitre more severe.
The study results have been letting see that the content of Mn, Cu and Mo is in the higher level than their Clarke in soil, in which some areas have the level surpassing the permitted content limit of causing endemic illnesses. Among these elements, Mo in water of many places has the normal content. It is worth to pay attention that F content in soil and water environments is very low, expressing its high deficiency. As for Zn and Co in the ecological environment of the Cát Bà Island are of normal content level.
IV. ZONING OF
ENVIRONMENTAL GEOCHEMISTRY RELATED TO ENDEMIC GOITRE IN VIỆT
Studying on factors of environmental geochemistry related to iodine deficiency illnesses in different ecological areas, we can preliminarily determine factors causing goitre and propose rational measures aiming to raise the effect of protection against iodine deficiency illnesses for each landscape of all the country.
- In the landscape formed upon carbonate, terrigenous interbedded with carbonate, volcano-terrigenous interbed-ded with carbonate formations, the environment has usually the pH degree from neutral to feebly alkaline, calcium-rich form, with the most part belonging to the calcium bicarbonate water having iodine and some other elements not low; they exist in the form of stable compounds, difficult to move with low biological absorption coefficient. In this landscape group, usually exist nests of goitre with high ratio and the urine iodine index usually of <3 µg/dl. The measures of water processing (water softening) will increase the ability of biological absorption of iodine and other elements, and increase the effect of the program of supplement of iodine in inhabitant community.
- The high mountain landscape, having soil and water rich in organic matters, is situated far from the sea, where the rainy water contains very low iodine content. In this environment, iodine exists in compound form with stable organic matters, difficult to be dissolved and to move in the environment. In this landscape group, the socio-economic life of inhabitants has many difficulties, leading to high ratio of goitre patients. In this area, the iodine supplementation should be associated synchronously with projects of clean water provision for raising the effect of iodine biological absorption of the body.
- In the landscape developed upon terrigenous sediments, magmatic intrusive and effusive rocks, and metamorphic ones belonging to the medium mountain and hill landscape having the environment not obstructing the iodine biological absorption, the supplementation with iodine needs to examine its existence in the proportion of bio-geochemical side with other biological elements in the environment together with the raise of socio-economic level of the community.
- The landscape group of deltaic plains, coastal plains, islands, mines and mineralization occurrences, concentrated residential and industrial quarters, urban areas and concentrated agricultural production areas, … different geochemical obstructions were formed caused by natural and man-made processes. These are important socio-economic areas of the country. The understanding and determination of geochemical obstructions to iodine biological absorption of the body form the basis of proposing rational protection measures against iodine deficiency illnesses in the community living on above geochemical landscapes.
V.
CONCLUSIONS
The endemic goitre is the rather widespread illness on the world. In our country, it exists and develops in inhabitant communities living from mountain to plain and island areas. Some localities having favourable socio-economic conditions have been carrying out the program of protection against iodine deficiency illnesses during many recent years, but the goitre still exists in the light to medium level. The cause of formation and development of this illness is in the ecological environment which is poor in nutritious iodine, as well as contains geochemical factors obstructing the ability of iodine biological absorption of the body.
It is necessary to carry out the study on environmental geochemical factors together with epidemiologic investigation on illnesses caused by iodine deficiency in different ecological areas aming to determine goitrogenous factors and propose rational measures for raising the effect of protection against disorders caused by iodine deficiency in inhabitant community in different landscapes of the country.
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