Arsenic Contamination occurs over 42 countries worldwide, people who are highly exposed to arsenic are likely to suffer from diseases like hypertensions, cancers in lungs, liver and black foot disease. Black foot disease is a type of skin lension and was found in Taiwan in 1968. The first two sites of discoveries of arsenic contamination in Taiwan were in Chinanan Plain and Southern Choushui alluvial fan. The Chianan Plain has a higher concentration then Southern Choushui area from 2005 to 2006 reports. In Mainland China, the highest arsenic concentration in Inner Mongolia reached 1.86mg/l, where the most contaminated area in the Mainland China. Arsenic removal strategies like coagulation, ion exchange and adsorption are used to remove arsenic from the water. In recent years, a new type of absorbent (Ce-Fe) is used to remove the arsenic in Inner Mongolia. However, the outcomes are not as effective as expected in the lab experiment, therefore further studies is required.
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Groundwater accounts a very minor part in the whole hydrological cycle. However, it is extensively used for drinking water supplies in most of the developing countries.
Around the world, there are 42 countries have been discovered the ground water have been contaminated with arsenic. Arsenic is both toxic to animals and the environment. Most of the arsenic is commercially produced in mining activities, when the reduction of arsenic trioxide is carried out. The IARC has classified inorganic arsenicals as Group I carcinogens based on the human epidemiological data. (J. C.Ng 2003)
The first discovery of chronic arsenism was in Taiwan in 1968, for the mainland China; was first reported in 1980s; till now, areas like Inner Mongolia, Shang Xi, Ning Xia, Jilin, Qinghai and countries like Vietnam, India and Bangladesh are still suffer from chronic arsenism problems. Figure.1 shows the areas in China and Taiwan where arsenicosis have been found. The red area indicates the new area investigated in 2004.
Figure 1. Epidemic Arsenicosis in China and Taiwan (G Sun 2003)
The aim for this report is to provide an overview on the chronic arsenism in Taiwan and remediation plan used in the past in Inner Mongolia.
Diseases - Arsenicosis and Blackfoot diseases
In various cases, high concentration of Arsenic has been associated with diseases like Black foot diseases, hypertension, diabetes and cancers of the nasal cavity, lung, liver, bladder, kidney and prostate. (SW Wang)
For people who are exposed to arsenic levels higher than 50 ug1-1 in drinking water, the chance of getting cancers can be as high as 1 in 100. (J.C.Ng.2003)
After 1997, there is evidence that the risks of liver and kidneys cancer may also increase due to the exposure to the inorganic form of arsenic. Figuer.2 shows photographs of typical skin lesions and caner found in patients who have chronically exposed to arsenic. In addition, The result have no significant difference between male and female, and affect people in all ages, but mostly adults. The youngest patient was three years old.
Figure 2 Typical Skin Lension and Cancer to patients has been chronically exposed with arsenic (J.C.Ng.2003)
The arsenic in the ground water in Taiwan is predicted form naturally in the sediments, especially in aquitard formations of marine sequences. Reduction and oxidation are the two most possible mechanisms causing the formation of arsenic. The arsenic can be formed in either way. Reduction process will be related to "Arsenic rich iron oxyhydroxides" and increased water pumping. (B.Nath 2008) The over extraction of local ground water resource causes land subsidence and gradual salinisation by the seawater. Moreover, it will cause excess oxygen dissolving and oxidize the immobile ions (minerals). The oxidation is the dissolution of "Arsenic rich iron sulphide", this is caused due to either the human activities or with buried organic deposits. (SW Wang 2007)
Chianan Plain and Southern Choushui alluvial fan
The high concentration of arsenic in groundwater was found in two catchments at south west of Taiwan: "Chianan plain" and "Southern Choushui River alluvial fan".
Both sites located on the south west of Taiwan with similar lithologies ages in the range of 3 to 9 ka. Chianan Plain is in between the two rivers: Pachang River and Tsengwen River. The plain is about 40km from east to west and 60km from north to south. (SW Wang 2007) Both rivers flow in the same direction from north to south (NE to SW). The second catchment - Choushui River alluvial fan is around 1000 km2 and bounds with two rivers. Figure 3 below shows the actual locations for the two major contamination areas and the number with square and triangles are where the hydrological station is located.
Always on Time
Marked to Standard
Figure 3. The main Arsenic contaminated area in Taiwan and the sample sites location (S.W. Wang 2007)
From 1994 to 2004, the Taiwan Sugar Company had conducted a groundwater survey at monitoring wells. The results show the Chianan Plain had a higher arsenic concentration, but in both areas, the concentrations were all above the WHO guideline value.
Results - Arsenic Concentration
0.30+/- 0.35 mg/L
Southern Choushui River Alluvial Fan
0.12 +/- 0.14 mg/L
Figure 4 National Taiwan Sugar Company Survey Result 2004 (S.W. Wang 2007)
In a more detailed analysis carried out in 2005 to 2006, the reports provide the chemical analysis in the area. The report has been supervised with Taiwan Environmental Protection Agency. The actual results will be supported at the appendix section. The analysis contains 15 parameters including Eh (electrical potential), pH, EC (electrical conductivity), TDS (total dissolved solid), NH4+, SO42-. Cl2-, Ca2+, Mg2+, Na+, K+, As and Fe concentration. In the results some values may show zero, this usually represent the components are below the detection limit. (S.W. Wang 2007)
The complete results will be provided in the appendix - R1 (2005, 06)
The 2005/06 result was published by S.W. Wang in 2007. The analysis has separated the Chianan Plain and Southern Choushui Area in depths - shallow, medium and deep. After that, a factor analysis is carried out. The arsenic concentration increases as the depth increase in the Chianan Plain area, the Choushui catchment have a relative lower value and some of them are not detectable. The average pH is around 7-8, some area are weakly saline.
R1 (B) shows the correlation coefficient calculated for all the parameters in the analysis. The correlation between arsenic to all the other aspects are all relatively low (below 0.4). The sodium is the least correlated = -0.18. (S.W. Wang 2007)
R1(C) will show the arsenic distribution in different depth in two areas.
The hydrological profiles in Chianan Plain have very little layer structure and the hydrological system is divided into five aquifers.
Figure 5. Cross Section Profiles for Chianan Plain (grey = clay, dotted = sand) (S.W. Wang 2007)
Miocene and Pleistocene sands and silts
Figure 6 Chianan Plain Aquifer Profile (S.W. Wang 2007)
Summary of the 2005/2006 results: (S.W. Wang 2007)
The high concentration of arsenic in the ground water occur in the lowermost (>170m) and the uppermost (Aquifer 1 in Figure 5)
Sites in the Choushui river alluvial fan, have high SO42- in ground water, this is caused by the seawater intrusion. The overall concentration here is higher than the mountain areas but still low if compare with Chianan Plain. The concentration here is influenced by the formation of clayey and the confined aquifers in middle and distal fan.
Mainland China (Inner Mongolia)
In 1983, the first chronic endemic arsenism cause by drinking water was found in Xinjiang Province and the most serious problems were in Inner Mongolia and Shanxi. The Mainland China declared the arsenic contamination or arsenicosis as endemic diseases throughout the country 9 years after in 1994. In Xinjiang, the cases were not as serious as the other province due to the changing of water. However, in 2004, Beijing had a high record in arsenic level with 0.05mg/l. the following table summarized up the results in the most affected area by arsenic contamination in Mainland China. The highest concentration observed in China is in Inner Mongolia with 1.86mg/l. (Y. Xia 2004)
Highest As level (mg/l)
Arsenism Patients #
Figure 7 Table showing the high Arsenic value in China and Taiwan (Y. Xia 2004)
At the Hetao area in Inner Mongolia is a major area where the water has been contaminated with arsenic. The main cause of high concentration of as is due to the long term migration of water from a metal rich upstream with an area where the As-rich rock is present and has been mined for 40 years. (H.Zhang 2002) The long migration of As from the upper stream has result mobilization of metal ions for a long period. Comparing this to Taiwan, this is an incidence where human activities have caused the main formation of arsenic in the ground water, rather than a natural mechanism of arsenic in the groundwater.
Controls of arsenism
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In the Chianan Plain and Inner Mongolia, the iron based inorganic adsorbent (Ce-Fe) is more commonly used in recent days. This is done by doping a small part of Ce salt into the iron salt solution. The graph below shows a lab experiment to test out both methods:
Figure (Y Zhang 2003)
The Ce-Fe method is compared with the activation alumina methods. The alumina has a slightly narrower range in pH 5-7 the adsorption and reaches the optimum at pH 6. The Ce-Fe method has a more consistent performance between pH 2-7.
Figure (Y Zhang 2003)
Unfortunately, in the case of Inner Mongolia, the Ce-Fe methods did not seems to work as well as in the lab experiment. The tests were carried out in tap water and the Zhijiliang River in Inner Mongolia. Both samples have a pH of 8 and the result is shown in Figure 8.
The adsorption in the Zhijiliang River is not effective as in the tap water, this problem has been identified and predicted that the reason for this can be caused by the high concentration of humic acid. The humic acid in the ground water may compete with the Arsenic (V) for adsorption site in the adsorbent.
The iron based adsorbent have give out a better performance to the activated alumina method, but still, the mechanism for the iron salt need more further studies. (Y Zhang 2003)
There are other strategies in removal of arsenic from the ground water, such as coagulation, ion exchange and adsorption.
Air oxidation and chemical oxidation are relatively simple and cheap like coagulation, but the air oxidation is a slower process and will speed up other oxidation process and it mainly removes "Arsenic (V)". Chemical Oxidation is a rapid process but requires an efficient pH control.
The second technique is by using major sorption and ion exchange, "Activated Alumina" is a more commercially used one. The only disadvantage is that it needs to be replaced after four to five generation. The ion exchange method is more expensive than all the other strategies mentioned above, it also requires a high level of maintenance, toxic sludge will form as a side effects. However, the ion exchange resin is more powerful, it is pH independent and it can be designed to remove specific type of arsenic.
Overall, the coagulation iron salts is more efficient then aluminum. Although the process is simple, cheap and works in a large range of pH, the disadvantages are that will produce toxic sludge and sometimes after the removal, it still not yet met the WHO standards.
The arsenic concentration is closely related to the redox activities in Taiwan, the most likely mechanism is the reductive dissolution of arsenic rich iron oxyhydroxides. In some of the shallower areas, the salinisation may be caused by the salt manufacturing activities and the reduction is more active in coastal area then the mountain areas. In recent years, the black foot disease was no new cases present in the Chianan Plain and the Choushui River area.
However, the old unused mining area in north of Taiwan (Jin-Shan) may have a high concentration of arsenic in the ground. The government have paid special attention to this, and after the problem have been solved, the old mining area will be developed into a new museum as a tourist attraction.
For Inner Mongolia, the contamination both from the natural weathering and human activities is still present, and in specific area the concentration level is still exceeding the WHO limit. Therefore, it is still a lot of work to solve the high arsenic content as well as to the other heavy metal in the ground water resource.
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