Summary: After months of wrangling, the USEPA recently settled on an arsenic standard of 10 ppb. Recognizing different types of arsenic becomes critical as researchers look for ways to design equipment to achieve this significant reduction. The following takes a look at the situation in Bangladesh and factors facing millions of people exposed to arsenic in drinking water there.


Arsenic is the 20th most abundant element in nature. Arsenic in drinking water has been reported in the following countries—Argentina, Australia, Canada, Chile, China, Greece, Hungary, India, Japan, Mexico, Mongolia, New Zealand, South Africa, Philippines, Taiwan, Thailand, the United States and former Soviet countries. As awareness of the menace spreads, new sources are discovered. The frightening arsenic presence in India and Bangladesh are the most spectacular examples (see World Spotlight this issue).

Large portions of the water supply in the United States, mostly in the Midwest and West, contain arsenic. The Safe Drinking Water Act (SDWA), as amended in 1996, required the U.S. Environmental Protection Agency (USEPA) to revise the existing drinking water standard for arsenic. The USEPA had initially argued for a level of 3 parts per billion (ppb), which is not only considerably lower than the previous 50 ppb, but also lower than the present World Health Organization (WHO) guideline of 10 ppb. Last October, USEPA Administrator Christine Whitman confirmed the standard would be set at 10 ppb.

A report from the USEPA in December 2000—Technologies and Costs for Removal of Arsenic from Drinking Water, Chapter 2, Arsenic Removal Technologies—shows that large purification plants may, at a considerable cost, adapt to remove arsenic. But for small plants, private wells and households, there’s no ready solution, which is also confirmed by WHO Fact Sheet No. 210 that was revised in May 2001.

Since the water treatment industry would have difficulties with compliance, the Scientific Advisory Board of the USEPA and the National Drinking Water Advisory Council were ordered to review the scientific basis before the new standard was released. This was one of the most debated environmental issues in the United States last year.

Characteristics of arsenic
Organic arsenic compounds that are found in foods pass through the body quickly and are therefore quite harmless. Inorganic arsenic is deposited in the body and concentrated over time and therefore causes long-term damage, the USEPA reported in its Rule Benefit Analysis of Aug. 9, 2001 (see FYI—Arsenic Poisoning).

Arsenic is difficult to detect. It’s tasteless, odorless and colorless, and a person can absorb significant doses without any apparent major breakdown in their system. A well-nourished and otherwise healthy person can withstand the poison for a long time while an undernourished individual will perish quickly. Babies and children are especially susceptible.

When dissolved in water inorganic arsenic forms ions, which are trivalent, As (III), or pentavalent, As (V). While arsenic in general is said to be about four times as poisonous as mercury, As (III) is considered 60 times more toxic than As (V), according to studies by the Dhaka Community Hospital.

It’s relatively easy to remove As (V)—a precipitated or particulate form of arsenic—with known water technologies, but difficult to remove As (III), or soluble arsenic compounds. The latter ion is also much more difficult to detect and few arsenic detection instruments can distinguish between As (III) and As (V). Many of the technologies that have been recommended thus far for combating arsenic do a good job at removing As (V), but not As (III).

Ensuing diseases
A number of diseases are suspected to be caused or aggravated by arsenic in drinking water according to the USEPA in Arsenic Rule Benefit Analysis. They are cancer of the lung, bladder, skin, prostate, kidney, nose and liver; stillbirths, post-neonatal mortality, Ischemic heart disease (heart attack), diabetes mellitus, nephritis (chronic inflammation of the kidneys), nephrosis (degenerative kidney diseases), hypertension, hypertensive heart disease, emphysema, bronchitis, chronic airway obstruction, lymphoma (tumors in the lymph nodes), black-foot disease and developmental deficits.

In other literature, additional conditions are suspected to be caused by arsenic in drinking water. They include Bowen’s disease, Basal cell carcinoma, Squamous cell carcinoma, enlargement of liver, jaundice, cirrhosis, non-cirrhotic portal hypertension, hearing loss, acrocyanosis, Raynaud’s phenomenon, megablastosis and goiter. Arsenic is also suspected of contributing to various other cardiovascular, pulmonary, immunological, neurological, peripheral vascular and endocrine diseases.

The epidemiological study of diseases caused by arsenic poisoning, however, is only in its infancy. For instance, a report from the National Academy of Sciences (NAS) from Sept. 12, 2001, says the USEPA has greatly underestimated the cancer risks of arsenic in drinking water.
According to a news report in April 19, 2001, a team of USEPA scientists at the agency’s Office of Research and Development laboratory in North Carolina discovered that arsenic may cause genetic damage (see http://www.gsenet.org/library/11gsn/2001/gs010419.htm).

Sources of arsenic in water
Arsenic is, and has been, used in many activities throughout human history, in medicine and industry. Ever since industrialization, thousands of tons of arsenic have been poured out as waste from industrial processing, everything from livestock farming, cotton and wool processing, wood preservation and mining. In North America and elsewhere, runoff from gold mining has contaminated river sediment and groundwater wells.

Arsenic is also used for killing weeds, insects and rats. Runoff from such activities has contaminated surface water and groundwater in many parts of the world like Lake Yangebup in Australia and the Oglalla aquifer in Texas.

In West Bengal and Bangladesh, as in many other areas, arsenic naturally occurs in groundwater. According to one theory, by lowering the water table by drawing water for irrigation, arsenic has been dissolved into groundwater due to intrusion of oxygen. According to another, arsenic is released in a spontaneous reduction process.

Safe drinking water limits
There is debate on how much arsenic the human body can handle without being harmed. A common figure is 12 ppb, according to the National Institute of Environmental Health Sciences.

In the 1960s, a large poisoning in Taiwan—involving 20,000 people—allowed a detailed study that led the WHO to lower the recommended MCL to 10 ppb in 1993. Although the international agency found that for health reasons a level of 2 ppb would have been preferable, difficulties in measuring at those levels at the time prevented such a ruling.

In the West Bengal case, about a million people may be consuming water in excess of 500 ppb of arsenic, and wells have been found that contain as much as 10,000 ppb.

Removal technologies
In large-scale applications, such as municipal or industrial treatment plants, there are established technologies for achieving reliable separation of arsenic. To remove As (III) in a large plant, it’s first oxidized into As (V). This oxidation is usually accomplished with chlorine or hydrogen peroxide. The second step is precipitation using lime or coagulation/flocculation with some salt while controlling water’s pH. Next is filtration. Activated alumina is often recommended as a complementary adsorptive media in the filtration process.

The USEPA’s report from December 2000 shows that As (III) is the most difficult substance ever encountered in the water purification business. When I first heard of the arsenic disaster in 1996 in a request for information on behalf of an Indian Development Bank in West Bengal, my immediate advice was to try reverse osmosis (RO), which I believed removed all ions to a high degree. When it was reported back that RO didn’t accomplish the desired results, I was full of disbelief. Later, I saw results from tests made for the USEPA in 1998 where the RO equipment tested removed 96 percent of As (V) but, surprisingly, only 5 percent of As (III).

It’s possible to achieve effective removal with RO, if combined with pre-oxidation and then some form of after-treatment such as anion exchange or activated alumina adsorption/filtration. The large number of steps may make operation complicated. In addition, additional difficulties include monitoring the result and disposal problems with resulting hazardous waste from RO.

Membrane distillation
Because of these findings, a priority for one company became designing equipment for arsenic removal based on a new technology—membrane distillation (MD)—which significantly removes arsenic in a simple and reliable way.

Membrane distillation appears to be a membrane technology, but actually works more like a distillation technology. All volatile organic compounds (VOC) are first removed by a degassing technology. Then the permeate from the degasser is fed next to a microporous hydrophobic membrane through which water molecules are transported by a partial pressure difference caused by heating the feed and cooling on the permeate side. In the latter process, all non-VOCs remain in the feed. There’s no carryover as in conventional distillation. In short, substances are either volatile or non-volatile.

The technology has been developed to prototype and pilot stages. Laboratory tests certify that the technology removes As (III) as well as As (V) to below the detection level (< 3 micrograms per liter) of state-of-the-art measuring instruments (AAS Graphite), i.e. more than 99.97 percent removal of both As (V) and As (III). The influent concentrations were 10,000 ppm.

An added advantage of the technology is that it doesn’t require expert monitoring and is easy to maintain and service. Therefore, it could be used in small plants, wellheads and individual households.


Arsenic Poisoning in South Asia

For over two decades, water from several million tube wells—providing about 95 percent of all drinking water—has been slowly poisoning Bangladesh villages.

“Bangladesh is grappling with the largest mass poisoning of a population in history because groundwater used for drinking has been contaminated with naturally occurring inorganic arsenic,” the United Nations World Health Organization (WHO) reported in September 2000.

Millions at risk
Research by Allan H. Smith, professor of epidemiology at the University of California at Berkeley, said between 33-to-77 million of Bangladesh’s 125 million people are at risk.

Whereas the WHO recommendation is 10 parts per billion (ppb), concentrations in many areas are above 3,000 ppb and even up to 10,000 ppb. Some experts warn that it’s a matter of time before contaminated water seeps through the entire country.

Remedies have been suggested from a large number of companies and international aid agencies. None of them has yet been proven viable and the Bangladesh people are alarmed, even in unaffected areas. The country’s government now finds the situation untenable and plans forceful measures. A Swedish company was recently asked by the government to establish a subsidiary in Bangladesh to test membrane distillation equipment on the problem and to survey other beneficial technologies and remedies.

Also, in large areas of the Indian state of West Bengal, groundwater has been found to contain levels of arsenic several hundred times the level recommended by the WHO for acceptable drinking water. Some 45 million people live in the affected area, and there are villages where as many as 40 percent of the people have visible symptoms of arsenic poisoning.

World Bank involvement
The World Bank has allocated $44.4 million to find a remedy in Bangladesh. The cost for the remedy itself may run into billions of dollars, independent experts say.

There are ways to avoid the contaminated water—transporting well water from non-afflicted sources, drilling new wells that don’t go into the arsenic carrying sediment, using purified surface water, and supplying bottled water for drinking. Considering the continuing spread of arsenic, purifying the water must be the long-term option.

Another report from WHO, “Arsenic in Drinking Water” (May 2001), however, states, “There are no proven technologies for the removal of arsenic at water collections points such as wells, hand-pumps and springs.”

While the arsenic levels may be daunting and the costs high, point-of-use/point-of-entry technologies are available to offer significant reductions. A single cure-all may not exist, but much can be done to improve the health risk faced.


Conclusion
To be able to refine the methods to combat the arsenic disaster, it’s a challenge to all water chemists to explain what makes the ion As (III) so different from other ions. What makes it so difficult to remove? And to all water equipment manufacturers, the challenge is to devise new methods and new equipment that remove As (III) in an efficient way. 

About the author
Aapo Sääsk is a Brown University graduate who is a resident of Stockholm, Sweden. He is a research company executive with Scarab Development AB who has worked with developing proprietary water purification and desalination equipment for more than 20 years. This includes application of membrane distillation for arsenic removal. The results are posted on www.scarab.se and Saask can be reached at email: [email protected]

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