Poisoned water threatens developing countries
Arsenic is widely distributed through the earth’s crust and is present in almost all waters in very small amounts.
However, in certain areas there are dangerous levels of this toxin in drinking water. One of the most serious cases is Bangladesh, where thousands of wells cause mass poisoning of the population.
Arsenic is a known carcinogen, and when constantly consumed it can affect the gastro-intestinal, respiratory and vascular systems, often resulting in cancers of the skin, lung and bladder.
During the 1990s, 900 million people around the world gained access to an improved water supply, yet 1.1 billion people in rural areas and urban slums still rely on unsafe drinking water from rivers, lakes and open wells.
Children, in particular, suffer from water-related illnesses. Each episode of diarrhoea can reduce their appetite and lower their calorie and nutrient uptake. Persistent diarrhoea, and severe diseases such as typhoid and dysentery, jeopardize children’s healthy development. Every year, nearly two million children die as a result.
It is believed that arsenic in Bangladesh originated in the Himalayan headwaters of the Ganges and Brahmaputra rivers, and remained dormant and embedded in the land.
The poisoning began as enormous quantities of water were pumped out from deep underground reservoirs. Water levels dropped and exposed arsenic-bearing pyrite to air, leading to oxidization – a reaction that flushed arsenic into the remaining water.
The combined high probability, moderate probability and low probability contamination zones cover about 60% of the country’s total area.
In the 1970s, international agencies headed by the United Nations Children’s Fund invested millions of dollars of aid money into digging shallow tube wells in Bangladesh. Due to a lack of facilities the water was never tested for arsenic.
With groundwater consumption increasing over the next two decades, the water from more than a million tube wells began to slowly poison Bangladeshi villagers. The World Health Organization says large-scale withdrawal of ground water from an estimated 10 million tube wells may be the main cause of arsenic contamination in Bangladesh.
Control of arsenic is more complex where drinking water is obtained from many sources – such as hand-pumps and wells – as is common in rural areas. Low-arsenic water is needed only for drinking and cooking. Arsenic-rich water can be used safely for laundry and bathing.
Discriminating between low-arsenic and high-arsenic sources by painting hand-pumps green or red can be an effective and low-cost way of rapidly reducing exposure, when accompanied by effective health education.
Several initiatives have been set up in Bangladesh to investigate water quality testing and control with a view to supplying arsenic-free drinking water. One positive outcome has been the testing of new types of treatment technology.
Only a few proven sustainable options are available to provide safe drinking and irrigation water. These include obtaining low-arsenic groundwater from shallow systems or deeper aquifers (more than 200m or 220 yards approx), rainwater harvesting, pond-sand filtration, household chemical treatment and piped water supply from safe or treated sources. But cost is once again the negating factor.
Alternative low-arsenic sources such as rainwater and treated surface water may be a valid solution in some circumstances. However, arsenic removal technology for piped water is costly and requires technical expertise. It is inapplicable in some urban areas of developing countries and in most rural areas worldwide.
New types of treatment technology – including co-precipitation, ion exchange and activated alumina filtration –are being field tested, but there are few proven methods of removing arsenic on a grand scale at high-risk water collection points.
Some studies have reported preliminary success in using packets of chemicals for household treatment, and some mixtures combine arsenic removal with disinfection.
One example – developed by the Pan American Health Organization’s Center of Sanitary Engineering and environmental science organizations in Lima, Peru – has been successful in Latin America, but the problem is still widespread.
Christina Galitsky, chemical engineer at the Lawrence Berkeley National Laboratory in the US, says the big problem in Bangladesh is not food – it is drinking water.
“In the 1970s, UNICEF dug wells all across the country so that Bangladeshis could stop drinking contaminated surface water. The motives were pure, but the wells were not. Most were in areas with high concentrations of arsenic – in some cases more than 100 times the level deemed safe by the World Health Organization.
“It has been called potentially the largest mass poisoning in the history of the world.”
Together with Ashok Gadgil, a senior scientist at the laboratory, Galitsky saw an opportunity. With a US$250,000 grant from the California Energy Commission and US$100,000 from the American Waterworks Association Research Foundation, they are developing a filtration system.
The system extracts nearly all the arsenic in a beaker of contaminated water. The researchers concede there is a lot of work to do, as they need to figure out how water should pass through their hybrid ash-and-iron substrate, and determine what real-world conditions might interfere with its performance.
But they believe filters made with their new medium could comply with stringent safety standards and still be affordable enough for Bangladesh households.
On the other side of the world, researchers at the University of Technology, Sydney, in Australia have developed an innovative absorption system – a sponge coated with iron oxide – that removes arsenic from water and can be used in any home.
Professor of Environmental Engineering Vigi Vigneswaran says the sponge is an ideal material because it is very porous and its surface facilitates arsenic absorption.
Vigneswaran says a sponge is cost effective, does not require large amounts of infrastructure to make and can be supplied to small communities as well as developing countries.
“Through extensive research and testing, it was found that the amount of arsenic absorbed onto the sponge was higher than for other materials.
“A typical calculation based on the field experiment showed that 0.6kg of iron-coated sponge packed in a PVC column 25cm in diameter and 80cm in height can provide safe water for a family of four people for three months before the iron-coated sponge becomes exhausted.
“The attractive feature is that the iron-coated sponge can be used by soaking in a bucket of water – enclosed in a PVC pipe with water poured through it – or added to a filter on a tap, making it easy to use anywhere.”
The project and research by Vigneswaran, Dr Huu Hao Ngo and PhD student Vin Nguyen was funded through the Australian Research Council’s ‘discovery and linkage’ program, which fosters collaboration and networking between Australia-based and overseas researchers.
Extensive laboratory testing suggested that by weight of material the iron-coated sponge was more effective at removing arsenic than other filtering materials. Vigneswaran says the method is ideal for developing countries like Bangladesh and Vietnam, where communities use groundwater that is highly likely to be contaminated with arsenic.
”This is a familiar product, which is available in the market. The particular sponge we use is manufactured by Adform Australia. However, we believe any sort of sponge with enough pores and sufficient retaining capacity for iron oxide coating can be used. The cost is minimal, as the technology is aimed at small communities in developing countries.”
Researchers at the University of Edinburgh in Scotland concur, and have genetically modified the bacterium E. coli to detect trace amounts of arsenic in drinking water. They claim the bacteria-based technology will eventually lead to safe, precise and easy-to-use field test kits.
Professor of Microbial Biotechnology Chris French says such tests could be as easy to use as home pregnancy tests and would not require a trained technician.
The Edinburgh group says E. coli has two unrelated genetic sequences that in combination allow effective arsenic detection. They hypothesized that when arsenic comes in contact with the modified E. coli, it activates the ‘arsenic switch’, whose gene in turn activates the breakdown of lactic acid.
After a while, the water turns red or yellow, depending on the presence or absence of arsenic. A potential drawback is the time lag – the biological interactions take about five hours.
In Australia arsenic is not a national problem. Some has been detected in groundwater and soil in Victoria, but mainly it is found in the outback. Research indicates groundwater sources in the Northern Territory are marginally affected by arsenic, but this needs to be verified.
In rural Victoria, concentrations of up to 16,000mg/kg of soil on residential properties, and 0.008mg/L and 0.22mg/L in groundwater and surface water have been reported. These exceed the National Health and Medical Research Council guideline of 0.007mg/L in drinking water and 300mg/kg in soil.
In recent years there has been a concerted effort to map the distribution of arsenic and identify contaminated wells in Bangladesh.
In some cases, scientists and aid workers have sent water samples to be tested in labs using fluorescence techniques – an expensive and time-consuming process. In other cases, they have used portable test kits. However, most of these field tests require training, and they produce toxic chemicals such as arsine gas.
Although 27% of shallow tube wells are known to be contaminated nationally, in many areas more than 90% are contaminated. The problem has been magnified because tube wells with high levels of arsenic are in areas where the percentage of contaminated wells is high.