Geology for Global Development

Geology for Global Development

Water Series (3): Arsenic Contamination in Drinking Water

Following our post about fluoride contamination last week, our water series is now focused on the equally serious problem of arsenic contamination.

Some arsenic is present in all groundwater sources (see table 1). Of course this is only a problem if the arsenic has the chance to leak into groundwater as it filters through the rock. Arsenic leaching is more likely to occur in groundwater that is hot, oxygen-depleted, alkaline or extremely acidic.

Table 1: table of different geological rock types and their associated arsenic content (from UNICEF arsenic report, 2008)

Rock or sediment type Average arsenic content (parts per million) Range of arsenic content (parts per million)
Sandstone 4.1 0.6 – 120
Limestone 2.6 0.4 – 20
Granite 1.3 0.2 – 15
Basalt 2.3 0.2 – 113
Alluvial sand 2.9 1.0 – 6.2
Alluvial silt 6.5 2.7 – 15
Loess 5.4 – 18

A 2008 UNICEF report found that over 137 million people in more than 70 countries are probably affected by elevated arsenic levels in their drinking water (above 10 parts per billion is considered a risk to health). Arsenic can be transferred into the body through drinking contaminated water, or eating food that was irrigated using contaminated water.

There is no available treatment for the suite of health problems, collectively known as arsenicosis, caused by the build up of arsenic in the body over several years. Arsenic exposure can cause cancer, as well as vomiting, blindness and paralysis. High arsenic levels are a major problem in SE Asia. In Cambodia concentrations of up to 250 parts per billion have resulted in cases of arsenicosis so severe that amputations are required.

Small child using a well in Bangladesh. Photo taken by Donald John Macallister whilst working on a water project.

Arsenic poisoning can often remain undetected for a long time, as the symptoms do not occur until after a long, slow period of toxin build-up in the body. It is often health workers that have the first opportunity to identify the problem, but many are not trained to recognize the effects of early arsenicosis – lesions on the skin.

Once a high-risk area is identified, water samples can be taken over a wide area to map contaminated wells. The samples can be analysed in the field or sent back to a permanent laboratory. Field testing is cheaper and the results can be conveyed back to the relevant communities immediately, but laboratory testing may be necessary if more precise results are needed.

The most effective way to reduce exposure to arsenic is to identify contaminated wells and explain to the affected communities why they should avoid them. Communicating the severity of arsenic poisoning can be difficult, as arsenic in water can’t be seen or tasted, and there are no immediate consequences of drinking arsenic-contaminated water.

In cases where a local, uncontaminated well cannot be identified, the only option may be to remove arsenic from drinking water by passing it through an ultrafiltration membrane. Polyelectrolytes (long-chained molecules that acts like salt and dissociate in water) form complex molecules with arsenic that are too large to pass through the membrane. These large molecules form more efficiently at higher pH (8.5), as arsenic becomes more negatively charged (-2) and so is more attracted to the positive polyelectrolyte. Conveniently, groundwater often has a slightly elevated natural pH. The filter should have grains with a high surface area and high absorptive capacity. Goethite amended sand works well, with added iron oxide.

Filtering out arsenic can cause the concentration of other elements to drop as well, some of which, such as chromium, may be beneficial. It is always more desirable to source water from an alternative well than to filter water from an existing well.


UNICEF have produced an excellent and extensive report documenting their knowledge and experience of working with arsenic contaminated wells. To learn more, you can read it for free online.

Hurricane Sandy: A round up of the coverage from Haiti to New York

We thought we would summarise the coverage of Hurricane Sandy and direct you to some of the wide-ranging political, scientific and development based discussion that has arisen in the last few weeks; simply follow the links in this article.

Hurricanes are just one of the many natural disasters that affect countries in the Caribbean, such as Haiti. They are rarely an issue further north, but Sandy is an exception as it passed through the Caribbean and then onto the East coast of the United States. The influence of the hurricane’s winds has been mapped in stunning detail. It is interesting to compare the preparation, devastation and subsequent clean up in a developing country with the effects of the same hurricane in an economic superpower. It is also interesting to see the way the US prepares for a major disaster in an area that doesn’t have a history of dealing with extreme weather events.

Compared to other natural hazards, our predictive power with hurricanes is very advanced. Once a hurricane has formed we can use satellite observations to track it’s course, normally leaving generous time to prepare and evacuate from danger zones. There was a call for people to collect water samples during Sandy to help us understand hurricanes even better next time around.

In the USA, Sandy took 88 lives and left up to 40,000 people without electricity or heating, just as the winter weather begins to bite. The damage in the US will cause long-term problems as the foundations of many buildings have been undermined. With NYC being a financial capital, there is also a large economic impact: the mayor had to waive public transport fees, the NY stock exchange closed due to weather conditions for the first time in 27 years and many people were forced to miss work. With the election looming in the USA, the hurricane will also have had a political influence. The response of the Bush administration to New Orleans (August, 2005) will be compared with the Obama administration’s response to Sandy. The hurricane is also likely to throw climate change, an issue that wasn’t mentioned by either candidate in the presidential debates, back onto the mainstream agenda. Was this storm ‘fueled by fossil steroids?

In Haiti there have been 54 deaths, but this number is expected to rise as the standing water  gives deadly cholera some breathing space and the anticipated crop failure, in an already strained agriculturally-dependent country, leaves people desperately hungry. There were also 200,000 people made homeless, and all this despite the country only catching the edge of the storm. There is likely to be a much slower recovery here than in the US. The multiple natural disasters Haiti has experienced in the past two years have depleted their resources and caused a complex web of problems. In some cases, people in Haiti were living in worse conditions before the storm hit than Americans are after it, many still in temporary camps after the 2010 earthquake or last year’s hurricane destroyed their homes. Lisa Laumann, the director of Save the Children in Haiti, thinks that ‘if the road infrastructure was stronger, and if there were better flood control, fewer people would die in emergencies like this’ [whilst speaking to the Guardian]. Many of the deaths in this event would have been avoidable with better resources and advanced preparation.


Water Series (2): Fluoride Contamination in Drinking Water

This week, as part of our ‘water series’ we will focus on fluoride contamination in drinking water. In some parts of the UK we add fluoride to our drinking water, because small amounts can help to protect your teeth. However, too much fluoride (>1.5mg/L) can lead to a serious medical condition called fluorosis, affecting the development of teeth and bones. This strong dosage dependency can lead to real battles in science communication. Even in the UK, where our fluoride levels are carefully controlled and maintained at a level that benefits us, there are public concerns and conspiracy theories about fluoride.

In places where water is not regulated at a centralised plant, many people have to drink from wells that have dangerously high levels of fluoride.  The main source of fluoride is contaminated groundwater, but other sources should also be taken into account when assessing safe concentrations. In the UK, toothpaste provides an extra source of fluoride, whereas in Ethiopia, the tea people drink is high in fluoride. Fluoride poisoning affects two hundred million people worldwide, and is a particular problem in Ethiopia.

The underlying control on fluoride concentration is geological. Fluorine appears in almost every kind of rock. The highest concentrations of fluoride occur in connection with intercontinental hot spots and along rift zones. In geologically unstable regions fluoride enriched fluids rise from the Earth’s crust or mantle up towards the surface sediments.

Rifting breaks apart continents and forms new oceans, often beginning with a 3-armed structure, such as the one in the Middle East/East Africa highlighted by the red lines. Normally the rift axis is underwater, but here one rift occurs on land, through the centre of Ethiopia. Source: Google Earth

The great rift valley cuts across the centre of Ethiopia with a NE-SW strike, pulling the country in two. The rift is an important geological site as this process normally occurs on the seafloor, and can rarely be observed above ground. Rocks in the valley are mostly young volcanics. Samples of drinking water from along the length of the valley have been analysed for their elemental concentrations using  ion chromatography and an ICP-MS and (a mass spectrometer that is common in most Earth Science departments, used for measuring the concentration of a whole range of elements in a liquid sample). Seventy eight per cent of the samples would fail EU drinking water regulations, and this is predominantly due to high fluoride levels. The contamination is a result of the water passing through the volcanic rocks in the rift valley.

To remove fluoride, water can be passed through a cleaning system at the point of access or within the home. One cost effective and widely available method for removing fluoride is to filter the water through charred animal bones. Fish bones or eucalyptus wood work just as well for communities that have an ethical objection to the use of animal products. Crushing and heating the bones increases the surface area, and so improves the absorbance capacity. The temperature that the bones are heated to is critical, and the ideal lies between 400 and 500 degrees centigrade. In Ethiopia large kilns are already in place, so most people have access to the necessary technology to remove fluoride from their water. The temperature can be monitored with waxed candles, as the fuse breaks when the temperature is too high, and can be controlled by altering the balance between extra fuel and air supply. The addition of simple ligands can double the Fluoride uptake, so if possible the charred material is treated with Aluminium oxides or sulphate to improve the efficiency.

The technology to remove fluoride from people’s water supply is well developed and easily accessible. However, the science alone is not enough. Collaborations between geologists, engineers, anthropologists, sociologists and entrepreneurs is needed to make a project a success. Social surveys and group discussions are used within communities to determine the best way to deliver the water purification treatment. In some cases it makes sense to treat the water centrally as this is more cost effective. However, in some communities it is more beneficial for families to treat their own water at home. A family can be issued with equipment the size of a bucket and can last up to 6 months. Entrepreneurs can also be involved in financing the scheme, aiming to transform it into a business that can continue to fund itself. This is a truly multi-disciplinary issue.