Current estimates place the human population of the Earth just less than 7 billion people, by 2100 this is due to increase to over 10 billion people (and possibly even double the current population). Just providing the basic resources to these people will be a major issue for the future and one of these basic resources is fresh water.
The major source of useable (and drinkable) water in the world is groundwater, however it only makes up about 0.6% of all the water on the planet. As the population of the world increases, the demand for groundwater is placing a large amount of stress on existing water sources. One region where this is perhaps exacerbated is south east Asia and specifically, Bangladesh. Although Bangladesh is built over the Bengal Delta, 97% of the population is reliant on the underlying groundwater. Post-independence, many wells were drilled to provide for the population, as the surface water was very polluted and mismanagemed. Just putting aside any water-use concerns you might have about this, there was a major flaw in this plan…the groundwater was contaminated with arsenic. Groundwater is usually contained within the pore spaces or fractures of underground rocks and depending on the source rocks the water can be enriched with certain minerals or elements.
Arsenic is a chemical element that can often be found naturally adjacent to gold deposits. It is famous as the preferred chemical poison in murder mystery novels. Arsenic poisoning results in the all the “normal” predeath symptoms Agatha Christie describes; the victim often retires after dinner due to a slight headache, later the nurse is called to deal with the vomitting and convulsions before, sadly, death arrives before the doctor.
On a cellular level, arsenic disrupts energy transfer in cells which leads to cell death. The main issue is that chemical arsenic is very similar to phosphorus (an essential element in the body) and hence arsenic can take the place of phosphorus in many reactions. This spells trouble for the body (not literally).
But seriously, in Bangladesh the cause of the arsenic contamination is mainly from the mineral arsenopyrite. It is found in grey clays and fine grained sediments in the Bengal Delta. Under normal circumstances the arsenic is bound up in this mineral and insignificant amounts would be released. Scientist suggest that the number of wells drilled into the aquifer (groundwater store) lowered the water table and this enhanced the release of the arsenic into the aquifer.
The World Health Organisation places a limit on the concentration of arsenic in drinking water at 0.01 mg/L. In a survey of 64 wells around Bangladesh, 59 wells had more than 0.01 mg/L and 43 wells had more than 0.05 mg/L. This is incredibly frightening given that most of the population uses this source for drinking and cooking plus irrigation of crops, including rice! Rice has the ability to retain arsenic in it’s structure. A study has shown arsenic levels in Bangladesh rice of up to 0.95 μg/g which is very close to the Australia New Zealand Food Standards Code (ANZFS) which states the total arsenic in cereals including rice must not exceed 1 mg/kg (equivalent to 1 μg/g). Tests completed in 2010 of long grain rice by ANZFS detected the equivalent of .43 μg/g of arsenic in Australian rice.
There is work being done to combat this issue. A simple test can be done at each well to identify whether or not the arsenic level is over the safe drinking guidelines and coloured tags are attached depending on the usability. This is often done by international volunteers and a lot more education needs to be done in communities for this to be successful. These volunteers are also able to install safety catches on the wells preventing injuries to (mostly) local women who collect the water. The United Nations Food and Agriculture Organisation recommends the raising of rice beds by 15 centimetres to reduce the amount of irrigation required and ultimately reduce the amount of arsenic being put into the crop. To counteract arsenic poisoning there has been a lot of work done using selenium dietary supplements. It appears the work so far has been reasonably successful.
This problem is not going to disappear soon and given the social problems already facing Bangladesh (poverty, health, education, governance) plus the potential impact from sea-level rise in the future (Top Climate Change Getaways) things are not looking too good. If you want to more information you can also have a look at a local Bangladesh site.