Poisoned Land - Arsenic in Argentina

24 June 2007

Interview with

Dr Michael Watts, British Geological Survey

Michael Watts has recently been looking at arsenic contamination in Argentinean soil.

ArgentinaMichael - This is a project that we're doing in collaboration with the University of Surrey, professor Neil Ward actually set up this work, we're doing this through co-sponsorship of a PhD student.  The idea is that she's looking at a northern region in Argentina, San Juan and La Riocha, well known for the wine.  It's also well known for high arsenic levels in the local water and in the soils.  What were doing is helping out local geoscience institutes and local universities and with local medics we're trying to build up a picture of what is actually going on.  We're building up information in three layers, working out the environmental geochemistry, surveying waters and soils for the arsenic content.

Chris -   Where is all this arsenic actually coming from in the first place?

Michael -   Well, the arsenic will actually be naturally occurring in the environment, but it may well be present in the water systems due to mining.

Chris -   The Victorians were very fond of it because it made very nice green wallpaper, and then made people go green and die.  But why is it toxic and why is it something we should be worried about?

Michael -   Well, it's a well-known poison, one of the issues is actually the chemistry of the arsenic and the form that it's present in the environment.  The toxicity and the availability to be taken up by humans is really dependent on the chemical form.  That could be the redox conditions, or the presence as an organic compound.

Chris -   So when people drink water or eat food or whatever that's been grown on arsenic contaminated land, that's a way that they can get the arsenic into their body?

Michael -   Yeah, or through hand to mouth contact, so if you've got a bit of soil on your hands, if you've done a bit of gardening, and you touch your mouth, or soil attached to vegetables.

Chris -   So how are you actually trying to study how much arsenic people are actually being exposed to?  Is there a way of doing that?

Michael -   Well with this Argentinean work we're sort of building up a survey of the waters and soils looking at agricultural products, and then that will lead to human studies.  With the help of local medical experts, we're collating information from rural communities and getting a medical history of the people, where there have been a number of health conditions or even deaths related to arsenic poisoning.  We really need to confirm this anecdotal link between environmental data and the end point when people are ending up with diseases.

Chris -   Someone was saying to me the other day that earthworms are proving really quite useful in trying to work out what's in the soil.

Michael -   That's some work we've been doing in the UK, it's been well documented that earthworms are excellent indicators of the health of the soil, and one of those uses is to look at the arsenic uptake in the earthworm and look at the effect on it's health.  We can do that by looking at cell damage as a result of exposure to arsenic.

Chris -   So rather than a canary in a cage, you've got an earthworm in the ground and you can use that as an index of the degree of contamination.

Michael -   Yes, there's a tentative link to humans there, it's more an indicator or eco-toxicity.  We do use another technique called the PBET, which is a Physiology Based Extraction Technique.  This is quite a popular technique for simulating the human gut.  We would do a laboratory-controlled experiment with a tube.  We put the soil into a tube and then add bile juices and acids and so on to simulate the stomach.

Chris -   So it's sort of like a stomach in a dish?

Michael -   Yeah, that's it really.  So we look at how much arsenic is released from the soil, so how much arsenic is available for the human to be taken up.  So rather than looking at the total arsenic in the soil, we're looking at the accessible arsenic, which is a very important point.

Chris -   If you discover there's lots of arsenic in the soil, what can you actually do to remedy the situation?

Michael -   That's quite a difficult issue.  One of the most expensive remedies is to actually remediate the land, take it away for landfill and replace it.  It's a very difficult thing to do, or seal the land.  For communities in Argentina it's a very difficult issue, because they are reliant on subsistence farming.  There might be a recommendation for filtering the irrigation water, whether there are engineering means to correct this, or maybe they source the water in other ways.

Chris -   So really avoidance rather than cure at this stage.

Michael -   It's a very difficult thing that's beyond our expertise at the moment we can build up the weight of evidence to suggest that the arsenic is there and it could be a problem, or maybe it's just perfectly happily sitting there, not causing any problems.  But building up the weight of evidence so that governments and institutions can come in and recommend methods of remediation.

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