Feature - Grids point to pollution solutions

eMinerals’ scientists are using grid computing to delve into the chemical substitutions that lead to arsenic contamination of drinking water. This image shows an arsenic atom (purple) substituted for a sulfur atom (cream) rather than an iron atom (red) in the structure of pyrite.  Image courtesy of Kat Austen and Marc Blanchard

eMinerals scientists will deliver new dirt on soil pollution at the 7th UK e-Science All Hands Meeting in Nottingham this week.

The eMinerals team, funded by the UK’s Natural Environment Research Council, is using grid computing to tackle some serious environmental problems, including arsenic contamination of drinking water and dioxin pollution of soils.

Over a series of thousands of calculations, researchers have simulated all possible interactions between dioxins and arsenic—extremely toxic pollutants—and the various rocks and soils in which they lurk.

Fools’ arsenic

Arsenic often appears in minerals rich in iron and sulfur, such as pyrite or “fools’ gold.” Unfortunately, the presence of these minerals near man-made wells can lead to arsenic contamination of drinking water.

Now, eMinerals scientists have found out precisely how arsenic is taken up and held in the pyrite structure, and the factors likely to lead to its release.

“We now know that arsenic replaces the sulfur in pyrite rather than the iron, and that pyrite is likely to dissolve more easily when arsenic is present,” says Kate Wright, an eMinerals scientist.  

This discovery raises the possibility that arsenic-containing iron sulfide rock can be stabilized by introducing additives that slow the rate at which it dissolves, thus reducing contamination of nearby water.

The dirt on dioxins

Dioxins are super-nasty industrial chemicals, now banned from use but still sticking around in polluted soils and clays.

Separating these toxic molecules from the ground they contaminate is a dirty business, but now, thanks to grid computing, eMinerals scientists understand more about the forces governing the interactions of soils and dioxins.

“Dioxin molecules with more chlorine atoms will bind more strongly to clay surfaces, and they also bind more strongly when there is a greater electrical charge on the surface,” says scientist Kat Austen. “However, since water competes with dioxin to bind to surfaces, the binding ability of a dioxin molecule is a balance between the binding strength of the dioxin to the surface, the water to the surface, and the dioxin to the water.”

Fully-chlorinated dioxin molecules, like this one in green, bind more strongly to clay surfaces like the red and purple pyrophyllite surface. This poses interesting challenges when it comes to remediating dioxin-polluted soils. Image courtesy of Kat Austen

Working environment

The results from both projects were reached after performing numerous simulations of the interactions between the different minerals in soils and rocks with all the known variants of the contaminants.

This was no small task: for example, there are 76 different variants of the dioxin molecule alone, as well as numerous mineral surfaces to which they can attach, which results in the need for thousands of serious calculations.  
 
To help crunch these numbers, the eMinerals project has developed a grid infrastructure consisting of clusters and condor pools (including campus grids) at the collaborating institutions and resources held on the National Grid Service and the North West Grid.
 
Without access to such grid resources, researchers would have to perform all of the simulations sequentially, taking too much time to be practicable, says Martin Dove, eMinerals principal investigator.  

Using the eMinerals infrastructure, researchers can submit all these jobs at once and see the results within a few hours.

“We can submit hundreds of jobs from the user’s desktop to a number of different compute grids, and get the data back with metadata attached and with the analysis done—and in a state that enables collaborators to understand what the simulations are saying,” says Dove. “We’re giving control back to the user.”

The data can be accessed remotely by collaborating scientists, as well as by those who originally submitted the job.

Martin Dove and other members of the eMinerals team will be discussing their results and demonstrating the eMinerals technology at the 7th UK e-Science All Hands Meeting in Nottingham on 10-13 September 2007.