Coastal freshwater wells could be sucking more pollution from the ocean than previously thought, according to a laboratory experiment which shows that salt in seawater pumps pollutants into neighbouring freshwater.

That could spell trouble for coastal communities that rely on well water to drink, as they do in some parts of Spain and North Africa.

Brian Berkowitz and colleagues at the Weizmann Institute of Science in Rehovot, Israel, split a fish tank into two compartments with a barrier of sand to study how pollution passes through aquifers – areas of porous rock that hold freshwater.

When organic pollutants like benzene, toluene, and trichloroethylene were dumped into freshwater on one side of the tank, with clean freshwater on the other side, the pollutants slowly leaked through the sand.

But when the pollutants were added to salt water, they shot through the sand much more quickly.
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