AUSTRALIA.
Until recently the only important concentrations of arsenic in
Australia have been due to mine
tailings of all sorts.
However in Perth, Western Australia , high levels of arsenic have been
discovered in boreholes,
(wells) as discussed in a paper by Appleyard
et al, a newspaper report
and recent release of
the Western Australia, Department of the Environment. The cause was
suggested to be oxidation of the FeOOH and peat in an oxidizing
environment. This suggestion is different from the suggestion by
John MacArthur in the introduction page, that
organic matter (peat) causes a reduction
of FEOH due to the anoxic
environment. But John notes: they have an interesting
situation in and around Perth. The coastal aquifer before development
was largely unconfined and unconsolidated sands and hosted natural
swamps and bogs in topographic depressions where the water table
cropped out. Being coastal, a lot of sea spay blew inland,
deposited in the swamps and formed pyrite - masses of it. Aquifer
development has now drawn down the water table, exposed the peats to
oxidation, and the pyrite is oxidising, too. So they have acid lakes
(pH 3) huge sulphate and lots of arsenic. But there's more!. The
oxidation of the peat is also supplying small organic molecules to the
groundwater, which is being drawn into the aquifer by massive
overpumping, so the entire aquifer in places, which was brown (FeOOH)
from top to bottom 30 years ago, is going grey as reduction proceeds
and FeOOH is dissolved - leading to high pH waters also arsenic
rich. It is simple geochemistry, but will be much misunderstood.
High levels in wells have been seen in northern New South Wales
in a coastal sandy area