Frogs are excellent 'barometers' of
pollution and, in particular, water contamination. Their continued exposure to any
contaminants - both inside their eggs and during metamorphosis - means they are extremely
sensitive. High levels of pollution often lead to high percentages of deformities
and other abnormalities. This would make them excellent indicators of contaminant levels
around the mine at Olympic Dam.
About the tenth frog John ever found in the
Roxby Downs area had an extra arm, setting off alarm bells and prompting John to contact
Mike Tyler, a frog expert from Adelaide University. Mike said that the frog was
"interesting, alarming, and meaningless". It is apparently perfectly normal for
one to five percent of frogs to exhibit abnormalities, and John was going to have to test
"hundreds or even thousands" of frogs. So he did.
There are a surprisingly large number of
frog species that live in the dry, desert-like Australian outback. While
regions that
receive soaking rains more often boast a larger number of frog species, the only species that
lives in the Roxby Downs region is the Trilling Frog (Neobatrachus centralis).
They spend most of their lives deep underground, emerging only after heavy
rains to
breed.
However, when they emerge, their abundance
is the stuff of legends...
"Only minutes earlier a 4WD had driven around the
swamp and in just thirty metres of tracks from a single car, 281 juvenile frogs had been
squashed. Armies of little hoppers swarmed past their fallen comrades. Anyone who has not
witnessed these swarms of frogs in the desert after rain finds it difficult to
comprehend."
So, with abundant frogs in the region, conducting
research into abnormalities was relatively easy. And the results? From tests conducted
between 1989 and 1997, abnormality rates have been consistently low - less than four
percent.
Unfortunately, in the case of Olympic Dam, trilling
frogs aren't the ideal bioindicator for a variety of reasons - not the least of which
being the fact that they can only be surveyed when they surface after rain.
This is only about every five years, which is not enough for an accurate picture.
"We need to find critters that can be easily and
regularly sampled that are also sensitive to pollutants. That was my main quest during
work hours for most of the 1990s."
Canaries were used by miners for years - if the caged
canary in the mine fell off its perch, the miners knew that the odorless but fatal gas
carbon monoxide, had risen to dangerous levels. While this is the exact opposite of
monitoring animals and birds for their benefit, the principle is similar
- John needed to find "canaries" that would clearly indicate their responses to
the mine and any pollutants.
The first candidates for this quest were Netted
Dragons, which respond rapidly and dramatically to disturbance and which, for some strange
reason, favour sites that have been cleared for roads, housing etc. However, most of the
obvious effects of the Olympic Dam mine are airborne pollutants - ground disturbance is
relatively minimal as Olympic Dam is an underground mine as opposed to open-cut.
"Although netted dragons are great indicators of
scrub that had been razed by bulldozers, cattle or fire, they only indicate the bleeding
obvious . . . I needed indicators of more subtle, pollution-related changes"
Bring on the Geckos - small, diverse and incredibly
well-adapted to the arid environment, they soon proved themselves to be excellent
indicators of airborne pollutants.
The first indication that something was wrong was the
considerably lower numbers of geckos caught near the mine than at control sites far
away. The second was that geckos near the mine were far less often 'gravid' - that is,
with eggs in their abdomen, measurable by looking closely at the almost transparent belly
wall of a female and counting the eggs inside.
"Partially in response to our initial
environmental findings, the ground concentrations of both sulphur dioxide and salt spray
were reduced in the early 1990s through modifications to both the smelter and the
ventilation bores.
"Sure enough, the next year when I surveyed the wildlife, more geckos in
both impact zones were gravid and gecko capture rates had also increased. These findings
suggested that geckos might be excellent indicators of the health of the environment and a
decade later they are still used as little outback canaries at Roxby."
Other good indicators of the environmental effects of
the mine are the birds, and bird numbers are also monitored regularly, with varying
results. Some are noticeably absent from the mine site, others regularly raise clutches of
healthy chicks in the immediate vicinity of the mining operation.
"The continued successful breeding by many bird,
reptile and mammal species near the mine site, together with the consistent recording of
low levels of abnormalities in metamorphling frogs, does indicate something that is
significant. While sulphur gases, salt spray and ground disturbance do affect some local
animals, most species appear to be either unaware of or unaffected by the slightly
elevated radiation levels found around the mine. I had answered, in my own mind, one of the
most controversial questions that I set out to solve when I first came to Roxby."
