An already rare population of koalas in South Australia is dying from a mysterious renal disease, which has been linked to aluminium deposits in kidneys.

Research funded by the Australian Koala Foundation has been probing the cause of the disease which causes animals to venture into domestic gardens and drink out of swimming pools or pet bowls.

According to Foundation Executive Director, Deborah Tabart, the disease is killing increasing numbers of South Australia's koalas. Koalas with kidney failure will "go to the bottom of a tree, drink water voraciously and die," she said. "A healthy koala will never sit on the ground. The sick ones haven't got the energy to climb back up the tree. They lose their vigour."

Research being undertaken at University of Adelaide working with Cleland Wildlife Park in the Adelaide Hills has implicated aluminium in the illness. Post-mortem electron microscopy of kidneys from koalas with renal disease has shown aluminium deposits and structural damage in each one.

The aluminium is thought to be coming from the gum leaves that make up the staple diet of koalas. Analysis of gum leaves from the Adelaide Hills area has revealed high levels of aluminium and silicon. Similar analyses showed no aluminium in bandicoots, brushtail possums and ringtail possums which share the same environment as the koalas

What is still unknown, however, is whether renal aluminium deposits in the koalas are the cause of the disease, or a secondary effect - since disease is known to trigger the absorption of aluminium into the bloodstream.

The threat to the South Australian koalas is compounded by the small genetic pool they come from, which may leave them vulnerable to genetic problems. According to Tabart, the original koala population in South Australia was hunted for its fur and had been wiped out by the 1920's. In the neighbouring state of Victoria there were only about 1000 individuals left, and now all the koalas living in the northwest of Victoria and in South Australia are descendants of this population.

"They are all from the original gene pool," said Tabart. "It is a genetic bottleneck...It may predispose them to getting ill more than a healthy population of koalas."

The research group is intending to produce a blood and urine profile to characterise renal disease in koalas. They also plan to compare koalas in South Australia with those in the Eastern Australian states, which come from a different genetic pool.

The Foundation has been hearing reports of koalas dying of kidney failure for several years now, said Tabart, citing a veterinarian in Victoria who had seen several koalas with renal failure.

"Also, a fellow in Gunnedah has been finding lots of koalas at the bases of trees," she said. "We are wondering if during the drought the gum leaves are doing strange things."