Turtles along northern Queensland's nearshore waters have tested positive for a metal at potentially harmful levels, according to a Queensland study.
Cobalt is a naturally occurring mineral found in most invertebrates, however testing of green turtles along Upstart, Cleveland and Shoalwater Bay found elevated cobalt levels associated with adverse health outcomes, Queensland Alliance for Environmental Health Services researcher Alex Villa said.
Following the mystery surrounding the mass stranding green turtles at Upstart Bay in 2012-2013, Mr Villa, lead author of the study published in Environmental Pollution, was called in with a group of researchers and veterinarians to evaluate the levels of metal in coastal green sea turtles in the same area.
"We don't know when turtles started to come up but when they were found, people at James Cook University jumped on it and sent us samples and said 'Hey, can you guys run some toxicology, we have turtles that are showing neurological symptoms, seizure type stuff, and they are not making it to rehab.'
"We ran the organic analysis and we didn't find anything, we ran the metals and we found some elements were extraordinarily high.
"We were left thinking what does this mean?"
The team took 49 samples of green turtles at Howick Group of islands in far north Queensland's Great Barrier Reef, removed from industrialised, urbanised and agricultural areas, to serve as a baseline against the populations from Cleveland, Upstart and Shoalwater Bay.
"The levels we found at the Howick Group of islands correspond with most animals, most animals are between 2 and 20 (parts per billion of cobalt) and with the turtles at an upper range we were seeing 33-36, whereas on average we were seeing 470 parts per billion of cobalt in the turtles at Upstart Bay," he said.
"The elevated levels we have at Cleveland average about 150.
"So these were pretty high numbers and now we can definitively say look, these are numbers that you wouldn't expect to see from turtles that weren't anywhere near some kind of industrialised, urbanised or agricultural activity so we were right to be concerned about these levels."
The team also found a strong correlation at Cleveland and Upstart Bay between the elevated presence of cobalt and active low grade inflammation, Mr Villa said.
"At Upstart Bay, the specific inflammation markers are associated with systemic liver dysfunction and that is pretty meaningful because the liver is a detoxifying organ," he said.
"At Cleveland, the inflammation is associated with muscular inflammation, another really tough one to pin down."
Other metals observed above the baseline at the three locations included molybdenum, manganese, magnesium, sodium, arsenic, antimony and lead.
According to veterinarian and co-author Dr Mark Flint, a quarter of 161 turtles examined at Upstart Bay also had mild to severe eye lesions.
"We don't know why this is occurring. The infection appears to be bacterial and not a virus, so it could be another indication that this is a population under pressure," Dr Flint said.
The extent and exact effects of metal exposure on the health of coastal populations of sea turtles remains unknown, however Mr Villa said James Cook University researchers would now be testing seagrass and sediment in the same areas to find out if there is a link between the levels of metals found in the sampled turtles and their surroundings.
"There is a tremendous amount of evidence so far pointing in the direction of cobalt and other metals that we found at Cleveland and Upstart Bay (as being a) rather a real contributor, in most likelihood...to the adverse effects we are seeing in a population that is already probably suffering from poor health," he said.