Rock oysters take up heavy metal

Algae and nutrients from sewage and grey water runoff can stir up more trouble for polluted waterways, according to new Brisbane research.

Russell Richards, a chemical engineering PhD student at The University of Queensland and Cooperative Research Centre for Coastal Zone, Estuary and Waterway Management at Indooroopilly, has used oysters to show how microscopic algae can affect how they absorb copper.

A single oyster can filter about 50 litres of water a day, sifting out impurities and absorbing a suite of heavy metals such cadmium, lead, chromium, zinc, copper and pesticides.

Scientists can tell the quality of water from the amount of copper in an oyster.

Mr Richards has found that it is not just dissolved toxic metals in the water that control how much and how fast oysters ingest copper.

It is controlled to a greater extent by microscopic algae called phytoplankton which absorb copper from the water and riverbed.

These algae are the preferred food for Moreton Bay’s most common oyster — the Sydney Rock Oyster — so the more algae there are, the more copper can be ingested by the oysters.

“It is well known that oysters are good biological indicators of water quality and have been used all over the world for this purpose,” Mr Richards said.

“My work indicates that planktonic algae play a significant, and previously under estimated, role in the accumulation process.

“Better knowledge of these uptake processes allows better judgement of the water quality based on the concentration in the oyster.”

He said reducing copper contamination in waterways could be achieved by controlling the conditions which caused algal blooms such as nutrient discharge from sewage or household wastewater.

To prove his findings, Mr Richards dropped 120 oysters into water at the Port of Brisbane Operations Base, near the mouth of the Brisbane River and another 70 oysters in the cleaner waters of North Stradbroke Island.

He measured their copper content, algae levels and the quality of surrounding water, each month, for 12 months.

After several months the port oysters had ingested about five times more copper than the island oysters which were unchanged.

From these results, Mr Richards has created a computer model that can predict how quickly and how much copper is absorbed into the flesh of an oyster under various water quality conditions.

Mr Richards found water temperature was important because it affected the growth rates of both the oysters and the algae.

Media: contact Mr Richards (phone: 07 3365 8398 (w), 07 3846 2896 (h), email: russellr@cheque.uq.edu.au) or Miguel Holland at UQ Communications (phone: 07 3365 2619, email: m.holland@uq.edu.au)