Heavy metal pollutants are linked to genetic mutations, stunted growth and declining fertility among small crustaceans in the Parramatta River, the main tributary of Sydney Harbour, new research shows.

The finding adds to mounting evidence that toxic sediments and seaweeds in Sydney Harbour are a deadly diet for many sea creatures.

The new findings, published in the journal, Science of the Total Environment, reveal genetic mutations among crustaceans (Melita plumulosa) in the Parramatta River but none among those in the cleaner Hawkesbury River.

Earlier this year, UNSW scientists revealed that copper-contaminated seaweeds in Sydney Harbour were killing 75 percent of the offspring of small crustaceans that feed on a common brown seaweed.

That study showed that the harbour's seaweeds have the world's highest levels of copper and lead contamination as a consequence of stormwater run-off, industrial wastewaters and motorised watercraft.

The new study found the mutations and lower growth and fertility persisted through several generations of M. plumulosa in controlled laboratory conditions, suggesting that genetic changes are causing permanent negative impacts.

"The lower fertility and growth rates among the creatures exposed to contaminants is probably a stress response," says the study's lead author, UNSW science honours student, Pann Pann Chung.

The crustaceans were randomly sampled from two sites within each river: Homebush Bay South and Duck River in the Parramatta River, and Mooney Mooney and Half Moon Bend in the Hawkesbury.

M. plumulosa is a shrimp-like creature found among rocks and mudflats on shorelines and tide zones, although little is known about its genetic history. A native to the south-eastern coast of Australia, the amphipod feeds on organic material in sand and sediment.

"These crustaceans are sensitive to heavy metals such as copper, cadmium and zinc and scientists use them as a 'test organisms' for assessing the toxicity of marine sediments, says Ms Chung. "They accumulate heavy metals inside their tissues and scientists use them to monitor environmental pollutants."

Other research has revealed that chronic exposure to metal toxicants is linked to DNA damage in earthworms, periwinkles and some fish species.