What we call microplastics are so tiny they can't be seen by the naked eye. But scientists say these micrometre-sized particles are posing an increasingly huge threat to the health of our oceans. Science reporter Jamie Morton talked to University of New South Wales ecologist Dr Mark Browne, who is taking part in this week's World Science Festival in Brisbane.

What are the big threats that these micro plastics are now posing to our oceans?

Aquatic contamination has increased by around 450 per cent in 60 years, and there is more contamination closer to large human populations.

We have demonstrated that chemically diverse fibres of microdebris are continuously emitted to the environment through washing of clothes, whilst others have shown that plastic microbeads in cleaning products are also present.

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Treatment plants divert some polymers from sewage effluent to sludge, but no current filtration methods completely eliminate their release.

Since most sewage is added to aquatic environments and ultimately enters the sea, marine habitat contamination is widespread and is a considerable risk to affect organisms far from the source of pollution.

Our recent Australian research showed that commercially and recreationally important marine fish are contaminated with plant (rayon, cotton, hemp, kenaf, flax), animal (wool, silk) and plastic (acrylic, polyester, polyamide, polypropylene) micrometre-sized polymers.

This mirrors other research around the world.

Microplastics are small enough to be ingested, enter organs and cause toxicity.

Laboratory trials show microplastics reduce foraging behaviour, growth and reproduction of bivalves and their associated assemblage of organisms.

Such results have fuelled concerns that microplastics are more harmful than plant and animal polymers; however, comparative studies are lacking.

Non-plastic particles can cause scar-tissue, cancer and death in humans, and indirect toxicity can arise from chemicals added during manufacture, or absorbed from sewage or stormwater.

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Micrometre-sized polymers have large surface-areas and small volumes so adsorb large quantities of chemicals but the chemical uptake and bio-availability vary with polymer.

Our studies show that these chemicals and polymers can degrade the immune system of some invertebrates - and kill organisms that support biodiversity.

Today, what are the biggest contributors of microplastics in our oceans and what types of consumer products are predominantly involved?

The most abundant forms of microplastic are fibres from clothing, but we also find a smaller numbers of material from abrasive beads in cleaning products - something first highlighted by New Zealand scientist Murray R Gregory, of Auckland University - as well as packaging and other products.

How has our understanding of this problem developed and improved over recent times?

Understanding of the sources, fate and impacts of microplastics has developed when government and industry have funded scientific work testing hypotheses using structured sampling and experimentation.

Unfortunately, a lot of work does not use this approach and this has reduced progress in understanding and reducing the impacts of microplastics.

The key questions remains; does this material cause ecological impacts? And are governments using robust science to replace problematic products with safer alternatives?

Is there any hope of reversing the microplastic pollution already in our oceans, through scientific means?

Governments and industry can tackle microplastic pollution by tasking ecologists and engineers to work together to identify and remove features of products that - if found as debris in habitats - might cause ecological impacts.

Similar approaches are already used to engineer infrastructure ecologically or to make less toxic "biocompatible" medical devices.

Jamie Morton was hosted at the World Science Festival by Brisbane Marketing.