Plastic bags don't disappear magically when you toss them

YOUR SAY: I AM responding to the diatribe against Coles and Woolworths unleashed by Andrew Bolt (TC July 17).

His argument regarding phasing out single-use plastic bags is based on a "perceived" inconvenience to customers, a swipe at the green movement and a study by the Productivity Commission that only 0.8% of bags enter the litter stream and that banning them could actually be worse for the environment.

Your free plastic bag is derived from propylene, a simple component of petroleum. It's man-made giant molecules with extremely strong long-chained carbon-carbon bonds.

Nature doesn't make things like that. Your bag is HDPE (high density polyethylene). Australia uses 4.5 billion of these annually. The US uses 100billion. The planet uses 1trillion. Only 1-3% get recycled.

Petroleum-based plastic never biodegrades, they never go away. Micro-organisms don't recognise them as food. Plastics in our ocean photodegrade, they break up due to UV light and mechanical action of wind and water. Even when they break down to the molecular or nanoparticle level they are still plastic. We call plastic bits smaller than 5mm microplastics.

There are now 46,000 microplastic fragments floating in every square kilometre of the world's oceans. We've all seen images of marine animals entangled in plastic - that's horrendous but it is the microplastics that we really need to be concerned about.

Most people don't know that plastics absorb contaminants from the surrounding water column, things like DDT, heavy metals, PCBs from fossil fuel compounds and PBDEs, the harmful compounds found in flame retardants. Within weeks, the surface of your HDPE shopping bag can become hundreds of thousands times more toxic than background levels in the ocean.

Zooplankton such as copepods, rotifers and krill are now ingesting the microplastics and the chemicals absorbed by the microplastics. The chemicals are cutting their energy intake in half. Their eggs are less likely to hatch. This is the base of the marine food chain we are talking about, are you with me? Everything else depends on the base.

The plastic continues absorbing for three-four years and so increases in toxicity. We are seeing male bivalve mussels turning into females. When fish eat the zooplankton, the chemicals and the bits of plastic bio-accumulate up the food chain, like mercury does. The digestive juices in the stomach of fish transfers the toxins into the tissues of the fish. Fish eating marine plastic are now seen to be developing tumours and liver problems. Humans eating seafood in Europe now consume 11,000 tiny pieces of plastic annually.

We throw stuff away but there is no "away". The world population now eats fish that have eaten other fish and zooplankton that have eaten toxin-saturated plastics. Our waste is starting to coming back to us on our dinner plate.

Bon appetit, Andrew!

- GEOFF CASTLE, Toowoomba

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