Green Central: click here to read Times Online's environment blog

What’s all the fuss about?

Plastic bags have been the target of several campaigns to get them away from the cash tills at supermarkets where they are handed out free. One of the main claims by campaigners is that plastic bags are responsible for huge numbers of marine deaths. Now, however, it turns out that the scientific support for the assertions has been misinterpreted and overstated.

So are they harmless to marine animals?

There is no scientific evidence to support the claim that 100,000 marine mammals have been killed by plastic bags. With no scientific data it is impossible to tell exactly how many deaths are caused by the bags but marine biologists say their effect is minimal. Post-mortems of whales have revealed plastic and plastic bags in some of them but in most cases it is hard for scientists to be even categorical that plastic products played a role, let alone the sole role, in the deaths.

Is it just plastic bags or is plastic in general a problem?

Plastic bags would appear to be a small part of the overall problem caused by plastic in terms of animal deaths. In the Pacific Ocean countless pieces of plastic have been found to be swirling round from 500 miles off the Californian coast across an area spreading as far as Japan. Some pieces will be from bags but most is formed of solid lumps.

Do other plastics cause a problem to animals?

Yes, but the scale is unclear. Reports and eyewitness accounts suggest that many birds can die because they ingest enough small lumps of plastic that their stomachs are filled with nothing else and they starve to death.

The plastics industry points out that only a tiny proportion of litter, less than 1 per cent, is formed of plastic bags. However, while by weight it may be small, its visual impact, litter campaigners would maintain, is disporportionately big because they will blow about in the wind and snag on trees and bushes.

How long do plastic bags remain in the environment?

Like much of the controversy over plastic bags, the evidence is unclear. Studies have suggested that some plastic can last 1,000 years before degrading but other suggest bags are unlikely to survive longer than 10-20 years. Biodegradable bags take months. More research is needed.

How widespread are they?

Everyone has seen them in streets and as with most litter they are more common close to human centres of habitation.

However, scientists from the National Oceanography Centre (NOC) in Southampton recently explored parts of the Portuguese coast and found plastic bags snagging on their equipment at 5,580 feet (1,700 m) beneath the waves.

Researchers from the British Antarctic Survey have reported plastics in the South Sandwich Islands, one of the most remote land areas in the world.

What happens when plastics break down in the seas?

This remains to be seen. The dynamics of marine ecosystems remain little understood so the impact of degraded plastic has yet to be assessed. Researchers from the NOC are organising funding for a study into the impacts of Man on the oceans. Lost fishing tackle and plastics will be among the study’s main targets.

Times Recommends

• Settlers burn Koran in mosque attack
• Gorillas threatened by charcoal trade
• Israeli anger at new Palestine food labels