Degradable Plastic Bags: Don’t pass the Turtle Test

Since speaking today with a turtle expert at the local environment protection agency and reading summaries of their autopsy reports I have become more attached to my green bags.

After posting Why Ban the Plastic Bag , a reader of this web-log sent me a long and interesting report titled ‘The Impact of Degradable Plastic Bags in Australia’ published in September 2003 by Melbourne University RMIT, Download file (983 kbs).

I had not realized that there are already a whole range of degradable plastic bags in use and that a significant issue is that they don’t disintegrate as soon as they are thrown away. It seems they are more water proof and freezer safe than degradable.

The Queensland Government’s Environment Protection Agency with Flinders University in South Australia and Seaworld on the Gold Coast were testing the longevity of biodegradable fishing bait bags (pg 61).

The RMIT report indicated that while the research was ongoing, there was already agreement, including with the recreational fishing industry, for the new bait bags at $8.70/kg to be phased in over a two year period and the non-degradable conventional polyethylene bags at $1.50/kg be phased out. Concern that too many plastic bait bags end up in the ocean, and sea turtles eat them believing them to be jellyfish, and die, was driving the move to degradable bags.

The report made reference to the work of Colin Limpus, a turtle expert at the Queensland Environment Protection Agency. According to the report Limpus believed biodegradable plastic bags were a step in the right direction but since they still take six months to degrade in seawater, they are not a complete solution. Limpus was concerned that because the thermoplastic starch is modified to reduce its sensitivity to moisture, that this may prevent digestive enzymes breaking them down, but he accepted that at least in theory, the bags should be digestable and perhaps even nutritious for turtles.

In 2003 Limpus was trying to organize a project to study the breakdown time of biodegradable plastics in the digestive tract of turtles. However, since sea turtles are threatened species he was proposing to use herbivorous fresh water turtles, which are not threatened, in a plastic feeding trial.

I phoned Limpus today to find out where the research was up to.

He indicated that based on the work of a University Honour’s student (being written up) he nolonger supported biodegradable bait bags. He said that the turtles can’t digest them, they may work in landfill, but they are a threat to wildlife.

I asked about plastic bags as a cause of death relative to other threats. Limpus said that autopsy work gave a indication of cause of death and that the relative contribution of plastic bags is available in the environment protection agency’s annual reports at
http://www.epa.qld.gov.au/nature_conservation/wildlife/caring_for_wildlife/marine_strandings . I had a quick look at some of these reports this afternoon and note that in the reports for marine turtles, causes of death include “intestine obstructed with plastic” including bait bags.

Limpus said that turtles ate partially disintegrated plastic from Chinese takeaway containers and icecream containers. He said these types of plastic containers, along with boat strike, were a bigger threat to most of our marine turtles than plastic bags.

Limpus indicated that degradable and non-degradable plastic bags were a particular threat to Leatherback turtles, an endangered oceanic species.

Ten of 33 dead leatherbacks washed ashore between 1979 and 1988 had ingested plastic bags, plastic sheets or monofilament according to this international website http://www.turtles.org/leatherd.htm.